Disclaimer: The following material is written in the interests of education and harm reduction. Just say know!!!



Heavy Metals



Rule 1: The more pure the fertilizers’ used in formulation, the fewer the contaminants. I.e. The use of analytical, food and pharmaceutical grade fertilizers vs. the use of horticultural grade fertilizers will reduce contaminants such as heavy metals.


Rule 2:  The higher the heavy metal levels in media and fertilizers, the higher the heavy metal uptake by plants. I.e. Heavy metal concentration in soils, substrates and fertilizers (compost etc) is the dominant factor in heavy metal plant tissue contamination.


Rock Phosphates (phosphorous) and Cadmium


The key problem regarding contaminants in hydroponic fertilizers are the heavy metals’, arsenic cadmium, selenium, cobalt, mercury and lead, with cadmium being the most notable of these where plant uptake is concerned.


Other than this, aluminum (Al), while not technically a heavy metal, is another key potential contaminant in soils and fertilizers. It is important to note that in medical terms, heavy metals are loosely defined and include all toxic metals irrespective of their atomic weight. “Heavy metal poisoning” can possibly include excessive amounts of aluminium, or beryllium (the fourth lightest element in the periodic table). For this reason we will also discuss aluminium in terms of a heavy metal during the course of discussion.


Cadmium (Cd)


Cadmium is a widespread, naturally occurring, element that is present in soils, rocks, waters, plants and animals. The chemical symbol for cadmium is Cd. It occurs naturally with deposits of zinc and phosphorus but, unlike these nutrients, it is not considered essential for life.


Phosphorus containing fertilizers can contain high levels of cadmium depending upon the source of rock phosphate used in manufacturing. For this reason, many countries (e.g. Australia, USA, UK, EU/EC members) have adopted regulations that determine acceptable levels of cadmium in phosphate fertilizers.


For instance, the ‘Fertilizer Industry Federation of Australia’ (FIFA) initiated a program in the 1990s to reduce the levels of cadmium in phosphate fertilizers. This was achieved by using low cadmium phosphate rock in the manufacturing of superphosphate and importing low cadmium, high phosphorus analysis fertilizers.


Cadmium and its compounds may travel through soil, but its mobility depends on several factors such as pH and amount of organic matter, which will vary depending on the local environment. Cadmium binds strongly to organic matter (e.g. humus and manure) where it will be immobile in soil and be taken up by plants, eventually, entering the food chain. 1

Research conducted in New Zealand demonstrates that equivalent levels of cadmium can exist in both organic and non-organic soils.




“Total cadmium concentrations were higher in the organic soil than those in the allophonic (non-organic) soil and may be explained by difference in bulk density. Without consideration of bulk density, the organic soil appeared to have much higher cadmium concentrations compared to the allophanic soil. However, when converted onto a volumetric basis, the organic soil appeared to have similar concentrations of cadmium to the allophanic one.” 2


[End Quote]


Other than this, aluminum (Al), while not technically a heavy metal, is another key potential contaminant in soils and fertilizers. It is important to note that in medical terms, heavy metals are loosely defined and include all toxic metals irrespective of their atomic weight. “Heavy metal poisoning” can possibly include excessive amounts of aluminium, or beryllium (the fourth lightest element in the periodic table). For this reason we will also discuss aluminium in terms of a heavy metal during the course of discussion.


While there is little data on the health risks that cadmium poses to cannabis users, cigarette smoking is a significant source of cadmium exposure. Although there is generally less cadmium in tobacco than in food, the lungs absorb cadmium more efficiently than the stomach.


Jarup, L (1998) notes that the population group at the highest risk of cadmium exposure is tobacco smokers. The absorption of cadmium in the lungs is 10-50%, while the absorption in the gastrointestinal tract is only a few percent. Smokers have about 4-5 times higher blood cadmium concentrations (about 1.5 micrograms/l), and twice as high kidney cadmium concentrations as nonsmokers.3 The national geometric mean blood cadmium level for adults is 0.47 μg/L. A geometric mean blood cadmium level of 1.58 μg/L for New York City smokers has been reported. The amount of cadmium absorbed from smoking one pack of cigarettes per day is about 1–3 μg/day. Direct measurement of cadmium levels in body tissues confirms that smoking roughly doubles cadmium body burden in comparison to not smoking. 4 This information has telling implications for cannabis users.


While cannabis is not classed as a hyperaccumulator plant (a plant that uptakes larges amounts of heavy metals from soil and/or fertilizers) it has high biomass and capability to absorb and accumulate heavy metals in roots and shoots.


Cadmium accumulates predominantly in the leaves of Cannabis sativa L, indicating that heaviest concentration of Cd is present in leaf and bud matter. 5


According to current knowledge, renal tubular damage is probably the critical health effect of cadmium exposure. Cadmium is first transported to the liver through the blood. It then bonds to proteins to form complexes that are transported to the kidneys. Cadmium accumulates in kidneys, where it damages filtering mechanisms. This causes the excretion of essential proteins and sugars from the body and causes further kidney damage. It takes a very long time before cadmium that has accumulated in kidneys is excreted from a human body. Where immunosuppressed individuals are concerned excessive cadmium levels can further suppress the immune system. 6


Unit Measurement Conversion Rates for ug and ng


μg (microgram = 1 millionth of a gram or, 1μg = 1/1,000,000g). 1000 micrograms = 1 milligram, and 1000 milligrams = 1 gram


To convert micrograms to milligrams, divide by 1000. E.g. 19,000 (μg) ÷ 1000 = 19 (mg)


ng (1 nanogram = 1 billionth of a gram) 1,000,000,000 ng = 1 gram


1,000,000 ng = 1mg.


Cadmium in Nutrients/Fertilizers


Let’s have a look at how much cadmium is found in phosphate fertilizers; firstly, a horticultural grade product from Australia. Monopotassium phosphate (MKP)


Certificate of Analysis Monopotassium Phosphate (MKP) 0- 52- 34, Horticultural Grade


Phosphor (P205)                   min 51.5%

Potassium (K2O)                  min 34%

Cl                                       max 60ppm

Na                                      max100ppm

Heavy Metals                       max 10ppm

Insolubles                            max 0.1%

Moisture                               max 0.5%


In this case, the manufacturer doesn’t list heavy metals separately. However, looking at this analysis we can see that there is a maximum of 10ppm (10mg/kg or 0.001%) of total heavy metals in our MKP product.  When you consider that there is 1000mg in 1gram and 1000grams in one kilogram, and that a liquid concentrate, two-part fertilizer may contain approximately 30g/L of MKP and/or MAP this number doesn’t seem unreasonable. I.e. With this information we have 0.000030ppm/L of total heavy metals in a fertilizer concentrate (max value) derived from phosphate fertilizers. Next – let’s say that in a worst-case scenario we have a “max” of 10mg/kg of heavy metals present in the MKP product and that 1/3 of this is cadmium. This would leave us with 3.333mg/kg of Cd in the phosphate fertilizer product or 0.000010 mg/L of Cd in a hydro concentrate solution. Keep in mind that I’ve used conservative numbers and Cd levels are likely to be lower.


I’ve oversimplified this for now and we’ll come back to it later. I.e. we also need to account for cadmium drawn from other sources (e.g. potassium nitrate, calcium nitrate etc).

Here’s a few more examples of phosphate fertilizers. In this instance, the heavy metal contaminants are listed separately.


Monopotassium Phosphate (MKP 0- 52- 34)

Main content, min 99.0 %

P2O5 ≥51.3 %

K2O ≥34.0%

Water insoluble, max 0.1 %

Moisture, max 0.2%

PH 4.4-4.8

As ≤0.0025%

Heavy metal (Pb) ≤0.0003%

Hg None

Cd ≤0.0002% (2mg/kg or 2ppm/kg)

Cr ≤0.0002%

F ≤0.002%

CL ≤0.01%


Monoammonium Phosphate (MAP 12- 61- 0)

Main content, min 99.0 %

P2O5 ≥61.0 %

N, ≥12.0%

Water insoluble, ≤0.1 %

Moisture, ≤0.2%

PH 4.4-4.8

As ≤0.0025%

Heavy metal (Pb) ≤0.0003%

Hg None

Cd ≤0.0002% (2mg/kg or 2ppm/kg)

Cr ≤0.0002%

F ≤0.002%

CL ≤0.01%


Di-Ammonium Phosphate (DAP 21-53-0)

(NH4)2HPO4 99%

P2O5 ≥53.0 %

N ≥20.8%

Water in soluble ≤0.1% 0

Moisture ≤0.2%

PH 7.8-8.2

As ≤0.0025%

Heavy metal (Pb) ≤0.0003%

Hg None

Cd ≤0.0002% (2mg/kg or 2ppm/kg)

Cr ≤0.0002%

F ≤0.002%

CL ≤0.01%

In all cases 2mg/kg of Cd.


Organic Phosphate Sources


Let’s have a look at an organic phosphate (phosphorous) source and compare the Cd numbers against non-organic fertilizers.


Bat Guano


Civa mg/kg                                              4, 8

Lead mg/kg                                             39, 6

Chromium mg/kg                                     29, 1

Zinc mg/kg                                             255, 1

Nickel mg/kg                                           26, 2

Cadmium mg/kg                                     3

Copper mg/kg                                        979, 8

Total phosphorus g/kg                             5

Total nitrogen %                                     8, 1

Total organic Matter %                            64, 7

Salinity %                                              0, 35

Electrical conductivity mS/cm                   13, 8

Humidity % 8, 7

pH – 2, 09


Looking at this analysis we have 3mg/kg of Cd (vey low cadmium levels by guano standards) – which puts us on track with non-organic sources of phosphate fertilizers – or at least at first glance. However, our non-organic phosphate fertilizer has 51.5% (515g/kg) elemental P while our organic phosphate fertilizer has 5% (50g/kg) of elemental P, so to achieve the same levels of P in NPK %w/v we are adding much higher levels of cadmium to an organic liquid fertilizer. For instance, to achieve a 1%w/v phosphorous target in a fertilizer concentrate we would use 19.4g/L of our Australian MKP product or 200g/L of bat guano giving us approximately 10.3 times the amount of Cd in an organic solution.  When you compare the numbers (the chemistry of organic vs. non-organic) things become much clearer…


A couple more guano products that are sold in North America.


Arsenic                       11.7000

Cadmium                    7.6000mg/kg

Cobalt                        12.6000

Lead                           1.200

Mercury                      0.0500



Arsenic                      13.3000

Cadmium                   10.0000mg/kg

Lead                          1.2000

Selenium                    5.5000

Mercury                     0.0500


Author’s note: Heavy metal contaminants in organic fertilizers become more problematic when you consider that kelp and other organic components used in formulation (e.g. fish by-product, blood and bone products, worm casting, molasses) often contain high levels of heavy metal contaminants. Burger J et al, studied Alaria nana kelp in Alaskan waters and found it contained high levels of cadmium, lead and selenium.8 Research investigating heavy metals in aquatic food chains has yielded similar findings.9


Let’s now compare these numbers to an inorganic full spectrum fertilizer.


Independent Lab Analysis of Heavy Metal Contaminants in Commercially Available Hydroponic Fertilizers


We tested numerous fertilizers in European, North American and Australian laboratories. In most instances we tested only for elemental N, P, K, Ca, S, Mg and microelement values in order to reverse engineer popular, internationally available formulas. However, in some cases, we conducted more thorough analysis where we tested for heavy metal contaminants.   I’ll now paste in an excerpt from one of these analyses (5 liquid samples from a European based multinational) so that we can evaluate Cd levels in off the shelf inorganic hydroponic fertilizer. (C following analysis – lab tests conducted in Australia on imported product).




In this analysis CA and CB (highlighted at top in red) represents Coco A and Coco B so we’ll look at this company’s two part Coco product.


Keep in mind that 1000 μg equals 1mg, so where we have <500 μg of Cd there is less than (< = less than) 0.5mg/L cadmium contaminant.


These formulas are reasonably concentrated (high mineral to water ratio) and therefore require a lower dilution rate (comparative to some other brands). For this reason the contaminant numbers listed at μg/L need to be considered with this in mind (i.e. a less concentrated product – higher water to mineral ratio – would perhaps reflect lower contaminant/L numbers). Let’s hypothetically say that you were using one of these products at 2.5ml/L at an EC of 1.2 (in solution). What this would mean is that you would have e.g. (worst-case scenario) 1 μg/L (0.001mg/L) of Cd in solution derived from CA (Coco A) and the same again derived from CB (Coco B). I.e. 1 μg/L (part A) + 1 μg/L (part B) = 2 μg/L or 0.002mg/L Cd in solution. Keep in mind that we’re dealing with a worst-case scenario and <500 μg/L Cd could mean 20 μg/L, 100 μg/L, or 300 μg/L.  Put simply Cd in solution is minimal in this instance.


Now let’s look at an additive that is very popular amongst cannabis growers. A bloom enhancer derived from monopotassium phosphate, and potassium  sulfate. It also contains amino acids (organics).


Element Lab Method Results
Arsenic EPA 3050B, 6010B 16.2 ppm
Cadmium EPA 3050B, 6010B < 5 ppm
Mercury EPA 7471A < 0.2 ppm
Lead EPA 3050B, 6010B 10.7 ppm
Nickel EPA 3050B, 6010B < 5 ppm



This products recommended use is 5ml/L which would add 0.02ppm of cadmium to the working solution. If we were using this product and our coco product we would then have a total of 0.021ppm of Cd in solution. I’ve oversimplified this somewhat (for instance we may be using our coco formula at 5ml/L in bloom) but the purpose is to demonstrate that where hydroponic fertilizers are concerned there will be at least some Cd in solution and this becomes available for uptake.


If these products were made with analytical, food, or pharmaceutical grade fertilizers (which contain minute levels of contaminants) our HM numbers would be lower again.


Cadmium in Leaf Tissue Analysis (Cannabis) 


Advanced Nutrients™ Pty Ltd conducted tissue analysis on multiple strains of high THC cannabis in 2002 – 2003. To date, this data provides the most accurate information (snapshot) about Cd and other HM levels in cannabis.


Six cannabis strains tested for Cadmium (results in mg/kg of dry plant matter)


These finding support that cadmium is uptaken by the plant at levels where low ppm of cadmium is present in solution.


Other Heavy Metal Contaminants


Arsenic (As)


The chemistry of arsenic leads to multiple chemical species that differ in toxicity. 10


Arsenic uptake and translocation occurs more readily in high phosphorous environments.11 However, research conducted in 2001 – 2002 by Andrew Kavasilas indicates low arsenic uptake by Cannabis in both hydroponic and soil settings (tissue analysis equals <0.1mg/kg As in all instances). 12 These findings are supported by further research which found lower than 1mg/kg arsenic in multiple cannabis strains (Advanced Nutrients 2003).


Nickel (Ni)

Nickel is moderately soluble. The likelihood of nickel toxicity in cannabis appears quite low. It is a nutritionally essential metal for some plants. There is no known biochemical function for nickel in humans. Contamination with nickel in fertilizers and related products seems an unlikely human health issue.


Lead (Pb)

While plants are known to concentrate lead in the roots, lead translocation to the shoots is very low.13 This view is supported by a finding that demonstrated significant lead translocation to the shoots of Indian mustard was observed only at relatively high concentrations of lead in a hydroponic nutrient solution and after the lead-binding capacity of roots was partially saturated. 14 Further research has demonstrated that lead uptake by Cannabis sativa is very low (0.6% of total lead content in soils). 15


Selenium (Se)

Depending on its concentration and chemical form, Se functions as an essential element or potential toxicant to humans. Factors that will influence selenium uptake by plants are pH, and selenium concentration in soils and nutrients. Research demonstrates that selenium uptake by cannabis is moderately low. 16


Chromium (Cr)

Chromium is found in all areas of the environment, including air, water and soil. Due to its wide industrial use, chromium is considered a serious environmental pollutant.

Research has shown that Cr distribution in crops does not depend on soil properties and concentration; the maximum quantity of element contaminant was always contained in roots and a minimum in the vegetative and reproductive organs of sample crops. This indicates low translocation of Cr from roots to leaf and bud tissue. 17


Further research has demonstrated that where cannabis is grown in soils containing high concentrations of Cd, Cr and Ni, Cr, Cd and Ni were considerably accumulated in the plant roots but only partially translocated to the above ground plant tissue, while chromium uptake was negligible. 18 


Aluminum (Al)


Aluminum is the most abundant metal in the Earth’s crust, and is the third most abundant element after oxygen and silicon.


It is still unknown whether there is a biological function for aluminum in the human body. Nevertheless, the average adult ingests approximately 8 to 9 mg/day of aluminum through food and water. Some aluminum is retained in the body; however, most aluminum that is ingested is excreted through urine in a few days or weeks.1


Debate is still ongoing about aluminum’s possible long-term toxicity to humans; however, aluminum has been linked to neurological conditions (e.g. Alzheimer’s disease) and respiratory conditions.


Christopher Exley et al (2006) note,




“Active and passive smoking of tobacco or cannabis will increase the body burden of aluminum and thereby contribute to respiratory, neurological and other smoking-related disease.”


[End Quote]


The clinical significance of this research is cited as:




“Tobacco and cannabis are hitherto unrecognized potent contributors to the body burden of aluminum.

Aluminum that is inhaled either from active or passive smoking is biologically available and is likely to be absorbed systemically.

Aluminum entering the lung and the olfactory system as either particulates or gaseous complexes may contribute toward smoking-related disease including asthma and neurological dysfunction.”  2

[End Quote]


This has telling implications for cannabis users.


Leaf tissue analysis conducted by Advanced Nutrients on high THC cannabis strains grown using hydroponic fertilizers demonstrates that high levels of aluminum (when compared to Cd and other potentially toxic heavy metals) are present in harvested cannabis. I.e. results from 6 samples of differing genetics (mg/kg of dry plant matter).



These numbers are appear high when comparing them to other HM contaminants; albeit that a healthy human will ingest 8 – 9 mg of Al a day and it would, therefore, theoretically require a person to smoke over 1kg of these samples a day to achieve this. However, as smoking significantly increases the Al body burden the relatively high levels of Al present in cannabis is noteworthy.


Aluminum Present in Advanced Nutrients Sensi Bloom


Sensi Bloom A

Soluble Salts mmhos/cm                                     365.

Copper Cu ppm                                                  52.4

pH                                                                    4.28

Zinc Zn ppm                                                      160.

Alkalinity ** ppm                                                445. *

Molybdenum Mo ppm                                          20.6

Calcium Ca ppm                                                 26640.00

Aluminum Al ppm                                               45.8

Magnesium Mg ppm                                            26.9

Nitrate NO3-N ppm                                             40702.57

Sodium Na ppm                                                  1856.00

Ammonium NH4-N ppm                                       2483.94

Chloride Cl ppm                                                  568.

Urea UREA-N ppm                                               11468.12

Boron B ppm                                                       213.

Total Nitrogen N ppm                                           54654.63

Iron Fe ppm                                                        1144.00

Phosphorus P ppm                                               20.8

Manganese Mn ppm                                            486.

Potassium K ppm                                                33500.00

Sulfur S ppm                                                      195.

P as P205 ppm                                                   47.6

K as K20 ppm                                                    40200.00


Sensi Bloom B


Soluble Salts   mmhos/cm                                 246.

Copper Cu ppm                                                4.28

pH                                                                  3.56

Zinc  Zn      ppm      .                                       863

Alkalinity **  ppm                                           .000 *

Molybdenum Mo ppm                                     1.36

CalciumCa  ppm                                             127.

Aluminum Al ppm                                           .000

Magnesium Mg ppm                                       6792.00

Nitrate NO3-N  ppm                                       16335.27

Sodium Na ppm                                             254.

Ammonium NH4-N ppm                                  483.

Chloride Cl ppm                                             325.

Urea UREA-N ppm                                         .000

Boron  B  ppm                                              .000

Total Nitrogen N  ppm                                   16818.10

Iron Fe  ppm                                                7.20

Phosphorus P ppm                                        20350.00

Manganese Mn ppm                                      1.57

Potassium K ppm                                          47660.00

Sulfur S  ppm                                               2771.00

P as P205 ppm                                            46601.50

K as K20   ppm                                            57192.00


Sensi Bloom contains 45.8ppm Al in concentrate, which equates to 0.1832ppm Al in working solution if diluted at 4ml/L (which is the company’s recommended dilution rate for this product during bloom).  What this may indicate is that Al in hydroponic solution is reasonably bioavailable to the plant.


Author’s note: I do not wish to imply AN products contain more aluminium than that of any other company’s formulations. In fact, we looked at a key competitor’s products in 2010 and found reasonably high levels of Al in their 3-part formulation. I.e.



This company recommends the use of their Micro product at 10ml/L in bloom. This means that 6.14ppm of Al would be present in feed solution. That’s 6.14 ppm Al using this product vs. 0.1832ppm (less than 1ppm) Al using AN Sensi Bloom. You can perhaps see why fertilizer choice (along with fertilizer quality/purity) in formulation is extremely important. I.e. The 3-part manufacturer looks as if they are using aluminum sulfate in formulation (either as a flocculent, pH adjuster/buffer or simply to boost EC). Either way, theoretically, if you were to use this company’s 3-part formulation you may have higher levels of Al present in the end product than if you were using AN Sensi Bloom.

Bongs and Aluminium – Mad Dogs and English Convicts


I’m going to briefly deviate for a moment and go off topic somewhat as I feel this is an extremely important point to raise regarding aluminium as a cannabis contaminant.


In some jurisdictions, highly enlightened Governments have begun banning bongs and vaporizers (smoking implements). For instance, the South Australian,Western Australian, and Victorian State Governments have all outlawed the sale and possession of bongs and vaporizers.


Besides being a flawed and politically laden exercise (rolling papers anyone?), the banning of bongs and vaporizers is also a misplaced and irresponsible policy (harm maximization) that places cannabis consumers at greater health risk. Given that cannabis is widely used (NZ and Australia has recently been shown to have the highest rates of cannabis use in the world), the significance of this shouldn’t be underestimated and ultimately more burden is likely to be placed on the Australian health system in jurisdictions where bong banning takes place.


Pechansky. F et al (2007) found elevated levels of aluminum in Brazilian crack users. The apparent reason – Brazilian crack users smoke crack using makeshift pipes made from aluminum cans5.


Similarly, cannabis users often construct makeshift bongs using aluminum foil or aluminum can for the cones of their pipes. Cannabis is then placed into the cone and combusted, at which point the combusted material enters the lungs, no doubt delivering at least some aluminum as well.


The message here is simple. If making your own bong avoid using aluminum foil or can in its construction.


More on Vaporizers


Additionally, laboratory studies by California NORML and MAPS have shown how vaporizers can efficiently transport cannabinoids without the risk of inhaling harmful toxins. These toxins that are present in marijuana are carcinogenic polynuclear aromatic hydrocarbons, which are key suspects in cigarette-related cancers. The study, conducted by Chemic Labs in Canton, Mass., tested vapors from cannabis heated in an herbal vaporizer known as the Volcano® (manufactured by Storz & Bickel GmbH&Co. KG, Tuttlingen, Germany and compared them to smoke produced by combusted marijuana.


In principle, vaporization offers medical cannabis patients the advantages of inhaled routes of administration: rapid onset, direct delivery into the bloodstream, ease of self-titration and concomitant avoidance of over- and under-dosage, while avoiding the respiratory disadvantages of smoking.


The vapors from the Volcano® were found to consist overwhelmingly of THC, the major active component in marijuana, whereas the combusted smoke contained over 100 other chemicals, including several polynuclear aromatic hydrocarbons (PAHs), carcinogenic toxins that are common in tobacco smoke. The respiratory hazards of marijuana and tobacco smoke are due to toxic byproducts of combustion, not the active ingredients in the plant, known as cannabinoids.


The study used a gas chromatograph mass spectrometer (GCMS) to examine the gas components of the vapor. The analysis showed that the Volcano® vapor was remarkably clean, consisting 95% of THC with traces of cannabinol (CBN), another cannabinoid. The remaining 5% consisted of small amounts of three other components: one suspected cannabinoid relative, one suspected PAH (Polycyclic Aromatic Hydrocarbon), and caryophyllene, a fragrant oil in cannabis and other plants. In contrast over 111 different components appeared in the gas of the combusted smoke, including a half dozen known PAHs. Non-cannabinoids accounted for as much as 88% of the total gas content of the smoke.6


Further research has been done on vaporisers as a delivery method. A laboratory study found that a vaporisation device provided an efficient and reproducible mode of delivery of THC.7A further pilot human laboratory study comparing a vaporiser to smoked cannabis found that the vaporiser was as effective as delivering THC but with little or no increase in carbon monoxide levels, a marker for toxins that may be generated by smoking.8



1. Brazilian female crack users show elevated serum aluminum levels (2007) Pechansky F, Kessler FH, Diemen L, Bumaguin DB, Surratt HL, Inciardi JA.

2. Aluminum in Tobacco and Cannabis and Smoking-Related Disease  (2006) C. Exley, A. Begum, M. Wooley, R. Bloor

3.  Tissue analysis conducted on multiple cannabis strains/samples by Advanced Nutrients™ through BC Research Inc (2002 -2003)

4. Aluminum in Tobacco and Cannabis and Smoking-Related Disease  (2006) C. Exley, A. Begum, M. Wooley, R. Bloor

5. Brazilian female crack users show elevated serum aluminum levels (2007) Pechansky F, Kessler FH, Diemen L, Bumaguin DB, Surratt HL, Inciardi JA.

6. Dale Gieringer, Joseph St. Laurent, Scott Goodrich (2004) Cannabis Vaporizer Combines Efficient Delivery of THC with Effective Suppression of Pyrolytic Compounds:       Journal of Cannabis Therapeutics, Vol. 4 (1) 2004

7. Hazekamp, A., Ruhaak, R., Zuurman, L., van Gerven, J., Verpoorte, R. (2006), ‘Evaluation of a vaporizing device (volcano) for the pulmonary administration of tetrahydrocannabinol’, Journal of Pharmaceutical Sciences 95(6): 1308–1317.

8. Abrams, D., Vizoso, H., Shade, S., Jay, C., Kelly, M., Benowitz, N. (2007), ‘Vaporization as a smokeless cannabis delivery system: a pilot study’, Clinical Pharmacology and Therapeutics, online publication, 11 April.



Mercury (Hg)


Mercury is released by natural sources like volcanoes, by evaporation from soil and water surfaces, as well as through the degradation of minerals and forest fires.  Mercury is also contained as a trace element in coal. The use of coal-fired power plants for generating electricity, make mercury emissions to the atmosphere from this source among the world’s largest sources of Hg pollutants.


Mercury and its compounds are highly toxic to humans, ecosystems and wildlife. High doses can be fatal to humans, but even relatively low doses can have serious adverse neurodevelopmental impacts, and have recently been linked with possible harmful effects on the cardiovascular, immune and reproductive systems 19


The efficiency of mercury absorption through the intestinal tract is approximately 10% as efficient as that of the lungs (WHO Task Group 1976). Approximately 80 (75 – 85%) percent of inhaled Hg vapors are absorbed by the lung tissues. This vapor easily penetrates the blood-brain barrier and acts as a neurotoxicant. 20 Batáriová et al note significant differences of Hg levels are found between smokers (0.80 μg/l) and non-smokers (0.92 μg/l). Therefore, mercury in vegetative matter that is smoked – as with Cd – can have a far more significant impact than that which is orally ingested. 21


Less than one percent of the mercury present in tobacco leaf remains in the ash after combustion; the rest of the Hg is inhaled into the lungs. Smoking Cannabis, therefore, can also introduce virtually the entire mercury burden into the lungs, where 75 -85% of inhaled mercury is absorbed and retained. 22


Plants uptake elemental mercury vapor (Hg0) through their leaves from air, and ionic mercury is taken up via the roots from soils. Subsequently the plants return part of this mercury as Hg0 to the environment. 23


Factors affecting plant uptake of Hg include organic content in soils, carbon exchange capacity, oxide and carbonate content, redox potential, and Hg contaminant levels in fertilizers. Mercury uptake in plants is typically related to environmental Hg contaminant levels (pollution levels).


Aquatic plants such as kelps are bioaccumulators (hyperaccumulators) of Hg. Many fish species also contain high levels of Hg. The consumption of fish is by far the most significant source of ingestion-related mercury exposure in humans, although plants and livestock also contain mercury due to bioaccumulation of mercury from soil, water and air. 24

Plants growing in volcanic regions typically contain high levels of mercury. For instance, cannabis sativa L. growing in Hawaiian soils has been demonstrated to contain mercury at about 1.5 to 4.6 ng of mercury per gram of plant material. 25


The FAO/WHO Expert Committee on food additives (1972) recommended, for the average adult, a “provisional tolerable weekly intake” of 300 ug of total mercury. In view of the higher rate of Hg absorption via smoking an additional risk to the cardiovascular, immune and reproductive systems and neurological well-being exists for cannabis smokers. In extreme cases, Siegel et al note that smoking as little as 100 grams of marijuana per week may lead to more mercury being taken into the body than the prescribed “provisional tolerable weekly intake.” 26


Research conducted in 2001 on 6 high THC cannabis samples (3 outdoor organic and 3 indoor hydro), yielded <0.1mg/kg Hg in all samples. 27


On this note, after reviewing the heavy metal content of dozens of commercially available organic and inorganic fertilizers, the Hg levels in most samples were relatively low with generally more Hg (by average) in organic fertilizers.


Just some of these fertilizers:

Non-organic full spectrum hydroponic fertilizers


Prod X Coco A

Cadmium                    <0.0400

Arsenic                       <0.5000

Lead                          <0.5000

Mercury                     <0.0050

Prod X Coco B

Cadmium                    <0.0400

Arsenic                       <0.5000

Lead                           <5.0000

Mercury                      <0.0050


Prod Y Flower A 4-0-6

Arsenic                        <0.5000

Cadmium                    <0.0400

Lead                          <0.5000

Selenium                    <0.5000

Mercury                     <0.0050


Product Y Flower B 0-4-4

Arsenic                      1.0000

Cadmium                   0.1000

Lead                          1.0000

Selenium                    0.1000

Mercury                    <0.0050


Product Y Grow A 4.3-0-3.1

Arsenic                      <0.2000

Cadmium                   0.5000

Lead                         <0.3000

Selenium                   <0.3000

Mercury                     <0.0030


Product Y Grow B 1.5-6.1-5.7


Arsenic                       <0.2000

Cadmium                    <0.0500

Lead                           <0.3000

Selenium                    <0.3000

Mercury                    <0.0030


Organic Examples


Organic full spectrum grow nutrient 3.5- 1- 5.5

Arsenic                       0.2400

Cadmium                    0.0330

Cobalt                         1.0000

Nickel                          4.0000

Lead                           <0.4000

Selenium                    <0.0040

Mercury                     <0.0100


Organic full spectrum bloom nutrient 2.5 – 2 – 5


Arsenic                        0.2100

Cadmium                    0.0950

Cobalt                        0.8500

Mercury                     <0.0100

Lead                          <0.4000

Selenium                   <0.0040

Mercury                    <0.0100



Arsenic                                      0.2500

Cadmium                                  <0.0030

Lead                                        <0.0410

Selenium                                   0.5600

Mercury                                     37.5000


Author’s note: This particular product (2- 14- 0 Steamed Bone Meal) is an extreme example of mercury content (37.5mg/kg Hg). It demonstrates that organic fertilizers can contain high levels of heavy metal contaminants. The ‘2-14-0 Granulated Steamed Bone Meal’ could be used as an N and P source in formulation but a better option would be the ‘Garden Safe Bone Meal’ (following) that contains NPK 6- 12- 0 and <0.0500 Hg, demonstrating product choice in organic formulation is important where contaminants are concerned (see below).



Arsenic                                      <10.0000

Cadmium                                   <0.5000

Lead                                           1.0000

Selenium                                    <10.0000

Mercury                                      <0.0500



Arsenic                                 28.6000

Cadmium                              1.0000

Cobalt                                   1.0500

Lead                                     1.0000

Selenium                               1.0000

Mercury                                0.1000


The kelp extract 1- 0- 19 powder example demonstrates relatively high levels of contaminants (As, Cd). Another kelp product such as Acadian – a Canadian product- could be used as a potassium fertilizer component instead. Acadian has Cd levels ‘below detection limits’ (BDL). NPK = 0.9- 0.96- 16.60. When looking at organic products always attempt to access tech sheets which list heavy metal content.


BIO-FISH 7-7-2

Arsenic                                      <0.5000

Cadmium                                    7.9000

Lead                                           1.2000

Selenium                                    <5.5000

Mercury                                      0.0500



Arsenic                                          25.6100

Cadmium                                       <0.1000

Lead                                              <0.1000

Selenium                                        <0.0500

Mercury                                         <0.2000



Arsenic                                      9.8800

Cadmium                                   1.5100

Lead                                          41.0000

Selenium                                    6.2100

Mercury                                      0.1100



Arsenic                                       3.1400

Cadmium                                    0.4430

Lead                                           48.1000

Selenium                                     1.6700

Mercury                                      0.1060



NPK = 4- 5 3

Arsenic                                       16.600

Cadmium                                    1.3000

Lead                                           6.2000

Selenium                                     5.5000

Mercury                                      0.2600


Data extracted from




Organic Mediums and Heavy Metals (HM)


In brief: Metal uptake by plants can be affected by several factors including metal concentrations, soil pH, cation exchange capacity, beneficial microbes, and organic matter content. Heavy metal (HM) concentration in soils and substrates is the dominant factor.


Coco Substrate

High Lignocellulosic, organic materials such as coco substrate are efficient at binding/bonding heavy metals. 1 This means that as fertilizers are added to high lignocellulosic, organic materials, there is potential for high heavy metal accumulation within the substrate.


This poses a problem when considering the widespread use of coco substrate and other organic mediums (e.g. peat based soils) amongst med growers.


Coco Tests

In order to measure heavy metal accumulation in coco substrate we analyzed an unused coir product for heavy metals.



Analysis of Buffered Coco Substrate for Heavy Metal Contaminants (unused coir)



ug/kg to mg/kg conversion

Cadmium                                    0.012

Chromium                                   19.656

Cobalt                                         1.364

Lead                                           1.216

Molybdenum                                0.204

Selenium                                     0.1108



The analysis was conducted on a 50L bagged Canna Coco product. Canna Coco is buffered with calcium nitrate and magnesium nitrate (Cal Mag) prior to sale. It is, therefore, probable that some of the heavy metal content in the analysis may derive from the use of these fertilizers in buffering. I.e. Heavy metals in coco substrate + heavy metals in fertilizers (via Cal Mag buffer) = total.


So let’s compare these numbers to some organic rating standards (soils and composts).


New Zealand Organic Regulations


Heavy metals in manures and composts must not exceed,

Metal                                    mg/kg

Zinc                                      1000

Copper                                  400

Nickel                                   100

Cadmium                              10

Lead                                    250

Mercury                                2

(Ref 2.)


Heavy Metal Limits for Organic Composts (European standards)

Cd                   0.7

Cr                   70

Hg                  0.4

Ni                   25

Pb                  45

(Ref 3.)


US Standard (Organic Composts)

Cd                   4

Cr                  100

Hg                  0.5

Ni                  50

Pb                  150

(Ref 4.)


Comparison of Contaminants in Coco Substrate Product Vs Organic Ratings  (mg/kg)



When looking at this table, the Coco sample has extremely low cadmium and lead levels and less than 1/3 maximum allowable chromium (based on European organic rating standards). Theoretically, if you were using low contaminant inorganic fertilizers, the heavy metal count in the end product would be extrmely low. Once again hydroponics is looking very good against organic standards.


Let’s now compare coco substrate to two organic potting mixes.



Cadmium                                      1.3000

Lead                                             6.2000

Mercury                                        0.2600



Cadmium                                      0.4430

Lead                                            48.1000

Mercury                                       0.1060


Comparison (mg/kg)



Once again, hydroponics is looking extremely good!




The Influence of pH on Heavy Metal Uptake


Among the many organic media properties that influence heavy metal uptake by plants, pH plays an important role.5


In experiments run by Autumn S. Wang et al (2005) cadmium uptake significantly increased in low pH (acidic) high metal concentration soils. The highest rates of Cd uptake occurred at pH 4.8 with a marked decrease in uptake at a higher pH of 5.28, with the lowest uptake rates at pH 6.07. 6 This looks positive due to the optimum pH range for nutrient availability (re cannabis) being 5.8 – 6.0 (with contaminant uptake being minimized within these ranges).


CEC and Heavy Metal Uptake


CEC relates to a soils/substrates ability to attract, retain, and exchange cation elements.


Cation elements are elements with positive electrical charges; these being potassium (K+), ammonium (NH4+), magnesium ( Mg++), calcium (Ca++), zinc (Zn+), manganese (Mn++), iron (Fe++), copper (Cu+) and hydrogen (H+). While hydrogen isn’t a nutrient it affects the degree of acidity (pH) of a substrate and, for this reason, is an important consideration.


Some nutrients have negative electrical charges. These are called anions and include nitrate (NO3 N), phosphate, sulfate, borate, and molybdate.


The word “ion” (as in cat –ion and an – ion) simply means a charged particle; a positive charge is attracted to a negative charge and vice-versa. This means both positive and negative charged nutrients/elements form a symbiotic relationship and are available for uptake.


High CEC values indicate that a soil or substrate has a greater capacity to hold cations and where there is high CEC there is a large nutrient reserve. Coco substrate has high CEC.

On the downside…


High CEC favors the presence of Cd and other heavy metals in organic media. Put simply, heavy metals bond with organic particles and these often become available for uptake.


Epstein (2003) notes that soils with low CEC such as sands have a much lower binding power as compared to clays with a higher CEC.7


Due to this, it is imperative that plants grown in high CEC medias are fertilized with the cleanest nutrients/fertilizers possible. This makes product choice (re organic or inorganic nutrients) in formulation imperative. E.g. Low contaminant fertilizers can be manufactured using low contaminant base components. In the case of home formulation, nutrients containing a high degree of analytical, tech and pharmaceutical grade elements can be produced for about the same cost that you are now paying for standard nutrients (formulated with hort grade components) from stores. For instance, phosphate fertilizers can be purchased in food grade and analytical grade calcium nitrate could be used to reduce overall heavy metal contaminants. This is yet another advantage of manufacturing nutrients at home.


Chelators and Heavy Metal Uptake


Well-formulated hydroponic nutrients ensure that there is a high level of nutrient availability in the correct forms and ratios. Nutrition that offers a diverse range of bioavailable elements will prove more effective than nutrition that has less diversity, particularly where trace elements (metals) are concerned. For this reason combinations of organic and synthetic chelates are demonstrated to benefit yields.


The common types of chelates used by most hydro nutrient manufacturers are the synthetic chelates, EDTA (ethylenediaminetetraacetic acid) and to a lesser extent DTPA (Diethylene triamine pentaacetic acid). Chelates such as EDTA and DTPA have a high affinity for e.g. iron and generally form stable complexes with the metal across a pH range from 4 to 7.


DPTA, EDDHA and EDTA are large molecules that aren’t taken up by the plant. Put simply, the chelator leaves the metal ion (micro element) on the roots for uptake and then remains intact in the solution, soil or media. What this means is the chelator remains active in the soil/media and can then chelate heavy metals making them more bioavailable for uptake (I.e. the chelator bonds with heavy metals such as cadmium and delivers them to the roots of the plant for uptake).


All manufacturers use synthetic chelates in formulation. For instance, typically Iron will be supplied as Fe EDTA, with some manufacturers using Fe DTPA and/or Fe EDDHA. The bottom line – chelates aid micro element uptake  – the downside is that heavy metals such as cadmium also become more bioavailable to cannabis when they are chelated. 1


Some manufacturers are now identifying with this issue. For instance, Yarra (an agricultural fertilizer manufacturer) is currently working on producing biodegradeable chelates for use in agriculture.


Other than this, organic chelators (e.g. amino acids, fulvic acid), unlike the synthetic chelators are absorbed into the plant and not left lying around to chelate heavy metals. This makes organic chelators ideal for reducing heavy metal uptake, while still ensuring optimum yields.


Organic Chelators


The synthetic chelate EDTA does not penetrate the root. The chelate leaves the metal on the root surface before the root absorbs it. The synthetic chelator is then left in the nutrient, soil or media. Upon entering the plant the metal will immediately become chelated again by organic acids such as citric acids, malonic acid, tartaric acid (tartrate), and some amino acids (e.g. glycine) which occur naturally within the plant. This chelation process will then enable the nutrients to move freely inside the plant to areas where they are most needed.. Which brings us to our next point. Micro Proteinates – otherwise known as ‘glycinates’ or ‘proteinates’ – which can be purchased as zinc, boron, calcium, magnesium, iron, manganese and copper.


Amino Proteinates/Glycinates (Organic Chelates)


Amino acids are the “building blocks” of protein without which the formation of any living tissue is impossible.


Amino acids such as glycine are organic chelating agents that are naturally occurring in plants.  Glycine is the simplest amino acid with a molecular weight of 75.  Chelates of glycine with cations such as iron, zinc, and copper have been extensively studied. For instance, research conducted in USSR established that glycinates greatly stimulate the growth of plants.  The results concluded that zinc glycinate (zinc glycine chelate) increased the total, stem, root, and foliage weights by 194, 215, 254 and 147%, respectively.  Respective effects of manganese glycinate (manganese glycine chelate) were 79, 108, 110, and 15%.


Glycinates (proteinates) are organic chelates and unlike the synthetic chelates are absorbed along with the metal into the plant. This offers distinct advantages over synthetic chelators.


Glycinates contain 2 moles of ligand (glycine) and one mole of metal. The plant recognises this molecule as a protein like nitrogen, allowing it to travel to the growing points such as flowers, fruit and berries where is it required.


Micronutrients in proteinate/glycinate form have a very stable structure. They can be easily absorbed through the roots and directly join the biochemical processes in the plant.


Research has demonstrated:


1.  Glycinates increase the availability of micronutrients compared to common synthetic chelates (e.g. EDTA, DTPA).

2.  Crops tend to produce higher yields where glycinates are used.

For this reason, the use of at least some glycinates in high-end med formulation is recommended.



1. B. Kos and D.Lestan Soilwashing of Pb, Zn and Cd using biodegradable chelator and permeable barriers and induced phytoextraction by Cannabis sativa


Biological Microorganisms and Heavy Metal (HM) Uptake


Microbial populations are known to affect heavy metal mobility and availability to the plant through release of chelating agents, acidification, phosphate solubilization and redox changes and, therefore, microorganisms (in some cases) have the potential to enhance HM uptake.


Research demonstrates that microorganisms such as Bacillus subtillus 8, mycorrhizae (AM, AMF, VAM) 9 and Trichoderma harzianum (Trichoderma SPP) 10 play a role in heavy metal uptake rates. Given these micros are used by many med growers (and others) as biological innoculants and plant growth enhancers/stimulants this becomes an important area of consideration.


Benefits of Microbes: In Brief


When researching the literature on microbes and heavy metal uptake, it became apparent that the interaction of microbes and heavy metal uptake from soils depended on several key factors. These were:


  • Most significantly – Heavy metal concentration in soils, substrates and fertilizers (compost etc) is the dominant factor in HM plant tissue contamination
  • Heavy metal type, relative to microbe species
  • Plant species
  • Nutrient levels and their effect on microbe colonization (biomass)


Beneficial microbes have been demonstrated to enhance root growth, plant growth, and yields. Other than this, microbes play an important role as biofungicides, crop protectants and plant immune stimulants. For this reason the role of beneficial microbes in sustainable agriculture and bio agriculture cannot be underestimated.


The good news first…


Beneficial Microbes can aid nutrient uptake and act as, among other things, (put simply) chelators of metal ions (I.e. make elements such as Fe, Cu, Mn, Zn more available for uptake and translocation).


The bad news is:


Optimum chelation will also increase the potential for heavy metal uptake. I.e. In chelating metals such as Fe, Cu, Mn, Zn you are also chelating heavy metal ions such as Cd, Pb and Hg.


Arbuscular Mycorrhiza Fungi (mycorrhizae referred to as AM, VAM or AMF)


Mycorrhiza (AM) improves nutrient transfer from the soil to the roots of the host plant. Numerous trials have demonstrated increased biomass, yield weights, and root growth in AM colonized crops.


Weissenhorn et al states that under optimized conditions of normal agricultural practices AM may increase plant heavy metal (HM) absorption. 11 However, Voros et al (1998) notes that many of the studies on heavy metal uptake in AM colonized soils are contradictory. 12


Research on Heavy Metal Uptake and AM


Citterio Et al (2004), in research with Cannabis Sativa grown in HM contaminated soils populated with Glomus mosseae, discovered that Cd uptake and translocation was increased in heavily contaminated soils, while it Cd uptake was not influenced in partially contaminated soils.




“… plants grown in artificially contaminated soil accumulated most metal in root organ. In this soil, mycorrhization significantly enhanced the translocation of all the three metals from root to shoot.” 13


[End Quote]


However, research on tobacco by M. Janoušková et al (2004) found that Cd uptake was reduced when AM was present in soils.




“AM decreased the Cd uptake of the tobacco plants per unit of shoot biomass in both experiments and decreased the Cd accumulation in the shoots of the transgenic tobacco relatively to the non-transgenic tobacco. “14


[End quote]


Further research supports these findings, T. Takács et al (2002) note that AM reduced Cd uptake in ryegrass 15: El-Kherbawy et al (1988) demonstrated that AM “significantly” reduced heavy metal uptake in experiments with Alfalfa (Medicago sativa L.).16


Seemingly, VAM reduce HM uptake in enriched soils and substrates due to the hyphal complexes of mycorrhizae providing absorptive surfaces within the cortical cells of the host roots, thereby excluding metals from the shoot.17


Mycorrhizae Viability in Hydroponic Settings


The key to AM viability in hydroponics is that mycorrhizae will not colonize efficiently in high phosphorous environments (e.g. hydroponics, where traditional nutrients are used). Put simply, AM fix phosphorous and where high phosphorous already exists in fertilizers, soils or substrates, AM colonization and translocation is demonstrated to be ineffective. 18 What this means (in layman’s terms) is that nutrients must be formulated specifically with low phosphorous (P) levels to cater for mycorrhizae colonization/viability.


AM friendly formulas should optimally deliver no more than 10ppm of P (as dilute feed solution) in order to achieve efficient AM colonization. E.g.


Element                  ppm (nutrient values on delivery)

N                                    105

P                                    10

K                                    138

Ca                                   85

Mg                                  25

S                                    46


Bacillus Subtillus


Where Arbuscular mycorrhiza fungi seemingly have the potential to reduce HM uptake, research demonstrates that Bacillus subtillus and Bacillus pumilus bacterial strains (16S rRNA gene sequence strains) increase HM uptake. 19


Research by Hawkins et al with Z. mays (corn) and S. bicolor (sorghum/maize) demonstrated that B.subtillus and B. pumilus play an important role in increasing metal availability in soil, enhancing Cr, Pb, Zn and Cu uptake. 20


Trichoderma Harzianum


Trichoderma spp (e.g. T. harzianum, T. viride, T. koningil, T. hamatum) facilitate robust root growth, increase plant growth, increases nutrient uptake and fertilizer utilization, and enhances plant greenness, which may result in higher photosynthetic rates. Trichoderma spp also have been known for a very long time to have the ability to control plant pathogenic fungi.

Trichoderma species are used to produce cellulases. They are particularly effective as antagonists of the growth of other fungi, many of them plant pathogens, with the result that trichoderma species are important biocontrol agents.


On the downside…..


J. S. Chauhan et al (2009) found that a combination of Pseudomonas fluorescens and Trichoderma harzianum enhanced the uptake of Zn and Cd in Indian mustard (Brassica juncea) from soils containing three different concentrations of Zn (300, 600, 900 mg/kg) and Cd (5, 10 and 15 mg/kg). 21




1. J.C Lgwe, E.C.Nwokennaya1 and A.A. Abia (2000) The role of pH in heavy metal detoxification by bioabsorption from aqueous solutions containing chelating agents

2. New Zealand Biological Producers Council. Organic soil management in New Zealand.

3 and 4. Heavy Metals and Organic Compounds from Wastes Used as Organic Fertilizers: Compost Quality Definition Legislation Standards. Technical Office for Agriculture (Austria)

5. Autumn S. Wang1,5, J. Scott Angle1, Rufus L. Chaney2, Thierry A. Delorme3

& Roger D. Reeves (2005) Soil pH effects on uptake of Cd and Zn by Thlaspi caerulescens.

6. Autumn S. Wang et al (2005)

7. Epstein, E (2003) Land Application of Sewage Sludge and Biosolids.

8. R. A. Abou-Shanab , K. Ghanem, N. Ghanem and A. Al-Kolaibe (2007) The role of bacteria on heavy-metal extraction and uptake by plants growing on multi-metal-contaminated soils

9. Weissenhorn, C. Leyval, G. Belgy and J. Berthelin (1995) Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

10. ADAMS P.   DE-LEIJ F. A. A. M.  LYNCH J. M. (2009) Trichoderma harzianum rifai 1295-22 mediates growth promotion of cracl willow (Salix fragilis) saplings in both clean and metal-contaminated soil

11. I. Weissenhorn, C. Leyval, G. Belgy and J. Berthelin. (2004) Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

12. T. Takacs, B. Biro and I. Voros (2002) Arbuscular mycorrhizal effect on heavy metal uptake in ryegrass (Lolium perenne L.) in pot cultured with polluted soils.

13. J. Citterio, N. Prato, P. Fumigalli, R. Aina, N. Massa, A. Santagostino, S. Sgorbati, G. Berta (2004) The arbuscular mycorrhizal fungus Glomus mosseae induces growth and metal accumulation changes in Cannabis sativa L.

14. M. Janoušková , D. Pavlíková T. Macek, and M. Vosátka (2004) Influence of arbuscular mycorrhiza on the growth and cadmium uptake of tobacco with inserted metallothionein gene

15. T. Takacs, B. Biro and I. Voros (2002) Arbuscular mycorrhizal effect on heavy metal uptake in ryegrass (Lolium perenne L.) in pot cultured with polluted soils.

16. M. El-Kherbawy, J,S. Angle, A. Heggo, and RL. Chaney (1988) Soil pH, rhizobia, and vesicular-arbuscular mycorrhizae inoculation effects on Growth and heavy metal uptake of alfalfa (Medicao sativa L)

17. Bradley R, Burr AJ, Read DJ (1982) The biology of mycorrhiza in the Ericaceae VIII. The role of mycorrhiza infection in heavy metal resistance. New Phytol 91:197-209

18. H.-J. Hawkins and E. George (2004) Hydroponic culture of the mycorrhizal fungus Glomus mosseae with Linum usitatissimum L., Sorghum bicolor L. and Triticum aestivum L.

19. R. A. Abou-Shanab , K. Ghanem, N. Ghanem and A. Al-Kolaibe: The role of bacteria on heavy-metal extraction and uptake by plants growing on multi-metal-contaminated soils

20. R. A. Abou-Shanab , K. Ghanem, N. Ghanem and A. Al-Kolaibe: The role of bacteria on heavy-metal extraction and uptake by plants growing on multi-metal-contaminated soils

21. J. S. Chauhan J. P. N. Rai (2009)  Phytoextraction of soil cadmium and zinc by microbes-inoculated Indian mustard (Brassica juncea)




In 2001, the NSW Government (Australia) issued a permit to Nimbin local Andrew Kavasilas to allow a limited amount of high THC cannabis to be grown for research and analytical purposes. The research was undertaken with the assistance of the Centre for Phytochemistry (and its commercial arm Australian Phytochemicals Ltd) at the Southern Cross University in Lismore NSW.


Kavasilas tested three strains of outdoor organically cultivated cannabis and three variations of indoor hydroponic cannabis (commercial NSW, commercial SA and “home grown”) for heavy metal contaminants. His findings suggest:

  1. Genetics seemingly play a role in heavy metal uptake and translocation rates of at least some heavy metals *1
  2. Nutrition (contaminant levels in soils and fertilizers) plays by far the most significant role in heavy metal contamination (i.e. the more heavy metals in solution/fertilizers and soils the higher the potential rate of contamination in plant tissue)
  3. That based on the growing procedures (trial methodology) organic nutrition/fertilizers resulted in less heavy metal contamination than inorganic hydro fertilzers; although this finding is largely inconclusive due to two other indoor samples (commercially grown indoor hydro cannabis from SA and NSW) yielding equivalent levels of heavy metal contaminants to three outdoor samples with only one sample – Kavasilas’ own home grown (hydro) indoors – yielding far higher levels of heavy metal contaminants than all other (5) samples. *2 Further, Kavasilas research is in contrast to more comprehensive testing conducted by Advanced Nutrients in 2002-2003.


*1 Kavasilas grew Afghan, Durban and Skunk x Northern Lights outdoors. Leaf tissue analysis found 1.10mg/kg of lead in Durban with <0.1 in both the Afghan and Northern Lights x Skunk. Chromium was 4.10 (Durban), 4.30 (Afghan) and 2.40 (Skunk x Northern Lights). If no other variables (i.e. nutrition, heavy metal content in soil, and feed rates) were influencing factors this indicates that various strains of cannabis may uptake, at least, some heavy metals at differing rates.


*2 Cadmium in all samples (3 x organic and 3 x indoor hydro) was <0.1mg/kg with the exception of Kavasilas’ own “home grown” sample at 3.70mg/kg. In all instances Kavasilas’ “home grown” indoor cannabis tested significantly higher for contaminants than two separate samples of indoor cannabis and three samples of outdoor (5 samples total). The two samples of “commercial” indoor cannabis tested at the same rates as outdoor cannabis with the exception of chromium where both indoor samples tested lower (by average) than outdoor samples.  Further research is recommended.


See findings below.  Extracted from Medical Uses of Cannabis by Andrew Kavasilas (2003)




Advanced Nutrients Research (tissue analysis) 2002 – 2003


COMMENTS: Total Metals, Samples Digested 22 Nov 02

METHODS: Standard Methods for the Examination of Water and Wastewater



White Rhino at 56 days had:


Strontium                   32.7

Cadmium                   <0.05

Chromium                   0.9

Lead                          <1

Aluminum                   7.4




When comparing the Advanced Nutrients data to that of Andrew Kavasilas’ data the results are for the most part consistent bar for Kavasilas’ own homegrown hydro which inexplicitly has higher levels of HM contamination than all other hydroponically grown produce. This raises concerns as to the accuracy of Kavasilas’ data in one instance.


What is apparent based on all tests is that low levels of cadmium, low levels of lead, low levels of chromium and low levels of arsenic are present in both hydroponically grown and organically grown cannabis. Aluminum, a non heavy metal element, but potentially toxic nevertheless, may also pose a problem and more research into this area is needed.


Further, comparing the two sets of data suggests that higher HM counts are present in organically grown produce than are present in hydroponically grown produce.


Recommendations for minimizing cadmium and other heavy metal exposure


  • Cannabis/medicine should be grown using hydroponic and/or organic growing methodologies using fertilizers (and soils re organics) that are low in heavy metal contaminants
  • Cannabis/medicine should ideally be grown using non-organic fertilizers formulated with laboratory, food, and/or analytical and pharmaceutical grade fertilizers to minimize HM contamination.
  • Where organic fertilizers are used, products should be tested for Cd and other HM levels or a guaranteed analysis that includes heavy metal content should be obtained.
  • Med dispensaries should collate a list of various organic and inorganic fertilizers (brands) and their heavy metal content – this information should then be made available to med growers. Lab tests for Cd and other contaminants should be conducted independently
  • Immunosuppressed individuals should eat or vaporize their medicine to minimize Cd and other contaminant absorption/exposure


Author’s note 1: Over the years I have seen various “hydro” manufacturers make claims as to the use of analytical or pharmaceutical grade elements in their products. After analyzing some of these products (and investigating through other means) it became clear that while they may (and I stress “may”) be incorporating some low contaminant fertilizers in formulation their use – if any – was extremely low, with the bulk of the formula being manufactured from standard horticultural grade base components. For instance, having looked at formulas from one company who claims to use pharmaceutical grade elements in formulation it became clear that the use of pharmaceutical grade components was minimal/minute (0.27% of the total mineral weight used in production). Other than this, after running lab analysis on another brand that claims to use analytical or food grade elements it became clear that if they were using analytical grade, the contaminant levels looked very much like standard fertilizers produced from hort grade products. After vieweing some of their promotional material (a video) where Yarra Fertilizers (hort grade products) appeared to be used in manufacture the sitution became somewhat dubious.  I.e. it looked like this particular manufacturer was engaging in suspect marketing.


Author’s note 2: Due to the higher purchase cost of analytical, food and pharmaceutical grade elements one must be wary of claims as to blends containing these (stated) elements (this may change and I will keep you advised/updated).  Put simply, the hydro industry is a cost driven market and manufacturers simply can’t formulate competitively priced products using expensive base components. By way of example, one manufacturer claims to use British Pharmaceutical grade elements in production. As a guestimate (based on component purchase prices, wholesale and retail markups) a product entirely formulated with these elements would need to retail at $400.00USD plus for a 5L set. This is yet another advantage of formulating yourself. I.e. for about the same cost that you pay for a hort grade product in stores you will be able to formulate using analytical, food grade and pharmaceutical grade components.



1. Department for Health and Human Services, Agency for Toxic Substances and Disease

Registry, 2008

2. The Ministry of Agriculture and Forestry, NZ

3. Jarup, L. (1998) Health effects of cadmium exposure—a review of the literature and a risk estimate

4. Department for Health and Human Services, Agency for Toxic Substances and Disease  Registry, 2008

5. P, Linger et al (2001) Industrial hemp (Cannabis sativa L.) growing on heavy metal

contaminated soil: fibre quality and phytoremediation potential

6. Marth, E et al (2000) Influence of cadmium on the immune system. Description of

stimulating reactions. Central European journal of public health

7. Food and Agriculture Organization of the United Nations.

8. Burger J et al (2001) Kelp as a bioindicator: Does it matter which part of 5 M long plant is used for metal analysis

9. Boening D et al (1999) Ecological effects, transport, and fate of mercury: a general review

10. Curtis L. and Smith. B (2002) Heavy Metal in Fertilizers: Considerations for Setting Regulations In Oregon Department of Environmental and Molecular Toxicology, Oregon State University Corvallis, Oregon

11. Gulz, P (2003) Arsenic Uptake of Common Crop Plants from Contaminated Soils and Interaction with Phosphate. University of Munich

12. Andrew Kavasilas (2003) Medical Uses of Cannabis, ISBN 0-9751806-0-6

13. Jones, Clement and Hopper (1973) Lead uptake from solution by perennial ryegrass and its transport from roots to shoots.

14. Kumar et al (1995) Phytoextraction: The use of plants to remove heavy metals from soils.

15. Kos, B. Gremen, H. Lestan, D (2003) Phytoextraction of lead, zinc and cadmium from soil by selected plants

16. Andrew Kavasilas (2003) Medical Uses of Cannabis

17. Golovatyj SE, (1999) Effect of levels of chromium content in a soil on its distribution in organs of corn plants. Soil Res Fert 197– 204.

18. Prato N et al (2003) Cannabis sativa for heavy metal contaminated soil restoration

19. European Commission (2005) Communication from the Commission to the Council and the European Parliament on Community Strategy Concerning Mercury

20 B. Z. Siegel, Lindley Garnier and S. M. Siegel (1988) Mercury in Marijuana

21. Batáriová A et al (2005) Blood and urine levels of Pb, Cd and Hg in the general population of the Czech Republic and proposed reference values

22. B. Z. Siegel, Lindley Garnier and S. M. Siegel (1988) Mercury in Marijuana

23. Patra M. and Sharma A (2000) Mercury Toxicity In Plants

24. United States Environmental Protection Agency (Dec 1997) Mercury study report to congress

25. B. Z. Siegel, Lindley Garnier and S. M. Siegel (1988) Mercury in Marijuana

26. B. Z. Siegel et al (1988)

27. Andrew Kavasilas (2003) Medical Uses of Cannabis, ISBN 0-9751806-0-6



Other Medical Marijuana Contaminants



Spores of fungi/moulds are common in cannabis. At least 88 species of fungi attack Cannabis and more are being discovered every year (McPartland & Hughes 1994, McPartland & Cubeta 1996).  Research has demonstrated that fungi spores survive in smoke inhaled from marijuana cigarettes. Most fungi are plant pathogens and their ingestion will typically not harm healthy humans; however, some fungi cause harm by producing secondary toxins.


Studies have reported levels of biological contaminants in cannabis, which include Aspergillus fungus and bacteria, potentially leading to fulminant pneumonia, especially among the immunosuppressed.


A.flavus (Aspergillus flavus), is a common mould that is found in the environment and produces aflatoxins. Aflatoxins are naturally occurring mycotoxins and are among the most carcinogenic substances known; they are just under 2000 times more toxic than even the most toxic pesticides. Aflatoxins survive combustion and, therefore, pose a risk to medial marijuana consumers.


A.flavus has a worldwide distribution. Although it is universally found in air, soil, dust and water, higher fungal burdens have been noted particularly in contaminated peanuts, corn, grains and decaying organic matter. Disease prevalence is highly variable with different institutions reporting different species of Aspergillus as the predominant pathogen.


The primary mode of transmission to humans is by inhalation. Aspergillus spores are released in the air and may remain airborne for prolonged periods. As a result, spores are ubiquitously found in air and contaminate anything they in contact with, including plants. There is increasing concern about contaminated food, environmental and occupational exposure to fungal spores of different species, especially to the aflatoxin-producing strains of A. flavus, in different parts of the world. Higher frequency of pulmonary function impairment and allergic respiratory diseases including asthma has been reported in farmers around the world. In addition to inhalation, a secondary route of transmission has been reported via contact with skin or wound (trauma and postoperative), contamination of intravenous solutions, wound dressings and marijuana inhalation.


About 185 different species of Aspergillus have been identified, of which 20 are documented to cause human disease. Aspergillus spores, upon inhalation, can lead to colonisation, allergic manifestations or invasive infection depending on the host’s immune system. Invasive aspergillosis is rare in people who have a good immune system but contributes to significant morbidity and mortality in immunosuppressed patients. “Aspergillosis” refers to several forms of disease caused by a fungus in the genus. The majority (approximately 80%) of invasive Aspergillus infections are caused by Aspergillus fumigatus. The second most frequent (approximately 15–20%) pathogenic species is Aspergillus flavus and to a lesser extent, Aspergillus niger and Aspergillus terreus. Aspergillus flavus has emerged as a predominant pathogen in patients with fungal sinusitis and fungal keratitis in several institutions worldwide.


Conidium (fungal spores) of the most commonly involved pathogenic Aspergillus species (spp.) are relatively small, with sizes ranging from 2 to 5 micron. Due to their small size, conidium will become deposited deep into the lung after inhalation. In most individuals, inhaled conidia will be cleared, without affecting the individuals health. Immunocompromised patients, however, are extremely susceptible to local invasion of respiratory tissues by deposited conidium, resulting in invasive aspergillosis. Aspergillus. Aspergillosis fungal infections can occur in the ear canal, eyes, nose, sinus cavities, and lungs. In some individuals, the infection can even invade bone and the membranes that enclose the brain and spinal cord. Most cases of invasive aspergillosis present with pneumonia. Therefore, it has been hypothesized that the inhalation of airborne Aspergillus conidium is a direct cause of pulmonary infection in immunocompromised patients.


While research is limited surrounding aspergillosis-related pulmonary illness, resulting from marijuana use by immunecompromised AIDS sufferers high fatality rates are shown in relevant medical research. Invasive aspergillosis occurs in advanced AIDS and most commonly affects the lungs, although brain involvement has also been frequently reported.


Other high-risk groups include bone marrow transplant recipients and patients with central nervous system or disseminated aspergillosis.


In one case a 34-year-old man presented with pulmonary aspergillosis 75 days after he had undergone a marrow transplant for chronic myelogenous leukemia. The patient had smoked marijuana heavily for several weeks prior to admission. Cultures of the marijuana revealed Aspergillus fumigatus with morphology and growth characteristics identical to the organism grown from open lung biopsy specimen. Despite aggressive antifungal therapy, the patient died.


In another case a 46-year-old patient with acute myeloid leukemia (AML) whose disease manifested as fever, chills and dry cough was admitted to hospital. Despite broad antibiotic coverage he remained acutely ill with spiking fever, shaking chills, and hypoxemia. A thorough investigation revealed that before becoming acutely ill the patient smoked daily tobacco mixed with marijuana from a “hookah bottle”. While waiting for tobacco and “hookah water” cultures, doctors started antifungal therapy. Resolution of fever and hypoxemia ensued after 72 hours. Tobacco cultures yielded heavy growth of Aspergillus species, suggesting that habitual smoking of Aspergillus-infested tobacco and marijuana caused airway colonization with Aspergillus. Leukemia rendered the patient immunocompromised, and allowed Aspergillus to infest the lung parenchyma with early occurrence of invasive pulmonary aspergillosis.


Moody et al. (1982) have evaluated waterpipes for smoking Aspergillus- contaminated marijuana. They found only a 15% reduction in transmission of fungal spores.


In yet other cases, Chusid et al. blamed Aspergillus fumigatus for causing near-fatal pneumonitis in a 17-year-old. They noted that the patient had buried his marijuana underground for “aging”, creating an ideal environment for microbiological contamination. Similarly, Llamas et al recovered Aspergillus fumigatus from marijuana owned by a patient suffering bronchopulminory aspergillosis, while Shwartz scraped Aspergillus flavus from the sinuses of a marijuana smoker who suffered severe headaches.


Aspergillus flavus contamination has been identified in Dutch coffee shop products.


Additionally, in research conducted by Steven L. Kagen et al (1983) the authors note:




“The possible role of marijuana (MJ) in inducing sensitization to Aspergillus organisms was studied in 28 MJ smokers by evaluating their clinical status and immune responses to microorganisms isolated from MJ. The spectrum of illnesses included one patient with systemic aspergillosis and seven patients with a history of bronchospasm after the smoking of MJ. Twenty-one smokers were asymptomatic. Fungi were identified in 13 of 14 MJ samples and included Aspergillus fumigatus, A. flavus, A. niger, Mucor, Penicillium, and thermophilic actinomycetes. Precipitins to Aspergillus antigens were found in 13 of 23 smokers and in one of 10 controls, while significant blastogenesis to Aspergillus was demonstrated in only three of 23 MJ smokers. When samples were smoked into an Andersen air sampler, A. fumigatus passed easily through contaminated MJ cigarettes. Thus the use of MJ assumes the risks of both fungal exposure and infection, as well as the possible induction of a variety of immunologic lung disorders.”

[End Quote]


A study by Verweij et al (2000) showed that samples of both tobacco and marijuana were heavily contaminated with filamentous fungi including A. fumigatus.


And in research conducted by M. Halt (1998), the level of toxigenic moulds and mycotoxins were analyzed in 62 samples of medicinal plant material. The most predominant fungi detected were: Aspergillus, Penicillium, Mucor, Rhizopus, Absidia, Alternaria, Cladosporium and Trichoderma. Aspergillus flavus, was present in 11 or 18% of the 62 medicinal plant samples. The medicinal plant samples, contaminated with A. flavus were also analyzed for the mycotoxins aflatoxin, ochratoxin and zearalenone; ochratoxin was found in one of the 7 samples analyzed. The study suggests that medicinal plant material, if stored improperly, allowed for mould growth after harvest.


Microbiological Toxins and Medical Marijuana Screening


The Dutch Medical Marijuana program was legalized in 2003. Growing, processing and packaging of the plant material are performed according to pharmaceutical standards and are supervised by the official Office of Medicinal Cannabis (OMC).

The quality is guaranteed through regular testing by certified laboratories. Under Dutch regulations medical marijuana should contain no heavy metals, pesticides, or fungus contaminants.


However, in the Netherlands a tolerated illicit cannabis market exists in the form of ‘coffeeshops’, which offers a wide variety of cannabis to the general public as well as to medicinal users of cannabis. Since cannabis has been available in the pharmacies, many patients have started to compare the price and quality of OMC and coffeeshop cannabis. As a result, the public debate on the success and necessity of the OMC program has been based more on personal experiences, rather than scientific data.
The general opinion of consumers is that OMC cannabis is more expensive, without any clear difference in the quality.
In 2005, a study was conducted in order to show any differences in quality that might exist between the official and illicit sources of cannabis for medicinal use. Cannabis samples obtained from randomly selected coffeeshops were compared to medicinal grade cannabis obtained from the OMC in a variety of validated tests. Many coffeeshop samples were found to contain less weight than expected, and all were contaminated with bacteria and fungi. No obvious differences were found in either cannabinoid- or water-content of the samples. The obtained results show that medicinal cannabis offered through the pharmacies is more reliable and safer for the health of medical users of cannabis.1


Similarly, Canada, like Holland, has a legalized medical marijuana program and thousands of Canadians are federally licensed to possess and use medical marijuana through Health Canada. In Canada, medical marijuana is tested not just for active ingredients such as THC, but for mold, fungus, pathogens — including bacteria — and metals, such as lead, cadmium, mercury and arsenic. Further, government regulated medical marijuana is gamma-irradiated for safety purposes to ensure no harmful mould spores are present.


A similar situation has occurred in the U.S. where, although, the U.S. medical marijuana industry is not legalized at a federal level, the industry itself, in some cases, has established standards to ensure that medical marijuana sold to consumers is not contaminated by aflatoxins.


For instance, Steep Hill Cannabis Analysis Laboratory notes, that while 85 percent of the marijuana tested at Steep Hill Lab has shown traces of mould, only 3 percent of those samples have been deemed unsafe under general guidelines for herbal products.2


Harborside Health Center, Oakland’s largest med dispensary, note on their website that approximately 2% – 4% of cannabis they test is found to show positives for pathogenic moulds at levels where the produce is rejected.3


However, these numbers appear low when compared to those of the Werc Shop which had a “Gold level of microbiological testing” and is modeled after USP ( U.S. Pharmacopeial Convention) designations levels for dried botanicals. USP Reference Standards are closely tied with the documentary standards published in the USP–NF, Food Chemicals Codex, and Dietary Supplements Compendium. Materials based directly on official monographs in the USP–NF—whose standards and procedures are enforceable by the U.S. Food and Drug Administration—are recognized for use in official standards in the United States, and their use is effective in demonstrating compliance with statutory requirements. Under USP testing procedures the WercShop sees approximately 30% failure rates in the microbiological classification.




1) Arno Hazekamp (2006) An evaluation of the quality of medical grade cannabis in the Netherlands




Prevention of Aflatoxins/Mycotoxins

Growroom Practices


Aspergillus spores drift on air currents, dispersing themselves both short and long distances depending on environmental conditions. When the spores come in contact with a solid or liquid surface, they are deposited and if conditions of moisture are right, they germinate (Kanaani etal., 2008). In all cases fungi consume organic material wherever humidity and temperature are adequate. For Aflatoxins this is a warm and moist/damp environment where fungi proliferate and mycotoxin levels can become high. Mycotoxins resist decomposition, so they can easily remain in cannabis product, post harvest. To minimize risk of aflatoxin infection ensure that air humidity (RH) is between 45-55% and that the growroom has adequate airflow. Use an exhaust fan during the night cycle as well as the day cycle because humidity climbs quickly during the night cycle in rooms that are not vented during this period.


Aspergillis grow abundantly on decaying vegetation where it has been found in large numbers in mouldy hay, organic compost piles, leaf litter and the like. Most species are adapted for the degradation of complex plant polymers. For this reason, the growroom should be kept clean of decaying organic matter at all times.


Fungal growth and aflatoxin contamination are the consequence of interactions among the fungus, the host and the environment. The appropriate combination of these factors determine the infestation and colonization of the substrate, and the type and amount of aflatoxin produced. However, a suitable substrate is required for fungal growth and subsequent toxin production, although the precise factor(s) that initiates toxin formation is not well understood. Water stress, high-temperature stress, and insect damage of the host plant are major determinig factors in mold infestation and toxin production. Similarly, specific crop growth stages, poor fertility, and high crop densities have been associated with increased mold growth and toxin production. Aflatoxin formation is also affected by associated growth of other molds or microbes . For example, preharvest aflatoxin contamination of peanuts and corn is favored by high temperatures, prolonged drought conditions, and high insect activity; while postharvest production of aflatoxins on corn and peanuts is favored by warm temperatures and high humidity.


As with people, aflatoxins can more easily colonize a sick plant (host) than a healthy plant. For this reason, optimal growroom conditions should be maintained (temperature, light, airflow, CO2 levels, RH etc) which, in turn, promotes optimal growth/yields and plant health. (Read more on optimum growroom parameters here)


Cleanliness is next to godliness! Thoroughly clean and bleach the growroom between and during crop cycles. Ensure any rotting vegetative matter is removed. Clean up water spills immediately as they can contribute to an increase in air humidity (RH).


Filter Inlet Air Using HEPA Filters


Because mycotoxins/aflatoxins are a common mould found in the outside environment, HEPA  (High-Efficiency Particulate Arresting) filters should ideally be placed on inlet fans to keep bacteria, pests, and fungus commonly found in outdoor environments from the growroom. HEPA filters are critical in the prevention of the spread of airborne bacterial and viral organisms and, therefore, infection in hosts. Research has shown that where HEPA filters are employed in hospital settings, aflatoxin counts are greatly reduced – if not eliminated totally. Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against airborne disease transmission.


Water Treatment


Aflatoxins/mycotoxins have been detected in water storage tanks and in chlorine treated mains water supplies.1 In one study it was shown that Norwegian municipal drinking water may be an important contributor to the transmission of a wide variety of mold species to water consumers2


It is important to note that RO water filtration does not remove fungal pathogens and, in fact, may increase their incidence due to biomass build up in the filters. For this reason, pharmaceutical grade marijuana production should incorporate treatment of water to remove aflatoxin/mycotoxin contaminates. There is a very simple way to do this.


Use of Beneficial Bacteria and Fungi is Solution (B.subtilus and Trichoderma spp.)    


Bacillus subtilis produces peptidolipid compounds of the iturin group that have been shown to have antifungal properties. In one study, the activity of iturin A, produced by B. subtilis strain B-3, was tested. Paper disks impregnated with various concentrations of iturin A were placed on agar plates seeded with conidia of toxigenic species of Fusarium, Gerlacia, Penicillium or Aspergillus. Most isolates were inhibited at where even low levels of B. subtilus were present. italicum, P. vindicatum, A. ochraceus and A. versicolor were most strongly inhibited.3


Calistru and McLean reported that two isolates of T. harzianum and T. viride were capable of inhibiting the growth of A. flavus.4 The primary mechanism of antagonism of Trichoderma is microparasitism. Trichoderma also produce volatile and non-volatile antibiotics to suppress target pathogens.


An added benefit to using beneficial bacteria and fungi in solution is they inhibit other pathogenic moulds such as pythium and fusarium – protecting the plants against all manner of disease (read more about beneficial bacteria and fungi in hydroponics here)




1)    Identification, Significance and Control of Fungi in Water Distribution Systems. Joan Kelley, Russell Paterson, Graham Kinsey: International Mycological Institute, Bakeham Lane, Egham,

2)    Sybren de Hoog and Ida Skaar Gunhild Hageskal, Ann Kristin Knutsen, Peter Gaustad, G (2006) Diversity and Significance of Mold Species in Norwegian Drinking Water

3)    M. A. Klich, A. R. Lax and J. M. Bland (1991) Inhibition of some mycotoxigenic fungi by iturin A, a peptidolipid produced by Bacillus subtilis

4)    C. Calistru, M McLean and P. Berjak (1997) In vitro studies of the potential for biological control of Asperellis flavus and Fusarium moniliforme by Trichoderma species.


Drying, Storage, and Handling


Fungi and bacteria can inhabit plant material after it has been harvested. For instance, Aspergillus is a commonly occurring fungi in the environment and once a crop has been harvested and there are no residual fungicide then it is still susceptible to Aspergillus.
The infestation by opportunistic fungi cannot occur in plant material below 15% moisture content (MC). Properly dried marijuana contains approximately 10% MC (material below 10% MC becomes excessively brittle). Consumers should prevent marijuana from reabsorbing moisture above 15% MC.




Dried cannabis should be stored in vacuum-sealed bags and/or sellable quantities (grams, eighths etc) stored/supplied in snap lock bags that can be air released and resealed immediately after use.




Med dispensaries and users should ensure that hygienic practices in handling cannabis products are adhered to.


Medical Best Practice


Carefully cultivated and harvested marijuana reduces the potential for contamination by microorganisms. For added protection, material must be screened for contamination before it is packaged for use as medical marijuana. Since opportunistic infections pose the greatest danger to immunosuppressed med users, marijuana should be sterilized by gamma irradiation. Lastly, consumers should be given careful instructions to ensure their marijuana does not become contaminated prior to use.


Preventative Sprays (Botanical)


Research has shown that, toxigenic fungi are sensitive to the 12 essential oils, and particularly sensitive to thyme and cinnamon. The oils of thyme and cinnamon at ⩽500 ppm have been shown to completely inhibit fungi.1


Additional research has shown that the growth of a toxigenic strain of Aspergillus flavus decreased progressively with increasing concentration of essential oils from leaves of Cinnamomum camphora and rhizome of Alpinia galanga incorporated into SMKY liquid medium. The oils significantly arrested aflatoxin B1 elaboration by A. flavus. The oil of C. camphora completely checked aflatoxin B1 elaboration at 750 ppm (mg/L) while that of A. galanga showed complete inhibition at 500 ppm only. The oil combination of C. camphora and A. galanga showed more efficacy than the individual oils showing complete inhibition of A. flavusproduction even at 250 ppm.2




1.    K.M Soliman. R.I Badeaa (2002) Effect of oil extracted from some medicinal plants on different mycotoxigenic fungi

2.   Bhawana Srivastava, Priyanka Singh, Ravindra Shukla and Nawal Kishore Dubey (2008) A novel combination of the essential oils of Cinnamomum camphora and Alpinia galanga in    checking aflatoxin B1 production by a toxigenic strain of Aspergillus flavus



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