News Ticker

OPINIONS: The dangers of contaminants in medical marijuana

By Trisha Scott
Las Vegas Lab director, Pazoo Inc.

With the legalization of medical marijuana expanding in several states, there’s a growing need to test products for the presence of contaminants that could be harmful to patients.


As this industry continues to flourish, and further knowledge about potential contaminants is gained, the number and types of contaminants that testing labs have to detect is only going to grow.

It is important to ensure these lots are below defined thresholds for fungal toxins, bacteria, heavy metals and pesticide residues. The cost to the grower if contaminants are detected is huge, since lots containing contaminants typically have to either be destroyed or can only be used for extracts, edibles, and topical products in instances where the contaminant is removed or degraded in the processing of these products.

Due to required growing conditions, patient safety concerns, and the complexity of these compounds, testing for pesticide residues is becoming one of the most important tests needed for contaminants in medical marijuana.

States have implemented requirements about growing medical marijuana under indoor controlled conditions, which has increased the use of pesticides on medical marijuana lots in order to maintain healthy plants.

There are states that do not require testing for pesticide residues, but many have established specific lists of pesticides that must be below particular levels in usable medical marijuana.

For example, independent testing laboratories in Nevada have to determine the amount of 22 pesticides found in each marijuana lot.


Acceptable quantities of pesticide residue varies greatly and solely depends on the health hazards of the active ingredients of those pesticides. For the more dangerous pesticides, quantities of more than 0.02 ppm (parts per million) is not allowed, while other pesticides can be present at 15 ppm.

For states that require testing for the presence of pesticides, determining the allowable amount is not simple.

There is little information known on what levels truly pose a health risk to the patient from residues in marijuana, nor what amounts of residues may be present in inhaled smoke.

Very few studies have been done, although up to 69% of pesticide residue has been found in smoked product (Sullivan, Nicholas et al. 2013. Determination of Pesticide Residues in Cannabis Smoke. Journal of Toxicology Volume 2013 (2013), Article ID 378168, 6 pages).

As the industry grows, states and testing labs need to have more information on the risks associated with these pesticides in medical marijuana, and the allowable amounts should be more consistent from state to state. There is the potential for increased testing and a decrease in allowable amounts, which has an impact on growers, but the goal is to provide safe medical marijuana products to patients.

Pesticide residue testing poses a unique issue in laboratories because there is a large range of chemical differences in the types of pesticides being screened.

While many other contaminants can use one detection method, pesticide residue testing can require more.

With the pesticides that need to be screened in Nevada, two different types of detection are needed. In order to identify the pesticide and the quantity, chromatography and mass spectrometry are required.

Due to the chemical composition of the residues, both gas chromatography and liquid chromatography must be used to accurately identify the required pesticide residues. The cost of these machines is a huge investment (hundreds of thousands of dollars) and it takes significant training to use and accurately evaluate the data from them.

Because of the potential for health risk, it is worth it for this industry to begin studying the genetics of marijuana strains for potential resistance or tolerance to particular pests.

Studies that identify particular genes that confer tolerance to a pest would open up the medical marijuana industry to genetic selection for pest tolerance and potentially decrease the use of some pesticides.

Trisha Scott is the lab director of the Las Vegas Lab owned by Pazoo, Inc (PZOO) – a unique organization whose commitment to health, wellness and safety includes best-in-class laboratory testing of medical cannabis and cannabinoids. To learn more about cannabis testing, please visit

Leave a comment