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Cannabis-Pesticide Testing Should Be Standardized Across the US, Say Researchers

By Alexander Beadle

Published: Sep 26, 2022   
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Regulators should take a closer look at the health risks presented by a growing cannabis market with no national-level guidance on contamination or pesticide use, a new study argues.

Published in Environmental Health Perspectives, the authors constructed a list of all contaminants covered by US state-level policies on medical and recreational cannabis. They then compared this list to data taken from the testing records of Californian cannabis flower and extract samples.

The researchers found that the contaminant levels seen in these samples may have otherwise flown under the radar in other states. Given the additional risks that contamination may present to medical cannabis users, the authors say that national-level guidelines should be strongly considered.

Approach to microbial contaminants needs improvement

The current federal prohibition of cannabis has led to a situation in which cannabis has been legalized in a state-by-state manner, with each jurisdiction imposing their own rules on how the drug should be regulated.

In lieu of any national-level guidance from the US Department of Agriculture, state-level public health agencies or other governing bodies have been left to ascertain appropriate targets and action limits for potential contaminants.

To review current cannabis contaminant regulations in the United States, the study authors searched for relevant regulatory documents in the official government websites of the 36 states (and the District of Columbia) that had legalized some form of cannabis as of May 2022.

In total, the researchers found a total of 679 contaminants listed in these regulations, which fit into five broad categories: pesticides (including insecticides, herbicides, and fungicides), solvents, microbes, inorganic compounds, and mycotoxins. Just sixteen contaminants were classified as “other”.

Pesticides were the most common class of contaminant found; 551 of the 679 total items identified were pesticides. Seventy-four solvents were named in these regulations, with just 21 microbes, 12 inorganic compounds, and 5 mycotoxins listed.

“In this study, we identified 21 microbes and 5 mycotoxins in the contaminant regulations in 36 states and Washington, DC. This accounts for less than 4% of all 679 regulated contaminants we found. In contrast, most of the reported contaminant outbreaks in 2020 - 2021 were caused by microbes,” lead study author Maxwell Leung, PhD, told Analytical Cannabis.

“Additionally, Fusarium mycotoxins – which were prevalent contaminants in several agricultural commodities – were not regulated by any jurisdiction. Taken together, these findings suggest that the current regulatory approach toward microbial contaminants requires further refinement,” Leung said.

Contaminant exposure may vary state-to-state

To examine the current contamination load in real-world cannabis samples, the researchers mined pre-existing anonymized data from 5,654 cannabis flower and 3,760 concentrate samples submitted to the Californian state-licensed cannabis testing laboratory, CannaSafe. These data were recorded between June 2020 and October 2021, well before the lab announced its intent to close this summer due to the issue of lab shopping.

Given the large scale of CannaSafe, the authors of this new study estimated that this data sample represents 6% of all cannabis testing conducted in California over that period. In that time, the average contamination test failure rate was 2.3% for flower and 9.2% for concentrate products. Across all submitted material, the flower samples contained some amount of 39 of the 103 regulated contaminants in Californian law, with the concentrated containing 61.

The authors note that the contaminant concentrations observed in these Californian samples would fall below the regulatory action levels set in many other legalized jurisdictions. This is an issue, they say, as it means some populations may be at a greater risk of contaminant exposure.

“The current discrepancy in state-level regulations suggests that some cannabis users may have a higher level of contaminant exposure in some states than in other states. Such a discrepancy may also confuse the manufacturers and discourage compliance,” Leung said.

“A national-level policy based on conventional human health risk assessment methodologies – similar to what has been applied to other agricultural and food commodities and drugs sold in the US – would provide better protection to recreational users as well as medical patients.”

A total of 42 legacy pesticides – chemicals that were once used in the US for pest control but which are now banned due to health concerns – were also included in the state-level pesticide lists. Many of the action levels for these appeared to be lifted directly from previous US Environmental Protection Agency tolerance documents. However, these were originally established for foods and so would not be transferable to smokable cannabis products.

“Legacy pesticides can sometimes be found in cannabis products. This is likely due to the fact that there is no federal guidance on what and how pesticides should be used in cannabis. As such, some cannabis growers resort to any pesticides they can find and many jurisdictions seem to see a need to regulate those pesticides,” Leung explained.

“For example, the insecticide chlordane was banned for use in the US in the 90s, but it was still one of the most commonly detected insecticides in cannabis in our study.”

Medical cannabis patients may be most at risk

Confusing state-level guidance on cannabis contamination is an irritating state of affairs for industry actors. But inconsistent exposure to pesticide contamination is a serious problem when it comes to medicinal cannabis use.

Patients who are immunocompromised or who have seizures may be particularly vulnerable to the health hazards of pesticide and microbial contamination in cannabis, the authors say. Immunocompromised patients would be at a greater risk of developing an infection if exposed to microbial hazards; previous research suggests that many of the insecticides detected in this study could target the neurotransmitter signaling pathways associated with seizures and epilepsy.

In order to evaluate the scale of this risk, the authors reviewed medical cannabis use reports from the 25 legalized jurisdictions where these data were publicly available. They found that the vast majority of patients were prescribed medical cannabis for treating pain, followed by post-traumatic stress disorder. There were nearly 45,000 vulnerable patients prescribed cannabis during cancer treatment, and approximately another 21,000 prescribed cannabis for epilepsy.

“The discrepancy in the current state-level regulations highlights a lack of information and standards to inform those regulatory decisions. Currently, there is no national survey on contaminants in cannabis (with our study being the largest one in open literature at this point). As such, each state is deciding on substances of concern individually and adding them to the regulations,” Leung said.

“Ideally, contaminant regulations should be based on the toxicity and exposure information of each contaminant,” Leung recommends. “It would require more research in both areas, particularly in susceptible patients who use cannabis for medical purposes. Having this information would allow us to assess contaminant health risks more accurately and improve the current regulatory approach.”


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