Template:Past, Present, and Future of Cannabis Laboratory Testing and Regulation in the United States/Laboratory testing of cannabis/Analytical aspects of cannabis/Contaminants

Generally speaking, a contaminant is an unwanted substance that may show up in the final product, be it recreational marijuana or a pharmaceutical company's therapeutic tincture. The following are examples of contaminants that laboratories may test for in cannabis products.

Pesticides: Pesticides represent an oft-discussed aspect not only of growing cannabis but also performing analytical testing on it. One of the core issues, again, is the fact that on the federal level marijuana is illegal. Because it's illegal, government agencies such as the Environmental Protection Agency (EPA) have historically failed to develop standards or guidelines for what's safe when it comes to residual pesticides in cannabis, let alone how to best test for them. Additionally, researchers have faced their fair share of difficulties obtaining product to test over the years. The end result is we're only now barely understanding how inhalation of pesticide-coated marijuana smoke affects long-term health, and standard methods for pesticide application and testing have been slow to develop. With numerous pesticide products and little oversight on what growers apply to their plants, combined with the technical difficulty of testing for pesticides in the lab, pesticides remain one of the most difficult contaminants to test for. That said, several classes of of pesticides are commonly applied during cannabis cultivation and can be tested for by labs:

• avermectins: function as an insecticide that is useful against mites, which are a common problem for cultivators
• carbamates: function as an insecticide, similar to organophosphates, but with decreased dermal toxicity and higher degradation
• heterocyclics: function as a broad set of compounds with many industrial uses, including as pesticides
• organochlorides: function as a broadly useful chemical in applications such as plastics, cleaning agents, insulators, and pesticides
• organophosphates: function as the base of many insecticides and herbicides, valued for its easy organic bonding
• pyrethroids: function as the base of most household insecticides and exhibits insect repellent properties

Solvents: In 2003, Canadian Rick Simpson published a recipe of sorts for preparing cannabis extract via the use of solvents such as naphtha or petroleum ether. Claiming the resulting oil helped cure his skin cancer, others hoping for a cure tried it, and the solvent method of preparation grew in popularity. Dubious healing claims aside, the solvent extraction method remains viable today, though it has evolved over the years to include less harmful solvents such as supercritical carbon dioxide, which has low toxicity, low environmental impact, and beneficial extraction properties. However, chemical solvents are still used, and if not evaporated out properly, the remaining solvents can be particularly harmful to sick patients using the extract. As for what solvents should be tested for, it gets a bit trickier, though Chapter 467 of United States Pharmacopeia and The National Formulary, the Oregon Health Authority's December 2015 technical report on contaminant testing of cannabis, and the Massachusetts Department of Public Health's response to public comments on cannabis testing provide helpful guidance. Listed solvents include benzene, butane, cumene, dimethoxyethane, ethanol, hexane, pentane and propane, among others.

Heavy metals: 2013 research on contaminant testing on the behalf of Washington State provides insights into heavy metals and why they're looked for in cannabis testing. That research, as well as other more recent sources, tell us:

• Heavy metals contribute to several health problems, including those of a neurological nature.
• Cannabis can "hyperaccumulate metals from contaminated soils."
• Research parallels can be found in tobacco research and how the FDA regulates heavy metal content in foods.
• The most prominently tested heavy metals include arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), and nickel (Ni).

Mycotoxins and microorganisms: "The ideal conditions for cannabis growth are also ideal for the growth of potentially harmful bacteria and fungi, including yeast and molds," say Shimadzu's Scott Kuzdzal and William Lipps, "therefore microbial contamination poses health risks to consumers and immunocompromised individuals." In truth, these concerns have already borne out. In fact, the University of California, Davis reported in February 2017 one of its patients had contracted an incurable fungal infection from inhaling aerosolized marijuana. They later tested 20 marijuana samples from Northern California dispensaries—using specialized techniques—and found a wide variety of potentially hazardous microorganisms.

The degree to which such contaminants commonly appear in grown and stored cannabis material and to which microbiological contaminants should be tested is not clear, however. As mentioned previously, the U.S. EPA has historically had little in the way of significant guidance on cannabis testing, including microbiological contaminants. Like heavy metal testing, parallels are drawn from microbial testing guidelines and standards relating to tobacco and food, where they exist. As warm, moist environments are conducive to microorganism growth, maintaining stable moisture levels during cultivation and storage is essential. Regularly measuring water activity—how moist something is—is particularly useful as a front-line preventative tool to better ensure microbial growth is limited. Regardless, testing of some kind is still required by many U.S. states, including for organisms such as:

• Alternaria
• Aspergillus
• Cladosporium
• Cryptococcus
• E. coli
• Fusarium
• Mucor
• Penicillium
• Salmonella
• Trichothecium