Setting pesticide residue tolerances on

Cannabis sativa inflorescence (and products made therefrom) for

human consumption in Washington state


Written by Nick Mosely and Zack Iszard



In this paper, we present a brief overview of topics critical to decision making when considering pesticide screening of Cannabis consumables. We discuss the inherent challenges faced when setting tolerance levels for any crop, as well as challenges unique to this crop, and we describe the methods used by the EPA and other similar agencies around the world to address those challenges. We present a framework for establishing limits in the absence of federal oversight which utilizes publically available toxicology data, including data made public by the federal government, to inform its decisions. We apply this framework to the 15 pesticides currently on the DOH's list for screening in Cannabis, and we propose that the state of Washington adopt the following limits for pesticides residues on Cannabis:


These limits are not fixed in nature, and as such they should not be set in stone. This is an evolving list, and as more data are generated the list and the limits will necessarily be updated.



The Washington state legal marijuana market is currently regulated by the Washington State Liquor and Cannabis Board (WSLCB) for recreational purposes under the Washington Administrative Code (WAC) 314-55. New regulation, posed to come into effect in the summer of 2016, will incorporate an extant medical marijuana market in this state into the legal marijuana market under the purview of the WSLCB in conjunction with the Washington state Department of Health (DOH).

The DOH has proposed new rules for medical marijuana (WAC-246-70) that act to supplement the rules enforced by the WSLCB. Included in these new rules are new quality assurance testing requirements including screening for pesticides, mycotoxins, and heavy metals. While the proposed rules describe tolerance levels for the latter two, the DOH is yet to define tolerance levels for pesticides.

Very limited research is available to guide decision making regarding what concentrations of pesticides should be allowed on or in cannabis products. Marijuana producers are disallowed from using pesticides primarily because the Environmental Protection Agency (EPA), the federal agency responsible for approving pesticides, is unable to approve pesticide use for cannabis crops or establish tolerance levels due to the plant's federal status as a Schedule 1 narcotic.

Cannabis industry stakeholders of Washington state are now tasked with establishing limits without guidance from the federal agencies typically responsible for such work. The difficulty is further compounded by the diverse and very unique methods by which this drug is administered, including combustion and inhalation, vaporization and inhalation, oral consumption, dermal application, sublingual application, suppository insertion, among others.


If the application of pesticides is not allowed on this crop, should the tolerance limit be zero?

Setting pesticide tolerance limits of zero for crop commodities is not appropriate. Pesticides are ubiquitous in our environment, and detectable levels can be found nearly anywhere if you look hard enough, even in drinking water. While we would certainly prefer not to find pesticides in our consumables, we do cope with the fact that exposure is a daily occurrence. Pesticide drift is a term that describes the airborne movement of pesticides away from their intended target, and that phenomena is considered normal in the agricultural field.

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Isn't smoking pesticides more dangerous than eating them?

That is a reasonable assumption to make. Though there does not exist much data to support that assumption, in the absence of evidence we should err on the side of caution. It is important to consider that the danger level presented by a pesticide exposure is influenced more by the size of the dose than by the route of exposure. The EPA has extensively investigated risk of exposure to pesticides from cigarette smoking [GAO] [Djordjevic], and has used that research to set tolerance limits for 37 pesticides approved for application on tobacco as well as 20 pesticides with tolerance limits for inadvertent exposure. The tolerance limits established for pesticides on tobacco are not much lower than the limits established for other crop commodities. Even tolerance levels for highly toxic and persistent pesticides, such as Dichlorodiphenyltrichloroethane (DDT), are not exceptionally low for tobacco (0.1 ppm). The agency justifies this through research analyzing data on toxicity and the residue levels that remain on tobacco and in tobacco smoke, which have generally concluded that the low levels of residues measured in tobacco smoke are a minor source of human exposure and do not pose health concerns that require mitigation [GAO]. The most dangerous cases of human inhalation exposure from pesticides occur when farm workers and farm neighbors are actively exposed to aerosolized pesticides during and after application. The level of exposure in these cases can be quite high and can pose a significant health risk [Lee].


How does the EPA determine tolerance limits?

Setting pesticide tolerances on any agricultural product for human consumption is not a simple, straight-forward, or easily referenced task. Ideally, the risk assessment is performed individually for each crop-pesticide combination. For sufficiently similar propositions to other approved combinations, data acquired from previous investigations can be used [EPA-1]. The EPA takes a multistep approach when determining recommended pesticide limits, or tolerances. This risk assessment process is a general evaluation of ecological or human risk from any anthropogenic environmental stressor [EPA-2]. Typically, tolerance limits are set for pesticide-crop combinations where application of the pesticide is approved, but sometimes limits for incidental exposure are also defined.

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Without EPA guidance, how can state governments make informed decisions about pesticide tolerance limits?

Such rigor as is executed by the EPA in determining tolerances for pesticides in the Unites States does not come cheap, and is beyond the capability of most state governments and even national governments. That said, the process used by the EPA to evaluate pesticides is both transparent and collaborative, enabling state and national governments to piggyback on that same effort to establish similar -- or even more rigorous -- standards for themselves. The cannabis industry of Washington state should be able to set reasonable pesticide tolerance limits using existing data and precedence.

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Have pesticide tolerance levels ever been established for Cannabis?

Yes. Colorado, Oregon, and Nevada have all drafted legislation that describe tolerance limits for pesticides on Cannabis, and mandate testing for pesticides on Cannabis in at least some circumstances. Colorado bases its tolerance limits for Cannabis on the federal tolerance limits for tobacco [DenverPost]. Nevada bases its tolerance limits on the most stringent acceptable standard for the pesticide residue on any food item, as set by the EPA [NV.GOV]. The Oregon Health Authority consulted a team of Toxicologists to set limits for Cannabis in that state [OHA]. In all of these cases, there has been acknowledgment that more research is needed to better inform these decisions. The states have all used different methods in determining tolerance levels, but nonetheless have come to similar conclusions. In all states, it is important for the laws describing tolerance limits to be subject to revision as more data and research comes to light.


[7 CFR]

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