The Pesticide Problem
To keep cannabis consumers safe, tests for pesticide residues must use multiple methods.
I recently attended the 2017 Emerald Conference in San Diego, California, a meeting devoted to the science of cannabis, where I chaired a session on Analytical Testing and Sampling Schemes (1). I gave the opening presentation, which focused on pesticide testing of cannabis, something I helped pioneer with the QuEChERS sample preparation method, in collaboration with Frank Dorman at the Pennsylvania State University (PSU).
We analyzed illicit cannabis provided by the PSU police (the only kind we could get, since Pennsylvania was not a medical marijuana state at the time) and found numerous incurred pesticides, including fungicides and insecticides at low to high ppb levels, a herbicide, and the pesticide synergist, piperonyl butoxide.
Since our original work, cannabis testing laboratories have been rapidly adopting the QuEChERS approach for analysis of pesticides in medical and retail cannabis, as US state programs try to determine how to regulate this new industry. Still to be determined: which pesticides can be safely used on cannabis, what pesticides to test for in cannabis and cannabis products, and the maximum levels of pesticides allowed. Since the US EPA has not authorized any pesticide specifically for use on cannabis, regulation falls to states (2). The number of pesticides proposed for determination by any one state is typically limited (3,4). This probably reflects the desire to start small by targeting the pesticides most commonly used on cannabis, while laboratories develop their skills and validate their methods. However, the high cost of capital equipment could also be influencing the list of pesticides tested for, as testing labs seem to be mainly purchasing LC-MS/MS over GC-MS/MS for this work.
The best suggestion I’ve seen for a cannabis-specific target pesticide list is from Rodger Voelker and Mowgli Holmes of the Cannabis Safety Institute (5). They applied toxicity, availability, and use-case rational and came up with just over 120 compounds. Importantly, the list includes pesticides that can only be monitored appropriately, or are monitored more easily, using GC. Indeed, if a cannabis testing lab only applies LC-MS/MS, then numerous pesticides could be missed. This is significant given that in the same document Voelker and Holmes report that over 70 percent of select cannabis flower samples in Oregon were contaminated with pesticides, some at very high levels.
The title of my presentation at the recent Emerald Conference included the words, “Cannabis is Food”, a nod in part to borrowing QuEChERS from the food safety community. We should remember that one of the most elegant parts of QuEChERS, by design of its inventors (6), was to produce an extract that could be used for LC and GC analyses, since we need both techniques for comprehensive coverage of pesticides we might encounter in food, and now cannabis.
- The Third Annual Emerald Conference, San Diego, California, USA, February 2-3, 2017.
- United States Environmental Protection Agency, Pesticide Use on Marijuana, 27 January 2016 bit.ly/2kce4V7
- Oregon Administrative Rules, Oregon Health Authority, Public Health Division, Chapter 333, Cannabis Testing, OAR 333-007-0400, Exhibit A, Table 3, Pesticide Analytes and Their Action Levels. bit.ly/2l10Q1z
- The Commonwealth of Massachusetts Executive Office of Health and Human Services, Department of Public Health, Bureau of Health Care Safety and Quality, Medical Use of Marijuana Program, Exhibit 5, Minimum Analysis Requirements for Residues of Pesticides and Plant Growth Regulators Commonly Used in Cannabis Cultivation. bit.ly/2lw0gGe
- R Voelker, M Holmes, Pesticide Use on Cannabis, Cannabis Safety Institute, June 2015. bit.ly/2lyfWcU
- M Anastassiades et al., “Fast and easy multiresidue method employing acetonitrile extraction/partitioning and ‘dispersive solid-phase extraction’ for the determination of pesticide residues in produce”, J AOAC Int, 86, 412–431 (2003).