Meeting the Demand for Pesticide Screening of Marijuana

Strong interest at the state level for legalization of both medical and recreational marijuana use has created a marijuana production industry in the US that is growing rapidly. In fact, half of the states have already legalized marijuana for one or both of these uses. The number of states allowing use of marijuana could also continue to grow after the fall election cycle, adding more impetus to the growth of the marijuana industry.

However, the federal ban on any use of marijuana is still in place, as marijuana is a Schedule 1 substance under the Controlled Substances Act, which means that quality and safety standards imposed by federal regulatory agencies such as the Food and Drug Administration (FDA) do not apply to the production of marijuana products. As a result, the implementation of safeguards to protect growers, dispensers and customers has been a struggle.

A marijuana testing industry has also emerged and is expanding to provide the ability to implement such safeguards, providing analysis of potency (cannabinoids), pesticides, fungicides, mycotoxins, residual solvents in marijuana extract products, and terpenes, which are responsible for the much of the aroma in marijuana.  The growth of this industry mirrors that of the marijuana products market, with marijuana testing estimated to approach $850 million by the year 2020, assuming full legalization. The urgent need for meaningful safety standards and proper testing has been underscored by numerous recalls of marijuana products in Colorado in recent years.

In fact, a report by the Cannabis Safety Institute in 2015 indicated that half of the cannabis (marijuana) soldby Oregon dispensaries contained one or more of the 65 pesticides that were monitored. The danger of exposure is greatly increased in popular marijuana extracts, in which the manufacturing processes may actually concentrate pesticides. In addition, the efficiency of transfer of pesticides into marijuana smoke may be as high as 70%. The urgent need for sensitive and comprehensive methods for pesticide analysis is critical.

Several testing companies across the United States are providing marijuana pesticide analysis. Many techniques are available to these laboratories, including ELISA, gas chromatography (GC) and liquid chromatography (LC). However, mass spectrometer (MS) detectors are the gold standard to provide sufficient accuracy of identification of pesticides, as they enable identification of low levels even in very complex matrices such as marijuana. As a result, LC-MS and GC-MS methods are the preferred standard for sensitive and accurate pesticide residue testing, as they minimize false positive and false negative results.

Because of the absence of federal or coordinated state oversight, there is no universally accepted list of pesticides that must be tested for in marijuana products. For example, the state of Oregon has established four categories of pesticides that must be tested for in marijuana products, but they include 491 different compounds, making comprehensive testing very difficult. Also, of the pesticides that are actually being used on marijuana, many do not fall in these classes.  For the most part, laboratories are left to determine their own lists of pesticide analytes. In addition, there is no federally mandated or validated method available for determination of trace levels of pesticides in marijuana products.

Given these realities, the best approach for establishing pesticide residue testing would be to adopt methods that provide highly accurate and sensitive detection of pesticides in the complex matrix of the marijuana plant. A good starting point is method AOAC 2007.01.  AOAC INTERNATIONAL is a globally recognized, not-for-profit association that develops voluntary consensus standards for analytical methods. Method AOAC 2007.01 has been validated for use with thousands of agricultural products.

The Oregon Growers Analytical  (OG analytical) marijuana testing facility has indeed adopted a method based on AOAC 2007.01 for its pesticide testing, using both GC-MS and LC-MS.  This method was in fact used in the study conducted by the Cannabis Safety Institute in 2015 to assess pesticide levels in medical marijuana in Oregon. Using a list of 65 pesticides, data was generated from 389 samples of marijuana flowers and 154 samples of marijuana concentrates. Many of these samples were found to contain pesticide residues at levels that were above those allowed by Oregon law, as well as above the levels typically mandated by the EPA for agricultural products.

Automation enables wide adoption of marijuana pesticide screening

Method AOAC 2007.01 uses QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation, which was developed to help monitor pesticides in a range of food samples. Unfortunately, the QuEChERS approach requires several manual steps such as sample comminution, shaking, centrifugation, and dispersive solid phase extraction (dSPE), making it a very labor-intensive process. Obviously, for method AOAC 2007.01 to be widely used by high-throughput testing laboratories for pesticide screening of marijuana, automation would be key.

GERSTEL has developed an automated sample preparation and analysis workflow for the screening of pesticides residues in various food matrices by LC-MS/MS, and it can be adapted for use for marijuana product screening. The automated of QuEChERS extracts was performed with disposable pipette extraction (DPX). The DPX tips retain the sorbent material with a screen. The use of these tips has been found to provide comparable results to those obtained using manual methods based on dSPE tubes.

Automation of the QuEChERS extract cleanup using DPX has been enabled by the GERSTEL MultiPurpose Sampler MPS XL configured with the DPX option. The sample preparation system was interfaced to an Agilent 1200 Infinity LC system with an MS/MS instrument as the detector. Two transitions per parent compound were monitored using a single Scheduled MRM™ method.

In a single run, more than 200 pesticides were monitored in extracts of fruits, vegetables, and spices, including many of the pesticides that OG Analytical screens. Both quantification and qualitative data were collected simultaneously, and linear calibration curves produced R2 values of 0.99 or greater, down to less than 10 ng/mL. More importantly, this workflow enabled a 15 minute persample cycle time, including “just-in-time” PrepAhead sample preparation performed on the MPS XL using GERSTEL MAESTRO software.

The demand for pesticide screening of marijuana will continue to grow as legalization expands. When laboratories expand or are created to meet this demand, they will need not only consistent and common sense pesticide regulations, but also the instrumentation and methodologies to rapidly, reliably and cost-effectively screen large numbers of pesticides present at trace levels.  GERSTEL provides the automated sample preparation solutions and method expertise to meet the growing demand.