Subscribe to Newsletter
Testing & Processing Pesticide analysis, Tools & technology

The Thin Green Line

On January 1, 2014, Colorado became the first state to allow legal sales of retail (non-medical) cannabis for adults over age 21. Colorado regulators working across multiple state agencies are tasked with oversight of the emerging cannabis industry. The numerous challenges regulators face must be addressed in the absence of guidance from the federal government – and there is little precedent. Testing of cannabis presents a unique set of challenges, and execution of some key regulatory requirements for laboratories, such as proficiency testing, has been complicated by the infancy of regulated cannabis testing, the limitations imposed by marijuana’s schedule I classification, and its tightly controlled legal structure.

How are Colorado regulators addressing some of these challenges?

When it comes to cannabis testing, product safety and accurate labeling information are the foremost concerns. However, when trying to define testing requirements there are substantial gaps in knowledge, largely due to a lack of research data; historically, most of the limited research conducted was focused on adverse effects.

The numerous challenges regulators face must be addressed in the absence of guidance from the federal government – and there is little precedent.

A prime example of a challenge arising from a lack of data is implementation of regulatory requirements for pesticide residue testing. No pesticides are registered for use on cannabis and, therefore, the potential health hazards posed by applying pesticides to marijuana have not been assessed, nor have tolerance limits been defined. Evidence from multiple states shows that some marijuana cultivators have resorted to illegal application of pesticides to save their valuable crops when threatened by insect infestation or fungal overgrowth. Because the potential health effects of these pesticides are unknown, Colorado has taken the position that until scientific studies are conducted to officially establish that a particular pesticide may be applied to cannabis, and tolerance limits established as necessary, the presence of any banned pesticide will be considered a threat to public health and safety.

Standard analytical methodologies for testing marijuana and the vast array of marijuana products do not currently exist, so labs are developing their own methods.

In an effort to address the fact that no pesticides are currently registered for use specifically on cannabis, the Colorado Department of Agriculture (CDA) has adopted rules establishing criteria to determine which pesticides may be allowed in cannabis cultivation. These criteria specify that the pesticide must have broad label language allowing it to be used on unspecified crops, must be suitable for use at the intended site of application (for example, a greenhouse), and must be approved for plants intended for human consumption. CDA maintains a list of approved pesticides based upon these criteria (1); any pesticide not on the list is banned for use on cannabis.

The Colorado Department of Public Health and Environment (CDPHE), in collaboration with the other state agencies and stakeholders, has been working to implement requirements for pesticide testing. Again, because health-based tolerance limits have not been established – and it is not analytically possible for a laboratory to test to a concentration of zero – it is necessary for states to define actionable or reporting limits for pesticides to ensure consistency of result reporting across laboratories, as each will have a unique limit of detection. Colorado, like some other states, has decided to base these limits upon laboratory detection capability, and we have conducted three multi-lab detection limit studies using cannabis matrices with several private marijuana laboratories and the CDA laboratory. The final study was conducted in June 2017 and those results will be used to inform Colorado’s reporting limits for banned pesticides in cannabis.

With time, I’m confident that standardization of cannabis related processes and regulations will be achieved.

Pesticide testing is only one example of the many challenges facing cannabis regulators. Gaps in knowledge and data also exist when it comes to defining testing requirements for other potential contaminants, such as microbials and residual solvents. Standard analytical methodologies for testing marijuana (a very complex matrix) and the vast array of marijuana products (edibles, tinctures, concentrates, and so on) do not currently exist, so labs are developing their own methods – each of which is considered intellectual property. Even the application of standard methods from other industries requires careful method optimization and validation due to the differences in the sample matrices and huge variety of matrix types – marijuana can be added to virtually anything! This is one reason that laboratory accreditation/certification is an essential requirement – accurate laboratory testing not only ensures accurate labeling, but protects consumers and patients, and also can protect a cultivator or manufacturer from possible liability. 

Regulators must tread carefully when defining cannabis testing requirements, to balance protection of public health and safety with the risk of making testing too expensive, potentially driving black market activities. Regulatory testing requirements are best constructed upon evidence-based science, but that can be difficult given the lack of currently available data. This has resulted in many regulatory changes during these first few years of legalized marijuana, and the system will certainly continue to change as knowledge advances. Nonetheless, with time, I’m confident that standardization of cannabis related processes and regulations will be achieved. Colorado’s state regulatory agencies continue to work diligently through these challenges, using the expertise of industry members, scientists and technical experts, and other interested parties, to ensure competent cannabis testing and protect public health and safety.



  1. Colorado Department of Agriculture, “Pesticide Use in Cannabis Production Information”. Available at Accessed 25 July 2017.

Receive content, products, events as well as relevant industry updates from The Cannabis Scientist and its sponsors.

When you click “Subscribe” we will email you a link, which you must click to verify the email address above and activate your subscription. If you do not receive this email, please contact us at [email protected].
If you wish to unsubscribe, you can update your preferences at any point.

Register to The Cannabis Scientist

Register to access our FREE online portfolio, request the magazine in print and manage your preferences.

You will benefit from:
  • Unlimited access to ALL articles
  • News, interviews & opinions from leading industry experts
  • Receive print (and PDF) copies of The Cannabis Scientist magazine