Six-year study finds streams contaminated with pesticides from illegal cannabis grows in Northern California

A newly published six-year study has documented stream contamination from illegal and banned pesticides used at trespass cannabis cultivation sites established on National Forest lands in northern California. Ecologists from the Integral Ecology Research Center (IERC), alongside collaborators from the U.S. Forest Service Law Enforcement and Investigations (USFS LEI), University of California Davis, and the California Department of Fish and Wildlife, published the findings in the Water Quality Research Journal.

The study employed a novel technology, polar organic chemical integrative samplers (POCIS), which were placed in streams near trespass cannabis cultivation sites to determine if any of the water soluble pesticides commonly used to protect cannabis plants could be detected in the nearby waterways. The POCIS were used to investigate water contamination at two spatial scales; the microscale, immediately upstream and downstream of cultivation sites, and at a larger watershed scale. Pesticides, including the illegal and banned insecticide carbofuran, were detected at 11% of the microscale locations downstream of cultivation sites during the first rain season following the last known pesticide application.

The results of this study help to better understand the risks that cannabis cultivation sites can pose to the local waterways. Streams within National Forest lands provide critical habitat for a variety of at-risk aquatic species, and also support over 50% of California's freshwater resources. These findings add to a growing body of research documenting the many deleterious effects that this illegal activity poses to the environment and wildlife. IERC has previously published studies documenting the poisoning of federally endangered species such as the fisher (Pekania pennanti) and Northern spotted owl (Strix occidentalis caurina) from rodenticides used at cultivation sites.

The study’s lead author, Ivan Medel, an Associate Ecologist with IERC, said, “This study is significant as it confirms that the highly toxic pesticides used within these cultivation areas do not only contaminate the sites themselves, but have the potential to negatively impact downstream waterways and habitats.” Because this research shows that hazardous materials can be carried into the nearby waterways during rain events, the results stress the need for proactive approaches to mitigate the impacts that these sites pose, as well as a continued need for additional research into the scope of the issue and its effects.

Medel went on to say “Being aware of these impacts can assist resource managers with watershed impact assessments and resource planning initiatives.” IERC has led the environmental investigation and clean-up of hundreds of illegal cultivation sites in conjunction with law enforcement from the U.S. Forest Service and California Department of Fish and Wildlife, removing trash, pesticides, and other hazardous materials from the forests. This approach has led to the removal of hundreds of toxic pesticide containers left on National Forest lands before they can leak out into the environment. Funding for the study was provided by a U.S. Fish and Wildlife Service Traditional Section 6 Grant, California Department of Fish and Wildlife, Plumas National Forest, a National Fish and Wildlife foundation Grant, U.S. Forest Service Law Enforcement and Investigations, and the County of Trinity, California.

Open Access Article

Ivan D. Medel, Mourad W. Gabriel, Greta M. Wengert, Michael S. Filigenzi, Deana L. Clifford. (2022). Passive monitoring of soluble pesticides linked to cannabis cultivation: a multiscale analysis. Water Quality Research Journal, 57(4), 233-246.
More information about Integral Ecology Research Center’s Cannabis and Ecology Research Program: http://www.iercecology.org/iercresearchprograms/ceprogram/
Additional publications from Integral Ecology Research Center on Toxicants in Wildlife and the Forest Environment: http://www.iercecology.org/publications-and-reports/toxicants-wildlife/