Researchers have found significant levels of potentially harmful chemicals at the sites of former illegal cannabis farms, years after the operations ended.
Scientists with the U.S. Geological Survey and the nonprofit Integral Ecology Research Center, with help from the U.S. Forest Service law enforcement, recently published their findings in the journal "Science of The Total Environment."
Researchers looked at three former cannabis grow sites on national forest land in Northern California, known as “trespass grows." They found pesticides, cannabis-related compounds like THC, rubber-related compounds known as plasticizers, and even pharmaceuticals. Concentrations were highest in topsoil but were also found in water and sediment.
Mourad Gabriel, co-founder of the Integral Ecology Research Center, said he was surprised to find such high levels of chemicals present years after growers abandoned a site.
“By documenting these contaminants, we are taking the first step in understanding the long-term ecological risks posed by illegal cannabis cultivation," he said.
Gabriel said the findings raise concerns about potential downstream effects on fisheries or humans.
“[We] can potentially create that kind of step ladder link of a potential correlation of exposure that may reside in humans from these source points," he said.
Gabriel said the study, which is the most comprehensive to date, provides a foundation for future research into ecological impacts from trespass grows. The paper notes there are thousands of sites in California alone.
In July, Siskiyou County declared a state of emergency over the widespread use of foreign-labeled pesticides at illegal cannabis farms.
Previous research from the Integral Ecology Research Center found that cannabis pesticides in Northern California had contaminated local waterways.
