By Andrea Michelson

Even as the legal cannabis industry booms, the black market persists with competitive prices and a lack of red tape on its side. As Jodi Helmer reports for JSTOR Daily, illegal growers set up an estimated 14,000 grow sites on federal and private lands in 2018—and that was just in Humboldt County, California.

Illegal cannabis growing operations pose a huge threat to the ecosystems of public forests, Eric Westervelt reports for NPR. Without any sort of regulations, illegal growers can use banned insecticides and other chemicals to shield their crops from pests. Using these substances excessively can have devastating consequences for nearby wildlife and water supply.

At one illegal growing site in California’s Shasta-Trinity National Forest, ecologists and law enforcement agents found evidence of toxicants like Bromethalin, a rat poison, and carbofuran, an insecticide that is banned by the Environmental Protection Agency. Speaking about carbofuran, wildlife ecologist Greta Wengert of the Integral Ecology Research Center (IERC) tells NPR, "It is incredibly toxic. A quarter teaspoon could kill a 600-pound black bear. So obviously just a tiny amount can kill a human. It remains in an ecosystem for a long period of time."

The effects of these toxicants can move through the ecological food chain, much like the long-term harms once posed by DDT. When the prey base—rodents, in this case—comes into contact with dangerous chemicals, every species that eats them is at risk of ingesting the chemicals as well. Some species, like a carnivorous weasel called the Pacific fisher, also pass the toxins to their offspring in utero and through the mother’s milk. The Pacific fisher is under consideration to be listed as an endangered species, in part due to high exposure to toxic rodenticide at illegal grow sites in the forests where it lives.

Mourad Gabriel, an IREC wildlife disease ecologist, tells NPR that he’s already seeing signs of contamination in aquatic ecosystems as well. Grow sites located uphill run the risk of poisoning nearby waterways with chemical runoff. What’s more, JSTOR Daily’s Helmer reports that trespassing growers will often divert water from streams to irrigate their plants, threatening local fish populations.

But even legal cannabis growing outfits have a high environmental toll. Cannabis a particularly thirsty plant, so the water cost is not limited to outdoor operations or illegal growing. Each individual plant requires almost six gallons of water per day, reports Clayton Aldern for Grist. That’s two gallons more than it takes to run one load in an energy-efficient dishwasher. To limit water use, the California State Water Resources Control Board has established strict guidelines, with prohibitions on using surface water for irrigation during the dry season, JSTOR Daily reports.

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