Final test results of DDT contamination on cannabis farms found concentrations in soil of the banned pesticide that exceeded the state threshold at five growers south of Malott.
All contaminated farms were in a 5-mile stretch, where there are 18 cannabis farms in all, the Washington State Liquor and Cannabis Board (LCB) said last week.
Affected growers and the Washington Department of Ecology have received money from the state to study ways to remediate the contamination.
The contamination was present at more than twice the level that requires action, LCB Communications Director Brian Smith said. The majority of the cannabis grown on the affected farms was sold in retail stores as concentrates, he said.
The LCB discovered the contamination in random tests of retail products. In all, 14 tested positive for DDT, with nine above the limit that requires action, and five below that limit. All contaminated products were recalled.
The growers did not apply DDT, which was banned in 1972 because of the harm it caused to wildlife. DDT is considered a probable human carcinogen.
But DDT was used widely in orchards from the 1940s until it was banned. The cannabis farms are on former orchard sites and LCB believes the contamination is a remnant from that era.
Samples of cannabis foliage, oil/rosin and water were tested in a Washington State Department of Agriculture (WSDA) lab earlier this year. Of the 97 total samples, WSDA detected DDT in 66 — 28 in foliage and 38 in oil/rosin. The majority of the contaminated samples had DDT above the action limit — eight in foliage and 36 in oil/rosin. Twenty-four more foliage samples could exceed the action limit if concentrated. Concentrating the plants into oils can increase contamination by a factor of five to 10, LCB said.
An administrative hold was placed on all products exceeding the action limit. Producers with contamination below that limit can sell their products, as long as they aren’t concentrated, LCB said.
The affected farms will be tested on a quarterly basis.
The 2023 state budget allocated $200,000 to WSDA to help farmers remediate their soils. Three growers applied for the funding, and each received one-third of the total, according to the WSDA report to the Legislature at the end of June.
Because it takes between three and eight months to grow a cannabis plant, and additional time for testing, there are no data yet on the efficacy of the grant money in reducing the levels of soil contamination, WSDA said. But the grants have been effective in relieving some of the economic burden on the farmers, who are experimenting with adding soil to reduce contamination on their farms, WSDA said.
The Legislature also allocated $5 million to Ecology for a pilot study to remediate soil contamination in Okanogan County and to recommend a statewide remediation program for DDT-contaminated soil by the end of next year.
DOE is in the planning phase for the study. It will have two parts, one to analyze contamination levels in soil and how much of that contamination is retained in the cannabis product. The second phase is a feasibility study to determine how much it would cost to grow plants in pots or to add clean soil to reduce the concentration of DDT, Ecology Central Region Communications Manager Emily Tasaka said.
The first part of the study will be done in a lab, where Ecology will plant cannabis in soil from the contaminated farms to determine how the level of soil contamination translates to the plant.
Ecology will follow up with test plots on farms to determine the cost of growing plants in pots or mixing in clean soil to reduce DDT concentration. The study won’t necessarily be done on farms in Okanogan County, but it will use soil from the contaminated farms, Tasaka said.
These are the first instances of DDT and DDE contamination found in cannabis in the state since it became legal in 2012.