Is your bug spray getting into the Willamette River? According to sampling done by the Long Tom Watershed Council (LTWC) over the past two years, some of the most frequently found pesticides in Amazon Creek are DEET, a chemical used in insect repellent sprays like OFF!, and diuran, an herbicide that interferes with photosynthesis. At a LTWC public meeting on July 24, Kevin Masterson of the DEQ and Jason Schmidt of the LTWC presented the results of the sampling and discussed the potential and largely unstudied danger of mixing multiple chemicals in creek water.

Masterson explained that DEET, which is applied directly to the skin to repel mosquitoes, is detected all across the country because it dissolves easily in water and breaks down at a relatively slow rate. Its presence in Amazon Creek could be due to people washing off with hose water, which slides off paved areas and directly into the creek water, connecting to the Willamette River through the Long Tom River and eventually getting to the Columbia River and Pacific Ocean. Other pesticides infiltrate the creek in a similar way, when rain washes chemicals off plants and pavement and pours through storm drains into the creek.

Schmidt and Masterson took water samples from five different sites along the creek and looked for approximately 105 pesticides and breakdown products, and the sampling showed 26 chemicals present in Amazon Creek, detected at varying levels of frequency.

“The good news here is that while it shows we’ve got a lot of detections, most of them are under the benchmarks the EPA Office of Pesticides has set for aquatic life,” Masterson says. The benchmarks show how highly concentrated a chemical can be in the water before it starts to have an adverse effect on organisms. In general, as long as the chemical level is below the EPA benchmark for a certain species, the water continues to be safe for that species.

One concern Schmidt and Masterson shared at the meeting dealt with the unknown impacts of 26 different chemicals mixing together at different concentration levels in the creek water. “It’s another wild card in this whole mix of issues here because if we find eight chemicals in one sample, what does that mean relative to additive percentages for the toxicity in a species?” Masterson asks. “Those are some unknowns that we need to take into account and prioritize.”