Imidacloprid and other insecticide detections in Oregon streams: Results from the Pesticide Stewardship Partnership program

The State of Oregon initiated the Pesticide Stewardship Partnership (PSP) in response to the detection of problematic levels of organophosphate insecticides in the Hood River Watershed. Sampling of streams began in 1999 and continues to the present. Over time the PSP program has expanded and currently operates in nine watersheds throughout Oregon. Those areas are being sampled for pesticides on a regular basis to determine if continued sampling and/or management measures are indicated. The pesticide detection database amassed by the PSP program over the last two decades provides valuable information on changes in pesticide use practices. While most of the pesticide detections have been herbicides, insecticides have generally been the compounds of greatest concern as their established benchmark levels are usually much lower than for other pesticides.

Sampling for imidacloprid was started in 2008 and, presently, imidacloprid is the insecticide that is most frequently detected statewide. The detection limit for imidacloprid is higher than the current aquatic health benchmark level thereby making any detection of imidacloprid above the established benchmark. In 2020, out of 469 samples there were 82 pesticide detections above the aquatic life benchmark of which 64 were insecticides and 45 of those were imidacloprid. Therefore, imidacloprid alone was responsible for over half of the statewide detections above the aquatic health benchmark. From 2016 to 2020 the six pesticides most commonly found above the benchmark include four insecticides: imidacloprid, chlorpyrifos, malathion, and diazinon.