USGS Finds Pesticides in River, Traces in Drinking Water

A 2000-2005 U.S. Geological Survey (USGS) study found a variety of pesticides in water samples from the lower Clackamas River mainstem and tributaries, along with trace-level detections of pesticides in treated drinking water samples.

The samples were collected from a drinking-water treatment plant that uses the river as a raw-water source, according to a recently released USGS report. All of the detections in drinking water were, however, far below existing U.S. Environmental Protection Agency drinking-water standards and other human-health benchmarks.

The Clackamas River Water Providers, a coalition of municipal drinking water providers, and the Clackamas County Department of Water Environment Services cooperated with the USGS in the study. The USGS also is working closely with Clackamas County Soil and Water Conservation District and state agencies that include the departments of Environmental Quality, Human Services, Agriculture, and Forestry on this issue.

A total of 63 pesticide compounds were detected in 119 water samples collected during storm and nonstorm conditions using low-level detection methods. More pesticides were detected in the tributaries than in the Clackamas River mainstem, and the fewest were detected in treated drinking water. One or more of 15 pesticides were detected in nine of 15 samples of drinking water. Most of the compounds analyzed for, however, were not detected -- 98 percent of the 1,790 individual pesticide analyses of finished drinking water were below laboratory method detection levels.

Pesticides were detected in all eight of the lower basin tributaries after heavy rainfall, with the largest pesticide contributions coming from Deep and Rock creeks. The herbicides atrazine and simazine were the most common, detected in half of the samples. High-use herbicides such as glyphosate and triclopyr/2,4-D, the active ingredients in RoundUP™ and Crossbow™, respectively, also were frequently detected.

Concentrations of four insecticides -- diazinon, chlorpyrifos, azinphos-methyl, and p,p'-DDE --exceeded EPA aquatic-life benchmarks during storms in seven streams, and concentrations of several other pesticides exceeded other, non-EPA benchmarks, including chlorpyrifos in the Clackamas River mainstem. Nearly one-quarter of the tributary samples had at least one pesticide that exceeded an aquatic-life benchmark. Further, "Benchmarks have not been established for many of the pesticides detected, and current regulations do not yet account for multiple compounds that often occur in a single sample," noted Kurt Carpenter, USGS hydrologist and lead scientist for the study.

Pesticide sources in the Clackamas River basin are difficult to identify because of the diverse land use in the basin and the multiple-use nature of most of the pesticides detected. According to Carpenter, more than 90 percent of the 51 current-use pesticides can be used on nursery or other agricultural crops; about one-half are commonly used on lawns and landscaping in urban areas, on golf courses, or along roads and right-of-ways; and some can be used on forestland. "Because pesticide-use data currently are reported only for the Willamette River basin as a whole, not for individual subbasins, watershed managers could benefit from more detailed reports of which pesticides are being used and where," Carpenter observed.

Results of the lower Clackamas River pesticide study are available in USGS Scientific Investigations Report 2008-5027, "Pesticide Occurrence and Distribution in the Lower Clackamas River Basin, Oregon, 2000-2005."

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