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Pesticides Seeping Into Urban Streams


Pesticide Stream Monitoring MapPesticides are seeping into an increased number of urban streams, according to a scientific report. The report looks at pesticide levels at USGS National Water-Quality Assessment sites. The sites are shown on the map at right. Some are urban, some are rural, and some are at mixed urban/rural sites.

(For larger view, click on map.)





Source: Stone, Wesley, Robert Gilliom and Karen Ryberg, 2014.

Source: Stone, Wesley, Robert Gilliom and Karen Ryberg, 2014.

The report focuses on pesticide levels during the decade from 2002-2011, and compares them to levels during the decade from 1992-2001. The report focuses on streams where pesticides were present at least 95% of the year. The first chart at right shows the percentage of streams in which at least one pesticide exceeded maximum aquatic-life benchmark. An aquatic-life benchmark is the level above which the pesticide is believed to be toxic for aquatic life.

From 2002-2011, pesticides exceeded aquatic benchmarks in 61% of agricultural streams, a decrease of 8%. They exceeded aquatic benchmarks in 90% of urban streams, an increase of 37%. And they exceeded aquatic benchmarks in 46% of mixed use streams, an increase of 1%.

In considering this information, it is important to understand that not all pesticides were included. Thus, results represent a minimum, and actual levels of contamination are almost certainly higher.

The stunning result here is the increase in the percentage of contaminated urban streams. The report states that the increase is primarily due to the use of fipronil and dichlorvos. Fipronil is an insecticide that did not come into common use until the late 1990s, so it has spread into streams relatively quickly. It is highly effective because it is slow acting. Thus, it is carried back to roach and ant nests, affecting the entire nest, not just a single individual. However, it has been found to be toxic to aquatic life, and the compounds into which it degrades in the environment may be even more toxic.

Dichlorvos is a popular insecticide in commercial use since the 1960s. The EPA lists it as a probable carcinogen and has restricted its used, but not banned it.

The report is national in scope, and unfortunately does not break out data for Missouri.


Stone, Wesley, Robert Gilliom, and Karen Ryberg. 2014. Pesticides in U.S. Streams and Rivers: Occurrence and Trends During 1992-2011. Environmental Science & Technology, 48,(19), 11,025-11,030. http://pubs.acs.org/doi/abs/10.1021/es5025367.

Weston, D.P. and M.J. Lydy. 2014. “Toxicity of the Insecticide Fipronil and its Degradates to Benchic Macroinvertebrates of Urban Streams.” Abstract. Environmental Science and Technology. 48,(2); 1290-97.

EPA. “Dichlorvose.” Air Toxics Web Site. http://www.epa.gov/ttnatw01/hlthef/dichlorv.html.

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