A new USGS study reports that 16 dissolved pesticides were consistently detected in small streams in 16 urban centers across five regions of the United States. These 16 pesticides can be considered as "urban signature pesticides" (USPs) that are common in small urban U.S. streams.
Deciphering the U.S. urban stream pesticide signature
The USPs represented some of the highest concentrations and detection frequencies of pesticides detected in urban streams within these five regions. Of the top two-compound pesticide mixtures observed in urban streams, most were composed of USPs, and the two-compound USP mixture carbendazim + prometon occurred the most frequently.
USP concentrations, the number of pesticide compounds present, and potential toxicity associated with pesticides increased with the degree of urbanization in the stream basin. Statistically, pesticide concentrations were better explained by the amount of urbanization in the stream basin than by region, reinforcing the concept of an urban pesticide signature. However, USP concentrations and frequency of occurrence did vary by region, conferring differences in potential toxicity to aquatic life—which was estimated by comparing measured pesticide concentrations to U.S. Environmental Protection Agency aquatic-life benchmarks. Concentrations and frequency of occurrence were generally higher in the Midwest, Southeast, and Northeast for insecticides and fungicides, and in the Midwest and Southeast for herbicides. Potential toxicity at urban sites was driven primarily by 3 of the 16 USPs: the insecticide imidacloprid (for invertebrate toxicity), the herbicide diuron (plant toxicity), and the fungicide carbendazim (fish toxicity). The severity of potential toxicity varied by region, urban center, and type of aquatic organism. Overall, pesticide concentrations were estimated to be toxic to invertebrates in 50% of urban streams across the five regions, compared to 3% of streams for plants and less than 1% of streams for fish.
The results identify for the first time the large degree of commonality in urban pesticide contamination across time and space in small urban U.S. streams. The suite of USPs identified here would make a logical core of target analytes for studies monitoring dissolved pesticides in urban streams, which could be supplemented as needed with other pesticides to meet local objectives.