Changes in pesticide occurrence in suburban surface waters in Massachusetts, USA, 1999-2010.

Pesticide occurrence was determined in two suburban surface waters in eastern Massachusetts, USA during 2009 and 2010. Out of 118 collected samples, 45 samples showed detections of one or more target pesticides. Among the herbicides, 2,4-D was the most frequently detected and imidacloprid was the most frequently detected insecticide. Comparison with data from 1999 to 2000 indicated fewer pesticide detections and lower pesticide toxicity index values in the current study. Regulatory phaseout of chlorpyrifos and diazinon from residential use by 2004 was reflected in the results by the absence of chlorpyrifos detections and lower detection frequencies of diazinon. Detected pesticide levels were below aquatic life benchmarks.