Environmental Health - Toxic Substances
Glyphosate Found in Wastewater Discharged to Streams
Glyphosate is the most widely used herbicide in the world, and is widely used to control weeds in both agricultural fields and in urban and suburban settings. In 2002, USGS scientists sampled the wastewater discharged into streams from 10 wastewater treatment plants. Although the observed concentrations were small, these results are the first to demonstrate that the discharge from wastewater treatment plants serving urban areas is a source of glyphosate to streams. Samples were collected from the treated wastewater and from the stream water—both upstream and downstream of the wastewater discharge. Glyphosate was more frequently detected in the wastewater (27%) and in the downstream samples (20%) than it was in the upstream samples (12%). No detections were observed in two reference streams located in areas with little human influence. The discharge of the streams and the wastewater outfalls in this study were generally lower when compared to the discharge of the streams in a study of the occurrence of glyphosate in streams draining agricultural areas, so further research is needed to determine the relative loads (mass) of glyphosate from various sources.
As with many studies on the occurrence of herbicides in streams, the degradates of the herbicide were more common than the parent compound. In this study of glyphosate, AMPA (aminomethyl phosphonic acid), a degradate of glyphosate, was found in higher concentrations and more frequently (68%) in wastewater than was glyphosate (18%). The results of this study can be used to assist water-resource managers make informed decisions regarding the environmental fate and effects of herbicides (and their degradates) that are applied in different land-use settings.
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