Chemical mixtures are common in small streams in the U.S.

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Mixtures of organic chemicals are ubiquitous in small U.S. streams, reports a new study by the U.S. Geological Survey. In many streams the mixtures could be affecting stream organisms.

USGS scientists collected 3 to 12 water samples from 305 small streams across four major regions of the U.S. as part of the USGS Regional Stream Quality Assessment. The samples were analyzed for 389 organic chemicals comprising pharmaceuticals, pesticides, and wastewater-indicator compounds. Pesticides and pharmaceuticals are designed to have a biological effect.

Two or more organic compounds—that is, a mixture—were detected at least once at 303 of the 305 stream sites. Further, a chemical mixture was detected in at least half of the samples collected at 252 sites with some urban or agricultural development in the watershed. These results indicate that exposure to multiple organic contaminants is common for small streams in developed watersheds.

The chemical mixtures measured presented a moderate risk of acute toxicity—mortality—at 44% of sites for aquatic invertebrates, which include stoneflies and mini-crustaceans. For nonvascular plants, which include some algae and are a key part of the aquatic food chain, there was a moderate risk of acute toxicity at 20% of sites. The mixtures presented a moderate risk of sub-lethal effects to vertebrates—organisms, such as fish and salamanders, with a backbone—at 99% of sites.

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Date published: March 4, 2019
Status: Active

National Water-Quality Assessment (NAWQA)

Our surface water, groundwater, and aquatic ecosystems are priceless resources, used by people across the Nation for drinking, irrigation, industry, and recreation. The National Water-Quality Assessment (NAWQA) Project is a leading source of scientific data and knowledge for development of science-based policies and management strategies to improve and protect our water resources.

Contacts: Mindi Dalton
Date published: February 28, 2019
Status: Active

Regional Stream Quality Assessment (RSQA)

The goals of the Regional Stream Quality Assessment (RSQA) are to characterize multiple water-quality factors that are stressors to aquatic life (contaminants, nutrients, sediment, and streamflow alteration) and to develop a better understanding of the relation of these stressors to ecological conditions in streams throughout the region.

Attribution: Water Resources