Environmental Health - Toxic Substances Hydrology Program

Chemical Mixtures and Environmental Effects

USGS Scientist collecting water samples in a stream
USGS scientist collecting water samples and measuring water field properties at North Sylamore Creek, Arkansas, on January 7, 2014. Water samples were analyzed for over 700 chemicals and a wide range of biological activity and toxicity. Photo credit: John Tyler Mays, USGS.

Our watersheds accumulate chemicals from various land uses and human activities across the landscape. As a result, environmental waters can have complex mixtures of natural and anthropogenic chemicals that include pesticides, fertilizers, pharmaceuticals, household chemicals, and a wide range of additional chemicals produced as waste byproducts of commercial and industrial activities. Assessment and minimization of the risks of exposure to complex chemical mixtures in the environment are priorities for human and environmental health organizations. The current lack of information on the composition and variability of environmental mixtures and a limited understanding of the potential combined effects of exposure to chemical mixtures are fundamental obstacles to timely identification the real versus perceived risks to humans and other organisms exposed to chemical mixtures.


USGS scientist collecting a water sample from Boulder Creek, Colardo

Complex Mixture of Contaminants Persists in Streams Miles from the Source

USGS scientists have shown that many currently used fungicides are transported from areas of intense use to nearby streams and groundwater ...

USGS scientist dissecting a fish

Chemical Combo and Intersex Fish Found at Smallmouth Bass Nesting Sites

USGS scientists detected a chemical soup of herbicides, pharmaceuticals, and hormones at fish nesting sites in the Potomac River watershed where endocrine disruption in smallmouth bass was also observed. ...

Cedar Creek in Congaree National Park, SC, showing old growth bottomland hardwood forest

Sources of Contaminants to Congaree National Park—USGS and National Park Service Working Together

A National Park Service (NPS) and USGS study determined the concentrations, potential for degradation, and potential for aquatic and terrestrial animal exposure to organic contaminants in water and sediment within the flood-plain/aquatic environments of Congaree National Park which is located downstream from urban and agricultural areas. ...

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Access to publications on chemical mixtures in the environment.


USGS scientist measuring dissolved oxygen

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