New Study Identifies Pesticide Mixtures in U.S. Rivers and Streams

Release Date:

A mix of multiple pesticides is common in many U.S. streams, reports a new study by the U.S. Geological Survey National Water Quality Program.

In the study of 72 rivers and streams across the contiguous U.S., five or more pesticides were detected in 88% of the more than 5,000 samples collected during 2013–17. Land use in the watersheds investigated spanned a range, including agricultural, urban, and mixed.

The potential for toxicity of the pesticide mixtures to fish was low, but about 12% of samples were predicted to have potential acute (rapid) or chronic (longer-term) toxicity to aquatic invertebrates. Potential toxicity was evaluated using the Pesticide Toxicity Index (PTI), a screening approach that uses the concentrations of all the pesticides in a water sample to estimate potential toxicity. Aquatic invertebrates—a critical part of the food chain—include cladocerans, a large group of miniature freshwater crustacean species, and benthic invertebrates, such as damselfly larvae.

In a given sample, a single pesticide compound generally was responsible for most of the potential toxicity of the pesticide mixture, based on the PTI score, but that pesticide varied among samples and aquatic groups. For example, in a sample with a PTI indicating potential chronic toxicity to fish, the greatest contributor to that toxicity was likely to be the herbicide acetochlor, the fungicide degradate carbendazim, or the synergist piperonylbutoxide. Identification of primary contributors to toxicity could aid efforts to improve the quality of rivers and streams to support aquatic life.


Citation: Pesticide mixtures show potential toxicity to aquatic life in U.S. streams, 2013–2017. Covert SA, Shoda ME, Stackpoole SM, Stone, WW. 2020. Science of the Total Environment,

Related Content

Filter Total Items: 4
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: March 2, 2019
Status: Active

Water Quality in the Nation’s Streams and Rivers – Current Conditions and Long-Term Trends

The Nation's rivers and streams are a priceless resource, but pollution from urban and agricultural areas pose a threat to our water quality. To understand the value of water quality, and to more effectively manage and protect the Nation's water resources, it's critical that we know the current status of water-quality conditions, and how and why those conditions have been changing over time....

Contacts: Lori Sprague
Attribution: Water Resources
Date published: March 1, 2019
Status: Active

Pesticides and Water Quality

Pesticides are chemicals designed to kill pests, including insects (insecticides), weeds (herbicides), and fungi (fungicides). The USGS assesses the occurrence and behavior of pesticides in streams, lakes, and groundwater and the potential for pesticides to contaminate our drinking-water supplies or harm aquatic ecosystems.

Contacts: Lisa Nowell
Date published: February 27, 2019
Status: Active

Surface-Water Quality and Ecology

Research by the USGS National Water Quality Assessment (NAWQA) Project on water quality of rivers and streams covers a broad range of topics, from nonpoint pollution issues to vulnerability of aquatic ecosystems. Dive in and find out more about current water-quality conditions, how and where water quality is changing, and the latest information on pesticides, nutrients, and other contaminants...

Filter Total Items: 1
Date published: July 9, 2020

Pesticide Toxicity Index (PTI) and maximum Toxic Unit (TUmax) scores and information for fish, cladocerans, and benthic invertebrates from water samples collected at National Water Quality Network sites during Water Years 2013-2017

During 2013-2017, the U.S. Geological Survey, National Water-Quality Assessment (NAWQA) Project, collected water samples year-round from the National Water Quality Network – Rivers and Streams (NWQN) and reported on 221 pesticides at 72 sites across the US in agricultural, developed, and mixed land use watersheds. Pesticide Toxicity Index (PTI) scores, a screening-