Water Quality Improvement Project
Wenatchee River Area:

Water quality issues

DDT is a problem because it exceeds water quality standards in the Mission Creek basin. DDT persists in the environment. It also biomagnifies as it moves up the food chain (plants, aquatic biota, fish, humans). In the early 1940s DDT was heavily used in orchards throughout the state, including the Wenatchee River watershed. In 1972 EPA banned registration and interstate sale of DDT for virtually all but emergency uses in the United States because of its persistence in the environment and accumulation in the food chain. DDT can also enter the Wenatchee River attached to suspended soil particles.

Wenatchee River Basin, Washington State.  Photographer unknown.

Why this matters

Dichloro-Diphenyl-Trichloroethane (DDT) is a colorless, odorless, chlorinated insecticide that is water resistant. It tends to accumulate in sediment, plants, aquatic plants and animals, and fish. DDT is regularly found in waters near fruit orchards. It has persisted in the environment for decades. Beginning in the mid-1940s, DDT was widely used to control orchard pests such as the codling moth (Carpocaspa Pomonella). In 1958, the U.S. Department of Agriculture (USDA) began a program to phase out DDT for its insect control programs due to concerns about its persistence in the environment and toxicity to non-target organisms, such as aquatic life. Use declined steadily until 1972, when the U.S. Environmental Protection Agency (EPA) banned DDT for all uses except for emergencies.

DDT transport to streams and movement within aquatic environments is often associated with erosion of contaminated soils, sediment re-suspension, and groundwater transport through the soil profile. As DDT is transported to streams, it is absorbed by the plant and animal life within the stream system and then moves up the food chain. DDT biomagnifies at higher levels in each step of the food chain.

Even though agricultural use of DDT was banned in 1972, DDT makes up the bulk of the pesticides sampled. Unlike pesticides used today, which break down relatively quickly, DDT takes a long time to break down in the environment. DDT attached to soil particles decades ago when it was commonly and liberally used. It remains there today along with other more recently applied pesticides.

Status of the project

In 1992, the Washington State Pesticide Monitoring Program (WSPMP), administered by the Washington State Department of Ecology (Ecology), began including lower Mission Creek as a target water sampling site due to the high density of fruit orchards in the basin. Ecology conducted more extensive sampling in three Mission Creek basin streams during 2000 and found elevated concentrations of pesticides in all three streams. Among the pesticides found, DDT was the most frequently detected and most consistently found at concentrations above water quality standards. High DDT concentrations and high DDT loads in Yaksum Creek indicated that most of the DDT loads in Mission Creek were contributed by Yaksum Creek.

Significant decreases in DDT can be achieved by using best management practices (BMPs) to decrease erosion of DDT-laden soils. Some examples of such BMPs are riparian buffers and irrigation efficiency improvements to decrease runoff. Waste pesticide pick-up programs should also be conducted in the Wenatchee Watershed to collect pesticides that contain DDT.

The TMDL assessment for DDT in the Mission Creek Watershed, Wenatchee River basin was completed in October 2004. The WQ Improvement Report (WQIR) was completed in July 2007. EPA approved the WQIR in August 2007.

Technical information

DDT Contamination and Transport in the Lower Mission Creek Basin, Chelan County: Total Maximum Daily Load Assessment (Ecology Publication)

Quality Assurance Project Plan: Total Maximum Daily Load Study for DDT Contamination and Transport in the Lower Mission Creek Basin, Chelan County, Washington (Ecology Publication)

Mission Creek Watershed DDT Total Maximum Daily Load: Water Quality Improvement Report (Ecology Publication)

Related information

DDT Contamination and Transport in the Lower Mission Creek Basin, Chelan County: Total Maximum Daily Load Assessment (Ecology publication)

Mission Creek Watershed DDT Total Maximum Daily Load Water Quality Improvement Report (Ecology publication)

WRIA 45: Wenatchee Watershed Information (Water web site)


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Last updated June 2015
  Water resource inventory area (WRIA) 45 map, Washington State.


WRIA(s): #45 (Wenatchee)
County: Chelan

Water-body Name:
Wenatchee Basin

Parameter: DDT

# of TMDLs: 9

Approved by EPA

Contact Info:
Lynda Jamison
Phone: 509-575-2434
Email: Lynda.Jamison@ecy.wa.gov

Central Region
Department of Ecology
1250 West Alder Street
Union Gap, WA 98903-0009