A newly released study by the Washington Department of Ecology concludes that fish caught from Potholes Reservoir are safe to eat.
During 2007-2008, central Washington's Potholes Reservoir was assessed for dieldrin, other chlorinated pesticides, and PCBs, according to the research report released this week. Dieldrin was the focus of the study because the reservoir was listed by the Environmental Protection Agency under Section 303(d) of the federal Clean Water Act for dieldrin failing to meet (exceeding) human health criteria in edible fish tissue.
As a part of the study scientists analyzed nine fish species and 35 fillet samples for the pesticide dieldrin (dee-EL-drin) as well as other older chlorinated pesticides. Relatively low amounts of dieldrin were detected in 70 percent of the fish tissue samples. A form of the banned pesticide DDT, called 4, 4'-DDE, was detected in small amounts in all the samples.
The Washington Department of Health evaluated the concentrations of pesticides measured in fish tissues and determined the fish were safe to eat.
"Based on concentrations listed in this study we see no potential health concerns from consuming these fish," said state health department toxicologist Dave McBride. "All concentrations were too low to be of concern, even for people who might eat the fish several times per week."
Dieldrin is an older, chlorinated pesticide widely used in the United States from 1950 to 1974 to control insect pests that attack cotton, corn, and other crops. Most uses of dieldrin were banned in 1985. As with dieldrin, the other chlorinated pesticides tested also were banned years ago. They bind to soil and don't easily degrade in the environment and also tend to accumulate in fatty tissues as they are passed along the food chain. The highest concentrations were found in the largest fish.
The amount of dieldrin and other chlorinated pesticides detected in the water itself or in the sediments did not violate water quality standards or sediment guidelines. Researchers found that the amount of the pollutants in the fish, water and sediments did not point toward conducting a formal Total Daily Maximum Load or water quality cleanup plan process.
Because Potholes Reservoir was listed as a body of water that violates water quality standards, the state agency was required to determine whether an extensive cleanup process is needed and if the fish from the reservoir were safe to eat.
That extensive cleanup process would have begun with a comprehensive report called a TMDL water quality cleanup plan. Such a plan would outline actions required to meet water quality standards within a 10 year timeframe.
Before launching the TMDL process, the department asked that it be allowed to conduct a screening-level study to evaluate the significance of dieldrin contamination and determine if a TMDL technical study was warranted.
The reservoir's most common fish species include walleye, yellow perch, black crappie, lake whitefish, and smallmouth bass.
Active sources of dieldrin were not identified in the study.
"We found that dieldrin is most likely recycling internally in the Potholes Reservoir food chain and accumulating in the larger, fattier, and longer-lived fish species" said Brandee Era-Miller, a scientist with Ecology's Environmental Assessment Program (EAP). She conducted the study with Randy Coots, also with EAP.
Era-Miller said that fish with less fat such as brown bullhead, black crappie, yellow perch, small-sized largemouth bass and walleye had lower levels of contaminants.
"Over time, concentrations of dieldrin in fish tissue should continue to decline in Potholes Reservoir," Era-Miller said. "Natural attenuation is the most practical course of action for reducing dieldrin in fish tissue from the reservoir." Natural attenuation means the concentration of the contaminant decreases in the environment by natural processes.
Lake whitefish, carp, walleye, and bass from Potholes Reservoir should be re-analyzed for dieldrin, DDT, and PCBs every five years to determine if concentrations are decreasing as anticipated, the report concludes.
The study can be found at: www.ecy.wa.gov/biblio/1003053.html
Ecology's web site is at: http://www.ecy.wa.gov