Freshwater mussels are embedded in the riverbed just under the water's surface.
Courtesy of Kaegan Scully-Engelmeyer

Science & Environment

Forest pesticides found downstream in coastal Oregon waters

By Monica Samayoa (OPB)
March 17, 2021 3:33 p.m. Updated: March 18, 2021 1 p.m.

Pesticides used on forests and in other applications have been found by researchers in watersheds along the Oregon Coast, raising concerns that aquatic species may be exposed to a toxic mixture of chemicals in the region.

Researchers from Portland State University found traces of a dozen unique pesticides — a combination of herbicides, fungicides and insecticides — in water samples and bivalves collected in downstream rivers and estuaries. The study finds that the mixing of these compounds once they enter aquatic ecosystems could have a negative impact on shellfish and other creatures living downstream — including harm to their hormonal processes and their reproduction and development. The paper, which was published in the journal, Toxics, also concluded that more research is needed to learn the extent at which these environmental impacts occur.


Currently, federal regulations for pesticide use are labeled on their containers. Each pesticide has its own limit for use, as well as restrictions and limits on applying near bodies of water. State agencies overseeing agriculture and forest practices also regulate each pesticide used. For many individual pesticides, the state has adopted rules that exceed the label requirements. But regulations do not consider the effects of multiple chemicals that intermingle in the environment — an issue that raises concerns for the paper’s authors.

For the study, researchers took water samples as well as tissue samples from Western pearlshell mussels, softshell clams and Pacific oysters. Bivalves like these are filter feeders so contamination in the water enters their tissue.

Researchers compared samples from eight Coast Range watersheds to what they found in “upstream management practices related to forestry and herbicide use,” said co-author Kaegan Scully-Engelmeyer. The team used the Oregon Department of Forestry’s notification system to help them better pinpoint what pesticides to test for.

Additional water sampling over a long period of time captures “the types of exposure that originate from pesticide used in a lot of these forestry scenarios,” said Scully-Engelmeyer, a graduate research assistant at PSU.

The team of researchers found at least one pesticide in 38% of the bivalve samples they took. The detected chemicals were present at a range of different levels in the 77 tissue samples from mussels, clams and oysters. The most contaminated organisms were collected in the Siuslaw and Smith watersheds. Some of the chemicals detected also included previously used and now banned pesticides, including DDT.

“DDT and its degradation products are known for their persistence and slow break-down in the environment,” Scully-Engelmeyer said. “It is not surprising that there are trace levels of contamination in some watersheds.”

He also said the longevity of each pesticide depends on their chemical makeup and the environment in which it was applied. Some pesticides break down more quickly than others.

One of the herbicides detected in the study, indaziflam, was found in 7% of bivalve samples.

Indaziflam, sold under the trade names Alion, Specticle and Esplanade, is widely used to kill weeds in orchards, Christmas tree farms, forests, nurseries, landscaping, lawns and grassy fields at parks and schools.

Although the focus for the study was on forest management practices, co-author Elise Granek stressed in an interview that these types of chemical contaminations are also linked to separate sources.


“These animals are being exposed to not just pesticides and herbicides from forestry but also from other sources. So pharmaceuticals, microplastics from waste water, treatment plant effluent and from septic release,” she said.

Granek, a professor of environmental science and management at PSU, said since there are no regulations that consider stressor effects of multiple compounds once they are mixed, it’s hard to know what amounts are safe for animals and people to be exposed to in these scenarios. Granek hopes the study will help agencies rethink the strategy of only having single contaminant benchmarks.

Oregon Department of Agriculture Pesticide Stewardship Specialist Kirk Cook said research regarding the effects of these kinds of stressors on organisms is ongoing and various scientists have begun to look into multiple chemical effects on endangered species like salmon.

In Oregon, commercial forests are treated with pesticides to prevent vegetation from competing with fir trees that are being grown so they can eventually be logged and milled into lumber.

In an email, Oregon Department of Forestry Public Affairs Specialist Nick Hennemann said the study shows that more research is needed but it can help inform policymakers’ decisions around water quality protections.

Hennemann said in an email that a water quality pesticides team made up of representatives from several state agencies and Oregon State University “generally agrees with the report’s conclusions, including the fact that additional information is needed to fill ‘gaps’ in our current knowledge regarding pesticide use.”

A timber industry lobbyist strongly disputed the study’s linking of pesticides to forest practices, contending that most of the report’s detected pesticides aren’t used on forests.

Related: A timber lobbyist called our investigation ‘completely bogus.’ We have the receipts to show it’s not.

“While the authors assert this study has implications for forestry practices, the results don’t say that at all,” said Sara Duncan, the director of communications for the Oregon Forest & Industries Council. She cited a 2020 report by the DEQ that found Oregon forest lands have the highest percentage of “excellent and good” water quality sampling sites, while the highest percentage of “fair to very poor” status sites were urban and agricultural.

“We continue to be confident that our practices robustly protect streams for drinking water and fish habitat,” Duncan said.

Scully-Engelmeyer said the research reaches no conclusions about the degree to which the detected pesticides may be harming shellfish or other life. But he said it’s important to begin to document the mixing of pesticides, which can help scientists better understand the environmental impacts.

“We’re currently in the middle of a lab experiment looking at the mixtures we’ve detected on the effects of softshell clams in a controlled tank experiment,” he said.

Oregon State University Assistant Professor Susanne Brander was not part of the study. As an ecotoxicologist, she is an expert in the kind of research involved. Brander said the study appears to be based on sound research. She said the findings underscore the challenges that regulators and scientists face in keeping up with the environmental impact of chemicals — hundreds of which are approved for use every year.


Tags: Science & Environment, Health, Water, Animals, Wildlife