Pesticides found in urban runoff can harm salmonids through their invertebrate prey

By on February 27, 2015

Whether or not you give much fuss over organic produce, the use of pesticides near your favorite fishing spot could be affecting the health and quality of the fish you’re targeting. A study from the University of California and Southern Illinois University found that pesticides contained in urban runoff can impact salmonids both through direct contact and through toxicity in their invertebrate prey.

While there are plenty of studies touting the negative effects of pesticides on aquatic life, the paper published in Environmental Toxicology and Chemistry focuses on insects not commonly used in toxicity testing. Caddisflies, mayflies and stoneflies are all standard fare for salmonids suchs as Chinook salmon and steelhead trout, two popular targets for anglers in the Pacific Northwest. Certain localized populations of each have been listed as endangered.

The researchers used California’s American River as the site of their field study. They built a laboratory on the banks of the river, providing easy access to fish and invertebrates, as well as river water for their flow-through testing system. In the flow-through system, the researchers exposed the salmon, trout and invertebrates to river water contaminated with urban runoff collected from storm events and studied the effects.

The common pesticide bifenthrin was found in urban runoff from five separate storm events. Surprisingly, the researchers observed no lethal or sub-lethal effects in salmon and trout exposed to the chemicals, though the paper does acknowledge the potential for indirect toxicity via their prey. Previous studies, however, have shown that bifenthrin harms salmonid reproductive health by disrupting endocrine production, particularly in females.

Although the fish seemed to get off easy in this study, their invertebrate prey met a considerably worse fate. Hyalella azteca, a small crustacean preyed upon by salmonids, faced high mortality in every exposure test. The other invertebrates managed better, but the researchers suggest that the large size of the American River likely dilutes runoff concentrations to more tolerable levels. In smaller tributaries, the invertebrates could face deadlier results.

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