Storm runoff presents salmon with toxic one-two punch, study shows

"What we think is happening is the stormwater is interfering with that genetic process," researcher Allison Coffin said.

By Brooks Hays

Feb. 12 (UPI) -- Even if salmon survive their initial exposure to polluted storm runoff, contaminants may leave them permanently disabled, new research shows.

In a previous study, researchers at Washington State University showed toxic runoff can kill salmon. In the latest study, scientists found runoff can also damage the hair-like sensors salmon depend on to navigate their watery surroundings and hunt for food.


"We're showing that even if the fish are surviving the stormwater exposure, they still might not be able to detect the world around them as well, which can make it harder for them to find food or more likely for them to get eaten," Allison Coffin, an assistant professor of neuroscience at WSU Vancouver, said in a news release.

Scientists began by collecting storm runoff from Washington State Route 520. They found larval zebrafish -- an ideal salmon model -- developed fewer lateral sensory hairs after being exposed to the runoff.

Sensor hairs operate similarly to the tiny hairs found in mammalian ears. Vibrations trigger the hairs to send electrical signals to the brain, helping the animal sense and interpret sound and motion.

Coho salmon embryos exposed to storm runoff also developed fewer hairs, but were not as impacted by the pollution as zebrafish.


Scientists also tagged sensor hair cells with a fluorescent protein. The cells glowed when activated. Researchers found the sensor hair cells of salmon and zebrafish exposed to stormwater glowed less intensely than control groups.

"These results suggest that developed hair cells survive acute stormwater exposure but that function is compromised," researchers wrote in the study, published this week in the journal Science Advances.

Stormwater often contains metals, suspended particles and a variety of polycyclic aromatic hydrocarbons. Scientists aren't sure why the fishes' sensor hairs aren't functioning properly after exposure, but it's likely a developmental process is being disrupted by exposure to toxins in the water.

A series of genes must be expressed in order for the lateral line of hairs to develop properly.

"What we think is happening is the stormwater is interfering with that genetic process," Coffin said.

Previous research showed stormwater filtering can prevent runoff from proving deadly to the young fish, but the latest study showed filtration methods had little effect on damage to sensory hairs.

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