A new study confirmed that toxic runoffs from urban roadways can cause killings of coho salmons in matter of hours. Despite the distasteful finding, the same researchers were glad to have discovered an easy solution to save the species: a simple soil-based filtration system.

Scientists have long suspected that runway wastes from urban areas are toxic to coho salmon (Oncorhynchus kisutch), but it was never proven until now.

In a the study, Seattle researchers initially created a mixture of artificial stormwater, containing a variety of metals, crude oil and other substances that can be found in urban runoff. They then exposed the species to the said solution, but produced no fatal results. In fact, the fish survived well as it would on clean water.

The initial results signify that there are other toxic contents in the actual runoff from leaking brake oils, dust and vehicle exhaust.

The next step is to test the effects of the actual runoff on the study subjects. So the researchers obtained the real mixture from the Northwest Fisheries Science Center of the National Oceanic and Atmospheric Administration (NOAA). The said runoff was collected from a downpipe that drains a Highway 520 onramp close to Montlake.

Jenifer McIntyre, a co-author and a researcher from Puyallup Research and Extension Center at the Washington State University said that when the team brought out the real thing, the fish became weak, sick and eventually died.

Seeing that the actual runoff caused fatal effects while the artificial mixture did not highlights the unsolved mystery of what particular chemical or mix of chemicals really cause the fish to die. Nonetheless, the researchers of the same study were able to devise a way on how to save the species.

The researchers filtered the runoff water through a column of sand, gravel, bark and compost, which measures about three feet in height. When the coho salmon were exposed to the said water, all the species survived as if it was exposed to clean water.

As per analyses, the filter was found to have decreased toxic heavy metals and polyaromatic hydrocarbons by about 58 percent and 94 percent respectively.

"What impressed me most was the effectiveness of the treatment," said McIntyre. She added that it is remarkable to detoxify a runoff that was able to kill the fish in a matter of hours.

The scientists said that it would take years to finally determine the exact chemical or mixture of chemicals that are killing the coho salmon.

The study was published Journal of Applied Ecology on Thursday, Oct. 8.

Photo: Roger Tabor (USFWS - Pacific Region) | Flickr