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Study finds water runoff carries potentially dangerous pesticides into West Linn creeks

To be a homeowner is, at times, akin to having tunnel vision.

You might be surrounded by other homes, properties and wildlife habitats, but if there’s a problem — say, weeds on the lawn — all that matters to you is taking care of your own land. Selfish? Perhaps, but in many cases other properties are unaffected by measures taken by homeowners.

SUBMITTED PHOTOS: TRAVIS WILLIAMS - Researchers found particularly high levels of pesticides at West Linns Tanner Creek, likely carried over in stormwater runoff from properties further up the hill. Pesticides like  bifenthrin and fipronil are known to be particularly dangerous to amphibians and invertebrates in rivers and creeks.

Such is not the case with pesticides, according to a recent study funded by Clackamas County MS4 co-permittees, the Clackamas River Water Providers and the USGS Cooperative Water Program. The study, titled “Storm-event-transport of urban-use pesticides to streams likely impairs invertebrates assemblages,” found particularly high levels of pesticides at creeks in West Linn and Lake Oswego, likely due to stormwater runoff from properties above the creeks.

West Linn’s Tanner Creek basin was specifically highlighted in the report, as the authors noted, “The highest concentration of bifenthrin (120 ng/L) occurred in the outfall to Tanner Creek, with the next highest concentration in Tanner Creek. Tanner Creek also contained the highest concentration of fipronil (127 ng/L) … These outfall-stream systems drain relatively high-elevation neighborhoods with large single-family houses, often with large lawns and manicured landscaping.”

The report eventually made its way to Travis Williams, executive director of the Willamette Riverkeeper organization, which works to “protect and restore” the Willamette River. After studying the findings, Williams knew it was time to get the word out.

“The Tanner Creek basin in particular really shot up out of that report,” Williams said. “It’s not to pick on West Linn, but it’s a good example of what can show up in these smaller sub-basins to the Willamette River and other larger bodies.”

Williams said bifenthrin (used to kill red ants) and fipronil (used on a variety of insects) can be “highly toxic to amphibians and other invertebrates.” The study, for its part, stated that, “While the limited duration and scope of our study preclude reaching unequivocal conclusions about the effect of bifenthrin on invertebrates in these streams, our results contribute to a growing body of scientific research linking pyrethroid insecticides — bifenthrin in particular — to toxic effects on stream invertebrates.”

“Depending on the density or volume of the material, it can have acute effects if it’s very strong and coming down to a creek or even something adjacent to a creek,” Williams said. “Over time it affects the reproduction capacity of animals.”

Williams added that bifenthrin is not particularly soluble, and thus “tends to hang around” in affected areas.

“It stays in the sediments and mud, basically,” Williams said.

In the long run, it all leads to the Willamette River — Williams’ primary concern.

“Even if (water) is held in a retention pond or a basin, the product can still make it to Tanner Creek and then to the Willamette River,” Williams said. “If you multiply and think of all the creeks in the area … it’s often the same issue, the same dilemma of how to control runoff and hopefully not use products in a way that they’re capable of going downstream."

Williams is clear, though: This isn’t about playing the blame game. Rather, he is simply hoping to raise awareness and convince homeowners to reevaluate their practices.

“What I’m hoping we can do is work with the City (of West Linn),” said Williams, who is a West Linn resident. “I talked to them and they’re very interested and open to communicating with homeowners, and potentially contractors who may or may not be using the (pesticide) materials … to see if there’s another product to use or another approach to red ants, or use it in a way that doesn’t contribute to runoff in the creeks.”

Though the City can help, Williams said ultimately in many cases it will be up to individual homeowners to make a change — or not.

“We’re really looking at that voluntary aspect of people saying, ‘Oh, I didn’t know that, maybe there’s something else I can use to deal with an issue on my property,’” Williams said.

Patrick Malee can be reached at 503-636-1281 Ext. 106 or This email address is being protected from spambots. You need JavaScript enabled to view it..