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Past trace measurements of cyantoxins fail to reappear, City will retest regularly

This story has updated from its original version.

PAMPLIN MEDIA GROUP PHOTO: LESLIE PUGMIRE HOLE - Wilsonville provides water for residents in Sherwood.After a water sample test Thursday, May 31, revealed trace levels of microcystin, a cyanotoxin produced by cyanobacteria — sometimes referred to as blue-green algae — the City of Wilsonville rushed a sample to a laboratory in Seattle for more thorough testing. Results received Monday, June 4, showed no detectable levels of contaminates.

As an additional measure to ensure the health of the water supply, Wilsonville is sending water samples to two laboratories to analyze seven straight days, from June 1-7.

While Wilsonville sent out press releases and notices through social media about last week's test results, given the trace amounts found the City was waiting until more complete testing was obtained before determining if a public advisory was necessary. The Environmental Protection Agency strongly recommends obtaining results from a confirmation sample prior to issuing a public advisory.

If necessary, a public advisory would likely apply to anyone who is under the age of 6, who has a compromised immune system, who is receiving dialysis treatment, who has a pre-existing liver condition, who is pregnant or nursing, or who has other sensitivity concerns. 

The City of Salem sent out a "vulnerable population" alert in late May because of cyanotoxins in its drinking water system, an alert many Wilsonville residents received because of a glitch in the software that sends texts to cell phones.

Oregon's adopted provisional health-based guideline value for microcystins – one of the four cyanotoxins of greatest concern in drinking water – is 0.3 micrograms per liter (µg/L). Wilsonville's first sample result was 0.34 µg/L, slightly over the guideline value and just above the minimum level of detection for the EPA-approved test method.

Unlike other water treatment plants, Wilsonville's state-of-the-art facility utilizes ozonation, a practice deemed very effective by the EPA for reducing potential exposure to cyanotoxins in drinking water by destroying microorganisms and degrading organic pollutants through the infusion of ozone. As a precaution to reduce cyanotoxins that may be present, the City has adjusted ozone levels.

"We're being abundantly cautious here, and providing information that allows our community members to make an informed decision," City Manager Bryan Cosgrove said last week. "We're diligently following protocols put in place by the EPA as well as recommendations from state and local authorities, and will put out an advisory if we receive confirmation that we're above acceptable levels."

Boiling water is not an effective method of removing cyanotoxins. Cyanotoxins are not absorbed through the skin, so daily tasks like washing hands, bathing, cleaning dishes, and laundry pose no health risk.

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