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UV, not filtration, should be used to protect Portland’s water (Guest opinion)


At Portland City Council, plans are being debated for treating water from the Bull Run watershed to prevent potentially human-infective cryptosporidium (crypto) oocysts from entering the Portland water supply. My research into treating water for crypto as a microbiology professor at Oregon Health & Science University may provide some insight that decision-makers can take into consideration.

Only two of the 15 known cryptosporidium species (there may be more) infect humans. These two specials can infect either humans, or humans and cattle. The other crypto species can infect a variety of other animals, birds and lizards, but not humans. Thus, even though the infective form of this protozoan — the oocyst — may be present in up to an estimated 87 percent of surface waters in this country, most don’t cause human infection.

The Bull Run watershed, the prized source of Portland’s water, is highly protected, both from humans and from grazing cattle. The only fecal organisms likely to be found in Bull Run water thus come from animals other than humans or cattle and cannot infect humans.

For a human to acquire disease caused by crypto, it is necessary to consume about 100 live crypto oocysts (from either humans or cattle) in the equivalent of a glass of water, about 8 ounces. The present crypto alert is the result of finding fewer than 100 oocysts — most or all of which were probably not infective for humans — not in a glass of water, but in thousands of liters of water over a period of months.

Ultraviolet treatment of drinking water has been shown to be an effective method of killing crypto oocysts.

Water filtration is an effective way of keeping oocysts out of our drinking water. It has the added advantage of removing many organic chemicals, and sediment as well. If the drinking water to be treated were from the Willamette River (as at Wilsonville) or from some other source less than pristine – where organic chemicals as well as microorganisms must be dealt with – a filtration system would be entirely in order. However, such a system, which can involve coagulation, sedimentation, ozonation, filtration and then secondary treatment with chlorine, would be neither necessary nor cost effective for treating Bull Run water.

The treatment method chosen should reflect the quality of the water in question. The Bull Run watershed is a treasure. It provides water to Portlanders of a quality matched by few other cities. So long as it remains protected from fecal contamination from humans and cattle, its water would be well-protected against cryptosporidium without filtration. Treating this water with ultraviolet light should be a perfectly adequate way of inactivating any protozoa that happened to be present.

— Ernest Alan Meyer is a professor emeritus of microbiology at OHSU. He lives in Newberg.

Source: http://www.oregonlive.com/opinion/index.ssf/2017/08/uv_not_filtration_should_be_us.html

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