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Environment

Water Danger Overstated

November 17, 2014 | A version of this story appeared in Volume 92, Issue 46

I find there is an even greater problem in addition to the complications cited by Elizabeth Wilson in the article “Toledo Water Danger Unclear” (C&EN, Aug. 11, page 9). The problem is that the state’s guidance either misinterpreted or overinterpreted the World Health Organization guideline of 1 ppb, which was the basis for the do-not-drink order.

The WHO guideline (2011) was derived from a tolerable daily intake (TDI) calculation for lifetime exposure to microcystin-LR for a 60-kg (132 lb) person consuming 2 L of water per day. The guideline was derived from a 13-week study in mice (a sensitive species), and a 1,000 factor was applied to the no-observed-adverse-effect level (NOAEL).

The state treated it as an acute or subacute exposure risk issue rather than a chronic one. So the health-based rationale for the do-not-drink order is questionable, at best. The order was extremely conservative and led to significant impacts to the population and the city.

I am a member of the WHO Guidelines Committee.

Joseph A. Cotruvo
Washington DC

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