An analysis of a sample of the town of Owasco's drinking water last week showed a minor level of toxins associated with harmful algal blooms, but officials say even that low level is likely a false positive attributable to the limits of the testing method and that the water remains safe.
According to sample results posted on the Cayuga County Health Department's website, a Sept. 5 sample of the town of Owasco's drinking showed levels of 0.186 micrograms per liter, or parts per billion (ppb), of microcystins, the type of toxins associated with harmful algal blooms.
Both the town of Owasco and city of Auburn's municipal water systems draw water from Owasco Lake, which has increasingly seen harmful algal blooms in the last few years. Auburn's water has not shown any signs of toxins this season.
Included with the sample result, however, is a note explaining that the value of 0.186 is above the testing method's detection limit, but below the U.S. Environmental Protection Agency's reporting limit of 0.3 ppb — at which point a do-not-drink order would be issued for babies, toddlers, the elderly, and people with compromised immune systems.
The difference, according to the EPA, is essentially that the detection limit is the absolute minimum amount a chemical can be detected at all in a sample that contains said chemical. The reporting limit, on the other hand, is the lowest level the sample can confidently say just how much of that chemical there is in the sample.
For the method the state Department of Health's certified laboratories use to detect microcystins, 0.15 ppb is the detection limit, while 0.3 ppb is the reporting limit, meaning any value between those two numbers are likely to be statistically unreliable.
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Combined with the fact that the sample of the raw water from Sept. 5 did not detect any toxins, according to Cayuga County Director of Environmental Health Eileen O'Connor, means the 0.186 ppb result was likely a false positive.
That means that at no point was the drinking water unsafe, and the county published the result for the purpose of being informative, O'Connor said.
"Since we had that value, we didn't want to not publish. We try to be as transparent as possible," O'Connor said.
The department sent additional samples for analysis the following day on Sept. 6, and also on Sept. 10. Both times, no toxins were detected in either the raw or finished drinking water, lending further credence to the idea that the Sept. 5 result was a false positive, O'Connor said.
Additionally, the sample result on the website for Sept. 5 shows the result of "less than 0.3" for the raw water, but O'Connor said that is more a particularly of the state's required reporting language than an indication that anything was detected but below 0.3 ppb.
"If we had a hint above the method detection limit, we would have put it there, but we did not," O'Connor said.