How Much Arsenic is Too Much?

Thursday afternoon, the Nova Scotia Department of Health announced that five of seven Sydney children who initially tested positive for arsenic contamination had been re-tested and found to be normal.

The headline in the Friday's Daily News: "Two Sydney kids test positive for arsenic - again." In the Chronicle-Herald: "2 children still above arsenic limit."

Is the glass 2/7 full or 5/7 empty?

A health department press release and Chief Medical Officer of Health Jeff Scott tried to strike a reassuring tone. They stressed that the re-testing - "confirmatory testing," they called it - involved the collection of urine over twenty-four hours, while the original test relied on a single sample, collected in the morning.

"The initial urine test may give what are referred to as false positives," the press release said, "because first-morning urine tends to be more concentrated."

Don't worry, be happy - but the media wasn't buying.

Cheerful dismissal of dismal data is something of a pattern with the Department of Health, whose officials sometimes sound like Reverso World versions of the little boy who cried wolf. The department never cries wolf, even when wolves are scratching at the hen house door or baying at the moon in the sheep pasture.

Scott's officials will still investigate those who re-tested within normal limits to determine what might have caused their transient elevated levels. But it won't pack them off to their family doctors.

There's reason to be sceptical of the re-testing. Urine tests only reveal arsenic exposure over the previous seventy-two hours. If children in Whitney Pier, Ashby, and North End Sydney experience intermittent exposures to arsenic, they could show up positive on one urine test and negative a few days later.

For example, the Canadian Press news agency reported that Lorne Toomey's stepdaughter tested positive in the first round of tests, but negative on re-test. Prior to the re-test, however, she and her family had been away from Sydney for ten days.

In a telephone interview, Scott acknowledged that some of the initial tests that showed children within normal limits could be false negatives.

He said the department chose not to check for arsenic in hair, an indicator of chronic exposure, because rates of hair growth and rates of deposition vary from individual to individual, making interpretation difficult.

The department did not check residents for elevated levels of seventeen other toxic chemicals found in soil tests, Scott said, because public health bodies have not developed benchmarks for those toxins against which results cane be judged, as they have with arsenic and lead.

So the news that five of seven children whose initial tests showed abnormal levels of arsenic now test OK is not cause for unbridled celebration.

Dr. Lesbia Smith, a University of Toronto epidemiologist who was consulted on the Sydney study, backed Scott's assertion that morning samples "may have problems because you expect (the test subjects) not to be well hydrated, and they could be concentrated."

Another possibility, she said, is that intermittent exposure could cause results to vary from one test to the next.

"That's in the nature of that particular type of testing and these dynamic exposures," she said. "It's a static test in a dynamic situation. If you run the tests again, you may get the same proportionate results, but with different people testing positive."

There are no plans to re-test children who tested normal in the first round to see if any are now over the limit.

Investigators believe about 500 pregnant women and children under six live in the affected area. They tested 261 for arsenic exposure, with thirteen positive results in the 247 results to come back from the lab so far. About 71 per cent of those tested were children, and "a small number" were pregnant women.

So they have sampled less than half of the target group, but since the sample was self-selected, it may not accurately reflect the population.

Smith said one way to judge the results would be to compare the percentage of positive results - urine with more than twenty micrograms of arsenic per litre - with similar surveys in other contaminated communities.

In Sydney, 5.9 per cent of those tested had unsafe levels of arsenic. That's more than twice as high as the 2.9 per cent unsafe levels recorded in Deloro, Ontario, site of an abandoned gold mine heavily contaminated with arsenic. The most extensive public health assessment ever undertaken in Ontario judged the community safe.

Havelock, Ontario, was used as a control community in the Deloro assessment because it has no history of industrial pollution. Only 1.9 per cent of those tested in Havelock had elevated levels, although the sample was small.

Another measure is the degree of toxicity uncovered by testing.

In Wawa, Ontario, a community severely contaminated by an Algoma steel mill, the highest arsenic level recorded in forty-four samples was 24.6 micrograms per litre. Scott refused to reveal the highest result obtained in Sydney.

A third measure, Smith said, is to compare mean arsenic levels in various communities. Scott said his department had not yet done any statistical analysis of the Sydney test results.

In short, useful information is being gathered, but it will be some time before anyone can say anything useful about it.

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