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Blood levels of BPA controversial: values reported for humans appear high, study charges.

The ubiquity of the compound bisphenol A in many plastic products, food-can linings, cash-register receipts and dental resins means that everyone is exposed to it. But new data raise red flags over the accuracy of previously reported human blood concentrations of BPA--amounts described over the years as being representative of the general population.

Those values appear to be roughly 1,000 times higher than most people actually encounter, toxicologist Justin Teeguarden of the Pacific Northwest National Laboratory in Richland, Wash., reported February 16.

Animal and human studies have linked exposures to BPA, a hormone mimic, with cardiovascular changes, altered behavior in children, prediabetic symptoms and reproductive impairments. So getting estimates of typical exposure right, Teeguarden said, is crucial to defining what intake levels should now be probed intensively by toxicity testing.

Toxicologist K. Barry Delclos of the National Center for Toxicological Research in Jefferson, Ark., described experiments in which rodents received seven doses of BPA daily from conception through birth and on into early adulthood. Amounts ranged from very low (2.5 micrograms per kilogram of body weight, in the range of probable human exposure) to a dose more than 100 times higher.

"We did not see clear adverse effects in the low-dose range," Delclos said. And although most animals were receiving hefty doses of BPA, his team detected none of the active form of the chemical in animals receiving less than 80 micrograms per kilogram of body weight per day. Blood levels were below the limits of detection.

His colleague Daniel Doerge shared preliminary data from studies in rodents and monkeys showing rapid breakdown of ingested BPA into inactive substances. Infants, however, proved far less effective than adults at breaking down BPA.

Such studies at NCTR and elsewhere have mapped the relationship between BPA consumption and amounts of the biologically active chemical that subsequently show up in blood and urine. Based on those studies, "there is no way that you could possibly expect to measure BPA in human blood," Teeguarden said.

He described performing four different analyses of BPA levels in urine from 28,765 people. Each analysis indicated that corresponding blood values in these people should be in the parts per trillion range or lower. Values would have to be 1,000 times higher to be picked up by currently available analytical techniques.

This finding raises suspicions, he argued, that previous studies finding measurable blood levels of BPA must reflect either "a very high, unusual exposure" or contamination--if not in the laboratory then during sampling.

Parts-per-trillion quantities of biologically active BPA are also one one-thousandth or less of the concentration that triggers endocrine action by any of several hormones, Teeguarden showed.

Developmental biologist Laura Vandenberg, a BPA researcher at Tufts University in Medford, Mass., expressed skepticism about this assessment. More than 25 studies have measured BPA in human blood, she said; Teeguarden appears to be arguing "that because his calculations say BPA shouldn't be there, then all of the measured blood values must be wrong."

Not necessarily, Teeguarden said. Reported blood values may be real, just not typical of most people.
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Title Annotation:AAAS Meeting; bisphenol A
Author:Raloff, Janet
Publication:Science News
Geographic Code:1USA
Date:Mar 9, 2013
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