POP surprise: wood preservative persists in plasma. (Science Selections).

Exposure to low concentrations of polychlorinated biphenyls (PCBs) in the womb has been linked with adverse neurodevelopmental effects in humans and animals. It has been hypothesized recently that hydroxylated PCB metabolites, or HO-PCBs, may be the actor behind these adverse effects. So Courtney D. Sandau, formerly of Carleton University in Ottawa, and a team of Canadian scientists set out to evaluate the potential health effects of in utero exposure to HO-PCBs and other halogenated phenolic compounds [EHP 110:411-417]. Although HO-PCBs were indeed correlated with signs of thyroid disruption, another phenolic compound turned out to be the surprise leader in terms of how commonly it showed up in cord blood samples.

Because the symptoms of PCB exposure can overlap with those of thyroid dysfunction, several investigators have speculated that the neurologic consequences of incidental exposure to PCBs are caused by thyroid disruption. Sandau and colleagues hypothesize that HO-PCBs may play a critical role in this effect. These metabolites have very high binding affinities to transthyretin, the protein that transports thyroid hormones across the blood-brain barrier to the developing brain; in fact, they can have up to 12 times the binding affinity of thyroxine, the ligand that normally binds to this protein. Although PCB concentrations have been previously measured in umbilical cord plasma, this is the first study to examine HO-PCBs and other phenolic compounds in that medium.

The scientists looked at concentrations of PCBs, a number of HO-PCBs, and other phenolic compounds such as pentachlorophenol (PCP), which also are known to have a high binding affinity for transthyretin. They measured these compounds in 10 randomly selected umbilical cord plasma samples from each of three regions in Canada. The people living in the three different regions have different diets and thus different PCB exposures. People in Quebec City, Quebec, have background PCB exposures similar to those of the general population of Canada. Nunavik Inuit eat seal and beluga whale blubber, which have high PCB concentrations. Subsistence fishers along the Lower North Shore of eastern Quebec eat fish, sea mammals, and seabird eggs, giving them an intermediate level of exposure. The samples came from various umbilical cord blood surveys, so there was no standard health history or other gathering of information to accompany them.

Unexpectedly, the scientists found that one of the most abundant persistent organic pollutants found in umbilical cord plasma was not an HO-PCB but the wood preservative PCP. PCP concentrations ranged from 628 to 7,680 pg/g wet weight in plasma and did not vary significantly across regions. PCP represented an average of 66-82% of the concentration of all phenolic compounds in each region. HO-PCB concentrations, as expected, made up about 10% of total PCBs.

PCP, used in wood preservatives, biocides, and disinfectants, is not banned in the United States or Canada. Other recent studies have found PCP to be the dominant phenolic compound in whole blood from Inuits as well as Latvian and Swedish fish eaters. Food is unlikely to be a major source of PCP because it is a volatile, soluble compound; it is found in air and water, but it does not accumulate in animal tissues.

Despite the small sample size, Sandau's team found a weak negative association between total phenolic compounds and free thyroxine concentrations, suggesting that PCP and HO-PCBs may alter indeed thyroid status in newborns, perhaps by disrupting thyroid hormone metabolism. The U.S. Centers for Disease Control and Prevention (where Sandau now works) and their collaborators at Laval University in Quebec will be looking for confirmation of these results on a larger population later this year.