Sorting out sources of perfluorinated chemicals
Infants can ingest small amounts of perfluorinated chemicals from breast milk, according to new research.
As regulators in Canada and the U.S. search for ways to limit human exposure to perfluorinated chemicals (PFCs), scientists are working furiously to develop a clear picture of how people worldwide have become contaminated with the compounds. Two ES&T research papers add important details to the exposure picture. Research published today on ES&T’s Research ASAP website (DOI: 10.1021/es060031f) reports the first measurements of PFCs in human breast milk, pointing out a source for newborns. Meanwhile, another paper recently posted to the ASAP website (DOI: 10.1021/es0600330) finds that the structure of the PFCs in human blood suggests that the source is due to current manufacturing processes and not a legacy.
PFCs are widely used in stain repellents, waterproof and greaseproof paper coatings, and a host of industrial applications. In the environment, they are persistent, tend to bioaccumulate, and may pose long-term health risks. Two of these chemicals, PFOS (perfluorooctane sulfonate) and PFOA (perfluorooctanoic acid), have been detected in human blood worldwide. But few researchers have looked for these chemicals in other human organs or tissues.
Paul Lam of the City University of Hong Kong and colleagues report detecting PFOS, PFOA, and several other PFCs in the breast milk of 19 new mothers in the rural seaside town of Zhoushan, China. PFOS levels range from 45 to 360 parts per trillion (ppt), with PFOA at 47–210 ppt. The researchers also found longer-chain PFCs at lower concentrations. These levels are far less than those in human blood. By comparison, a similar group of women from the same hospital had about 100 times more PFOS in their blood and 10 times more PFOA.
The authors attempt to estimate the risk of this exposure and suggest that the highest concentration of PFOS in milk, 360 ppt, may pose a small potential health risk. But they acknowledge that such estimates are fraught with uncertainty. “It is premature to make any conclusions about what these data mean,” says 3M epidemiologist Geary Olsen, whose views were echoed by other scientists contacted for this article.
The low levels are good news, says University of Alberta biochemist Jonathan Martin. “It is not surprising that perfluorinated chemicals should be found in breast milk, but it is reassuring that they are not concentrated in breast milk like other contaminants of concern, such as polychlorinated biphenyls,” he notes.
Kurunthachalam Kannan of the New York State Department of Health says, “This is an interesting study suggesting that infants can be exposed to perfluorinated chemicals through breast feeding in addition to transplacental transfer.” But he notes that scientists in Japan have found much higher levels of PFCs in fetal cord blood; this suggests that breast milk is a minor source by comparison.
Zsuzsanna Kuklenyik and colleagues at the U.S. Centers for Disease Control and Prevention (CDC) earlier had looked for PFCs in two breast-milk samples from the U.S. but found very little. However, the China study uses a new analytical approach that is more sensitive than CDC’s method.
In the second paper, University of Toronto chemists report on PFC isomers in human blood. PFCAs (perfluorocarboxylic acids), such as PFOA, exist in two isomers: linear forms produced by the telomer process currently used by DuPont and other manufacturers, and branched isomers from a now-mothballed process developed by 3M. Amila De Silva and colleagues studied the isomer distribution in 16 pooled human-blood-serum samples from North America. They report that most of the PFCAs are the linear isomers. As long as biological mechanisms, such as greater elimination of branched isomers, are not in play, this finding strongly suggests that the telomer process is a significant source.
De Silva and colleagues also measured the relative abundance of PFCAs in blood samples on the basis of the carbon chain lengths. In human blood, they find that chains with even numbers of carbon atoms are relatively more abundant than those with odd numbers. Arctic biota, on the other hand, have more of the chemicals with odd-numbered carbon chains. The Arctic biota pattern is consistent with one event—the breakdown of fluorotelomer alcohols to yield PFCAs. The pattern in North American blood indicates that the sources of human exposure are more complex than just abiotic degradation of a volatile precursor, says De Silva.
“We now have considerable evidence that people are exposed to precursors,” says Scott Mabury, who is coauthor of the paper. “Now, we need to find out about these precursors: Are they reactive? Are they toxic? We don’t know, but we should find out,” he says.
