Insult to newborn immunity: organochlorines in mother's diet.

In remote Atlantic coast villages of Canada, residents of small fishing communities who rely on marine food for subsistence often absorb unusually high doses of chemicals including organochlorines, a group of persistent industrial and agricultural chemicals that bioaccumulate in the aquatic fond chain. Previous studies have shown that prenatal exposure to some organochlorines can result in suppression of children's immune systems. Now a team of researchers led by Houda Bilrha of the Centre Hospitalier Universitaire de Quebec-Laval University Medical Center in Quebec City has located a biomarker of immune system function--a chemical imbalance--that could indicate damage caused by organochlorines [EHP 111:1952-1957].

The organochlorine family includes polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichlorethylene (DDE), hexachlorobenzene (HCB), polychlorodibenzo-p-dioxins (PCDDs), and polychlorodibenzofurans (PCDFs). Once released, organochlorines circulate with atmospheric currents, traveling northward (in the Northern Hemisphere) from southern latitudes into the globe's colder regions. The chillier temperatures there cause the chemicals to be deposited on the sea surface by rain or snow, or they adhere to the sea surface through a process called vapor phase adsorption. Once thus trapped there, organochlorines accumulate in fatty tissues of organisms and biomagnify in the food chain. In colder regions, relatively high levels of these compounds have been found in the bodies of animals and people, as well as their offspring.

The Mid and Lower North Shore of the St. Lawrence River, a remote Atlantic coast region of Quebec, comprises 21 communities spread over a shoreline of several hundred kilometers extending from Sheldrake to Blanc-Sablon. A large proportion of the residents rely on marine food for subsistence. Several surveys conducted since 1990 have revealed that communities on the Lower North Shore, in particular, are overexposed to PCBs, mercury, and dioxin-like compounds, compared to other populations in southern Quebec.

Bilrha and colleagues examined a study population of 47 pregnant women who had resided for at least five years in subsistence fishing communities of the Mid and Lower North Shore. The reference group comprised 65 women who were residents of two nearby non-subsistence fishing communities and who therefore could be expected to have lower exposure to food chain contaminants.

Cord blood samples were collected when each woman gave birth, and were analyzed for concentrations of mercury, 14 PCB congeners, and 11 chlorinated pesticides and metabolites. The researchers also isolated immune cells from cord blood samples to test their responsiveness to immune insult by exposing them to phytohemagglutinin, a mitogen used to assess potential for T cell responses. Once stimulated, immune cells normally respond by producing cytokines, small proteins that mediate and regulate immune system function. The researchers tested whether cytokine production by immune cells collected from cord blood was impaired in newborns that had been exposed to PCBs and other organochlorines in utero.

As expected, mean concentrations of p,p'-DDE, HCB, and PCBs were significantly higher in the subsistence fishing group than in the reference group. DDT is not as persistent at its main metabolite DDE and was not detected in most participants. More importantly, the researchers found that lymphocyte cells of newborns exposed to higher concentrations of PCBs and DDE secreted fewer cytokines than those of control newborns.

These results suggest that DDE and PCBs subtly affect the immune system of young children, which could potentially make them more susceptible to infectious diseases. The authors are planning an epidemiological study to investigate whether these subtle biological effects translate into a higher risk of infectious disease in infants from these coastal populations.