July 31, 2003

PCBs in Farmed Salmon: PCBs alter brain development

PCBs alter human brain development

Six of seven major epidemiology studies conducted over the past decade report that infants and children with higher PCB exposures during development score lower on numerous measures of neurological function, ranging from decreased IQ scores to reduced hearing sensitivity (Schantz et al. 2003).

Some of these effects have been noted at low levels. A study of Michigan children found that PCBs at 9.7 ng/ml (parts per billion or ppb) in maternal serum during fetal development can cause adverse brain development, and attention and IQ deficits that appear to be permanent (Jacobson et al. 1996). Notably, it was the maternal PCB levels, and not the PCB levels in children at 4 and 11 years of age (by which time child PCB levels had decreased substantially), that was associated with IQ deficit, underscoring the importance of in utero exposures from a mother's consumption of PCB-contaminated fish. PCBs have also been linked with altered levels of thyroid hormones in Dutch and Japanese infants (EPA 2002). Thyroid hormones are critical for proper growth and brain development.

Children from two studies, the Michigan and Dutch cohorts, with higher cord blood levels of PCBs were also found to have lower body weight at birth and/or later in childhood (Patandin et al. 1998, Schantz et al. 2003). Low birth weight is increasingly recognized as a risk factor for insulin resistance or Type II diabetes, high blood pressure, and cardiovascular disease later in life (Godfrey et al. 2001, Hales et al. 2001). Even if these lower birth weight babies “catch up” later, the damage may have already been done. A substantial number of studies have found that low birth weight followed by an accelerated growth rate during childhood is a significant risk factor for high blood pressure, stroke, insulin resistance and glucose intolerance (Eriksson et al. 2000a, Eriksson et al. 2002a, Eriksson et al. 2000b, Eriksson et al. 1999, Eriksson et al. 2002b, Forsen et al. 2000, Ong et al. 2002).

New data, slated for publication in the August 2003 issue of Environmental Health Perspectives, found that male babies were more likely to have low birth weight if their mothers lived in zip codes that contain, or are next to, a PCB-contaminated hazardous waste site (Baibergenova et al. 2003). A similar effect was noted for female babies, but the effect was not as strong and did not reach statistical significance.

PCBs have long been known to damage the immune system in laboratory animals. In fact, the studies conducted to date have not been able to find a PCB dose that does not impact the immune system (EPA 2002). The animal studies show that PCBs can alter the size of important immune organs, impair the development of immunity and increase vulnerability to infections.

Overall, the available human studies also show that PCBs impair the immune system. A number of studies have shown that exposure to PCBs, especially early in life, appears to make people more susceptible to chicken pox or infections like those of the inner ear and respiratory tract (ATSDR 2000, Weisglas-Kuperus et al. 2000). Other findings include decreased levels of antibodies and lymphocytes, which are critical in mediating proper immune response (ATSDR 2000).


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