PCBs had a more obscure purpose, but the chemicals made a name for themselves nonetheless. Between 1929 and the mid-1980s, PCBs were popular as cooling fluids in electrical equipment and machinery because of their reputation for durability and fire resistance (EPA 1979).

Concerns about PCBs’ health effects and persistence surfaced in the 1970s, and  Monsanto, the major U.S. manufacturer of the chemicals, stopped producing them in 1977. The EPA phased out most uses of PCBs shortly thereafter. Levels of the chemical in people and wildlife have since declined, but three decades later we continue to ingest PCBs when we eat fish, meat, or dairy products (ATSDR 2002).

Because PCBs accumulate in sediment in rivers, lakes, and coastal areas, fish contain particularly high levels of the chemicals. Levels in fish can be 2,000 to more than a million times higher than levels in surrounding waters (EPA 1999). Because of PCB contamination, the Washington State Department of Health recommends limiting consumption of fish and shellfish from many of the state’s water bodies (WDOH 2006).

Women who consume PCBs in their diet readily pass them to their children in breast milk: infants may get 6 to 12% of their lifetime exposure to PCBs from breastfeeding alone (ATSDR 2002). At levels typically found in women and children around the world, PCBs can have profound effects on intellectual development.

In studies of large numbers of children in the U.S., Germany, and the Netherlands, those with greater prenatal exposures (measured by levels in umbilical cord blood or the mother’s blood) performed worse on tests of brain development than children with lower exposures (Shantz 2003). The same body of research also revealed lower birth weights and slowed growth in children with higher PCB levels. In each of these studies, the mothers of the most-exposed children obtained PCBs from fish or other common sources.

Researchers who followed children in Michigan from birth to age 11 found that these effects persist (Jacobson 2002). They compared children from sport-fishing families, whose mothers ate above-average amounts of Lake Michigan fish, with children whose mothers ate no Lake Michigan fish. The sport-fishers’ children, who had greater prenatal exposures, showed intellectual deficits as infants, at age 4, and again at age 11, when they displayed attention deficits, lower IQs, and poorer reading comprehension. While the mothers of the most-exposed children in this study had PCB levels several times those of our participants, other studies have found similar effects at lower levels (Shantz 2003).

In addition to cognitive damage, PCBs cause tumors in laboratory animals (Ross 2004) and have been classified by the EPA as probable human carcinogens. Studies suggest the chemicals are also toxic to the immune system, reproductive organs, and thyroid.

PCBs are a major contaminant in Puget Sound, and evidence is accumulating that they are a serious threat to the Sound’s wildlife, too. Puget Sound’s endangered orca whales have accumulated PCBs to the point that they rank among the most contaminated marine mammals in the world (Ross 2006). Levels in orcas already exceed those needed to cause health effects such as immune system depression.

Figure 8:  PCBs were measured in participant blood serum.