The health risks posed by industrial POPs can perhaps best be illustrated by PCBs, a large family of more than 200 compounds. First manufactured in the United States in 1929, PCBs quickly became ubiquitous in industrial production because of their capacity to conduct heat without conducting electricity. As electricity came into widespread use during the first half of this century, PCBs were used as insulators in refrigerators, capacitors, and in the manufacture of electrical insulation and hydraulic fluids . By 1989, total world production of PCBs (excluding the Soviet Union) had reached 1.5 million metric tons . As of 1994, only two countries reported having entirely banned PCBs, and only six reported having restricted their use .
As with many chemicals, high-level exposures to PCBs have been shown to be extremely dangerous to human health. In 1968, a serious mass intoxication occurred in Japan from a large-scale PCB contamination of rice-bran oil. More than 1,700 people became ill, and about 20 died. A similar mass poisoning, called Yu-Chen, occurred in Taiwan in 1979, with more than 2,000 identified victims . For the lower exposures typically encountered in the environment, evidence of health effects is less clear. Even so, laboratory and field observations on animals, as well as clinical and epidemiological studies in humans, suggest that adverse health effects from PCB exposure may include immune dysfunction, neurological deficits, reproductive anomalies, behavioral abnormalities, and cancer.
The Great Lakes
Much of the evidence supporting low-level health effects from PCBs and other POPs in humans has been collected around the Great Lakes region in the United States. Home to roughly 36 million people, the Great Lakes basin has been a major industrial and agricultural area for many years. Until the 1970s, POPs, heavy metals, polyaromatic hydrocarbons (PAHs), and other pollutants were routinely disposed of in the lakes . In the 1970s and 1980s, people began to observe ill effects in fish, birds, and mammals, including signs of reproductive failure, biochemical changes, congenital malformations, and population declines .
These findings prompted extensive clean-up efforts, and since the early 1970s, levels of many pollutants have dropped significantly by as much as 90 percent . Some of the most damaging compounds still persist at significant concentrations, however. The U.S. and Canadian governments are jointly studying whether these contaminants have resulted in adverse health effects for the populations living around the lakes .
A primary finding of the Great Lakes research is that the major route of exposure to these chemicals is through contaminated food, such as locally raised meat and locally caught fish. Preliminary results have shown that a greater than average consumption of Great Lakes fish contaminated with PCBs and mercury compounds can damage the neurological system in the developing fetus .
Children are clearly at greater risk from PCBs than adults because primary exposure can occur not only during development in the womb but also through the mother’s breast milk. In utero exposure to PCBs has been linked with deficits in fetal and postnatal growth, neurological anomalies at birth, delays in developing gross motor functions, and reduced short-term memory in infants . A recent study in the Great Lakes region has shown that those effects can continue into school age, leading to diminished IQ and short- and long-term memory deficits, and shortened attention span . Similar findings have been documented among Taiwanese children whose mothers had ingested rice oil contaminated with PCBs and dibenzofurans . These chemicals have also been implicated in damage to the immune system.
Because researchers have documented substantial reproductive effects in wildlife populations exposed to Great Lakes contaminants, concern has arisen over possible reproductive effects in humans. To date, evidence is inadequate to conclude that environmental contaminants damage human reproductive functions at the levels currently measured in the general population around the Great Lakes . (See Are Hormone Mimics Affecting Our Health?.)
So far, studies do not show that the general public living near the lakes is at elevated risk from chemical contamination . Certain groups, however, such as Native Americans, poor urban families, Southeast Asian immigrants, and anglers may be at higher risk because these groups tend to rely on fish for a greater part of their diets, increasing their exposure to contaminants . In some cases, these chemical exposures may compound the health risks these groups already face, for instance, from low nutritional status and lack of prenatal care . In addition, nursing infants, as well as the developing fetus, may be at special risk because of the intrinsic sensitivity of developing organisms and organ systems and the elevated exposures of nursing infants. U.S. EPA estimates that nursing infants may face exposures 40 to 50 times higher than adults .
The lack of data in developing countries makes it difficult to assess the global scale of POP pollution and its health consequences, but it is possible to make some inferences. Incinerators equipped to deal with POPs are expensive, and the few that exist are almost all located in developed countries . In many developing countries, industrial wastes are burned in open dumpsites, which can release high levels of POPs into the immediate vicinity. Concern is mounting that the history of environmental contamination in the Great Lakes region is repeating itself in many industrial and agricultural areas of the developing world. In Cameroon, for instance, growth in industries such as oil refineries, electroplating, and power generation is creating large quantities of wastes contaminated with metals and POPs. Scientists have measured extremely high PCB loads in the surrounding area .
Furthermore, as the experience with the Great Lakes has shown, even after decades of expensive cleanup, concentrations of many pollutants, including dioxins, PCBs, and methyl mercury, can remain unacceptably high in some fish species . In many parts of the world, fish represent an important source of protein, so levels of PCBs are an important health concern.