The environmental movement cut its eyeteeth on the controversy over polychlorinated biphenyls, or PCBs, which first came to public attention in the 1960s. PCBs were once widely used in industrial applications, particularly as electrical insulating and heat-exchange fluids. Concern over possible adverse effects on the environment and human health, however, resulted in the prohibition of PCB production in the U.S. and most other industrialized countries.
Even though complaints about PCBs still emanate from some so-called public interest groups, human exposure to these compounds is declining, continuing a trend that began decades ago. The reason this statement can be made with certainty is because environmental levels of PCBs have been measured for potential or possible exposure in a wide variety of systems various aspects of the environment, food sources, and human and animal body fluids and in each case, PCB levels have declined.
PCBs in the environment and animals (wildlife) have dramatically and consistently declined over the years. From a public health perspective, trends in human body content of PCBs are most relevant to the assessment of risk and potential for harm to human health. Here, the picture is encouraging and undisputed. Human exposure to PCBs is far lower than it was just 25 years ago. As a result, levels of PCBs in body tissue samples and breast milk have consistently declined. There is indeed little supportive evidence to suggest that adverse effects are occurring from PCB exposure in today s environment.
An estimated 1.1 billion pounds of PCBs were produced in the U.S. between 1929 and 1977, when the main U.S. manufacturer voluntarily ceased production. Two years later, the U.S. Environmental Protection Agency (EPA) made the ban official, barring all PCB production and strictly regulating any continued use of the compounds.
While low levels of PCBs may remain in the environment for some time to come, their presence is continuing to decrease, primarily as a result of the cessation of production, along with the rise in environmental control measures and regulations that have been enacted over the past two decades. In turn, there is less uptake by lower-food-chain sources of exposure (fish) and lower amounts of PCBs in foodstuffs in general. This decreased exposure has resulted in lower human body burdens of PCBs.
It is ironic that concern in some quarters over PCBs in the environment seems to be growing, despite all the encouraging evidence to the contrary.
PCBs have been associated with health effects in laboratory animals, but typically these occur at very high dose levels relative to realistic human environmental exposures. PCBs have been shown to cause tumors in laboratory animals under conditions of high-dose lifetime exposure, conditions that are not relevant to human exposures. For purposes of regulation, several governmental or advisory agencies have concluded that there is sufficient evidence to consider PCBs to be animal carcinogens.
However, studies of workers who were exposed to high levels of PCBs by inhalation and/or skin contact over long periods of time have not demonstrated an increased risk of cancer. What is more, groups of exposed workers have been followed for years, and these individuals continue to show no statistically significant change in the incidence of cancer or death from other causes. In fact, skin and eye irritations remain the only consistent health effects in workers that can be definitively attributed to PCBs.
There is also no compelling reason to believe that PCBs exert any biologically significant endocrine-modulating (or hormonal) effect in humans exposed to realistic environmental levels. Although research continues today, notably on increasingly subtle effects such as neurobehavioral and neurodevelopmental effects in infants and children, there is no convincing, consistent evidence to support a causal connection between current low-level PCB exposure and clinically significant effects.
General population exposure to PCBs in fish and other foodstuffs has been significantly reduced, and PCB levels in humans are now typically very low. Thus, little benefit to public health can be expected to result from continued investigation into this class of chemicals. Furthermore, excessively stringent and expensive requirements for the removal of trace levels of PCBs from the environment cannot be justified by what is now known about PCBs and their potential effects on human health.
A version of this paper appeared in the journal Ecotoxicology and Environmental Safety.