Most environmental epidemiology has been concerned with relatively few health outcomes, such as the neurologic and mental outcomes associated with lead and methyl mercury, respiratory disease associated with air pollution, and malignant neoplasms associated with exposures to various chemical agents in the environment. However, there is increasing evidence that a much broader array of health outcomes—such as neurologic, respiratory, and reproductive end points—may also be associated with environmental exposures. Examples of the environmental associations that have been investigated are a link between congenital malformations and trichloroethylene in drinking water, increased hospitalization of children and adults for asthma associated with air pollution, and the neurologic consequences of exposures to lead and solvents in the environment (NRC, 1991). The factors causing many noncancer outcomes, the underlying mechanisms of causation, and relative contributions of the various causal agents have not been clearly delineated. Further, an individual or community may experience more than one health outcome. Persons may be exposed to multiple chemicals (sometimes from the same source), each producing different outcome events, or a single chemical can be responsible for different outcomes in the same or different individuals.
Research into many outcomes potentially related to environmental exposure is at an early stage of development. In part, this is because there has been little effort to measure the incidence and prevalence of many chronic diseases. It is difficult to identify, monitor, and study populations at risk. Finally, more-refined measures of disease that can be applied to groups of persons are needed.
This chapter provides a brief overview of health outcomes that have been associated with environmental exposure. We also review outcomes for which evidence from toxicologic or occupational studies suggests associations with environmental exposure, but where current environmental-epidemiologic data are inadequate to provide definitive information about risk.
A diverse and growing literature characterizes the effects of air pollution on human health. Progress over past decades has elucidated the link of an array of respiratory outcomes to air pollution. Adverse effects on the respiratory tract of air pollutants such as ozone or airborne particles are highly nonspecific and not easily detected clinically. Nevertheless, for many common diseases, even small relative risks (RRs) may translate into significant numbers of cases of disease because of the large size of the exposed population.