|WIT's World Ecology Report - Vol. 06, No. 2 - Critical Issues in Health and the Environment (WIT, 1994, 16 pages)|
Assessment of the effects of contaminants on the health of populations is complicated by several factors. Frequently, there are insufficient data to determine how much exposure has occurred. Gender, age and lifestyle can all dramatically affect how individuals respond. Humans consume a wide range of foods and. beverages and nearly always consume foods grown or produced from within their community and from elsewhere. Frequently, the types of food and the amounts consumed are seasonal and dependent on sociological and ethnic factors. Finally, humans are nearly always exposed to complex mixtures of environmental contaminants, rarely to single chemicals, and they are frequently exposed to other substances such as medications, alcohol and tobacco products, all of which may interact.
To sort through these difficulties, scientists endeavor to combine the results of studies with human populations and laboratory animals to predict toxic effects associated with exposures. Human epidemiological studies can focus on general populations, occupational groups or individuals with unusual accidental exposures. Some studies consider groups displaying similar adverse effects (e.g., cancer) and look for possible common exposure. Other studies consider common population exposures (e.g., to PCB) and look for group effects. Each type of study contributes some information but not a complete picture of exposure and effect. Studies with laboratory animals are also useful because, unlike the human studies, experimental conditions can be rigorously controlled, exposure varied through control of dose and detained biochemical and pathological changes monitored. While most animals, including humans, have similar basic cellular mechanisms, it is important to keep in mind that different species respond in different ways to the same amount of a contaminant.
The effects of contaminants on human populations are dependent on the toxic properties of the contaminants themselves and on the amount, route and duration of exposure. The amount absorbed (dose) is affected by the route of exposure (via mouth, lungs or skin). The magnitude of the effect is dependent on whether it is received all at once, over a long period of time, continuously, intermittently, alone, or in conjunction with other substances.
SOURCE: Toxic Chemicals in the Great Lakes,
Department of Fisheries and Oceans, Canada, March 1994 Toxicology for the
Citizen, Michigan State University,