Introduction to Toxicology: Occupational & Environmental
Humans live in a chemical environment and inhale, ingest, or absorb from the skin many of these chemicals. Toxicology is con-cerned with the deleterious effects of these chemical agents on all living systems. In the biomedical area, however, the toxicologist is primarily concerned with adverse effects in humans resulting from exposure to drugs and other chemicals as well as the demonstra-tion of safety or hazard associated with their use.
Occupational toxicology deals with the chemicals found in the workplace. The major emphasis of occupational toxicology is to identify the agents of concern, identify the acute and chronic diseases that they cause, define the conditions under which they may be used safely, and prevent absorption of harmful amounts of these chemicals. Occupational toxicologists may also define and carry out programs for the surveillance of exposed workers and the environment in which they work. Regulatory limits and voluntary guidelines have been elaborated to establish safe ambient air con-centrations for many chemicals found in the workplace.
Governmental and supragovernmental bodies throughout the world have generated workplace health and safety rules, including short-and long-term exposure limits for workers. These permissi-ble exposure limits (PELS) have the power of law. Copies of the United States Occupational Safety and Health Administration (OSHA) standards may be found on OSHA’s website at http://www.osha.gov. Copies of the United States Mine Safety and Health Administration (MSHA) standards may be found at http://www.msha.gov.
Voluntary organizations, such as the American Conference of Governmental Industrial Hygienists (ACGIH), periodically pre-pare lists of recommended threshold limit values (TLVs) for many chemicals. These guidelines are periodically updated, but regulatory imperatives in the United States are not updated except under certain extraordinary circumstances. These TLV guidelines are useful as reference points in the evaluation of potential work-place exposures. Copies of current TLV lists may be obtained from the ACGIH at http://www.acgih.org.
Environmental toxicology deals with the potentially deleterious impact of chemicals, present as pollutants of the environment, onliving organisms. The term environment includes all the sur-roundings of an individual organism, but particularly the air, soil, and water. Although humans are considered a target species of particular interest, other species are of considerable importance as potential biologic targets.
Air pollution is a product of industrialization, technologic development, and increased urbanization. Humans may also be exposed to chemicals used in the agricultural environment as pesticides or in food processing that may persist as residues or ingredients in food products. Air contaminants are regulated in the United States by the Environmental Protection Agency (EPA) based on both health and esthetic considerations. Tables of regulated air contaminants and other regulatory issues that relate to air contaminants in the United States may be found at http://www.epa.gov. Many states also have individual air con-taminant regulations that may be more rigorous than those of the EPA. Many other nations and some supragovernmental orga-nizations regulate air contaminants.
The United Nations Food and Agriculture Organization and the World Health Organization (FAO/WHO) Joint Expert Commission on Food Additives adopted the term acceptabledaily intake (ADI) to denote the daily intake of a chemicalfrom food that, during an entire lifetime, appears to be without appreciable risk. These guidelines are reevaluated as new infor-mation becomes available. In the United States, the Food and Drug Administration (FDA) and the Department of Agriculture are responsible for the regulation of contaminants such as pes-ticides, drugs, and chemicals in foods. Major international problems have occurred because of traffic among nations in contaminated or adulterated foods from countries whose regu-lations and enforcement of pure food and drug laws are lax or nonexistent.
Ecotoxicology is concerned with the toxic effects of chemical and physical agents on populations and communities of living organ-isms within defined ecosystems; it includes the transfer pathways of those agents and their interactions with the environment. Traditional toxicology is concerned with toxic effects on individ-ual organisms; ecotoxicology is concerned with the impact on populations of living organisms or on ecosystems.