Regulatory limits and voluntary guidelines have been elaborated to establish safe ambient air concentrations for many chemicals found in the workplace. Governmental and supragovernmental bodies throughout the world have generated workplace health and safety rules, including shortand long-term exposure limits for workers. These permissible exposure limits (PELs) have the power of law in the United States. Copies of the US Occupational Safety and Health Administration (OSHA) standards may be found on OSHA’s website at http://www.osha.gov. Copies of the US Mine Safety and Health Administration (MSHA) standards may be found at http://www.msha.gov. In addition to the PELs that appear in the OSHA publications and on the website, OSHA promulgates standards for specific materials of particularly serious toxicity. These standards are developed following extensive scientific study, stakeholder input at hearings, public comment, and other steps such as publication in the Federal Register. Such standards have the force of law and employers who use these materials are obligated to comply with the standards. OSHA standards may be found in full on the OSHA website at http:// www.osha.gov.
Voluntary organizations, such as the American Conference of Governmental Industrial Hygienists (ACGIH), periodically prepare lists of recommended threshold limit values (TLVs) for many chemicals. These guidelines are periodically updated. Regulatory imperatives in the United States may also be updated from time to time when new information about toxicity becomes available. However, this process is slow and requires input from many sources except under certain extraordinary circumstances. In those cases, emergency alterations to standards may be made and an emergency temporary standard may be promulgated after appropriate regulatory procedures. The ACGIH TLV guidelines are useful as reference points in the evaluation of potential workplace exposures. Compliance with these voluntary guidelines is not a substitute for compliance with the OSHA requirements in the United States. TLVs do not have the force of law. 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, on living organisms. The term environment includes all the surroundings 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. Scientific study of signal occurrences in animals often provides early warning of impending human events as a result of ecotoxic impacts.
Air pollution is usually a product of industrialization, technologic development, and increased urbanization. On rare occasions, natural phenomena such as volcanic eruptions may result in air pollution with gases, vapors, or particulates that are harmful to humans. 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 primary and secondary 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 within the USA also have individual air contaminant regulations that may be more rigorous than those of the EPA. Many other nations and some supragovernmental organizations regulate air contaminants. In the case of adjoining countries, transborder air and water pollution problems have been of concern in recent years. Particulates, radionuclides, acid rain, and similar problems have resulted in cross-contamination of air and water in different countries. Maritime contamination, too, has raised concern about oceanic pollution and has had an impact on the fisheries of some countries. This type of pollution is now the subject of much research and of new international treaties.