About 190 toxic substances have been designated as hazardous air pollutants (HAPs) by USA under the Clean Air Act Amendment of 1990. Some HAPs possess specific chemical & physical properties, and are grouped into persistent organic pollutants (POPs) and endocrine-disrupting chemicals (EDCs). More seriously, a few of HAPs are known carcinogens to humans. The objective of this paper was to review the hazards of HAPs in line with the international concern about their environmental and carcinogenic risks in recent years. To protect human health and the environment from POPs, the Stockholm Convention on POPs and the national programs on EDCs were established. Furthermore, several international organizations or programs have developed a classification system to evaluate the carcinogenicity of an agent to humans. They include the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP) of the U.S. Department of Health and Human Services, the U.S. Environmental Protection Agency (USEPA), and the American Conference of Governmental Industrial Hygienists (ACGIH). It was found that some organochlorine pesticides (i.e., chlordane, heptachlor, hexachlorobenzene, pentachlorophenol and toxaphene) and unintentional byproducts (i.e., dioxins) are blanketed into HAPs, POPs and EDCs. These semivolatile organic compounds can be released into the atmospheric environment by anthropogenic sources as a result of their volatilization and deposition, thus posing a potential health risk when exposed to inhaled air and food chain.
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