After about 20 years of commercial production, health hazards began to be reported in workers exposed to<unk> s: chloracne, severe skin rashes and liver disease that led to deaths of workers. A conference about the hazards was organized at Harvard School of Public Health in 1937, and several more publications dealing with<unk>  hazards appeared before 1940.<unk> s containing three or more chlorines per molecule have typically been found more hazardous than those with fewer, but as the maximum of eight is approached, hazards appear to decrease. There was a lag of about 40 years between disclosure of<unk>  hazards and government regulation. In the U.S. exposure to<unk> s was drastically reduced after 1976, following enactment of the Toxic Substances Control Act. Major equipment manufacturers banned<unk> s in their products, and major<unk>  producers discontinued operations. By 1983 worldwide<unk>  production had almost halted except for small amounts used in testing and research. Until recent years duPont produced a synthetic rubber, Neoprene FB, made in Northern Ireland using pentachloronaphthalene. Increased cancer risks have been suspected but so far not shown. Current concerns about<unk> s include their release as byproducts of waste incineration.
Polychlorinated naphthalene
Alkylphenol
Nitrobenzene
Naphthalene
Polychlorinated dibenzodioxins
Polychlorinated biphenyl
Coal tar
Benzene