INTRODUCTION 



Accidental contamination of the environment by polychlorinated dibenzo- 

 para - dioxins (PCDDs), especially 2,3,7,8-tetrachlorodibenzo - para - dioxin 

 (2,3,7,8-TCDD) , has been associated with poor reproduction of herring gulls 

 ( Larus argentatus ) in Lake Ontario (Stolzenburg and Sullivan 1983), with the 

 closure of selected rivers in Missouri to anglers due to high residues in fish 

 (Powell 1984), with the destruction of fish and wildlife in Vietnam during 

 military defoliation operations using phenoxy herbicides (Rappe 1984), and 

 with the death of livestock and wildlife in Missouri (Powell 1984) and Italy 

 (Fanelli et al. 1980b). For example, in 1976, massive kills of small animals 

 (predominantly rabbits and poultry) occurred within the first few weeks after 

 a chemical plant explosion in Seveso, Italy, in which 2,3,7,8-TCDD was 

 released; many humans were hospitalized (Fanelli et al. 1980b). Levels of 

 2,3,7,8-TCDD in milk from dairy cows and tissues of pigs, chickens, cattle, 

 goats, and sheep from Seveso were sufficiently elevated to pose a risk to 

 human health. Accordingly, all domestic livestock in the most seriously 

 afflicted areas were destroyed. In eastern Missouri during 1971, waste oil 

 contaminated with 2,3,7,8-TCDD was applied to control road dust (Powell 

 1984). Later, hundreds of horses kept in riding arenas became sick, and 75 

 died; deaths were also observed among dogs, rodents, chickens, cats, and birds 

 near the treated areas. Soils in Times Beach, Missouri were so heavily 

 contaminated with 2,3,7,8-TCDD that it was permanently evacuated in December 

 1982. The U.S. Environmental Protection Agency had earlier announced that 

 they would buy the dioxin-contaminated city of Times Beach; once purchase is 

 completed the city will no longer exist officially (Powell 1984). 

 Approximately 22 kg (48.4 pounds) of 2,3,7,8-TCDD were involved in the Times 

 Beach incident (Westing 1978). 



PCDDs are present as trace impurities in some commercial herbicides and 

 chlorophenols. They can be formed as a restilt of photochemical and thermal 

 reactions in fly ash and other incineration products. Their presence in 

 manufactured chemicals and industrial wastes is neither intentional nor 

 desired. The chemical and environmental stability of PCDDs coupled with their 

 potential to accumulate in fat has resulted in their detection throughout the 

 global ecosystem. The number of chlorine atoms in PCDDs can vary between one 

 and eight to produce up to 75 positional isomers. Some of these isomers are 

 extremely toxic, while others are believed to be relatively innocuous. The 

 most toxic and extensively studied PCDD isomer is 2,3,7,8-TCDD. In fact, it 

 is the most toxic synthetic compound ever tested under laboratory conditions. 

 This isomer is produced during the synthesis of 2,4,5-trichlorophenol , which 



