Heptachlor formation

Although technical chlordane is a mixture of compounds, two metabolites — heptachlor epoxide and oxychlordane — can kill birds when administered through the diet (Blus et al. 1983). These two metabolites originate from biological and physical breakdown of chlordanes in the environment, or from metabolism after ingestion. Heptachlor can result from breakdown of cis- and trans-chlordane, eventually oxidizing to heptachlor epoxide oxychlordane can result from the breakdown of heptachlor, m-chlordane, tra .s-chlordane, or fram-nonachlor (Blus et al. 1983). Heptachlor epoxide has been identified in soil, crops, and aquatic biota, but its presence is usually associated with the use of heptachlor, not technical chlordane — which also contains some heptachlor (NRCC 1975). Various components in technical chlordane may inhibit the formation of heptachlor epoxide or accelerate the decomposition of the epoxide, but the actual mechanisms are unclear (NRCC 1975). 

Death. Occupational mortality studies of pesticide workers exposed to heptachlor have not revealed an excess number of deaths in these cohorts compared to the general U.S. population. This may possibly be explained as a healthy worker effect. The ERA has described human case reports in which convulsions and death were reported following suicidal ingestion of technical-grade chlordane, which typically contains 6-30% heptachlor, but these effects cannot be attributed to heptachlor or heptachlor epoxide. There are no controlled, quantitative human data for any route of exposure. Acute lethality data were located for animals exposed via the oral and dermal routes. Both heptachlor and heptachlor epoxide may be considered very toxic via the oral route on the basis of acute animal data in rats and mice. Intermediate oral exposure to these compounds also caused up to 40% and 100% mortality in rats and mice, respectively. There appear to be differences in sensitivity in males and females in some species with the males being most sensitive. Heptachlor epoxide is more toxic than heptachlor. Heptachlor may be considered very toxic to extremely toxic via the dermal route on the basis of acute lethality data in rats and mice. The severity of acute effects may possibly depend upon the extent of formation of heptachlor epoxide and the species tested. 

Trichlorobenzene. Trichloroethylene Hydrogen azide, see Alachlor. Aldicarb. Atrazine Hydrogen bromide, see Ethylene dibromide Hydrogen chloride, see Atrazine. Captan. Carbon tetrachloride. Chloroform. Chlorpropham. Chlorpyrifos. 1.2-Dichloroethane. Diuron. Endrin. Formaldehyde. Heptachlor. Heptachlor epoxide. Hexachlorocyclopentadiene. Linuron. Methyl chloride. Methylene chloride. Methyl formate. Monuron. Propanil. Tetrachloroethylene. Trichloroethylene. Vinyl chloride Hydrogen cyanide, see Acetontrile. Alachlor. Aldicarb. 

The photochemical decomposition of heptachlor (44) yields through the excited singlet state the mono-dechlorination isomer pair 48 and 49, while triplet-sensitisers (e.g. acetone) give rise through the triplet state to the formation of 2,3,4,4,5,... 

Epoxidation or the insertion of an oxygen atom into a carbon-carbon double bond can frequently result in the formation of products with greater environmental toxicity. Various microorganisms can catalyze the reaction of the chlorinated cyclodiene insecticides aldrin, isodrin, and heptachlor to their more toxic epoxide derivatives. 

In the calculations presented, heptachlor is degraded into heptachlorepoxide in all environmental media (with a fraction of formation ff = 0.9), aldrin is degraded into dieldrin in all environmental media (jf = 0.9), too, whereas DDT degrades into DDE in the atmosphere (jf = 0.9), and in equal parts (hothff= 0.5) into DDE and DDD in all the other media. Degradation half-lives were extracted as experimental values from the literature [37,38] where possible, or calculated with QSAR software (especially for OH reactions) [39]. 

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