HHC agrochemicals include insecticides, fungicides, and herbicides (Table 2). Dichlorodiphenyltrichloroethane (DDT) and its derivatives (dichlorodiphenyldichloroethy-lene (DDE), dichlorodiphenyldichloroethane (DDD),
Table 4 Percentage of various congeners in commercial PCB mixtures
Compound Dichloro Trichloro Tetrachloro Pentachloro Hexachloro Heptachloro Octachloro
Arochlor-1242 16 49 29 S 1 0.1 ND
Table 5 Sites with high levels of HHC
PCB Lake Michigan (Waukegan Harbor) Great Lakes®
St. Lawrence Seaway® New York (Hudson R.)
Wisconsin (Sheboygan R.) TCDD Italy (Sveso)
Maryland (James R.) Kepone Maryland (Chesapeake Bay)
Fish, birds, human
Fish, piscivorous birds Fish, whales Fish, birds, marine animals Fish, birds Wildlife, livestock, humans Wildlife
Invertebrates, fish, wildlife aDDT, DDE, and dieldrin also present.
PCDDs are flat molecules with varying substituents of chlorine resulting in 75 possible congeners (Table 3). These are chemically stable and highly lipophilic with limited solubility in organic solvents. These are not commercial products and exist as by-products formed during synthesis of chlorinated phenols, as well as during the incineration of chlorinated aromatics and dispersion of chlorophenols. The most toxic PCDD is TCDD.
Chlorinated anilide herbicides, such as propanil, have been shown to be contaminated with extremely toxic tetrachlorazo- and tetrachloroazoxy-benzenes. The latter can also be produced on microbial degradation of these herbicides.
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