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22 Superior ranged from 2 to 7µg/g wet weight, and the one lake trout sample collected from Lake Huron (station 106, 1977) contained 9.0 µg/g wet weight (Appendix A). Since comparatively little toxaphene has been used in the Great Lakes watershed, atmospheric transport from areas to the south and southwest offers the most cogent explanation for the accumulation of these residues in the upper lakes, as has been postulated for other contaminants (Eisenreich et al. 1981). Until recently, toxaphene was the organochlorine insecti- cide used most extensively in American agriculture. Most of the toxaphene used in the United States was applied to cotton (Eichers et al. 1978). This complex, broad-spectrum mixture of compounds was also used against pests attacking fruits and vegetables, grains, turf, and ornamentals; to protect livestock from various ectoparasites; and to control certain weeds (Anonymous 1981b). However, as recently as 1976, 86% of the 14.1 million kg used annually on major field crops in the United States was applied to cotton (Eichers et al. 1978). Consequently, most use occurred in the Southeast, the mid-South, and the Southwest. Yet toxa- phene residues have become virtually ubiquitous, and con- centrations in fish from the Upper Great Lakes now exceed those from most major rivers draining the Nation's cotton-producing regions. Dacthal In a collaborative survey of residues in fish of the lower Rio Grande, Texas (White et al. 1983), unknown chromato- graphic peaks in the polar Florisil fraction were identified as dacthal (dimethyi tetrachloroterephthalate), a widely used, persistent, broad-spectrum herbicide (Anonymous 1981x). Subsequent quantitation of dacthal residues in all 1978-79 NPMP samples revealed measurable quantities (>0.01 µg/g) at 34% of the stations sampled. Residues were highest at stations 42 and 96, which are in the agricultural region of the lower Snake River valley in Washington and Idaho (Fig. 1; Appendix A). Other Insecticides Three compounds-HCB, -y-BHC (lindane), and a-BHC - all declined in mean and maximum concentration and in percent occurrence from 1976-77 through 1978-79 (Tables 4-7). Residues of a-BHC, a volatile isomer present in the BHC mixture that was used before 1974 primarily against cotton pests, slid not exceed 0.05 µg/g at any station in 1978-79, and only trace amounts (0.02 µg/g) of lindane were found (Table 4). In 1976-77, residues of ce-BHC ex- ceeded 0.1 µg/g at stations 1, 8, 45, 54, 64, 69, 76, and 84, and lindane exceeded 0.1 µg/g at stations 64 and 76 (Fig. 1; Appendix A). Relatively high residues of a-BHC, as well as of other insecticides, at station 54 (Raritan River at High- land Falls, New Jersey) have recently been attributed to an abandoned chemical dump that was operated by a pesti- cide formulator (Larini 1980). However, the widespread distribution of a-BHC residues has probably resulted from atmospheric transport. Even though mixtures containing a-BHC are no longer used in most agricultural applications, significant (> 0.5 ng/ma) concentrations have recently been measured in air samples collected at diverse locations throughout the United States (U. S. Environmental Protec- tion Agency 1980). Hazards of Persistent Organoehlorine Residues in Fish to Piseivorous Fishes and Wildlife As previously reported (Schmitt et al. 1981), the whole- body residues measured in NPMP fish samples cannot be compared directly with standards determined for the pro- tection of human health, which are based on residues in "edible portions" (usually skinless fillets). Whole-body sam- ples include the viscera, with its higher lipid content, and therefore contain proportionately greater amounts of the lipophylic contaminants. However, the whole-fish residues are representative of the contaminant levels to which pisci- vorous fish and wildlife would be exposed, and can there- fore be compared with the following criteria established by the National Academy of Science (NAS) and National Academy of Engineers (NAE) for the protection of fish- eating wildlife (NAS-NAE 1972): DDT and its metabolites, 1.0 µg/g (total); dieldrin, aldrin, endrin, BHC, heptachlor epoxide, chlordane, and toxaphene, 0.1 µg/g, either singly or in combination; and PCB's, 0.5 µg/g (total). We com- puted the percentage of the samples collected at each sta- tion each year that exceeded these criteria for the com- pounds measured, and graphically tabulated the results (Fig. 4). Dacthal residues had not been documented in fish at the time the criteria were established; however, since dacthal is a persistent, chlorinated hydrocarbon pesticide, we included it among the residues for which 0.1 µg/g is the criterion. The NAS-NAE criteria were exceeded by 50% or more of the samples collected at 80 stations (76% of the total) in 1976-77 and at 81 stations (75%) of the stations in 1978-79 (Fig. 4). When the 78 stations with complete data for the period 1974 through 1979 were considered, the pro- portion of stations where 50% or more of the samples col- lected exceeded at least one of the criteria was nearly identical for all three collection periods: 1974, 68%; 1976-77, 67 %; and 1978-79, 67 %. As reported for 1970-74 (Schmitt et al. 1981), geographic trends remained fairly consistent from 1976-77 through 1978-79; stations generally exceeded the same criteria in each collection period (Fig. 4). The potential threat that residues of persistent, toxic ma- terials accumulated by fish may pose to piscivorous fish and wildlife has been further demonstrated by recent evidence (e. g., Aulerich and Ringer 1979; Young et al. 1979; Ohlen- dorf et al. 1981; Fry and Toone 1981). Yet, the criteria for whole-fish residues (NAS-NAE 1972), which are currently the only single reference for evaluating the possible biologi- cal significance of organochlorine residues in fish, were