7942 - Laserfiche WebLink

Home Browse Search

19 seen in fish, and if present indicate recent exposure. Aldrin residues were detected in 1977 samples from station 90 (Kansas River at Bonner Springs, Kansas) and station 76. Because so little aldrin was detected in the 1976-77 samples, 1978-79 samples were screened only for aldrin; none was found. The International Joint Commission (1979) reported that dieldrin levels in whole bloaters from Lake Michigan in- creased from 0.27 µg/g in 1969 to 0.55 µg/g in 1978. Our data corroborate these findings; dieldrin residues ranged from 0.37 to 0.72 µg/g wet weight in five bloater samples from three Lake Michigan stations in 1977, and from 0.27 to 0.72 µglg in six bloater samples collected from these stations in 1979 (Appendix A). Residues in lake trout from these stations ranged from 0.29 to 0.33 µg/g in 1977, and from 0.36 to 0.50 µg/g in 1979. Dieldrin residues in samples from Lake Superior remained low (<0.1 µg/g) through- out this period (Appendix A). Statistical analysis of 1974 laboratory cross-check results showed that detection thresholds for dieldrin were lower at CNFRL than at DWRC (Schmitt et al. 1981). It is there- fore impossible to compare percent occurrence of dieldrin in 1976-79 with that in 1974. However, dieldrin was de- tected at about 80% of the stations sampled in 1978-79, down from about 93% in 1976-77. Chlordane, a long-lived multi-residue insecticide, re- placed dieldrin as the most nearly ubiquitous of the cyclo- diene compounds. Cis-chlordane, the most abundant component of the technical chlordane mixture, was detected at about 93% of the stations sampled in 1976-77 and at 94% in 1978-79 (Table 4). Trans-nonachlor, the second most abundant component, was found at 70% of the sta- tions in 1976-77 and 93% in 1978-79. The remaining two components that we quantified directly, trans-chlordane and cis-nonachlor, as well as the chlordane metabolite oxychlordane, occured less frequently. Generally, chlordane residues were highest in Hawaii (station 100), in the Corn Belt, and in the Great Lakes. Where residues were signifi- cant, cis-chlordane was usually the most abundant com- ponent, followed by trans-nonachlor, trans-chlordane, cis- nonachlor, and oxychlordane. Although chlordane is no longer used in agriculture, it is still registered for use against a variety of pests in and around buildings (Anonymous 1981a). Consequently, chlordane residues are common in the sediments of streams that receive urban runoff (Truhlar and Reed 1976). Chlordane residues in NPMP samples col- lected in 1970-74 were not reported quantitatively due to analytical difficulties (Schmitt et al. 1981). For 1976-79, ANOVA indicated significant increases in mean residues of cis-chlordane, cis-nonachlor, and trans-nonachlor from 1976-77 to 1978-79 (Tables 5 and 6). However, significant station-year interaction for these three components suggests inconsistent temporal trends among the stations. Heptachlor was formerly used as a soil insecticide (Eichers et al. 1978); it also is a minor component of technical chlordane (National Research Council Canada 1974). Since both heptachlor and chlordane were used on many of the same crops, residues of heptachlor (and its metabolite, heptachlor epoxide) and chlordane tend to occur together (Fig. 2). Average residues of heptachlor and heptachlor epoxide appear to be increasing slightly; ANOVA revealed a significant increase from 1976-77 to 1978-79 (Tables 6 and 7). (Results for years before 1976 were not sufficiently free of analytical interferences for statistical testing.) Percent occurrence remained essentially unchanged from 1976-77 through 1978-79; residues were detected at 53% of the stations in 1976-77 and at 55% in 1978-79 (Table 4). Heptachlor residues were highest at station 100 (Manoa Stream, Hawaii) in both 1976-77 and 1978-79, in association with high residues of chlordane and dieldrin (Table 8). Like dieldrin residues, heptachlor residues at station 76 declined markedly between 1970-74 and 1976-79. Nationally, residues of endrin appear to have declined from 1976-77 through 1978-79 in terms of maximum con- centration, mean concentration, and in percent occurrence (Tables 4-6). Comparisons with earlier years were clouded by differing analytical resolution, as reported for several other compounds (Schmitt et al. 1981). Most noticeable was the decline in endrin levels at the Cotton Belt stations, where residues have traditionally been the highest-stations 14, 15, 59, 80, and 81 and (as a result of chemical spills) station 76 (Appendix A). In fact, the highest endrin residue measured in fish from the 1978-79 collections did not come from the South; a bloater from northern Lake Michigan (station 105) contained 0.11 µg/g wet weight (0.82 µg/g lipid weight) endrin. Endrin was also present at greater than trace levels in most of the other samples collected from Lakes Michigan and Superior in both 1978-79 and in 1976-77. Because endrin occurred at trace levels in fish from many remote regions, it is likely that some of the endrin accumulating in Great Lakes fish has resulted from atmos- pheric transport. However, endrin was used for insecticidal purposes in the Great Lakes States as recently as 1976, when 5 million kg were applied to major field and forage crops (Eichers et al. 1978), and it is still used to protect orchards from rodent damage (Anonymous 1981a). Toxaphene Mean residues, as well as percent occurrence, of the heav- ily used insecticide toxaphene increased significantly (Tables 4-6). During a period when residue levels and occurrence outside the cotton-producing regions increased rapidly, toxaphene residues within the cotton-farming areas (e.g., the Southeast, mid-South, Texas, and California Central Valley) remained relatively stable (Table 7). Mean residue concentrations in fish from Lake Michigan reached levels as high as fish from some of the most heavily contaminated stations in the Cotton Belt (Table 8); lake trout from Lake Michigan typically contained 5-10 µg/g toxaphene (wet weight). Toxaphene residues in lake trout from Lake