7942 - Laserfiche WebLink

Home Browse Search

15 or declining lipid weight total DDT residues, but signifi- cant increases occurred in one or more homologs at nine stations (Table 7). Residues at most of these sites were low, and most increases were attributable to DDE. However, significant increases in other homologs occurred at stations 14, 15, 24, 30, 57, 80, 100, and 113 (Table 7). Of the sta- tions showing increases, total DDT exceeded 1.0 µg/g in at least one sample from stations 14 (Tombigbee River at McIntosh, Alabama), 42 (Snake River at Lewiston, Idaho), 57 (Altamaha River at Doctortown, Georgia), and 80 (Yazoo River at Redwood, Mississippi). When we ranked the top 10 stations in order of decreasing mean residue levels for six compounds (Table 8), station 16 (Rio Grande at Mission, Texas) moved from fourth highest in p,p'-DDE and total DDT in 1976-77 to second highest in 1978-79. High residues of DDT also occurred regularly at stations 80, 14, and 28 (Arkansas River at Pine Bluff, Arkansas), and at all three Lake Michigan stations (21, 104, and 105). Although most of the stations evidencing high levels of DDT probably reflect a long history of agricul- tural use, at least two stations also have known or suspected point sources of DDT contamination: (1) McIntosh, Ala- bama (station 14) is the home of a chemical manufactur- ing complex that produced DDT commercially until the mid-1960's (D. Schultz, personal communication). Our finding of high levels (up to 2.5 µg/g) of o,p'-DDT homologs in fish from this station is further evidence of non-agricul- tural source; o,p'-homologs are considered to be impuri- ties in technical DDT, and they are only rarely present in appreciable concentrations in environmental samples (Henderson et al. 1971). (2) Pine Bluff, Arkansas (station 28), is near the site of a government arsenal complex to which elevated DDT residues may be attributable (D. Schultz, personal communication). A high percentage of p,p'-DDT in a whole-fish sample probably indicates that the DDT was accumulated recently. Samples in which p,p'-DDT represented the highest per- centage of the total p,p'-homologs-about 67% in 1977 and 74 % in 1979 - were collected at station 100 (Manoa Stream, Honolulu, Hawaii); however, total DDT residues were gen- erally low at this station (<0.5 µg/g in all samples). A high percentage of p,p'-DDT (>20%) accompanied high total DDT residues (>_ 1.0 µg/g) in at least one sample from each of the following stations: 115, 104, 55, 14, 21, 80, 4, 42, 107, and 22 in 1976-77; and 115, 21, and 14 in 1978-79 (Appendix A). The high percentage of p,p'-DDT at station 14 (McIntosh, Alabama) is probably due to the presence of a manufacturing facility, as mentioned previously. High residue levels (2.9 µg/g total DDT) and high percentages of p,p'-DDT (36-40 %) were present in striped mullet col- lected at station 115 (Colorado River at Yuma, Arizona) during both periods. (Corresponding levels and percentages in other samples listed above were considerably lower.) We attribute the higher residues and percentages in the striped mullet to the migratory habits of this species. The fish sam- pled probably frequented sections of the Lower Colorado River constituting the international border with Mexico. This area is intensively farmed, and DDT is still used (D. Stalling, personal communication). Polychlorinated Biphenyls The occurrence of PCB's apparently increased between 1974 and 1978-79; they were found at 93% of the stations sampled in 1974 (Schmitt et al. 1981), 92% in 1976-77, and 98% in 1978-79 (Table 4). Maximum concentrations did not change appreciably; concentrations approaching 100 µg/g wet weight and 500 µg/g lipid weight were measured as recently as 1978 (Table; Appendix A). Of the four PCB mixtures measured, residues resembling Aroclor 1254 were the most widespread; they were found at 84% of the stations sampled in 1976-77, and at 98% in 1978-79 (Table 4). Residues resembling Aroclor 1260 were present at 84% of the stations sampled in 1976-77 and at 88% in 1978-79, and Aroclor 1248 residues were present at 39% of the stations in 1976-77 and 42% in 1978-79. No residues resembling Aroclor 1242 were found in 1976-77, as compared with about 14 % reported in 1973 and about 5% in 1974 (Schmitt et al. 1981). This apparent disappearance of Aroclor 1242 residues in fish is not sur- prising; unlike the more highly chlorinated components that dominate the Aroclor 1248, 1254, and 1260 mixtures, the components that are most prevalent in the 1242 mixture are rapidly degraded. The residues that remain respond to chromatography in a manner that makes them resemble the other mixtures. Significant differences between means for 1976-77 and 1978-79 were revealed by ANOVA only for lipid weight total PCB; none of the individual Aroclor mixtures nor the wet weight total PCB residues differed significantly for these years (Tables 5 and 6). When the 1974 data were also con- sidered, 1974 residues of Aroclors 1254 and 1260 were sig- nificantly different (1254 higher, 1260 lower) from cor- responding residues for 1976-79 (Table 6). However, total PCB residues were not significantly different. Since a dif- ferent laboratory performed the 1974 analyses, the apparent anomaly most likely resulted from differences between laboratories in the interpretation of the multiple chromato- graphic peaks typical of PCB mixtures. The 1974 analyses were performed by the Denver Wildlife Research Center (DWRC), FWS. Chemists at CNFRL who performed cross- check analyses on 47 of these 1974 samples found that, by comparison, DWRC slightly underestimated Aroclor 1260 but slightly overestimated Aroclor 1254 and total PCB (Schmitt et al. 1981). The overestimate of Aroclor 1254 was believed to have resulted from DWRC's inclusion of some early eluting peaks that CNFRL has routinely included in its estimates of Aroclor 1248, but excluded from Aroclor 1254. Results of ANOVA for 1974-79 data have a pattern that resembles the 1974 cross-check results-declining Aroclor 1254 and increasing Aroclor 1260 (Table 6). This similarity between the results presented in Table 6 and the