Twenty-two bottom-sediment samples were collected from Town Lake in Austin, Texas, in 1991 and 1992 and analyzed for chlorinated insecticides by a reconnaissance-quality, electron-capture gas chromatography screening method developed by the U.S. Geological Survey (USGS). Four different chlorinated insecticides (aldrin, chlordane, dieldrin, and p,p'-DDT) and two degradation products of p,p'-DDT (p,p'-DDD and p,p'-DDE) were detected in these samples. The most significant insecticides detected were chlordane, which was detected in 20 of the 22 samples at concentrations that ranged from 26 to 140 micrograms per kilogram, and p,p'-DDT, which was detected in all 22 samples at concen- trations that ranged from 5 to 40 micrograms per kilogram. Degradation products of p,p'-DDT were detected in all 22 samples. Concentrations of p,p'-DDD ranged from not detected to 117 micrograms per kilogram and for p,p'-DDE from 9 to 97 micrograms per kilogram. Of the 22 samples collected, 15 also were analyzed by the standard USGS laboratory analytical method for chlorinated insecticides to determine the comparability of the two methods. Correlation coefficients were calculated for chlordane (0.8662), p,p'-DDT (0.6393), p,p'-DDD (0.9401), p,p'-DDE (0.8595), and dieldrin (0.3819). A paired sign test at the 95 percent confidence level showed no significant difference between the screening method and laboratory analytical method for all detected insecticides except aldrin. P-values were calculated from the data for chlordane (l.0000), p,p'-DDT (0.1796), p,p'-DDD (l,0000), p,p'-DDE (0.1796), and dieldrin (0.2891).
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USGS Numbered Series
Determination of chlorinated insecticides in bottom sediment using an electron-capture gas chromatography screening method, Austin, Texas, 1991 and 1992