| Abstract: | In 1965, the U.S. Geological Survey initiated a monthly monitoring program on 3 streams in Texas, screening for 9 of the more commonly used organochlorine insecticides: Aldrin, DDD, DDE , DDT, dieldrin, endrin, heptachlor, heptachlor epoxide, and lindane. Later, the herbicides 2,4-D; 2,4,5-T; and silvex were added. In 1967 a quarterly monitoring program was initiated at 26 sites on the principal streams of the State and a survey of the occurrence of pesticide residues in ground water. By 1970, the Geological Survey had developed methods for measuring pesticide residues in sediment, and in that year, the quarterly analysis of stream-bottom materials at 39 sites was added to the data collection program. Geological Survey pesticide data for 108 sites on nontidal reaches of streams in Texas have been summarized by Rawson (1974). The pesticides studied are widely distributed in surface waters in Texas. The most widely distributed chlorinated-hydrocarbon insecticides were dieldrin at 77 sites, DDT at 67 sites, lindane at 59 sites, and chlordane at 38 sites. The most widely distributed phosphorothioate insecticide was diazinon, which was detected at 80 sites. Small amounts of each of the chlorinated-hydrocarbon herbicides were widely distributed (2,4,5-T at 96 sites, 2,4-D at 78 sites, and Silvex at 47 sites). Although only chlordane, in 2 samples from 1 site exceeded the maximum limit recommended for water to be used for public supply, 1 or more pesticides in at least 1 sample from 57 sites exceeded the maximum environmental level for marine waters recommended by the National Technical Advisory Committee. (Woodard-USGS) |
