Pesticides and Water Quality - Texas Center for Policy Studies

near Knott, Texas. Reports of cattle deaths in the area resulted in studies demonstrating that the deathswere the result of ingestion of arsenic by the cows.Further investigation by TDA concluded that the contamination was the result of historic use of arsenic oncotton and poor management practices for cotton gin waste. 121 Movement of arsenic pesticides throughuncemented or uncased wells was also identified as one possible source of the problem. One hundredrural water wells were sampled, and arsenic was found above the drinking water standard in 34 wells. 122As a result, many farms in Howard and Martin Counties installed their own water treatment systems.Farmers in the area agreed to a temporary prohibition on use of arsenic-based pesticides.A more recent report suggests that the arsenic contamination in Howard and Martin Counties should beattributed to “point sources,” e.g., cotton gins and gin trash. 123 The report does not, however, explain howthis conclusion was reached. Moreover, the report does not explain the source of the nitratecontamination that was found along with the arsenic contamination in the earlier TDA study. Thus,leaching from the locations of the arsenic applications would still appear to be one of the likely sources.b. Investigation of contamination in Dawson, Comanche, El Paso, Haskell, Hidalgo, Knox, Lynn,Stonewall, and Terry Counties: Because of the contamination found in Howard and Martin Counties,TDA began a more comprehensive evaluation of potential pesticide contamination of ground water inselected West Texas counties. As a result, a number of pesticides and fertilizers were identified in theground water in these counties between 1988 and 1990. The agency apparently stopped testing in 1990.Pesticides confirmed in the ground water were arsenic, atrazine, dicamba, prometon, bromacil, picloram,triclopyr, metolachlor, 2,4,5-T, and 2,4-D. 124c. Investigation of contamination at pesticide applicator sites: In the 1980s, a number of studies weredone to evaluate pesticide contamination at aerial and ground applicator sites. In one study, about 1000sites were examined. At a number of the sites, ground water was found to be contaminated withpesticides, including ethyl and methyl parathion, pydrin, arsenic, 2,4-D, chlorpyrifos, atrazine,cypermethrin, permethrin, trifluralin, molinate and DDT. 1252. Testing by Water Supply Systemsa. Periodic testing of drinking water: Every supplier of drinking water to the public with 15 or moreconnections has to test periodically for contaminants. The frequency and number of contaminantsevaluated depends on the size of the system. Of the almost 90 water systems which are monitoring andhave had detections of pesticides in treated water between 1995 and 1997, (§II D), 9 get all or part of theirwater from ground water sources. Ground water-based systems detecting pesticides in finished drinking121 Texas Department of Agriculture, Investigation of Arsenic Contamination of Groundwater Occurring Near Knott, Texas,(Texas Department of Agriculture: Austin, 1988).122 Many of these wells also exceeded the drinking water standard for nitrates, suggesting movement of fertilizers into theground water.123 Texas Ground Water Protection Committee, Joint Groundwater Monitoring and Contamination Report – 1996, SFR-56,(Texas Natural Resource Conservation Commission: Austin, 1997), p. 65.124 Rick Piltz and Lea Aurelius, "TDA Analyzes Rural Water Wells for Pesticides,”, in Grassroots, (Texas Department ofAgriculture: Austin, Spring 1988), p.3.125 See letter report of Engineering Science, Inc. to the Texas Water Commission dated July 20, 1987 (TCPS files).37