Pesticides and Water Quality - Texas Center for Policy Studies

Table 3d. Pesticide Sampling (Sediment) at Fixed TNRCC Monitoring Stations(1983-1997)Year # Stations Sampled # of Samples*1983 48 541984 47 511985 48 621986 46 481987 52 601988 46 501989 29 291990 10 121991 10 101992 11 121993 20 221994 22 231995 14 161996 13 151997 20 28* Sampling event may include analysis for up to 40 different pesticides.Source: TNRCC Storet database, from information request to TNRCC.2. Statewide SWQMP Results. Of the 32 pesticides generally tested at SWQMP stations betweenSeptember 1984 and August 1994, 22 have never been detected in water above detection limits and onlythree (2,4-D, 2,4,5-TP and diazinon) have been detected above detection limits in water more than tentimes (Table 4). 18 It should be noted, however, that the SWQMP station testing is not geared to when orwhere pesticides are being used within the stream segment. The samples thus reflect essentially randomtests at a very limited number of fixed sampling stations.Table 4. Results of Individual Measurements of Pesticides in Water, Sediment and Fish Tissue,(1984-1994)MediumTotal individualpesticide samplesTotal individualpesticidedetections abovedetection limit% detection rate Number ofpesticides withmore than 10detections abovedetection limitWater 18,189 125 0.7% 3Sediment 21,900 564 2.6% 8Fish Tissue 11,432 917 8.0% 6TOTAL 51,521 1,606 3.1% 10Notes: First three columns include PCB samples and detections.Source: Texas Natural Resource Conservation Commission, The State of Texas Water Quality Inventory-1996,Volume 1 (Austin: TNRCC, 1996), 214.Pesticides have been found more frequently in sediment and fish tissue than in the ambient water itself.Eight pesticides have been detected in sediment samples more than 10 times over the 10-year period,while six pesticides have been detected more than 10 times in fish tissue samples (Table 5). 19 In fact,about eight percent of all measurements for pesticides in fish tissue detected at least one pesticide. Still,many of the pesticides for which this random sampling is conducted have not been found above detectionlimits by TNRCC’s SWQMP monitoring in either fish tissue or sediments. 20 Many of the frequently18 Ibid at 208.19 Ibid. at 215.20 Ibid.7