U.S. Department of the Interior Water-Quality Assessment of the Trinity River Basin, Texas U.S. Geological Survey Pesticides in a Coastal Prairie Agricultural Area, 1994-95 Open-File Report 96-124

M.F. Brown use that includes rice farming with irrigation the Trinity River Basin. The area receives an diversions and return flows. Pesticide samples average of 134 centimeters (cm) or 53 inches Abstract were collected from streams in three water­ (in.) of rainfall per year. In calendar year 1994, sheds in the coastal prairie area near Dayton 152 cm (60 in.) of rain fell at Anahuac and 178 and Anahuac, Texas (fig. 1), during 1994-95. Agriculture is a major land use in the coastal cm (70 in.) fell in the Dayton area (National This report discusses the results of that sam­ prairie area located in the southern part of the Oceanic and Atmospheric Administration,. pling along with land use, crops, and pesticide Trinity River Basin. Crops grown in the area 1994). The coastal prairie is the only area use in the three watersheds. include rice, sorghum, and soybeans. Pesti­ within the river basin where rice is grown. cide-use estimates for the area show that com­ Because of the water requirements for rice, a pounds with the highest use are the herbicides: Study Area Description more complex hydrologic system of rice irri­ molinate, propanil, thiobencarb, metolachlor, gation canals and drainage canals for return acifluorfen, bentazon, and atrazine and the The southern part of the Trinity River Basin flows is required. Natural drainage has been insecticides: carbaryl and methyl parathion. can be described as a coastal prairie with altered because of roadways and drainage More than 20 pesticide samples collected almost level relief, clay-rich soils, and a sub­ canals in the flat terrain. An example of the from each of three streams in the coastal tropical climate. The coastal prairie makes up hydrologic system in one of the coastal prairie prairie resulted in detections of 29 different about 5 percent (2,230 square kilometers) of watersheds, West Prong Old River, is shown in pesticide compounds. The most frequently detected compounds were the herbicides: atrazine, metolachlor, and molinate, which Table 1 . Watershed size, land use, and crops were detected in more than 75 percent of [km2, square kilometers; , no data] the samples. Herbicides were detected more Land use Crops frequently than insecticides. Maximum con­ Drainage (percentage of watershed area) (percentage of watershed area) centrations of atrazine, metolachlor, and Watershed area (km2) llrKar, Agricul- molinate occurred in the spring and were 4, Urban 1.9, and 200 micrograms per liter (\lg/L), ture respectively. Almost all concentrations of East Fork 112 25.4 73.2 0.6 10.5 atrazine and metolachlor were below drinking Whites Bayou>u 28 2.6 53.7 43.7 4.8 water standards; no standard is available for West Prong 75 4.4 92.2 2.1 5.6 5.9 20 molinate. Concentrations and estimated loads and percent of applied compound lost to the streams were generally higher in the water­ sheds where more of the pesticides were EXPLANATION applied to crops. | | Trinity River Basin

Introduction Gaged Watersheds: | | East Fork Double Bayou The Trinity River Basin was among the first | | Whites Bayou 20 hydrologic systems under full implementa­ tion of the National Water-Quality Assessment | | West Prong Old River (NAWQA) Program. Planning and analysis ^F Surface-water sampling site of existing information began in 1991. Inten­ sive data collection began in 1993. With its mouth on Trinity Bay (fig. 1), the Trinity River contributes substantial amounts of freshwater .EAST FORK !" ', DOUBLE BAY^U j to Galveston Bay, which was selected by Con­ ' gress as an estuary of national significance and included in a priority list for the National Estuary Program. Previously, inflow to Galveston Bay from the Trinity River has been estimated from measurements 70 miles upstream from the mouth. As a part of the NAWQA study, the water quality in the coastal prairie area immediately upstream from the bay was assessed. The area has a Figure 1 . Location of Trinity River Basin and coastal prairie area, Texas. complex hydrologic system and diverse land figure 2. Other agricultural activities in the to sample water quality. The location of Geographic Information and Retrieval System area include the production of grain sorghum these watersheds is shown in figure 1, and (GIRAS) files (Ulery and others, 1993). Cate­ and soybeans as well as cattle ranching. the drainage areas, land use, and crops grown gories that made up less than 1 percent of the in each watershed are shown in table 1 above area and are not shown in the table include Three watersheds, East Fork Double Bayou the map. water, wetlands, and barren land. These data (or simply East Fork), Whites Bayou, and also have been updated with information from West Prong Old River (West Prong), which The land-use information is based on topo­ the 1990 census, which indicates areas of new urban development (Hitt, 1994). All three of give spatial coverage and represent the land graphic maps and high-altitude aerial photo­ the watersheds have more than half of the area use of the coastal prairie area, were chosen graphs from the 1970's and was available from devoted to agriculture which includes, in addi­ tion to cropland, pasture and any other agricul­ tural areas such as turf farms, orchards, nurseries, or feedlots. East Fork is the largest watershed. The Anahuac oil field occupies 25 EXPLANATION WEST PRONG OLD RIVER percent of this watershed and is classified as urban. Whites Bayou is the smallest of the RICE OTHER STREAMS three watersheds and is located just to the west SORGHUM WATERSHED BOUNDARY of East Fork. Whites Bayou also has the high­ est percentage of mixed and evergreen forest. 1 KILOM ETE R SOYBEANS The third watershed, West Prong, is located on I the west side of the Trinity River and includes the highest percentage of land in agriculture.

The crop information was obtained by use of aerial photographs of the watersheds taken dur­ ing the sampling period and assistance from Consolidated Farm Service Agency (CFSA) officials in Liberty and Chambers Counties. 30 03'45 The aerial photographs were taken at a scale of 1:24,000, and the watershed boundaries and crop information from the CFSA were overlaid on images of the aerial photographs (Zey, 1995). The crops identified through the CFSA account for most of the cropland in the water­ sheds. The remainder of the agricultural area may be accounted for by hay (which is gener­ ally not treated with pesticides), pasture, turf farms, and very small areas planted in rye. Figure 2 is an example of an image from the aerial photographs overlaid with the watershed boundary and crops of the West Prong water­ shed. Rice is the dominant crop in the water­ sheds of both East Fork and Whites Bayou. Rice is planted between April and mid-June, depending on the weather. The West Prong watershed has the greatest variety of crops; sorghum and soybeans are grown in addition to rice. Sorghum is planted as early as the first part of March, and soybeans are planted in the May to June timeframe. There are also some turf farms in West Prong.

Pesticide Applications

Pesticide-use estimates were made for the crops grown in the coastal prairie area. This was done by multiplying the area planted for a given crop in each watershed by a pesticide application rate estimate from the Texas Agricultural Extension Service (Bill Harris, written conimun., 1991, and Glenn Avriett, Figure 2. Streams and crops in the West Prong Old River watershed. written conimun., 1995) and by the percentage of county area of that crop that was treated be related to its physical and chemical proper­ ties or its changing use. Propanil is less water HERBICIDE INSECTICIDE soluble (130 mg/L at 25°C) than molinate (880 2,4,5-T aldicarb 2,4-D 'aldicarb sulfone mg/L at 20°C), has a much shorter soil half- 2,4-DB 'aldicarb sulfoxide life of 1.5 days compared to 3 weeks (Meister acifluorfen azinphos, methyl- alachlor carbaryl Publishing Company, 1995), andpropanil atrazine carbofuran breaks down rapidly in water. The use estimate *atrazine, desethyl- 'carbofuran, 3-hydr- benfluralin chlorpynfos for propanil was adjusted to reflect its bentazon DD£,P,P'- partial replacement by quinlorac, but the esti­ bromoxynjl diazmon bromacil dieldrin mate may still be high. Acifluorfen and benta- butylate disulfoton zon, although shown to be extensively used, chloramben r ethoprop clopyralid fonofos were not frequently detected. This could be cyanazine HCH, alpha explained by their physical and chemical prop­ DCPA HCH, gamma- dacthal, mono-acid- malathion erties. Both of these compounds break down dicamba methiocarb quickly in water and the presence of sunlight. dichlorprop (2,4-DP) methomyl dietnylaniline oxamyl Acifluorfen has a half-life in water with dinpseb parathion, ethyl- continuous light of 92 hours, and bentazon diuron parathion, methyl- EPTC permethrin, cis- has a half-life in water with photodegradation ethalfluralin phorate of less than 24 hours (U.S. Environmental fenuron propargite fluometuron propoxur Protection Agency, 1985 and 1987). linuron terbufos MCPA 50 100 MCPB Three herbicides were frequently detected but metolachlpr DETECTIONS, IN PERCENT metribuzin did not show up in the agricultural use esti­ molinate mates. These were tebuthiuron, simazine, and napropamide neburon prometon. All three of these compounds may norflurazqn be used for weed control in industrial areas oryzalin pebulate EXPLANATION and along highways. Simazine is also associ­ pendimethalin Total bar length represents ated with turf production and may be used on picloram pronamide percent of detections for turf farms in the area. prometon samples from all sites. Bar propachlor colors show distribution of propanil detections between sites. Only seven insecticides were detected at the propham silvex (2,4,5-TP) (Number of samples varies coastal prairie sites, and all of these were simazine by compound from 61 to 64.) detected in less than 25 percent of the samples. thiobencarb tebuthiuron East Fork Double Bayou The most frequently detected insecticide was terbacil carbofuran, which was used on rice. Diazinon tnallate Whites Bayou triclopyr was the second most frequently detected triflurahn West Prong Old River insecticide but was not included in the com­ 0 50 100 pounds used on rice, sorghum, and soybeans. DETECTIONS, IN PERCENT Diazinon is used on home gardens and farms * pesticide degradation product to control a wide variety of insects. It is also used around homes for control of grubs in Figure 3. Distribution of pesticide detections. lawns as well as control of fleas and ticks. It is frequently detected in the Trinity River Basin, especially in the urban areas. Malathion was detected in 11 percent of the samples and Concentrations user of a public water system. The HA is a was also not included in the compounds used nonregulatory level of contaminants in drink­ for rice, sorghum, and soybeans. It may be In addition to pesticide occurrences, it is ing water that may be used for guidance in the used in the study area for mosquito control. important to consider the levels at which they absence of regulatory limits. The HA listed Two insecticides that had relatively high use are present in the streams. Concentrations of in the table is a health advisory established rates, carbaryl and methyl parathion, were the three herbicides that were detected in more for an individual's lifetime (70 years) expo­ detected in less than 10 percent of the samples. than 75 percent of the samples are shown in sure to drinking water. This HA is established The physical and chemical properties of these figure 4. Table 3 lists the maximum and to protect against adverse health effects not insecticides may be responsible for the low median concentrations of the three com­ related to cancer and is based on a body number of detections. Carbaryl has been pounds. Comparing the concentrations in weight of 70 kilograms (150 pounds) and con­ shown to have a half-life in streamwater of the streams to available water-quality stan­ sumption of 2 liters per day of drinking water 24 hours (Wauchope, 1978). Methyl parathion dards provides a frame of reference. The U.S. (NowellandResek, 1994). also degrades rapidly in water with a photo- Environmental Protection Agency (USEPA) degradation half-life of 8 days during the sum­ maximum contaminant level (MCL) and Concentrations of these herbicides in the three mer. Similarly, ethyl parathion, which was health advisory (HA) for the compounds are watersheds appear to be consistent with the used on the crops but not detected in any sam­ listed in table 4. The MCL is the USEPA stan­ crop and pesticide-use data. Atrazine and ples, has a half-life in water with photodegra­ dard for the maximum permissible level of a metolachlor were frequently detected in East dation of 1 to 10 days (Howard, 1989). contaminant in water that is delivered to any Fork and Whites Bayou, although no sorghum Table 3. Selected pesticide concentrations, estimated loads, and percentage lost to or soybeans were grown in the watersheds. stream However, concentrations were lower in these [u,g/L, micrograms per liter; kg/yr, kilograms per year] two streams than in West Prong, where atrazine and metolachlor were applied to Median Estimated Estimated percentage Watershed Maxil m Pesticide con°en ,rf on concentration load of amount applied sorghum and soybeans in the watershed. The (H9/L) (H9/L) (kg/yr) lost to stream highest concentration of atrazine, 4 u,g/L, was in March at West Prong. This value exceeds East Fork Double Bayou the MCL of 3 u,g/L, but all other concentra­ atrazine 0.21 0.05 1.35 * * tions of atrazine at all of the sites were below metolachlor .03 .01 .54 the MCL. The application of atrazine in the molinate 20.0 .28 35.2 1.0 pre-emergent product Bleep on sorghum, Whites Bayou which is planted in March, corresponds to this atrazine .37 .03 .53 * peak concentration. Metolachlor concentra­ metolachlor .02 .01 .15 * tions were also highest at West Prong, but the molinate 200 .10 30.4 7.8 seasonal peak was a little later, with 1.9 u,g/L West Prong Old River occurring in May. This may correspond to atrazine 4.0 .25 10.1 2.5 application of metolachlor to soybeans, which metolachlor 1.9 .06 7.1 1.5 are planted in this timeframe. All values of molinate 9.6 .03 11.8 .9 metolachlor were well below the HA of 100 * No estimated applications of this pesticide for this watershed. u,g/L. Molinate concentrations were highest in the two watersheds where rice is the pre­ Table 4. Selected pesticide standards dominant crop, East Fork and Whites Bayou. [USEPA, U.S. Environmental Protection Agency; u,g/L, micrograms per liter] All three watersheds show a similar seasonal pattern with the highest molinate concentra­ USEPA maximum contaminant level USEPA health advisory Pesticide tions occurring in May and June, correspond­ ing to the beginning of the rice-growing season atrazine 3.0 3.0 and the application of molinate. The highest metolachlor no standard available 100 molinate concentration was 200 u,g/L at molinate no standard available no standard available Whites Bayou. No drinking water standards are available for molinate.

DC 10 i i i i i i i i i i i U \ Loads K " _ atrazine While concentrations show the levels of the u "1 ; pesticides in the stream, loads are necessary to D. A ^.M M show the total amount of pesticides transported __ A £ B B _ by the streams over time. Yearly loads for 1 °-1 A 4^ A A atrazine, metolachlor, and molinate were esti­ JM * «,^, , ,««P , *, , * , , * 0 0.01 mated using the unbiased stratified ratio esti­ i i i i i i i i i i i g 10 \ mator method (Thomann and Mueller, 1987). 0 This method uses the concentrations and dis­ 5 1 - m metolachlor z '\ charges measured during sampling along with z- 0.1 - ^ _- the mean flow for the period to determine the O m A A lAMAv _ _ ^ _ load. It also allows for the data to be divided i= 0.01 99 . AW^T~Tk X Jli+ S A 2 6^ into two or more "seasons" to allow for vari­ able flow or concentrations. In this case, for H 0.001 i i i i i i i i i i i each watershed and pesticide combination, the z 3,88 i i i i i i i i i i 0 100 r data were split into two groups; one group At^ A molinate : was the growing season, which was deter­ o 10 r " ! AjftO ^^^^ ^ - mined from the seasonal concentration graph, UJ 1 r and the other group contained the rest of the Q ' 1 A % ^A 3 g 0.1 data (when the concentrations were generally lower in the fall and winter). Using a mean fc 0.01 si o B B a ad A Bi value for flow made the load estimate possible £ 0.001 i i i i i i i i i i i - M AMJJASONDJF even though flow was not measured as fre­ 1994 1995 quently during the fall and winter. Also, for the compounds which show a significant yearly EXPLANATION load, the load during the fall and winter made A East Fork Double Bayou Open symbols indicate value is "less than" value shown. up a very small percentage (0.3 to 2.8 percent) Whiter Ravnu Minimum reporting level for atrazine is 0.017 (.ig/L, y metolachlor is 0.009 ug/L, and molinate is 0.007 ng/L. of the yearly load because of the low concen­ West Prong Old River trations during this period. The mean flow MMHMMW ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ for the entire sampling period was 1.5 cubic meters per second (m3/s) at East Fork, 0.5 m3/s Figure 4. Seasonal pesticide concentrations for selected compounds. at Whites Bayou, and 0.6 m3/s at West Prong. Table 2. Estimated pesticide applications by crop and watershed Pesticide Sampling [kg, kilograms; , none known to be applied] Water samples were collected at one site in Estimated amount applied each of the three watersheds from March 1994 ^ r 'Pesticide (kg) Pesticide iraae through February 1995. More than 20 samples Crop active ingredient name East Whites West were collected at each site. Additional samples Fork Bayou Prong were collected to assure that consistent field RICE and laboratory results were produced. Sam­ acifluorfen Blazer 49.5 5.50 17.6 pling frequency varied from weekly during bentazon Basagran 165 18.3 58.6 the spring and summer growing season to once every 2 months during the winter. Stream carbaryl Sevin 554 61.6 197 stage was measured at each sampling and carbofuran Furadan 269 29.9 95.6 three times per week at each site from April methyl parathion Penncap-M 165 18.3 58.6 through September. molinate Ordram, Arrosolo 3,520 391 1,250 [n addition to gas chromatography/mass pendimethalin Prowl 66.0 7.33 23.4 spectrometry and high-pressure liquid chro- propanil Propanil, Arrosolo 2,090 232 742 matography methods for pesticides, laboratory thiobencarb Bolero 990 110 351 analyses included major inorganic ions, nutri­ SORGHUM ents, and suspended sediment. Field measure­ ments included stream stage and discharge, atrazine Bicep 410 water temperature, pH, dissolved oxygen,

chlorpyrifos Lorsban 29.7 and specific conductance. ethyl parathion Parathion 37.1 metolachlor Bicep 481 Pesticide Results SOYBEANS acifluorfen Blazer 691 The coastal prairie pesticide data were sum­ alachlor Lasso 287 marized as frequency of detections for each pesticide. Concentrations of the most fre­ bentazon Basagran 346 quently detected compounds were graphed

carbaryl Sevin 173 versus time and compared to available water- linuron Lorox 86.4 quality standards. The amounts of these fre­ methyl parathion Penncap-M 259 quently detected compounds transported in metolachlor Dual 259 the streams over time were also estimated and compared to the amounts applied in the metribuzin Lexone 86.4 watersheds. permethrin Ambush 49.2 Occurrence with the pesticide. These estimates are given Sorghum is treated with a much smaller The first level of data analysis for the pesti­ cides is to identify which compounds are in table 2. Only those pesticides included in number of pesticide compounds. The herbi­ present, or occurring, in the streams. One mea­ NAWQA laboratory analyses are shown. cides atrazine and metolachlor are used in combination (as the trade name Bicep) for pre- sure of pesticide occurrence is the frequency of detections among all the samples. Figure 3 The compounds with the highest use on rice emergent weed control. Two insecticides are used. Ethyl parathion is used for the control is a bar graph showing the distribution of are the herbicides molinate and propanil. detections for all the pesticide samples in the These compounds are used individually and in of midges, and chlorpyrifos is used to control sorghum headworm. coastal prairie area. The figure lists herbicides combination (as trade name Arrosolo) to con­ and insecticides separately and shows that trol a variety of grasses and broadleaf weeds. Several herbicides are used for weed control herbicides are much more frequently detected Another herbicide, quinlorac (trade name on soybeans. Acifluorfen is used in the great­ than insecticides. Facet), which is not included in NAWQA est amount, followed by bentazon, alachlor, analyses, is replacing some of the propanil metolachlor, linuron, and metribuzin. Three Three herbicides atrazine, metolachlor, and use. The other herbicides used on rice are insecticides are used on soybeans. Methyl par­ molinate were detected in more than 75 per­ cent of the samples. These three herbicides thiobencarb, acifluorfen, bentazon, and pen­ athion is used for the control of stink bugs, and were among the most highly used compounds dimethalin. Most of the herbicide applications carbaryl and permethrin are used for worm control. on rice, sorghum, and soybeans. Desethyl- for rice are before planting or very early in atrazine, a breakdown product of atrazine, was the growing season. The insecticide carbaryl Other pesticide uses have not been quantified also detected in nearly 70 percent of the sam­ is used on rice to control stink bugs and army but may include use of 2,4-D for weed control ples. Thiobencarb was detected in about 40 worms. Carbofuran is used to control rice in canals and on rights-of-way, the use of vari­ percent of the samples and was also among the water weevils, and methyl parathion is used ous herbicides and insecticides on turf farms most highly used compounds. Propanil was for additional stink bug control. The use of in the area, and additional herbicide use for the second in estimated total use but was only the insecticides on rice varies from year to control of vegetation in industrial areas such detected in 16 percent of the samples. The year with the severity of insect problems. as oil fields. low number of detections for propanil could For East Fork and Whites Bayou, the growing The most frequently detected compounds bentazon: Washington, D.C., Office of season mean flow was lower than that for the were the herbicides atrazine, metolachlor, Pesticide Programs, Fact Sheet 64,10 p. rest of the year (1.4 m /s during the growing and molinate season compared to 1.8 m3/s for East Fork and ____1987, Acifluorfen health advisory draft In general, concentrations and loads of 0.5 m /s compared to 0.6 m /s for Whites report, August 1987: Washington, D.C., atrazine, metolachlor, and molinate were Bayou). At West Prong, the growing season Office of Drinking Water. highest in the watersheds where more mean flow was greater at 0.8 m3/s compared had been applied to rice, sorghum, and with 0.2 m /s during the rest of the sampling Wauchope, R.D., 1978, The pesticide content soybeans period. of surface water draining from fields A review: Journal of Environmental Quality, Peak concentrations of atrazine, v. 7, no. 4, p. 459-472. Like the concentrations, the loads of these pes­ metolachlor, and molinate occurred in ticides were higher in the watersheds where the spring around the time of their applica­ Zey, E.B., 1995, National Water-Quality they were applied to crops. The estimated tion Assessment Program A GIS application loads are listed in table 3. Estimated yearly Maximum concentrations of atrazine and for the Texas Coastal Prairie Survey: loads for molinate were greater than 11 kilo­ metolachlor were almost always below College Station, Texas A&M University, grams per year (kg/yr) in each of the three drinking-water standards set by USEPA; Rangeland Ecology and Management, watersheds, while atrazine and metolachlor no standards are available for molinate Professional Paper, 42 p. loads were clearly greater in West Prong, where the pesticides are known to be exten­ References Any use of trade, product, or firm names is for sively applied. descriptive purposes only and does not imply endorsement by the U.S. Government. The percentage of pesticide applied that was Hitt, Kerie, 1994, Refining 1970's land-use lost to the stream was calculated using the esti­ data with 1990 population data to indicate mates of pesticide use and yearly loads. This new residential development: U.S. Geological Survey Warer-Resources In 1991, the U.S. percentage could not be calculated for atrazine Geological Survey, U.S. and metolachlor in the two watersheds where Investigations Report 94-4250, 15 p. Department of the Interior, the use of the pesticides on the major crops Howard, P.H. (ed.), 1989, Handbook of began a National Water- was not documented. The percentages are also environmental fate and exposure data for Quality Assessment listed in table 3. In the West Prong watershed, organic chemicals, v. Ill Pesticides: the percentage lost to the stream for atrazine Chelsea, Mich., Lewis Publishers, 684 p. (NAWQA) Program. The long-term goals was 2.5 percent and for metolachlor was 1.5 of the NAWQA Program are to describe the percent. The percentage lost to the stream for Larson, S.J., Capel, P.O., Goolsby, D.A., status of and trends in the quality of a molinate was near 1 percent in both the East Zaugg, S.D., and Sandstrom, M.W, 1995, large representative part of the Nation's Fork and West Prong watersheds and 7.8 per­ Relations between pesticide use and riverine surface- and ground-water resources and cent in Whites Bayou. As discussed above, flux in the Mississippi River Basin: to identify the major factors that affect the Whites Bayou showed the highest single con­ Chemosphere, v. 31, no. 5, p. 3,305-3,321. quality of these resources. In addressing centration of molinate at 200 M-g/L. In compar­ these goals, the NAWQA Program witt ison, a study of relations between the use of 26 Meister Publishing Company, 1995, Farm produce water-quality information that is pesticides and riverine flux in the Mississippi chemicals handbook '95: Willoughby, Ohio, useful to policymakers and managers at River Basin in 1991 showed values for loss of Meister Publishing Company, 922 p. Federal, State, and local levels. atrazine from 0.6 to 2.0 percent and meto­ National Oceanic and Atmospheric Studies of up to 60 hydrologic systems lachlor from 0.5 to 0.9 percent. Values for all Administration, National Ocean Service, that include parts of most major river 26 pesticides ranged from less than 0.01 to 1994, Climatological Data Texas: basins and aquifer systems are the building 10.5 percent (Larson and others, 1995). Asheville, N.C., National Climatic Data blocks of the national assessment. The 60 Center [variously paged]. study units range in size from less than 1,000 to more than 60,000 square miles Summary Nowell, L.H. and Resek, E.A., 1994, and represent 60 to 70 percent of the Standards for pesticides in water, in Ware, Nation's water use and population served Water-quality samples were collected from G.W, ed., Reviews of environmental by public water supplies. Twenty three watersheds in the coastal prairie area contamination and toxicology, v. 140: New investigations began in 1991,15 immediately upstream from Trinity Bay. The York, Springer-Verlag, 221 p. investigations began in 1994, and 20 are three watersheds are representative of this area scheduled to begin in 1997. where agriculture is an important land use and Thomann, R.V. and Mueller, J.A., 1987, the major crops grown are rice, sorghum, and Principles of surface water quality modeling and control: New York, Harper Collins soybeans. Results of this sampling include the Information on technical reports and Publishers, 644 p. following: hydrologic data related to the NAWQA Ulery, R.L., Van Metre, PC., and Crossfield, Program can be obtained from: Twenty-nine pesticides were detected in one A.S., 1993, Trinity River Basin, Texas: or more of more than 60 surface-water sam­ Water Resources Bulletin, v. 29, no. 4, Project Chief Trinity River Basin ples from the three coastal prairie streams p. 685-711. NAWQA Study ' U.S. Geological Survey Herbicides were detected more frequently U.S. Environmental Protection Agency, 1985, 801 ICameron Road than insecticides Pesticide fact sheet for bentazon and sodium Austin, TX 78754-3898

February 1996