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Agricultural chemicals in ground water: Extent and implications

Published online by Cambridge University Press:  30 October 2009

George R. Hallberg
George R. Hallberg
Affiliation:
Supervisor of Environmental Geology, Iowa Department of Natural Resources, Geological Survey Bureau, Iowa City, IA 52242
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Abstract

The accelerated use of agricultural chemicals over the past 20–30 years has increased production and generally has been profitable, but it has also had an adverse impact on ground water quality in many major agricultural areas. The contamination of ground water, related to nitrogen fertilizers and pesticides, from widespread, routine land application, as well as from point sources has become a serious concern. Ground water contamination also impairs surface water quality. Research, world-wide, has shown increases in NO3-N in ground water concurrent with major increases in N-fertilization. Many shallow ground water supplies now exceed recommended NO3-N drinking water standards. While many sources contribute N into the environment, synthetic fertilizers have become the major component. There are clear economic incentives to improve management; harvested crops often account for less than 50 percent of the purchased fertilizer inputs. Pesticides are appearing in ground water with unanticipated frequency, and while their concentrations are generally below acute toxic levels, many are of concern for possible chronic effects. Such widespread contamination is of real concern because of the potential for long-term and widespread exposure of the public through drinking water. Surveys of farmers indicate a desire to improve management practices and reduce chemical inputs. Promoting the principles of alternative, sustainable agriculture is a necessary element in the resolution of these problems.

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Articles
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American Journal of Alternative Agriculture , Volume 2 , Issue 1 , Winter 1987 , pp. 3 - 15
Copyright
Copyright © Cambridge University Press 1987

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References

1.Aldwell, C. R. and Bush, B.. 1986. Agriculture and groundwater must co-exist. Environ. Geol. and Water Sci. 9:(1–2).Google Scholar
2.Anderson, H. A., Belluck, D. A., and Sinha, S. K.. 1986. Recommended public health related groundwater standards-1986; Summary of scientific support documentation for NR 140.10. Wisc. Div. of Health, Dept. Health and Social Serv., Madison, WisconsinGoogle Scholar
3.Anderson, L. J., and Kristiansen, H.. 1984. Nitrate in groundwater and surface water related to land use in the Karup Basin, Denmark. Environ. Geol. 5:207–212.CrossRefGoogle Scholar
4.Baker, D. B. 1985. Regional water quality impacts of intensive row-crop agriculture: Lake Erie Basin case study. J. Soil and Water Cons. 40(1): 125–132.Google Scholar
5.Baker, D. B., Krieger, K. A., Richards, R. P., and Kramer, J. W.. 1985. Gross erosion rates, sediment yields, and nutrient yields for Lake Erie tributaries:implications for targeting. In: Perspectives on Nonpoint Source Pollution, USEPA, EPA 440/5 85–001, Washington, DC, pp. 251–255.Google Scholar
6.Baker, J. L. 1985a. Conservation tillage: Water quality considerations. In D'Itri, F. M., (ed.), A Systems Approach to Conservation Tillage. Lewis Publ. Inc., Chelsea, Michigan 48118, pp. 217–238.Google Scholar
7.Baker, J. L. 1985b. Sources and fates of material influencing water quality in the agricultural Midwest. In: Perspectives on Nonpoint Source Pollution, EPA 440/5 85–001, pp. 467–470. U.S. Environ. Prot. Agency, Washington, DC.Google Scholar
8.Baker, J. L., and Johnson, H. P.. 1981. Nitrate-nitrogen in tile drainage as affected by fertilization. J. Environ. Qual. 10:519–522.CrossRefGoogle Scholar
9.Baker, J. L., and Johnson, H. P.. 1983. Evaluating the effectiveness of BMPs from field studies. In Schaller, F. and Bailey, G. (eds.). Agricultural Management and Water Quality, Ia. State Univ. Press, Ames, Iowa, pp. 281–304.Google Scholar
10.Baker, J. L., and Laflen, J. M.. 1983. Water quality consequences of conservation tillage. J. Soil and Water Cons. 38:186–193.Google Scholar
11.Beven, K., and Germann, P.. 1982. Macropores and water flow in soils. Water Resources Res. 18(5):1311–1325.CrossRefGoogle Scholar
12.Blackmer, A. M. 1986. Potential yield response of corn to treatments that conserve fertilizer nitrogen in soils. Agron. J. 78(4): 571–575.CrossRefGoogle Scholar
13.Blackmer, A. M. 1987. Losses of fertilizer N from soils. In: Proc. Conservation Tillage on Wet Soils, pp. 51–61. la and Mn Chapters, Soil Conserva. Soc. Am., Ankeny, Iowa.Google Scholar
14.Blair, A., and Thomas, T. L.. 1979. Leukemia among Nebraska farmers: a death certificate study. Am. J. Epidemiol. 110:264–273.Google Scholar
15.Burden, R. J. 1982. Nitrate contamination of New Zealand aquifers: a review. New Zealand Jour. Sci. 25:221–227.Google Scholar
16.Butler, M. K., and Arruda, J. A.. 1985. Pesticide monitoring in Kansas surface waters: 1973–1984. In: Perspectives on Nonpoint Source Pollution, pp. 196–200. USEPA, EPA 440/5 95–001, Washington, DC.Google Scholar
17.Carey, M. A. and Lloyd, J. W.. 1985. Modelling non-point sources of nitrate pollution of groundwater in the Great Ouse Chalk, U.K. J. Hydrol. 78:83–106.CrossRefGoogle Scholar
18.CAST. 1985. Agriculture and groundwater quality.Council for Agric. Sci. and Technol., Rept. No. 103. 62 pp.Google Scholar
19.Clark, E. H. II, and Richardson, N. B.. 1986. Agriculture not sole culprit. Solutions, J. Fluid Fert./Ag. Chem. Ind. 30(5):32–36.Google Scholar
20.Cohen, S. Z., Creeger, S. M., Carsel, R. F., and Enfield, C. G.. 1984. Potential pesticide contamination of groundwater from agricultural uses. In Krueger, R. F., and Seiber, J. N., (eds.). Treatment and Disposal of Pesticide Wastes, pp. 297–325. Am. Chem. Soc., Washington, DC.Google Scholar
21.Cohen, S. Z., Eiden, C., and Lorber, M. N.. 1986. Monitoring ground water for pesticides. In W. Y. Garner et al., (eds.). Evaluation of Pesticides in Ground Water, pp. 170–196. Am. Chem. Soc., Symp. Ser. 315.Google Scholar
22.Csaki, F., and Endredi, I.. 1981. Pollution by nitrates of the subsurface waters in Hungary. Proc. Int. Symp. Groundwater Quality, Noordwijkerhout, Netherlands; Studies in Environ. Sci. no. 17, Elsevier, Amsterdam, pp. 89–94.Google Scholar
23.Cook, Ken. 1986. The big seep—commentary. J. Soil and Water Cons. 41(4):235–237.Google Scholar
24.Curry, D. S. 1987. Assessment of empirical methodologies for predicting groundwater pollution from agricultural chemicals. In Fairchild, D. M. (ed.). Groundwater Quality and Agricultural Practices, pp. 227–246. Lewis Publ. Inc., Chelsea, Michigan.Google Scholar
25.Davis, S., Bingham, F. T., Shade, E. R., and Grass, L. B.. 1969. Water relations and salt balance of a 1000-acre citrus watershed. In: Proc. First Internat. Citrus. Symp. 3:1771–1777.Google Scholar
26.DeVault, G. 1986. Spend less, make more, and keep EPA off your back. The New Farm. 8(5):2, 40–41.Google Scholar
27.Dorsch, M. M., Scragg, R. K., McMichael, A. J., Baghurst, P. A., and Dyer, K. F.. 1984. Congenital malformations and maternal drinking water supply inrural South Australia: a case control study. Am. J. Epidemiol. 119:473–486.CrossRefGoogle Scholar
28.E.E.C. (European Economic Community). 1980. Council directive relating to the quality of water intended for human consumption. Off. Jour. Eur. Communities, No. 80/778/EEC, v. 23, L229.Google Scholar
29.Egboka, B. C. E. 1984. Nitrate contamination of shallow groundwaters in Ontario, Canada. Sci. Total Environ. 35:53–58.Google Scholar
30.Elfving, J. 1986. “Fingerprinting” pollution at Iowa's Big Spring. EPA J. 12(4):19.Google Scholar
31.Embleton, T. W. et al. , 1986. Citrus nitrogen fertilizer management, groundwater pollution, soil salinity, and nitrogen balance. Applied Agric. Res. 1:57–64.Google Scholar
32.Exner, M. E., and Spaulding, R. F.. 1974. Groundwater quality of the Central Platte region, 1974. Resource Atlas No. 2. Conservation and Survey Division, University of Nebraska-Lincoln. 48 pp.Google Scholar
33.Fairchild, D. M. (ed.). 1987. Groundwater quality and agricultural practices. Lewis Publ. Inc., Chelsea, Michigan.Google Scholar
34.Federal Register. 1987. Inert ingredients in pesticide products; policy statement; Notice by Environ. Protec. Agency. Fed. Reg. 52(77):13305–13309.Google Scholar
35.Fiore, M. 1987. Chronic exposure to aldicarb-contaminated groundwater and human immune function. Pesticides and Groundwater: A Health Concern for the Midwest, pp. 199–203. The Freshwater Foundation and the USEPA, Navarre, Minnesota.Google Scholar
36.Gianessi, L. P., Peskin, H. M., Crosson, P., and Puffer, C.. 1986. Nonpoint source pollution: Are cropland controls the answer? Rpt. prepared for the U.S. Environ. Prot. Agency, U.S.D.A., Soil Conserv. Serv., and U.S. Geol. Surv. under EPA Coop. Agreement CR811858-01. Resources for the Future, Washington, DC.Google Scholar
37.Glotfelty, D. E., Seiber, J. N., and Liljedahl, L. A.. 1987. Pesticides in fog. Nature 325:602–605.CrossRefGoogle ScholarPubMed
38.Gordon, J. E., and Shy, C. M.. 1981. Agricultural chemical use and congenital cleft lip and/or palate. Arch. Environ. Health 36(5):213–221.Google Scholar
39.Hallberg, G. R. 1985. Groundwater quality and agricultural chemicals: a perspective from Iowa. Proc. North Central Weed Control Conf. 40:130–147.Google Scholar
40.Hallberg, G. R. 1986a. Agrichemicals and water quality. Colloquium on Agri-chemical Management and Water Quality. Board on Agric, Nat'l. Res. Council. Nat'l. Academy Press, Washington, DC.Google Scholar
41.Hallberg, G. R. 1986b. Overview of agricultural chemicals in ground water. Agricultural Impacts on Ground Water, pp. 1–67. Nat'l. Water Well Assoc., Worthington, Ohio 43085.Google Scholar
42.Hallberg, G. R. 1986c. From hoes to herbicides: agriculture and groundwater quality. J. Soil and Water Conserv. 41(6):357–364.Google Scholar
43.Hallberg, G. R. 1987. Nitrates in groundwater in Iowa. In D'Itri, F. M., and Wolfson, L. G. (eds.), Rural Groundwater Contamination, in press. Lewis Publish., Inc., Chelsea, Michigan.Google Scholar
44.Hallberg, G. R., Libra, R. D., Bettis, E. A. III, and Hoyer, B. E.. 1984. Hydrogeologic and water-quality investigations in the Big Spring Basin, Clayton County, Iowa: 1983 Water-Year. Ia. Geol. Surv. Rept. 84–4. 231 pp.Google Scholar
45.Hallberg, G. R., Libra, R. D., and Hoyer, B. E.. 1985. Nonpoint source contamination of groundwater in karst-carbonate aquifers in Iowa. In: Perspectives on Nonpoint Source Pollution, USEPA, EPA 440/5 85001, Washington, DC pp. 109–114.Google Scholar
46.Hallberg, G. R., Baker, J. L., and Randall, G. W.. 1986. Utility of tile-line effluent studies to evaluate the impact of agricultural practices on groundwater. In: Agricultural Impacts on Ground Water, pp. 298–326. Nat'l. Water Well Assoc., Worthington, Ohio.Google Scholar
47.Hallberg, G. R., Libra, R. D., Long, K. R., and Splinter, R. C.. 1987. Pesticides, groundwater, and rural drinking water quality in Iowa. In: Pesticides and Groundwater: A Health Concern for the Midwest, pp. 83–104. The Freshwater Foundation and the USEPA, Navarre, Minnesota.Google Scholar
48.Hardell, L., and Sandstrom, A.. 1979. Case-control study: soft tissue sarcomas and exposure to phenoxyacetic acids or chlorophenols. British Jour. Cancer 39:711–717.Google Scholar
49.Hargett, N. L., and Berry, J. T.. 1983. 1982 fertilizer summary data. Natl. Fert. Develop. Ctr., TVA, Muscle Shoals, Alabama. 136 pp.Google Scholar
50.Harris, L. 1986. Recent events, public concern challenge leadership to act. In: U.S. Water News, March, 1987, p. 7.Google Scholar
51.Hill, A. R. 1982. Nitrate distribution in the ground water of the Alliston region of Ontario, Canada. Ground Water. 20(6):696–702.Google Scholar
52.Hinkle, M. K. 1983. Problems with conservation tillage. J. Soil Water Cons. 38:201–206.Google Scholar
53.Hoar, S. K., Blair, A., Holmes, F. F., Boysen, C. D., Robel, R. J., Hoover, R., and Fraumeni, J. F. Jr., 1986. Agricultural herbicide use and risk of softtissue sarcoma. J. Am. Med. Assoc. 256:1141–1147.Google Scholar
54.Holden, P. 1986. Pesticides and groundwater quality: issues and problems in four states. Nat'l. Research Council, Bd. on Agric. Nat'l. Acad. Press, Washington, DC. 124 pp.Google Scholar
55.Holmberg, Mike. 1986. Wastes money, pollutes well water—the N overdose. Successful Farming 85(2):26.Google Scholar
56.Howard, K. W. F. 1985. Denitrification in a major limestone aquifer. Jour. Hydrol. 76:265–280.Google Scholar
57.Hoyer, B. E., Combs, J. E., Kelley, R. D., Cousins-Leatherman, C., and Seyb, J. H.. 1987. Iowa Groundwater Protection Strategy. Environ. Prot. Comm., Ia. Dept. Nat. Res. 105 pp.Google Scholar
58.Isacson, Peter, Bean, J. A., Splinter, R., Olson, D. B., and Kohler, J.. 1985. Drinking water and cancer incidence in Iowa. III. Association of cancer with indices of contamination. Am. J. Epidemiol. 121:856–869.CrossRefGoogle ScholarPubMed
59.Jacks, G., and Sharma, V. P.. 1983. Nitrogen circulation and nitrate in groundwater in an agricultural catchment in southern India. Environ. Geol. 5(2):61–64.Google Scholar
60.Johnson, H. P., and Baker, J. L.. 1973. Ames reservoir environmental study, Appendix 4, Chapts. 2 and 3. ISWRRI-60-A4, Iowa State Water Res. Inst., Ames, Iowa.Google Scholar
61.Kapp, J. D. 1986. Implementing best management practices to reduce nitrate levels in northeast Iowa groundwater. In: Agricultural Impacts on Groundwater, pp. 412–427. Nat'l. Water Well Assoc., Worthington, Ohio.Google Scholar
62.Keeney, D. R. 1982. Nitrogen management for maximum efficiency and minimum pollution. In F. J. Stevenson (ed.). Nitrogen in Agricultural Soils, pp. 605–649. Agronomy Monograph 22.Google Scholar
63.Keeney, D. R. 1986a. Sources of nitrate to groundwater. CRC Critical Reviews in Environmental Control 16(3):257–304.Google Scholar
64.Keeney, D. R. 1986b. Nitrate in ground water agricultural contribution and control. Agriculture Impacts on Groundwater, pp. 229–351. Nat'l. Water Well Assoc., Worthington, Ohio 43085.Google Scholar
65.Kelley, R. D. 1987. Pesticides in Iowa's drinking water. In: Pesticides and Groundwater: A Health Concern for the Midwest, pp. 115–135. The Freshwater Foundation and the USEPA, Navarre, Minnesota.Google Scholar
66.Kelley, R., Hallberg, G., Johnson, L., Libra, R., Thompson, C., Splinter, R., and DeTroy, M.. 1986. Pesticides in ground water in Iowa. Agriculture Impacts on Groundwater, pp. 229–351. Nat'l. Water Well Assoc., Worthington, Ohio 43085.Google Scholar
67.Kidwell, Boyd. 1985. Families worry as water quality drops. Progressive Farmer 100(9):28–3O.Google Scholar
68.Klaseus, T. 1987. Minnesota pesticide monitoring surveys, interim report. In: Pesticides and Groundwater: A Health Concern for the Midwest, pp. 137–158. The Freshwater Foundation and the USEPA, Navarre, Minnesota.Google Scholar
69.Kricker, A., McCredie, J., Elliott, J., and Forrest, J.. 1986. Women and the environment: a study of congenital limb anomalies. Community Health Studies 10(1):1–11.Google Scholar
70.Kudeyarov, V. N., and Bashkin, V. N.. 1980. Nitrogen balance in small river basins under agricultural and forestry use. Water, Air, and Soil Pollut. 14:23–27.Google Scholar
71.Legrand, H. E., and Stringfield, V. T.. 1973. Concepts of karst development in relation to interpretation of surface runoff. U.S. Geol. Surv. Jour. Res. 1:351–360.Google Scholar
72.Libra, R. D., Hallberg, G. R., Hoyer, B. E., and Johnson, L. G.. 1986. Agricultural impacts on groundwater quality: the Big Spring Basin study, Iowa. In: Agricultural Impacts on Groundwater, pp. 253–273. Nat'l. Water Well Assoc., Worthington, Ohio.Google Scholar
73.Libra, R. D., Hallberg, G. R., and Hoyer, B. E.. 1987. Impacts of agricultural chemicals on groundwater quality in Iowa. In Fairchild, D. M. (ed.). Ground Water Quality and Agricultural Practices, pp. 185–217. Lewis Publ. Inc., Chelsea, Michigan.Google Scholar
74.Lockeretz, W., Shearer, G., and Kohl, D. H.. 1981. Organic farming in the corn belt. Sci. 211:540–547.Google Scholar
75.National Research Council. 1978. Nitrates: An environmental assessment. Environmental Studies Board, Commission on Natural Resources, Coordinating Committee for Scientific and Technical Assessment of Environmental Pollutants, Nat'l. Acad. of Sci. Press, Washington, DC.Google Scholar
76.National Research Council. 1987. Regulating pesticides in food; the Delaney paradox. Comm. on Sci. Regulatory Issues, Underlying Pesticide Use Patterns and Agric Innovation. Nat'l. Acad. Press, Washington, DC.Google Scholar
77.Nielsen, E. G., and Lee, L. K.. 1987. The magnitude and costs of groundwater contamination from agricultural chemicals. USDA-Econ. Res. Serv., Nat. Res. Econ. Div., Staff Rept. AGES87O318. 54 pp.Google Scholar
78.Nowak, P. J. 1983. Adoption and diffusion of soil and water conservation practices. The Rural Sociologist 3(2):83–91.Google Scholar
79.Nowak, P. J. 1984. Strategies for increasing the adoption of conservation strategies. The Rural Sociologist 3(4):243–246.Google Scholar
80.Oberle, S. L., Keeney, D. R., Bundy, L. G., Klemme, R. M., and Kelling, K. A.. 1987. Development of a nitrogen management model for corn in Wisconsin. In: Proc. 1987 Fert., Aglime, and Pest Mngmt. Conf., v. 26, in press. Madison, Wisconsin.Google Scholar
81.OECD (Organization for Economic Co-operation and Development). 1986. Water Pollution by Fertilizers and Pesticides. OECD, Paris, France.Google Scholar
82.Olsen, R. J., Hensler, R. F., Attoe, O. J., Witzel, S. A., and Peterson, L. A.. 1970. Fertilizer nitrogen and crop rotation in relation to movement of nitrate nitrogen through soil profiles. Soil Sci. Soc Amer. Proc. 34:448–452.CrossRefGoogle Scholar
83.Olson, R. A. 1985. Nitrogen problems. In: Plant Nutrient Use and the Environment, pp. 115–138. The Fertilizer Inst., Washington, DC.Google Scholar
84.Olson, R. A., Frank, K. D., Grabouski, P. H., and Rehm, G. W.. 1982. Economic and agronomic impacts of varied philosophies of soil testing. Agron. J. 74:492–499.Google Scholar
85.Padgitt, Steven. 1986. Agriculture and ground water quality as a social issue: assessing farming practices and potential for change, pp. 134–144. Agricultural Impacts on Ground Water. Nat'l. Water Well Assoc, Worthington, Ohio 43085.Google Scholar
86.Papendick, R. I., Elliott, L. F., and Dahlgren, R. B.. 1986. Environmental consequences of modern production agriculture: How can alternative agriculture address these issues and concerns? Am. J. Alternative Agric. 1(1):3–10.CrossRefGoogle Scholar
87.Pierre, D. 1983. The impact of agriculture on water quality. Fert. and Agric 85:51–62.Google Scholar
88.Pimentel, D., and Levitan, L.. 1986. Pesticides: amounts applied and amounts reaching pests. Bioscience 36(2):86–91.Google Scholar
89.Pimental, D. et al. , 1978. Benefits and costs of pesticide use in U.S. food production. Bioscience 28(12):772–784.Google Scholar
90.Pins, K. 1986. Poll: Iowans want limits on ag chemicals. The Iowa Poll, Des Moines Sunday Register, Nov. 16, 1986, sec. A, p. 1 and 8.Google Scholar
91.Pratt, P. F. 1984. Nitrogen use and nitrate leaching in irrigated agriculture. In Hauck, R. D. (ed.). Nitrogen in Crop Production, pp. 319–333. Am. Soc. Agron., Madison, Wisconsin.Google Scholar
92.Pratt, P. F. et al. , 1975. Utilization of animal manures and sewage sludges in food and fiber production. Council Agric. Sci. Tech., Rept. 11. 96 pp.Google Scholar
93.Probst, J. L. 1985. Nitrogen and phosphorous in the Garonne Basin (France). J. Hydrol. 76:281–305.CrossRefGoogle Scholar
94.Quinlan, J. F., and Alexander, E. C. Jr., 1987. How often should samples be taken at relevant locations for reliable monitoring of pollutants from an agricultural, waste disposal or spill site in a karst terrane? A first approximation. In Beck, B. F. (ed.). Proc. 2nd. Multidisciplinary Conference on Sinkholes and Environmental Impact of Karst, in press. Orlando, Florida.Google Scholar
95.Quinlan, J. F., and Ewers, R. O.. 1985. Ground water flow in limestone terranes: strategy, rationale, and procedure for reliable, efficient monitoring of groundwater quality in karst areas. In: Proc. 5th Nat'l. Symp. and Expo on Aquifer Restoration and Ground Water Monitoring, pp. 197–234. Nat'l. Water Well Assoc, Worthington, Ohio.Google Scholar
96.Schepers, J. S., and Martin, D. L.. 1986. Public perception of ground water quality and producers dilemma. Agricultural Impacts on Ground Water, pp. 399–411. Nat'l. Water Well Assoc, Worthington, Ohio 43085.Google Scholar
97.Singh, B., and Sekhon, G. S.. 1978. Nitrate pollution of groundwater from farm use of nitrogen fertilizers—a review. Agric. and Environment 4:207–225.CrossRefGoogle Scholar
98.Spaulding, R. F., Gormly, J. R., Curtiss, B. H., and Exner, M. E.. 1978. Nonpoint nitrate contamination of ground water in Merrick County, Nebraska. Ground Water 16:86–95.Google Scholar
99.Tevis, Cheryl. 1986. Groundwater pollution emerges as a rural issue. Successful Farming 84(1):D5–6.Google Scholar
100.Thomas, G. W., and Phillips, R. E.. 1979. Consequences of water movement in macropores. Jour. Environ. Qual. 8:149–152.CrossRefGoogle Scholar
101.Tomlinson, T. E. 1970. Trend in nitrate concentrations in English rivers and fertilizer use. Water Treat. Exam. 19:277–289.Google Scholar
102.Trcka, P. A. 1987. Huntting takes steps to protect groundwater. Solutions 31(1):64–68.Google Scholar
103.Vrba, J. 1983. The impact of human activities on groundwater systems. Environ. Geol. 5:9–10.CrossRefGoogle Scholar
104.Wallace's Farmer. 1987. Farmers oppose fertilizer, chemical tax. Wallace's Farmer editorials, 04 11, 1987, p. 11.Google Scholar
105.Walter, John. 1985. Groundwater pollution: who's liable? Successful Farming 84(13):24.Google Scholar
106.Wauchope, R. D. 1978. The pesticide content of surface water draining from agricultural fields—a review. J. Environ. Qual. 7:459–472.Google Scholar
107.Wehtje, G., Spaulding, R. F., Burnside, O. C., Lowry, S. R., and Leavitt, J. R. C.. 1983. Biological significance and fate of atrazine under aquifer conditions. Weed Sci. 31:610–618.Google Scholar
108.Westerman, R. L. 1987. Efficient nitrogen fertilization in agricultural production systems. In Fairchild, D. M. (ed.). Ground Water Quality and Agricultural Practices, pp. 137–152. Lewis Publ. Inc., Chelsea, Michigan.Google Scholar
109.White, R. E. 1985. A model for nitrate leaching in undisturbed structured clay soil. Jour. Hydrol. 79:37–51.Google Scholar
110.WHO (World Health Organization). 1978. Nitrates, nitrites, and N-nitroso compounds. Environmental health criteria 5. Geneva World Health Organization. 107 pp.Google Scholar
111.Zaki, M. H., Moran, D., and Harris, D.. 1982. Pesticides in groundwater: the aldicarb story in Suffolk County, N.Y. Am. J. Pub. Health 72:1391–1395.Google Scholar