Chapter 10
The Effect of Ammonia on Atrazine Sorption and Transport 1
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S. A. Clay , D. E. Clay , Z. Liu , and S. S. Harper 1
Department of Plant Science, South Dakota State University, Brookings, SD 57007 Land and Water Sciences, Tennessee Valley Authority, Muscle Shoals, AL 35660 2
Ammonia application increased soil solution pH and decreased atrazine sorption to soil. K values for atrazine were 5.2 in nonamended soil (pH = 5.7) and 2.9 and 2.2 for ammonia-amended soils at pH 7.8 and pH 8.9, respectively. Atrazine sorption was affected differentially by base treatments of K O H and NaOH compared to NH OH. These results suggest that factors other than pH modification influenced atrazine sorption characteristics. Incubation of atrazine in NH OH extracts from soil indicated that hydroxyatrazine (HA) could be formed, however, in the presence of soil, H A was not detected. Partition coefficients for H A at pH values of 5.7, 7.8, and 8.9 were 130, 0.7, and 0.1, respectively. Ammonia application increased the potential of atrazine to leach through soil. f
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The prediction of herbicide and degradate mobility through soil is important in assessing the vulnerability of aquifers to chemical contamination. Herbicide mobility is inversely related to herbicide sorption values due to the soil retardation of the mass flux of the herbicide (7, 2, 3). Therefore, as sorption to soil decreases, the potential for herbicide movement increases. Herbicide sorption to soil is often measured by laboratory batch equilibration techniques. The partition coefficient, K , quantifies sorption and is the quotient of the concentration in the solid soil phase divided by the concentration in the liquid. Fertilizer applications may influence the sorption characteristics of ionizable herbicides because of increased or decreased soil pH or competition for exchange sites (4, 5). Sorption of some ionizable herbicides are not strongly influenced by soil pH and D
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therefore, not affected by fertilizer applications. For example, dicamba, a benzoic acid herbicide, had low K values ( 0.81 for all regression lines. 2
The adsorption and desorption data suggest two possibilities when investigating the influence of base amendments on atrazine movement in soil. The first possibility is that atrazine mobility will be decreased because there is a higher proportion of the applied atrazine irreversibly bound to soil. However, base treatments may increase atrazine mobility due to increased desorption from soil. Solution Effects on Atrazine. The alkalinity of the N H O H and K O H sorption solutions used in these studies may have catalyzed the hydrolysis of atrazine to H A (9). TLC analyses of sorption and desorption solutions extracted from soil did not contain any detectable levels of HA. However, H A has been shown to have strong affinity for soil (72, 16) with K f ^ values of 26 (pH 6) to 60 (pH 4.5) and no desorption detected at either pH (11). Therefore, H A may not have been present in solution even if formed 4
Meyer and Thurman; Herbicide Metabolites in Surface Water and Groundwater ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
10. CLAY ET AL.
Effect of Ammonia on Atrazine Sorption and Transport
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due to strong adsorption to soil. Another possibility is that H A may have been in sorption solutions but at concentrations below detection limits. Therefore, the effects of NH4OH and K O H soil solution extracts on atrazine in the absence of soil were investigated. Only parent atrazine was detected by TLC techniques (Rf value = 0.8) after a 1-day incubation in soil solution extracted with CaCl . However, when atrazine was incubated for 8 days in solutions extracted with NH^OH or K O H , about 10 to 20% of the C was determined to be H A (Rf value = 0.53). 2
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Hydroxyatrazine Adsorption. The results of the above study indicate that H A may form in alkaline solution extracts and that amounts may be quite high if incubation time is long enough. H A sorption to soil decreases as pH increases (11), however, sorption of H A to high pH soils is not well documented. Therefore, a 1-day batch equilibration study was conducted to determine the sorption of H A to ammonia-treated soils. The H A sorption coefficients for the Brandt soil at pH 5.7 was 130. The K values for H A sorption using N H O H solution were 0.7 at pH 7.9 and 0.1 at pH 9 which indicates that H A sorption was even less than atrazine sorption at these same pH values. Evaluation of both the incubation and sorption data indicates that H A indeed may form and if formed may be leached due to it's weak sorption to soil at high pH. H A most likely was not detected in the basic sorption solutions because it was not formed during one-day batch equilibration with atrazine. H A was probably not detected in desorption solutions (even if formed over the 5-day desorption period) due to dilution with "clean" desorption solutions and the low amounts that would have been formed. D
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Atrazine Movement Through Ammonia-Amended Soil. A study was conducted to determine if decreased sorption and increased desorption of atrazine due to N H O H addition increased the leaching potential of atrazine. About 23% of the applied C was leached from unfertilized soil columns compared to 33% leached from ammonia-treated columns. The leachate did not contain detectable levels of HA. The amount of C in the surface 2 cm of soil from ammonia-treated columns was 11% less than the amount measured in the untreated columns. 4
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Conclusions The results of this study indicate that the application of ammonia fertilizer changed soil chemical characteristics, including increasing solution pH and D O C content, that influenced atrazine sorption, desorption, and movement. However, comparison with other basic treatments indicate that pH modifications do not influence atrazine sorption characteristics equally. The increase in soil pH generally decreased atrazine sorption and increased desorption isotherms. Hydroxyatrazine formed from atrazine in soil solutions extracted with NH OH. Although not detected in sorption solution extracts, sorption of hydroxyatrazine at pH 7.9 and 9 was very low. Ammonia application also increased the amount of atrazine leached through soil columns. These data suggest that ammonia-based fertilizers that increase soil pH have the potential to increase atrazine movement in the soil. Field research has shown that DOC and atrazine movement below N H O H bands was much greater than in areas where N H O H bands were not 4
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present (13, 17). Two mechanisms are working in concert to increase atrazine movement below fertilizer bands. These mechanisms are: i) the effect of the fertilizer slot on water flow; and ii) the effect of increased pH on atrazine sorption. The leaching study shows that soil changes induced by ammonia application are sufficient by themselves to increase atrazine movement through soil.
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Acknowledgments Partial support for this projects was provided by Tennessee Valley Authority and USDA-CSRS. Mention of products in this publication does not represent an endorsement of the authors or of the South Dakota State Experiment Station or criticism of similar ones not mentioned. Literature Cited 1. Helling, C.S. Soil Sci. Soc. Am. Proc.,1971, 35, 737-743. 2. Scheunert,I.In Fate and PredictionofEnvironmental Chemicals in Soils, Plants, and Aquatic Systems. Mansour, M., Ed.; Lewis Publishers: Boca Raton, FL, 1993, pp. 1-22. 3. Weber, J. In Agrochemical Environmental Fate: State of the Art. Leng, M.L.; Leovey, E.M.K.; Zubkoff, P.L., Eds.; Lewis Publishers: Boca Raton, FL, 1995, pp. 99116. 4. Clay, S.A.; Koskinen, W.C.; Allmaras, R.R.; Dowdy, R.H. J. Environ. Sci. Health 1988, B23, 559-573. 5. Madrid, L.; Morillo, E.; Diaz-Barrientos, E. In Fate and Prediction of Environmental Chemicals in Soils, Plants, and Aquatic Systems. Mansour, M., Ed.; Lewis Publishers: Boca Raton, FL, 1993, pp. 51-59. 6. Kissel, D.E.; Cabrera, M.L.; Ferguson, R.B. Soil Sci. Soc. Am. J., 1988, 52, 17531796. 7. Norman, R.J.; Kurtz, L.T.;, Stevenson, F.J. Soil Sci. Soc. Am. J., 1987, 51, 809812. 8. Liu, Ζ.; Clay, S.A.; Clay, D.E.; Harper, S.S. J. Agric. Food Chem., 1995, 43, 815819. 9. Esser, H.O; Dupuis, E.; Ebert, E.; Marco, G.J.; Vogel, C. In Herbicides - Chemistry, Degradation, and Mode of Action. Kearney, P.C.; Kaufmann, D.D., Eds, Marcel Dekker: New York, 1975, Vol 1; pp 129-208. 10. McGlamery, M.D.; Slife, F.W. Weeds, 1966, 14, 237-239. 11. Goetz, A.J.; Walker, R.H.; Wehtje, G.; Hajek, B.F. Weed Sci., 1988, 37, 428-433. 12. Clay, S.A.; Koskinen, W.C. Weed Sci., 1990, 38, 262-266. 13. Clay, S.A.; Scholes, K.A.; Clay, D.E. Weed Sci. 1994, 42, 86-91. 14. Clay, S.A.; Allmaras, R.R.; Koskinen, W.C.; Wyse, D.L. J. Environ. Qual., 1988, 17, 719-723. 15. Pennington, K.L.; Harper, S.S.; Koskinen, W.C. Weed Sci., 1991, 39, 667-672. 16. Schiavon, M. Ecotox. Environ. Safety, 1988, 15, 46-54. 17. Clay, D.E.; Clay, S.A.; Liu, Z., Harper, S.S. Biol. Fertil. Soils, 1995, 19, 10- 14.
Meyer and Thurman; Herbicide Metabolites in Surface Water and Groundwater ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
