Submitted to: American Chemical Society Symposium Series
Publication Type: Book / Chapter
Publication Acceptance Date: 10/31/2003
Publication Date: 10/31/2003
Citation: Clay, S.A., Clay, D.E., Moorman, T.B. 2003. Comparison of atrazine and alachlor sorption, mineralization, and degradation potential in surface and aquifer sediments. In: Gan, J.J., Zhu, J.C., Aust, S.D., Lemley, A.T., Editors. Pesticide Decontamination and Detoxification. American Chemical Society Symposium Series. New York, NY: Oxford University Press. p. 199-210.
Interpretive Summary: Pesticides and their metabolites have been found in groundwater where they represent a potential health risk if the enter drinking water supplies. Alachlor and atrazine are herbicides which have been found in groundwater and have very low maximum concentration limits (MCL) as defined by EPA. Our study examined how fast these herbicides were degraded by the indigenous microorganisms in sediments beneath an agricultural production field in South Dakota. We found that degradation was slower in the absence of oxygen. The microorganisms were most active in the upper part of the soil profile and in the aquifer. We identified several of the metabolic products of the biotranformation of alachlor. We also determined the effects of adding nitrate or carbon to the microorganisms. Very little atrazine degradation was detected below the root zone. This information will impact the scientific knowledge base concerning biological processes in aquifer sediments. Our improved ability to understand the microbial proccesses in aquifer sediments will allow us to better manage herbicides for improved water quality.
Technical Abstract: Atrazine and alachlor have been used for controlling weeds in crops. These herbicides and their degradation products also have been detected in surface and ground waters. The objective of this study was to determine atrazine and alachlor sorption and degradation potentials at four soil depths and in aquifer matrix materials. Sorption potentials decreased with sample depth but were similar between herbicides at each depth. Mineralization potential differed between herbicides with twice as much alachlor mineralized at each depth as compared to atrazine. After a 112-d incubation at 10 C, atrozine degradation products were not detected in sample extracts, whereas alachlor degradaion products were present in both soil and aquifer matrix samples. Alachlor degradation prodects detected in A-horizon soil included the ethanesulfonic acid (ESA) and oxanilic acid (OAA) forms of alachlor. In aquifer extracts, two degradation products were formed, one cochromatographing with OAA-alachlor and an unidentified product. The ESA degradation product of alachlor has been detected frequently in aquifers at higher concentrations than alachlor. Its presence may be due to transport through the soil profile. ESA-alachlor has been reported to be much less toxic than alachlor to mice and rats based on oncogenic, acute toxicity, and genotoxic studies.