Atrazine Biodegradation in a Cisne Soil Exposed to a Major Spill

Authors: SHAFFER, ELIZABETH - MALCOLM PIRNIE; Sims, Gerald; CUPPLES, ALISON - MICHIGAN ST UNIVERSITY; SMYTH, CHARLES - UNIVERSITY OF ILLINOIS; Chee Sanford, Joanne

Submitted to: International Journal of Soil, Sediment, and Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2009
Publication Date: 5/1/2010
Citation: Shaffer, E., Sims, G.K., Cupples, A.M., Smyth, C., Chee Sanford, J.C. 2010. Atrazine Biodegradation in a Cisne Soil Exposed to a Major Spill. International Journal of Soil, Sediment, and Water. 3(2):1-26.

Interpretive Summary: Atrazine has been used for over 50 years for the control of a variety of weeds in agricultural crops, most notably maize. Extensive use, moderate persistence, and limited soil sorption have resulted in offsite movement of atrazine. Experiments were performed to characterize atrazine degradation in a soil exposed to high levels of atrazine through a single chemical spill. The soil exhibited enhanced atrazine degradation relative to soils typical of agricultural production areas, even though the soil contained an elevated nitrate concentration, which had been expected to suppress atrazine degradation. An atrazine-degrading microorganism, referred to herein as ES-1, was isolated from the soil by using atrazine as a substrate for growth. Based on properties of the organism, and the sequence of its 16S rRNA gene, the isolate appeared to be a species of Arthrobacter. In pure culture, the isolate rapidly converted atrazine to cyanuric acid, which was also shown to accumulate in the soil. Results suggested the primary factor limiting degradation of the herbicide in this soil was non-uniform distribution in the soil, leading to reduced availability to microorganisms capable of degrading atrazine. Though the findings were consistent with Arthrobacter being responsible for degradation in this soil, attempts to confirm this using DNA-based stable isotope probing were inconclusive. The impact of this work is to provide another highly active reference organism that degrades atrazine, and to establish the role of bioavialbility in atrazine degradation in a soil with very active herbicide degraders. These results will also be useful in further development of techniques to determine organisms responsible for biological processes in soil samples.

Technical Abstract: Conventional soil tests, culture-based microbial methods, and the novel method of 15N-DNA stable isotope probing (SIP) were employed to illustrate atrazine biodegradation as related to the physiochemical properties of an atrazine-exposed Cisne soil. This soil exhibited enhanced atrazine degradation. Mineralization underestimated the rate of atrazine dissipation demonstrated by the accumulation of several metabolites. The soil showed high ambient concentrations of NO3-; however NO3- did not suppress atrazine degradation. Atrazine natural attenuation was limited by incomplete distribution through the unsaturated soil matrix. Direct plating experiments from the Cisne soil isolated an atrazine-degrading microorganism, ES-1. Analysis of the 16S rRNA gene sequences from the isolate confirmed that ES-1 is closely related (99%) to Arthrobacter sp. In pure culture, the isolate rapidly converted atrazine to cyanuric acid. Accumulation of this product was consistent with metabolites in the Cisne soil, suggesting that isolate ES-1 influenced in-situ remediation of atrazine. 15N- SIP experiments were conducted using 15N-ethylamino-atrazine. The results of these experiments failed to establish a causal relationship between in-situ atrazine-degradation and ES-1 enrichment; however these results are likely due to isotopic dilution. Further experiments using 13C-ethyl/isoproylamino-atrazine may yet verify a link between ES-1 and the enhanced natural attenuation exhibited in the Cisne soil.