RELATIONSHIPS BETWEEN ATRAZINE DEGRADATION, SOIL PROPERTIES AND MICROBIAL POPULATIONS

D.L. Tyess, P.J. Shea, S.D. Comfort and N.B. Stolpe

University of Nebraska, Lincoln, NE, 68583-0915, 402-472-1533


ABSTRACT

Correlations of soil characteristics with relative rates of pesticide degradation often fail when multiple soil types are studied. Our objective was to provide a variety of soils with the same population of atrazine-degrading microbes and correlate degradation rates with soil characteristics. Soils from profiles of a Sharpsburg silty clay loam (Typic Argiudoll), Ortello sandy loam (Udic Haplustoll) and Hord silt loam (Pachic Haplustoll) were inoculated with surface soil of a Hord silt loam that had a history of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] application and a demonstrated capacity for enhanced atrazine mineralization. Experiments were performed by static incubation of 25 g soil maintained at 22║C and -50 kPa water content. Treatments included soils (type and horizon) that were either inoculated or uninoculated. Unlabeled and 14C-ring labeled atrazine were applied to yield an initial concentration of 3.2 Ámol kg-1. 14CO2 was trapped in 15 ml of 0.5 N NaOH and activity determined by scintillation counting. 14CO2 samplings occurred every 7 to 10 d for 80 d. In addition, samples from each soil-horizon combination were frozen every 20 d and extracted with CH3OH for determination of atrazine and degradates. Bound (unextractable) residue was determined by biological oxidation to 14CO2 for mass balance determinations. Atrazine degradation and mineralization rates were correlated to soil properties. Results indicated that inoculated soils generally produced higher rates of atrazine degradation and mineralization. Degradation and mineralization among inoculated soils were found to correlate (either positively, negatively or variably) with atrazine adsorption coefficients (Kd) and soil properties such as NO3-N, P, and organic C concentrations and pH. We also observed that some soils, in particular those with high pH, did not show increased mineralization when inoculated. These results illustrate the importance of both soil characteristics and the presence of specific microbial populations on atrazine degradation in soil.

KEY WORDS

atrazine, degradation, soil characteristics, microbial populations

This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.