INFLUENCE OF ORGANIC AMENDMENTS ON BIODEGRADATION OF ATRAZINE AS A NITROGEN-SOURCE

Carbon and N dynamics may be particularly important for selective enrichment of microorganisms that are capable of using xenobiotics as sources of N for growth. To investigate this hypothesis in relation to s-triazines, a soil microcosm study was performed to determine the effect of organic amendments differing in complexity and C/N ratio, and the effects of inorganic N addition on atrazine mineralization in a soil having a 15-yr history of prior exposure to this herbicide. When the soil was spiked with 100 mg/kg of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) in the absence of organic amendments, 73% of the atrazine was mineralized after 11 wk. Soils amended with rice hulls, starch, and compost yielded mineralization rates of 88, 75, and 59% in the same period, respectively. In contrast, <10% of the atrazine was mineralized in soils amended with glucose, Sudan hay, or sodium citrate. All treatments receiving supplemental inorganic N had a considerably lower rate of atrazine mineralization than corresponding treatments without N addition. However, the different effects of the organic matter supplements suggested there was no relationship between the C/N ratio of the soil and atrazine mineralization. An atrazine-degrading consortium was subsequently isolated for further characterization. The results demonstrate that while atrazine mineralization is suppressed under high N conditions in this soil, the mineralization rate also is influenced by poorly understood population dynamics related to the nutrient composition and complexity of specific organic amendments.