Anaerobic biodegradation of atrazine under different redox conditions

Abstract

The indiscriminate use of atrazine herbicide in Brazil and worldwide has several adverse effects on human health and ecosystems, and can be found in soil, ground and surface water, in the air and also in living beings. The biodegradation of this compound can occur through different redox conditions, with the participation of aerobic and anaerobic microbial consortia, generating different degradation metabolites intermediates. However, due to its leaching potential, it is more commonly found in deep soil layers under anaerobic conditions, which highlights the importance of studies in these conditions. This research was carried out with the enrichment of denitrifying microorganisms, sulfate reducing bacteria and methanogenic arches, in anaerobic reactors under different redox conditions (denitrifying, sulfetogenic and methanogenic). Our experimental procedure consisted of two distinct tests, the first being called pure anaerobic reactors (PAR) and the second called composite anaerobic reactors (CAR). The two assays differ in the inoculum used and the carbon sources available in the reactors. We made 6 reactors for each different redox condition, 3 biotic, 2 abiotic, and 1 blank (control). We observed in this study that the removal of atrazine depends on biotic and abiotic factors, which may occur in both ways, and that physicochemical factors such as adsorption and chemical hydrolysis may have significant effects on this process. The results of the tests indicate that there was no variation in atrazine removal between different redox media, 87% (± 7%) for the denitrifying condition, 88% (± 7%) for the sulfetogenic and 92% (± 7%). for methanogenesis, in biotic reactors with atrazine and soil organic content as the only carbon sources for bacteria in the reactors. However, the variation in the results found in RCA supplemented with complementary sources of acetate carbon for denitrifying reactors, lactate for sulfetogens and acetate and formate for methanogens, and reactors without this supplementation (RPA), indicates that high atrazine removal (100%) within 70 days of analysis for supplemented reactors should be done in shorter time periods.