Assessing the efficiency and the side effects of atrazine-degrading biocomposites amended to atrazine-contaminated soil

Even decades after being banned in Europe, atrazine and its main metabolites can still be found in soils. While bioaugmentation using pesticide-degrading bacteria is already employed as a strategy for remediating polluted soils, there is still a need to improve its efficiency. Therefore, investigating the application of carrier materials to deliver and stabilize pesticide-degrading microorganisms in situ emerges as an interesting approach for further exploration. Here, we generated atrazine-degrading biocomposites by cultivating either a single strain or a 4-species bacterial consortium as biofilms on zeolite, which serves as the carrier material. Using a microcosm experiment, we then evaluated their efficiency to mineralize ¹⁴ C-atrazine in an agricultural soil comparing to free-living cells, and assessed the side effects of the two inoculation methods on the native soil bacterial community using 16S rDNA amplicon sequencing. We showed that, right after inoculation, the atrazine mineralization potential of the free-living cells was higher than that of the biocomposites. However, microcosms inoculated with the biocomposites displayed significantly higher atrazine mineralization potential than the ones inoculated with free-living cells after 15 and 45 days of incubation, not only indicating a higher efficiency but also a better stability in the soil environment, further confirmed by qPCR of the atz genes. We also showed that the inoculation of free-living cells and biocomposites differently influences the diversity and composition of the native microbial community, and that these effects are modulated by the scenario of atrazine contamination during soil inoculation. Altogether, our results provide a thorough evaluation of the efficiency and the ecotoxicological impact of atrazine-degrading biocomposites in soil.