Evaluation of the environmental fate and ecotoxicological impact of the pesticide chlorpyrifos in soil for improvement of its environmental risk assessment

Pesticides protect crops from various pests but can also harm nontarget organisms. To minimize risks for the environment and human health, a huge amount of studies are carried out and evaluated during the authorization process of each pesticide. However, the prediction of the environmental fate and ecotoxicological impact of a pesticide remains difficult. Several 100 formerly used pesticides are now banned because unexpected risks emerged decades after their authorization. Risk assessment documents of the organophosphate insecticide chlorpyrifos (CHL) particularly lack information about its degradation and potential transformation products in soil, and its impact on non-target microorganisms supporting soil ecosystem services with impact at the global scale. Within the frame of a large European Marie Curie project, we studied the environmental fate of CHL in a lab-to-field dissipation study by (i) quantifying CHL and its main transformation product 3,5,6-trichloropyridinol (TCP), (ii) screening for known and new transformation products, and (iii) measuring its sorption to soil. Furthermore, the ecotoxicological impact of CHL on the soil bacterial community was estimated by (i) Illumina next-generation sequencing of 16S rDNA amplified from extracted soil DNA, and (ii) monitoring the adaptation of soil microorganisms to repeated CHL exposure by analysis of CHL mineralization. Main results are (i) the identification of known and one new transformation products of CHL, (ii) no effect of CHL on the diversity of the bacterial community in our lab-to-field experiment, (iii) but adaptation to repeated CHL exposure as shown by improved CHL mineralization and by microbial diversity analysis. For further research on CHL biodegradation and as potential candidates for bioremediation, we isolated a CHL-degrading bacterial consortium.