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Understanding the fate and ecotoxicological effects of pesticides largely depends on their molecular properties. We recently developed "TyPol" (Typology of Pollutants), a classification method of organic compounds based on statistical analyses. It combines several environmental (sorption coefficient, degradation half-life) and one ecotoxicological (bioconcentration factor) parameters, to structural molecular descriptors (number of atoms in the molecule, molecular surface, dipole moment, energy of orbitals, etc.). The present study attempts to extend TyPol to the ecotoxicological effects of pesticides on non-target organisms, based on data analysis from available literature and databases. It revealed that relevant ecotoxicological endpoints for terrestrial organisms (e.g., soil microorganisms, invertebrates) that support a range of ecosystemic services are lacking as compared to aquatic organisms. The availability of ecotoxicological parameters was also lower for chronic than for acute ecotoxicity endpoints. Consequently, seven parameters were included for acute (EC50, LC50) and chronic (NOEC) ecotoxicological effects for one terrestrial (Eisenia sp.) and three aquatic (Daphnia sp., algae, Lemna sp.) organisms. In this new configuration, we used TyPol to classify 50 pesticides into different clusters that gather molecules with similar environmental behaviors and ecotoxicological effects. The classification results evidenced relationships between molecular descriptors, environmental parameters, and the added ecotoxicological endpoints. This proof-of-concept study also showed that TyPol in silico classification can successfully address new scientific questions and be expanded with other parameters of interest.

Microbial communities driving the nitrogen cycle contribute to ecosystem services such as crop production and air, soil, and water quality. The responses to herbicide stress of ammonia-oxidizing and ammonia-denitrifying microbial communities were investigated by an analysis of changes in structure-function relationships. Their potential activities, abundances (quantitative PCR), and genetic structure (denaturing gradient gel electrophoresis) were assessed in a microcosm experiment. The application rate (1 × FR, 0.45 μg g(-1) soil) of the mesotrione herbicide did not strongly affect soil N-nutrient dynamics or microbial community structure and abundances. Doses of the commercial product Callisto® (10 × FR and 100 × FR) or pure mesotrione (100 × FR) exceeding field rates induced short-term inhibition of nitrification and a lasting stimulation of denitrification. These effects could play a part in the increase in soil ammonium content and decrease in nitrate contents observed in treated soils. These functional impacts were mainly correlated with abundance shifts of ammonia-oxidizing Bacteria (AOB) and Archaea (AOA) or denitrifying bacteria. The sustained restoration of nitrification activity, from day 42 in the 100 × FR-treated soils, was likely promoted by changes in the community size and composition of AOB, which suggests a leading role, rather than AOA, for soil nitrification restoration after herbicide stress. This ecotoxicological community approach provides a nonesuch multiparameter assessment of responses of N-cycling microbial guilds to pesticide stress.