Assessing the soil microbial toxicity of iprodione using advanced biochemical and molecular tools: Put the blame on the metabolite 3,5 dichloroaniline

Iprodione is a broad spectrum contact fungicide of the dicarboximide family, commonly used in conventional farming. It is known to negatively impact also non target organisms, via its major metabolite 3,5-dichloroaniline (3,5- DCA). However, little is known about the impact of iprodione or its main dichloroaniline metabolite on the structure and function of the soil microbial community. Thus the soil microbial toxicity of iprodione and 3,5-DCA was investigated in a microcosm where iprodione was applied at four dose levels x0, x1, x10 and x100 the recommended dose. Effects of iprodione and 3,5-DCA on key soil microbial enzymatic activities and on total bacterial diversity shifts using Illumina sequencing of the 16S rRNA gene amplicons were used to assess toxicity of the given compounds. In parallel the dissipation of iprodione and formation/degradation of 3,5- DCA was determined. Iprodione negatively correlated with the activities of acid-phosphatase, beta-glucosidase and leucine-aminopeptidase, while 3,5-DCA showed stronger negative correlations with more enzyme activities including phosphomonoesterase, phosphodiesterase, chitinase, leucine-aminopeptidase and potential nitrification. Db-RDA showed that pesticide dose rate as a factor explained 20 % of the observed variance in the enzyme activities measurements with significant differences observed between control (x0) and x100 dose rate for potential nitrification, leucine-aminopeptidase, phosphomonoesterase and phosphodiesterase. The persistence of the effects of iprodione and 3.5-DCA on the soil microbial functions increased with the applied dose with significant effects observed until, 7, 15 and 42 days in the x1, x10 and x100 dose rates respectively. Dissipation measurements revealed that the dissipation of iprodione was not affected by the dose rate (t1/2=10-14 days) compared to 3,5-DCA whose high formation at the x100 dose rate resulted in its accumulation in soil. Diversity measurements of the bacterial community is on the way and the complete dataset will be presented during the conference.