Abstract
The impact of two pesticides (S-metolachlor and propiconazole) and their respective main metabolites (ESA-metolachlor and 1,2,4-triazole) on bacterial denitrification in groundwater was studied. For this, the denitrification activity and the bacterial diversity of a microbial community sampled from a nitrate-contaminated groundwater were monitored during 20 days in lab experiments in the presence or absence of pesticides or metabolites at 2 or 10 μg/L. The kinetics of nitrate reduction along with nitrite and N2O production all suggested that S-metolachlor had no or only little impact, whereas its metabolite ESA-metolachlor inhibited denitrification by 65% at 10 μg/L. Propiconazole and 1,2,4-triazole also inhibited denitrification at both concentrations, but to a lesser extent (29–38%) than ESA-metolachlor. When inhibition occurred, pesticides affected the reduction of nitrate into nitrite step. However, no significant differences were detected on the abundance of nitrate reductase narG and napA genes, suggesting an impact of pesticides/metabolites at the protein level rather than on denitrifying bacteria abundance. 16S rRNA gene Illumina sequencing indicated no major modification of bacterial diversity in the presence or absence of pesticides/metabolites, except for ESA-metolachlor and propiconazole at 10 μg/L that tended to increase or decrease Shannon and InvSimpson indices, respectively. General growth parameters suggested no impact of pesticides, except for propiconazole at 10 μg/L that partially inhibited acetate uptake and induced a decrease in microbial biomass. In conclusion, pesticides and metabolites can have side effects at environmental concentrations on microbial denitrification in groundwater and may thus affect ecosystem services based on microbial activities.
Highlights
One consequence of the increasing use of pesticides is the presence of both parent molecules and transformation products in various environmental matrices and notably groundwater, with metabolites being even referred to as emerging groundwater contaminants (Jurado et al, 2012; Lapworth et al, 2012; Baran and Gourcy, 2013; Lopez et al, 2015)
The impact of pesticides on denitrification was tested in batch conditions in the presence of fungicide and herbicide (S-metolachlor) or their major metabolites (1,2,4triazole and ESA-metolachlor, respectively) at two concentrations (2 and 10 μg/L)
The current study demonstrates that some pesticides and metabolites can have a negative impact on the activity of the denitrifying community in groundwater at environmental concentrations
Summary
One consequence of the increasing use of pesticides is the presence of both parent molecules and transformation products (metabolites) in various environmental matrices and notably groundwater, with metabolites being even referred to as emerging groundwater contaminants (Jurado et al, 2012; Lapworth et al, 2012; Baran and Gourcy, 2013; Lopez et al, 2015). The effects of pesticides on soil microbial ecosystems mainly depend on the type of pesticides and their concentration, as well as time after application They depend on the microbial community structure and on the diversity of the microbial processes that are taking place in the studied soil. It was demonstrated that some metabolites obtained after the biological and physicochemical transformations of pesticides can be more persistent and/or more toxic than the parent molecules (Bollag and Kurek, 1980) Taking all together, these factors increase the difficulty to evaluate the risks associated with pesticides use and to predict the net effects of pesticides on soil ecosystem health (Yang et al, 2011; Staley et al, 2015). The bioavailability/sorption/biodegradation of pesticides can vary a lot for the same pesticides according to the studied system (Jacobsen and Hjelmsø, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
