Assessment of the ecotoxicological impact of captan@ZnO35–45nm and captan@SiO2 20–30nm nanopesticide on non-target soil microorganisms – A 100-day case study

Abstract

Nanopesticide application should enable efficient pest management with smaller doses of an active ingredient. Nevertheless, the environmental risk assessment of nanopesticides is currently in its initial stages due to limited access to nanopesticides. Therefore, we synthesised nanofungicides with captan as an organic active ingredient and ZnO35–45nm or SiO2 20–30nm as nanocarriers (captan@ ZnO35–45nm and captan@ SiO2 20–30nm) and evaluated their environmental risk by testing different microbial parameters as its potential biomarkers. First, physicochemical analysis (SEM-EDS, XPS, and FTIR) confirmed the presence of captan in nanofungicides, and they maintained 43–61 % antifungal efficiency against pathogen fungi compared to captan. Second, a laboratory toxicity assay (spot test) showed that nanofungicides generally revealed 10–100-fold lower growth inhibition of non-target microbial strains compared to captan. Next, the effect of nanofungicides on the abundance, structure and function of non-target soil microorganisms was evaluated during the 100-day microcosm using orchard soil and compared to control, captan, and nanocarriers. The changes in the total number of bacteria, ammonia-oxidising bacteria (AOB) and fungi were enumerated using the copy number of the qPCR approach based on the copy number of 16S rRNA, amoA and ITS genes. The functional potential and microbial structure were estimated based on Community Level Physiological Profiles (CLPPs) and Phospholipid Fatty Acids (PLFAs) profiles. Generally, results indicated that nanofungicides affected soil microorganisms by changing, in different scale, various microbial parameters, but their negative effect was generally lower than pesticide. Although qPCR results revealed the harmful effect of all tested compounds on total bacteria number (16S rRNA) on day 42, and captan@ZnO35–45nm and nanocarrier SiO2 20–30nm still affected amoA gene copy number on day 100, but the total fungal abundance in orchard soil was not affected. Furthermore, the analyses of functional and structural microbial diversity indicated the recovery process that was the fastest for captan@SiO2 20–30nm nanofungicide. On the contrary, ZnO35–45nm increased and prolonged the negative effect of captan in synthesised nanofungicide and generally exerted a more profound and/or longer effect than SiO2 20–30nm nanocarrier. Therefore we conclude that SiO2 20–30nm has better potential to be used as a nanocarrier compared to ZnO35–45nm. More studies are needed but soil microorganisms as sensitive biomarkers should be used for environmental risk assessment of nanopesticides.