Soil enzyme activity and microbial population play important roles in maintaining soil fertility and ensure crop yield. Paichongding (IPP) is a novel cis-nitromethylene neonicotinoid insecticide, which was recently developed in China. In this study, in order to better understand IPP ecological toxicity, the impact of IPP on soil enzyme activity and microbial population in soils was investigated. The results showed that, urease activity was inhibited by IPP before 75 days incubation, after that this inhibiting effect gradually weakened. IPP had different stimulating effects on the activities of dehydrogenase, protease, and catalase. They were consistently stimulated from the initial time in soils. The results of microbial population indicated that the number of bacteria increased after IPP application compared with the control, fungal number increased before 45 days incubation and then decreased. While actinomycete number decreased during degradation period. DT50 (half-life value), k (degradation rate constant) of IPP in S1 (yellow loam soil), and S2 (Huangshi soil) were found 90 days and 173 days, 0.0077 day(-1), and 0.0040 day(-1), respectively.

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Chiral insecticide paichongding (IPP) is a member of cis-nitromethylene neonicotinoid insecticides used in China. IPP was the promising replacement for imidacloprid as a result of its higher activity against imidacloprid-resistant insects. Two pairs of enantiomers, RR/SS-IPP and SR/RS-IPP, were separated by preparative high-performance liquid chromatography and employed in an aqueous system to investigate their biodegradation process. In this study, the strains G1-13/G1-14 and G2-19 with effective IPP degrading capability were isolated from agricultural soils. G1-14 was mutated from G1-13 by ultraviolet light exposure. Sequence alignment of 16S rRNA proved that these three strains belonged to the genus of Sphingobacterium. The degradation rate of RR/SS-IPP by Sphingobacterium sp. G1-13 and G1-14 reached 13 and 30% within 6 and 4 days, respectively. The degradation rate of SR/RS-IPP by Sphingobacterium sp. G2-19 could reach 35% within 5 days. Degradation intermediates (I1-I6) of enantiomers were detected, and two possible biodegradation pathways were proposed on the basis of the identification of metabolites.

Graphene (GN) and graphene oxides (GOs) are novel carbon nanomaterial; they have been attracting much attention because of their excellent properties and are widely applied in many areas, including energy, electronics, biomedicine, environmental science, etc. With industrial production and consumption of GN/GO, they will inevitably enter the soil and water environments. GN/GO may directly cause certain harm to microorganisms and lead to ecological and environmental risks. GOs are GN derivatives with abundant oxygen-containing functional groups in their graphitic backbone. The structure and chemistry of GN show obvious differences compared to those of GO, which lead to the different environmental behaviors. In this study, four different types of soil (S1-S4) were employed to investigate the effect of GN and GO on soil enzymatic activity, microbial population, and bacterial community through pyrosequencing of 16S rRNA gene amplicons. The results showed that soil enzyme activity (invertase, protease, catalase, and urease) and microbial population (bacteria, actinomycetes, and fungi) changed after GN/GO release into soils. Soil microbial community species are more rich, and the diversity also increases after GO/GN application. The phylum of Proteobacteria increased at 90 days after treatment (DAT) after GN/GO application. The phylum of Chloroflexi occurred after GN application at 90 DAT in S1 soil and reached 4.6%. Proteobacteria was the most abundant phylum in S2, S3, and S4 soils; it ranged from 43.6 to 71.4% in S2 soil, from 45.6 to 73.7% in S3 soil, and from 38.1 to 56.7% in S4 soil. The most abundant genera were Bacillus (37.5-47.0%) and Lactococcus (28.0-39.0%) in S1 soil, Lysobacter and Flavobacterium in S2 soil, Pedobacter in S3 soil, and Massilia in S4 soil. The effect of GN and GO on the soil microbial community is time-dependent, and there are no significant differences between the samples at 10 and 90 DAT.

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