Aerobic biodegradation kinetics and pathway of the novel cis-nitromethylene neonicotinoid insecticide Paichongding in yellow loam and Huangshi soils

• The degradation characteristics and mechanism of IPP in soils were studied.
• The IPP-degrading strain, Sphingobacterium sp. P1-3, was inoculated in soils.
• Eight metabolites of IPP degradation in soils were observed and identified.
• Three new metabolites of IPP degradation in soils were determined and identified.
• IPP biodegradation pathway A and pathway B in soils were proposed.

Biodegradation of Paichongding (IPP), a recently developed cis-nitromethylene neonicotinoid insecticide, was investigated in two different soils under aerobic condition. IPP degradation rate was strongly affected by soil physic-chemical characteristics and the inoculation of IPP-degrading bacteria. Inoculation of IPP-degrading bacteria can increase degradation rate and decrease DT50 (half-life value). The removal ratio of RR-IPP, SS-IPP, SR-IPP and RS-IPP at 60 days after treatment (DAT) reached 30.17%, 28.06%, 51.48% and 45.76% in Yellow clayed soil (S1), 20.04%, 19.78%, 36.22% and 40.59% in Huangshi soil (S2), respectively. DT50 of IPP in S1 and S2 decreased after inoculation of Sphingobacterium sp. M3-1. Furthermore, based on the identified eight metabolites (M1–M8) by LC–MS/MS and their behavior, a biodegradation pathway of IPP in soils was proposed. New metabolites, M4, M6 and M7 were observed and determined in soils. Biodegradation of IPP involved continuous biocatalytic reactions such as nitro reduction and elimination, hydrolysis, C-N cleavage, de-methyl, and ether cleavage reactions. Finally, IPP was bio-transformed into M7 and M8.