Fate characteristics of the four stereoisomers of paichongding [IPP, 1-((6-chloropyridin-3-yl)methyl)-7-methyl-8-nitro-5-propoxy-1,2,3,5,6,7-hexahydroimidazo[1,2-a]pyridine] in aerobic sterilized and nonsterilized fluvio-marine yellow loamy soil were investigated using a (14)C tracer technique combined with HPLC and LC-MS/MS. Results showed that the mineralization and bound residue (nonsterile/sterilized soil, % of applied amount) of four stereoisomers of IPP were 1.76-6.10/0.33-0.82 and 12.01-31.20/6.58-20.81 at 100 days after treatment. Seven and five incomplete intermediates of IPP were detected in nonsterilized and sterilized soil, respectively, and a possible degradation pathway was proposed. Degradation mainly occurred on the tetrahydropyridine ring, including oxidation and elimination of the methyl, propyl, and nitro groups. All of these results suggest that soil microbial activity greatly contributes to the epimeride-selective mineralization, formation of bound residue, and degradation of IPP in loamy soil. The identified transformation intermediates could be used for further study on their toxicity to target and nontarget species.