Occurrence and microbial degradation of fipronil residues in tropical highland rhizosphere soils of Kerala, India

The aim of the current study was to analyze the abundance and activity of soil microflora in response to fipronil residues, as well as conjointly to isolate and identify bacteria for the bioremediation of fipronil contaminated soils in the cardamom plantations of Idukki district, Kerala. Soil samples collected from rhizosphere areas of six completely different cardamom plantations were analyzed for fipronil residues, physicochemical properties, biochemical properties, and microbial abundance. Biodegradation studies using isolated bacteria were done both in liquid medium and in soil microcosm fortified with fipronil. Fipronil residues were detected in all sampling sites. Canonical correlation analysis revealed that the influence of fipronil on soil physicochemical properties was more pronounced than that on soil microbial properties. The presence of fipronil residues in the soil did not adversely affect bacterial abundance and activity. Two bacterial strains Staphylococcus arlettae and Bacillus thuringiensis could degrade fipronil in both liquid culture and soil. Paired sample T-test and degradation kinetic study recorded that the bacterial strain S. arlettae was more efficient (81.94%) in fipronil degradation than B. thuringiensis (65.98%). The results revealed the potential for in situ bioremediation of fipronil contaminated soil by bioaugmentation using efficient bacterial isolates.