Bioremediation of carbofuran by isolated bacteria from soil

Abstract

Among available pesticides, carbofuran is widely used as a pesticide in all parts of Sri Lanka to improve the quality and yield of food crops by protecting against pests. Lack of knowledge on the fate and behaviour of pesticides in the Sri Lankan environment has contributed to public perceptions, fueled by local media about increasing adverse health effects due to exposure to pesticides.

In the present study laboratory experiments were conducted to isolate carbofuran degradable bacteria in soil samples collected from cultivation land in Medirigiriya where carbofuran is used as a major pesticide for agriculture. Seventeen bacteria strains were isolated from soil enrichment experiments by pour plate method. Tentative identifications were done using morphological and chemical analysis and it was confirmed that all bacteria isolates belong to gram negative and rod shape. Out of twelve, three isolates namely BC–3, BC–12 and BC–15 were selected for degradation study based on their morphological differences. Others were kept on agar slant and degradability of carbofuran by bacteria was detected by GC analysis. The bacteria isolates BC–3 and BC–12 showed a significant degradability of carbofuran, while the isolate BC–15 bacteria did not. BC–3 isolate removed 50% (±2) of the carbofuran thirteen days after incubation at 37°C (± 2) when the concentrations of pesticide were at 0.3 ppm and 0.5 ppm. The bacterial strain BC–15 showed a slow rate of degradation of carbofuran when compared with the BC–3 and BC–12 strains. In BC–15 inoculated experiment, residual carbofuran was detected even after three weeks of incubation. BC–3 bacteria showed a half life of thirteen days for 0.3 ppm and 0.5 ppm concentrations. In all bacteria strains showed high half life when concentration of carbofuran was 0.1 ppm. In contrast, variation in half life values were detected for the three different concentrations of carbofuran for BC–12 bacteria.

The results of the present study suggest that some bacterial strains in soil play an important role in biodegradation of carbofuran along with other photochemical and hydrological reactions. Further studies are being conducted to ascertain the potential impact of bacterial isolates on carbofuran.