Aerobic versus Anaerobic Microbial Degradation of Clothianidin under Simulated California Rice Field Conditions

Microbial
degradation of clothianidin was characterized under aerobic
and anaerobic California rice field conditions. Rate constants (k) and half-lives (DT50) were determined for
aerobic and anaerobic microcosms, and an enrichment experiment was
performed at various nutrient conditions and pesticide concentrations.
Temperature effects on anaerobic degradation rates were determined
at 22 ± 2 and 35 ± 2 °C. Microbial growth was assessed
in the presence of various pesticide concentrations, and distinct
colonies were isolated and identified. Slow aerobic degradation was
observed, but anaerobic degradation occurred rapidly at both 25 and
35 °C. Transformation rates and DT50 values in flooded
soil at 35 ± 2 °C (k = −7.16 ×
10–2 ± 3.08 × 10–3 day–1, DT50 = 9.7 days) were significantly faster
than in 25 ± 2 °C microcosms (k= −2.45
× 10–2 ± 1.59 × 10–3 day–1, DT50 = 28.3 days). At the field
scale, biodegradation of clothianidin will vary with extent of oxygenation.