Degradation and mineralization kinetics of acephate in humid tropic soils of Malaysia

TY - JOUR

T1 - Degradation and mineralization kinetics of acephate in humid tropic soils of Malaysia

AU - Chai, Lian-Kuet

AU - Wong, Mee-Hua

AU - Mohd-Tahir, Norhayati

AU - Hansen, Hans Chr. Bruun

PY - 2010/4

Y1 - 2010/4

N2 - Acephate is poorly sorbed to soil, thus the risk of leaching to the aquatic environment is high if it is not quickly degraded. The effect of soil moisture, temperature, microbial activity and application rate on acephate degradation has been studied in three Malaysian soils to examine and identify critical variables determining its degradation and mineralization kinetics. First-order kinetics could be used to describe degradation in all cases (r2 > 0.91). Acephate degraded faster in air-dry (t1/2 9-11 d) and field capacity (t1/2 10-16 d) soils than in the wet soils (t1/2 32-77 d). The activation energy of degradation was in the range 17-28 kJ mol-1 and significantly higher for the soil with higher pH and lower clay and iron oxide contents. Soil sterilization caused a 3- to 10-fold decrease in degradation rates compared to non-sterile soils (t1/2 53-116 d) demonstrating that acephate degradation is mainly governed by microbial processes. At 5-fold increase in application rates (25 μg g-1), half-life increased slightly (t1/2 13-19 d) or was unaffected. Half-life from acephate mineralization was similar to those from degradation but much longer at the 5-fold increase in acephate application rates (t1/2 41-96 d) demonstrating that degradation of metabolites is rate limiting. Thus, application of acephate should be restricted or avoided during wet seasons with heavy rainfall and flooded soil as in paddy cultivation. Sandy soils with low microbial activity are more prone to acephate leaching than clayey soils rich in humic matter.

AB - Acephate is poorly sorbed to soil, thus the risk of leaching to the aquatic environment is high if it is not quickly degraded. The effect of soil moisture, temperature, microbial activity and application rate on acephate degradation has been studied in three Malaysian soils to examine and identify critical variables determining its degradation and mineralization kinetics. First-order kinetics could be used to describe degradation in all cases (r2 > 0.91). Acephate degraded faster in air-dry (t1/2 9-11 d) and field capacity (t1/2 10-16 d) soils than in the wet soils (t1/2 32-77 d). The activation energy of degradation was in the range 17-28 kJ mol-1 and significantly higher for the soil with higher pH and lower clay and iron oxide contents. Soil sterilization caused a 3- to 10-fold decrease in degradation rates compared to non-sterile soils (t1/2 53-116 d) demonstrating that acephate degradation is mainly governed by microbial processes. At 5-fold increase in application rates (25 μg g-1), half-life increased slightly (t1/2 13-19 d) or was unaffected. Half-life from acephate mineralization was similar to those from degradation but much longer at the 5-fold increase in acephate application rates (t1/2 41-96 d) demonstrating that degradation of metabolites is rate limiting. Thus, application of acephate should be restricted or avoided during wet seasons with heavy rainfall and flooded soil as in paddy cultivation. Sandy soils with low microbial activity are more prone to acephate leaching than clayey soils rich in humic matter.

U2 - 10.1016/j.chemosphere.2010.01.046

DO - 10.1016/j.chemosphere.2010.01.046

M3 - Journal article

C2 - 20189217

SN - 0045-6535

VL - 79

SP - 434

EP - 440

JO - Chemosphere

JF - Chemosphere

IS - 4

ER -