Dissipation behavior of hexachlorocyclohexane isomers in flooded rice soil

Abstract

Hexachlorocyclohexane and its α‐, β‐, γ‐, and δ‐HCH isomer's dissipation behavior in flooded soil under the cover of rice crop was studied with the recommended (2.5 kg a.i./ha) and double the recommended doses. The degradation flux of each isomer continued to increase for 60 days after treatment and then decreased. Among the different isomers, the β‐isomer degradation was the slowest, followed by δ‐, α‐ and γ‐isomers. Several reasons are suggested for this degradation behavior of different HCH isomers. Partition distribution coefficients (K_d) of all isomers showed a positive correlation with incubation time and their respective degradation rates. This study was compared with non‐flooded plots where all the isomers persisted for a longer period. Measurable translocation and accumulation of β‐isomer was observed in rice grains at harvest from higher treatment, but not the recommended dose.

Key words:

• Hexachlorocyclohexane
• α, β, γ, δ‐HCH isomer
• dissipation
• degradation flux
• half‐lives
• K_d
• flooded soil
• rice

Notes

Authors for correspondence USDA‐ARS‐Soil Physics Research Unit, Dept. Soil & Env. Sci. University of California, Riverside, CA 92521