Persistence of hexachlorocyclohexane isomers in soil planted with rice and in rice rhizosphere soil suspensions

Abstract

The relative persistence of α-, β- and γ-isomers of hexachlorocyclohexane (HCH) was studied in a flooded soil with and without rice seedlings under greenhouse conditions. β-HCH was more stable than α- and ϒ-HCH in both planted and unplanted systems. α- and γ-HCH decreased to negligible levels (5.5% for the α-isomer and 2.4% for the γ-isomer) after 30 days in planted and unplanted soils. During the same period, 30.9% of the added β-HCH was recovered from planted soil and 50.6% from unplanted soil. Likewise, in anaerobically (H₂ + CO₂ atmosphere) incubated mineral salts solution inoculated with suspensions from rice rhizosphere and non-rhizosphere soils, γ-HCH decreased to low levels (< 15%) within 5 days. Most of the added β-HCH was recovered from mineral solution inoculated with nonrhizosphere soil suspension even after 30 days while β-HCH decreased to 53.6% of the original level in mineral solution inoculated with rice rhizosphere soil suspension. The data reveal that the degradation of anaerobically unstable HCH isomers is not retarded by the possible aeration of a flooded soil by rice roots.