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Degradation of Gamma-BHC in Rice Soils¹

ABSTRACT

The biodegradation of the organochlorine insecticide, -BHC (-isomer of 1,2,3,4,5,6-hexachlorocyclohexane) was evaluated for four Philippine rice soils: Casiguran sandy loam, Luisiana clay, Maahas clay and Pila clay loam. Rapid degradation of the insecticide was observed under flooded soil conditions. The rate of degradation for -BHC was highest in Casiguran sandy loam; none of the parent insecticide remained in the soil after 1 month of incubation at 30C. Organic matter levels were related directly to rate of decomposition. Molecular oxygen, nitrate, and manganic oxide retarded the rate of -BHC degradation. Increased temperature increased the rate of -BHC degradation, and it appears that -BHC residues are unlikely to be a problem in the tropical rice-growing areas.

¹ Contribution from the Dept. of Soil Microbiology, the International Rice Research Institute, Los Baños, Laguna, Philippines. Mailing address, P. O. Box 583, Manila, Philippines.

² Soil Microbiologist and Research Assistant, respectively, the International Rice Research Inst., Los Baños, Laguna, Philippines.

Received for publication August 19, 1969. Accepted for publication February 13, 1970.