DECOMPOSITION OF ALPHA-HEXACHLOROCYCLOHEXANE AND BETA-HEXACHLOROCYCLOHEXANE IN SOIL UNDER FIELD CONDITIONS IN A TEMPERATE CLIMATE

A field experiment was made to establish whether in temperate climates the microbial degradation of hexachlorocyclohexane (HCH) occurs at a rate suitable for soil sanitation. Contaminated sandy loam soil (6 m3) was collected sieved and homogenized. The initial pollution levels were 367 ± 60 mg α-HCH kg-1 and 280 ± 25 mg β-HCH kg-1. After 23 weeks of field exposure α-HCH in moist soil (water content 6-18%) decreased to 107 ± 8 mg kg-1, and in slurry (water content 50%) to 62 ± 11 mg kg-1. In anaerobic slurry, α-HCH was not biodegraded. β-HCH concentration was not affected under aerobic or anaerobic conditions. Regular tillage of soil, covering with black PVC film or extra aeration did not affect degradation in moist soil. However regular stirring slightly accelerated degradation in the aerated slurry. The total number of microorganisms remained more or less constant but the number of α-HCH degrading organisms in moist soils and slurry increased from 103 to 107 g-1 dry soil. Basal respiration increased in moist soil but was constant in aerated slurry. The decomposition rate of glutamic acid increased with a decreasing concentration of α-HCH. It was concluded that degradation of α-HCH in moist soil (land-farming) and aerated slurry was possible in a temperate climate and that cultivation or covering with black PVC film were not useful. © 1990.