Persistence and fate of 14C-gamma-HCH in an Indian sandy loam soil under field and laboratory conditions

The persistence, binding and degradation of 14C-gamma-HCH were studied for one year under field conditions in Delhi, India. The surface treatment of HCH to a sandy loam soil during the monsoon, winter and summer seasons resulted in rapid dissipation in the initial 60 days. However, less than 1% of the initial HCH was lost in the final six months. After one year, the soil burden of HCH was about 15% of the initial concentration, of which bound residues accounted for more than three quarters. The observed time for 50% dissipation of HCH varied from 30 to 45 days although the calculated T50 values ranged from 124 to 147 days. Incubation of HCH treated soils at 15, 30 and 45 deg. C showed increased CO2 evolution and volatilization at higher temperatures. Volatilization was predominant and showed a six-fold increase with rise in temperature from 15 to 45 deg. C. Higher temperatures also enhanced degradation and binding of HCH. When HCH-treated soil samples in quartz, glass and dark tubes were kept under sunlight for 42 days, higher rates of mineralization and volatilization occurred in the quartz tubes. The major loss of HCH was due to volatilization which was enhanced further by flooding the soil. Similarly, degradation of HCH to PCCH was also influenced by sunlight, while flooding resulted in further degradation to TCCH. The present studies demonstrated that under Indian sub-tropical conditions HCH dissipated rapidly by volatilization, evidently due to higher soil temperature and intense solar radiations. (author). 9 refs, 4 figs, 3 tabs