MINERALIZATION AND VOLATILIZATION OF POLYCHLORINATED-BIPHENYLS IN SLUDGE-AMENDED SOILS

Polychlorinated biphenyls (PCBs) are toxic organics of concern limiting the reuse of sewage sludge on agricultural lands. The mineralization and volatilization of PCBs (14C-Aroclor 1254) were monitored for 240 d in three calcareous soils from New Mexico [USA], amended or unamended with sewage sludge. Two first-order rate constants were used to describe both processes and to compare treatment effects of sludge addition, PCB concentration (5, 50, 500 mg/kg), soil textural class, and length of sludge incubation with soils prior to experimentation. Total loss of PCBs ranged from 8 to 33%. Fifty and 95% disappearance times ranged from 2.5 to 5.9 yr and 6.1 to 26.3 yr, respectively. Treatment effects on total loss closely paralleled those of volatilization. Volatilization of organics ranged from 5 to 31%, and was the major means of loss of 14C in unamended soils and all 500 mg PCB/kg treatments. Volatilization, and thus environmental transport, was decreased by sludge addition. Exposure of the soil to sludge prior to experimentation had no effect on volatilization when compared to fresh sludge additions. carbon-14-organic volatile loss was greater in two sandy loams than in a clay soil. Comparing PCB concentrations, volatilization was generally greatest at 50 mg/kg and least at 500 mg/kg, with comparatively smaller differences between 5 and 50 mg/kg. Degradation of 14C-Aroclor 1254 to 14CO2 ranged from 1 to 11%. Overall, 14CO2 evolution, and thus detoxification increased with sewage sludge addition and decreased with increasing PCB concentration. Mineralization exceeded volatilization in sludge-amended soils at 5 mg PCBs/kg. During the first 60 d of incubation, previous exposure of the soil to sewage sludge increased mineralization in the 5 and 50 mg PCB/kg treatments. In no case did sewage sludge additions increase the environmental hazard of Aroclor 1254 in these soils.