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Mineralization and Volatilization of Polychlorinated Biphenyls in Sludge-amended Soils¹

ABSTRACT

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, 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.

Key Words: Aroclor 1254 • degradation • first-order rate constant • toxic organics

¹ Journal article 1240, Agric. Exp. Stn., New Mexico State Univ., Las Cruces, NM 88003. This study was supported by funds from the Dep. of Energy under contract no. DE-AC04-83AL21776.

² Research Specialist, Professor, and Laboratory Assistant, respectively, Dep. of Agronomy and Horticulture, New Mexico State Univ., Las Cruces, NM 88003.

Received for publication April 23, 1986.