Loss of PCBs from Municipal‐Sludge–Treated Farmland

Abstract

The Madison (Wisconsin) Metropolitan Sewerage District (MMSD) has been conducting field tests on the application of municipal sewage sludge on farmland. The sludge, which has been stored for more than 20 years in lagoons, is slightly contaminated with PCB. This paper presents the results of the first two years of data on the disappearance of PCB from the surface‐soil layer of cropland. Eight different treatments of cropland with PCB‐contaminated sludge were included in the experiment. Each treatment was replicated three times, giving 30 test plots in all (24 sludge applications and six control plots). The concentrations of each PCB congener in the surface‐soil layer (between soil depth of 0 to 12 in.) were measured for five sampling seasons. The 2‐, 3‐, and 4‐chlorinated PCB isomers, which make up three‐fourths of the total PCB concentration, disappeared from the soil, but the 5–8‐chlorinated PCB isomers did not. A first‐order PCB degradation model was adequate to describe the disappearance of PCB in the surface‐soil layer. The value of the first‐order rate constant for disappearance of PCB from the surface‐soil layer was independent of sludge loading rate, sludge PCB concentration, and whether the sludge was a one‐time or repeated‐annual application.