Declining PCB concentrations in the UK atmosphere: Evidence and possible causes

PCB air concentrations have been measured at a meteorological site in north west England since 1992. Examination of this data set, comprising over 200 data points, suggests that PCB levels are decreasing with average congener specific half-lives ranging from approximately 2 to 6 yr. With the exceptio n of congener 52,which shows the steepest decline, the slopes of other ICES congeners included in this study (i.e., 28, 101, 118, 153, and 138) were n ot found to be significantly different from each other. A U.K, mass balance model has been used to examine which factors are likely to be controlling present and future air concentrations. This allowed a range of fate scenari os to be examined and the controlling fate processes to be scrutinized. Est imates of fluxes using contemporary soil and air concentrations suggest tha t the observed longterm decrease of PCB levels in U.K, air is likely to be influenced by several factors, including existing primary emissions and rec ycling, volatilization from soil, advective losses from the U.K. atmosphere , reaction in the atmosphere, and soil fate processes such as microbial deg radation.