Estimating the contribution of degradation in air and deposition to the deep sea to the global loss of PCBs

A series of theoretical and semi-empirical approaches, including the zonally averaged global fate and transport model Globo-POP, were used to estimate the rate of loss of selected polychlorinated biphenyl (PCB) congeners from the global environment, and the relative contribution of atmospheric degradation and transfer to the deep sea to this loss. The atmospheric fate of PCBs is highly dependent on the OH radical concentration, temperature and the latterʹs influence on the gas/particle partitioning equilibrium. The PCB loss was found to be very congener specific. Atmospheric reaction with the OH radical is the major loss process for the lighter and intermediate PCB congeners, whereas particle-bound transfer to the deep sea dominates the loss of the congeners with a large number of chlorine substituents. As concentrations in air and seawater decline more rapidly than in the terrestrial environment, other loss processes such as degradation in soils are gaining in relative importance with time. Estimated lifetimes of the PCBs in the global environment are on the order of decades, with significant differences between congeners. Research needs are identified that would allow improvements of these estimates.