Evidence of latitudinal fractionation of polychlorinated biphenyl congeners along the Baltic Sea region

Annual cycles of the atmospheric concentrations of PCBs were determined at 16 (mostly rural) stations around the Baltic Sea between 1990 and 1993. The concentration levels of individual congeners were found to be influenced b y their physical-chemical properties, ambient temperature, and geographical location, Median levels of PCBs were similar at all stations except at one urban site near Riga. A latitudinal gradient with higher levels in the sou th was found for the sum of PCB as well as for individual congeners, and th e gradient was more pronounced for the low volatility congeners. As a resul t, the high volatility congeners increased in relative importance with lati tude. Generally, PCB concentrations increased with temperature, but slopes of the partial pressure in air versus reciprocal temperature were different between congeners and between stations. In general, the low volatility con geners were more temperature dependent than the high volatility PCB congene rs. Steep slopes at a sampling location indicate that the concentration in air is largely determined by diffusive exchange with soils. Lack of a tempe rature dependence may be due to the influence of long-range transported air masses at remote sites and due to the episodic or random nature of PCB sou rces at urban sites.