Wet deposition of polychlorinated biphenyls in the eastern Mediterranean.

Abstract

The concentrations of polychlorinated biphenyls (PCBs) were measured in rain samples collected from a semiurban and a marine background site of the eastern Mediterranean. The concentration of sigmaPCB (sum of 54 PCB congeners) in the city of Heraklion (2.9 +/- 1.9 ng L(-1)) was not significantly higher than the corresponding concentration measured at the background sampling station of Finokalia (1.9 +/- 0.9 ng L(-1)). In both sites, the sum of tri- and tetrachlorinated congeners accounted for more than 55% of sigmaPCB in rainwater. For all samples, the percentage of particle-bound PCBs ranged between 6.6% and 63.8%, providing an average value of 31 +/- 18%. The washout ratios of particulate PCBs (WP) were constant for individual congeners regardless the degree of chlorination. Average WP values ranged between 1.9 x 10(5) and 5.2 x 10(5) while a value of 2.7(+/- 1.3) x 10(5) was deduced for sigmaPCB. The corresponding washout ratios for gaseous PCBs were substantially lower and ranged between 7 x 10(3) (PCB 99) and 1.3 x 10(5) (PCB 180). Washout ratios of gaseous PCBs were also calculated based on Henry's law, and they were found to be 30-920 times lower than those obtained from field measurements. On the basis of our data, the wet deposition flux of sigmaPCB in the eastern Mediterranean should approach 820 ng m(-2) yr(-1). This flux is similar with the values recently reported for several background sites of the United States and Europe, but it is 1 order of magnitude lower than the flux of PCBs measured in the western Mediterranean 16 yr ago.