Research Evidence of Latitudinal Fractionation of Polychlorinated Biphenyl Congeners along the Baltic Sea Region CECILIA AGRELL,* ,† LENNART OKLA, † PER LARSSON, † CECILIA BACKE, † AND FRANK WANIA ‡ Chemical Ecology and Ecotoxicology, Department of Ecology, University of Lund, Ecology Building S-223 62 Lund, Sweden, and WECC Wania Environmental Chemists Corp., 280 Sim coe St., Suite 404, Toronto, Ontario, Canada, M5T 2Y5 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 by 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 south was found for the sum of PCB as well as for individual congeners, and the gradient was more pronounced for the low volatility congeners. As a result, the high volatility congeners increased in relative importance with latitude. 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 congeners were more temperature dependent than the high volatility PCB congeners. Steep slopes at a sampling location indicate that the concentration in air is largely determined by diffusive exchange with soils. Lack of a temperature 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 sources at urban sites. Introduction During the last two decades several studies on persistent organic pollutants (POPs) in air have been conducted both in remote and ruralareas (1 and referencestherein).Emphasis has traditionally been on spatial distribution, but during recent years the focus has shifted to mechanistic approaches usingdata coveringlonger time periods (1-5).These studies have shown that many POPs show cyclic fluctuations over the year, with atmospheric concentrations peaking during the summer. Higher summer temperatures enhance vola- tilization from surface media, i.e., water, ice, snow, plants, soil,and bedrock.Once airborne,POPsmaymigrate through the atmosphere as gases and sorbed to aerosols. Deposition from the atmosphere is enhanced in low-temperature regions. Possibly a fractionation process occurs so that less volatile compounds are deposited close to the source and more volatile compounds travel further toward the poles. A contaminant mixture with both high and low volatility compounds, such as the PCBs, will change its composition along a temperature or latitudinal gradient (6). This means that the proportion of high volatility PCBs in air should increase relative to low volatility PCBs when approaching the polar regions. Latitudinalgradients have been observed for PCBs in fish liver (7) and in sediments (8), for HCB and HCHs in foliage (9), and for HCB, R-HCH, γ-HCH, and pentachloroanisol in treebark (10). Lead et al. (11) argue that to test the global fractionation hypothesis, concentration data are required for longer time periods at different latitudes. They conclude that for latitudinal data obtained at only one sampling occasion, only the effect of temperature and a compound’s physicochemical properties on air-vegetation partitioning can be observed. They measured the concentration of PCBs in moss (Hylocomium splendens) collected in remote areas in Norway in 1977, 1985, and 1990. A change in congener profile was observed, in that over time, the low volatility groups decreased more in the South then they did in the North.These observationsare tentativelysuggested to provide evidence for the process of global fractionation. A field study was initiated in October 1990 in order to determine polychlorinated biphenyls (PCBs) in air at 16 sampling stations, located on islands or close to the coast of the BalticSea.Samplingwascarried out continuouslyduring one year for most of the stations, and up to two years for some stations. Establishing the spatial and temporal vari- ability of the atmospheric concentrations of PCBs over the Baltic Sea is important because in large water bodies the water is responding fairly rapidly to contaminant levels in the atmosphere (12). This study is the first to combine long- term temporalmeasurementsofair concentrationswith large spatial coverage (latitude 54°00′ to 65°44′) that allows the investigation of latitudinal trends in atmospheric concentra- tions. Recently,Wania et al.(13)presented two models to explain how air concentrations depend on temperature. The first assumes equilibrium between the atmosphere and the Earth’s surface. The second also include the kinetics of air-surface exchange and predicts atmospheric concentrations when advection in air and reversible exchange with a surface is taken into account.Based on these models it is hypothesized that the relationship between the logarithm of the partial pressure of PCBs in air (ln p A) and inverse temperature (1/ T) can be used to determine how air concentration is controlled by local (re-) evaporation vs by advection of contaminated air masses. Hoff et al. (14 ) came to a similar conclusion when analyzing data from the Great Lakes region. In this paper we attempt to evaluate this hypothesis by testing it on our field data. Experimental Section Sixteen sampling stations were located as close to the sea as possible and preferentially in the vicinity of meteorological stations (Figure 1). Nine stations were situated on the mainland within 5km ofthe shoreline,and five stations were on islands. Air was sampled with high-volume samplers at 2 m above the ground. Approximately 1000 m 3 of air was drawn through two polyurethane foam (PUF) plugs in series by means of an electric pump at a rate of 30-50 L/min *Corresponding author phone: 46 46 222 3781; fax: 46 46 222 3790; e-mail address: Cecilia.Agrell@ecotox.lu.se. † University of Lund. ‡ WECC Wania Environmental Chemistry Corp. 10.1021/es980867l CCC: $18.00  1999 American Chemical Society VOL. 33, NO. 8, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1149 Published on Web 02/27/1999