Foliar nitrogen responses to elevated atmospheric nitrogen deposition in nine temperate forest canopy species

Despite its ecological importance, broad-scale use of foliar nitrogen as an indicator of ecosystem response to atmospheric N deposition has heretofore been obscured by its poorly understood intrinsic variability through time, space, and across species. We used a regional survey of foliar N conducted within a single growing season to observe that eight of nine major canopy tree species had increased foliar N in response to a gradient of N deposition in the Adirondack Park, New York. These results (1) add important foliar N evidence to support N saturation theory, (2) strongly reinforce the conclusion that N deposition is affecting the N status of forest ecosystems in the northeastern U.S., and (3) extend N saturation theory by identifying that temperate forest canopy species differ in their foliar N response to N deposition. Interestingly, species-specific differences were strongly related to two functional traits that arise from within-leaf allocations of N resources--leaf mass per area (LMA) and shade tolerance. Thus, combining species-specific knowledge of these functional traits with existing foliar N-centered remote sensing and ecosystem modeling approaches may provide a much-needed avenue to make broad-scale assessments of how persistently elevated rates of N deposition will continue to affect temperate forest ecosystems.     

Survey of dioxins, dioxin-like PCBs and marker PCBs in German feeds of plant origin

Within a representative survey the levels of dioxins (PCDD/PCDF), dioxin-like PCBs and marker PCBs in 206 German feed samples were analysed in the years 2004/2005. The sampling plan included compound feed (N = 115) and roughage and succulent feed (N = 91) and reflected the representative feeding situation in Germany. The median content of WHO-PCB-TEQ in analysed feed samples was 0.017 ng/kg [88% dry matter (d.m.)] and consequently more than a factor of 10 below the action level of 0.35 ng/kg (88% d.m.). A differentiation between compound feed and roughage and succulent feed showed that compound feed [median 0.007 ng/kg (88% d.m.)] were significantly lower contaminated with dioxin-like PCBs than roughage and succulent feed [median 0.058 ng/kg (88% d.m.)]. The median sum contents of the six marker PCBs were 0.16 μg/kg (88% d.m.) for compound feed and 0.56 μg/kg (88% d.m.) for roughage and succulent feed. The median of the WHO-PCDD/F-TEQ was 0.03 ng/kg (88% d.m.), the maximum level of 0.75 ng/kg (88% d.m.) was not exceeded. The median of the WHO-PCDD/F-PCB-TEQ was 0.05 ng/kg (88% d.m.) and consequently a factor of 25 below the maximum level of 1.25 ng/kg. Additionally the samples of roughage and succulent feed were analysed according to their contents of ash insoluble in HCl, representing a degree of the proportion of earthy components in feed. A slight correlation was found between ash insoluble in HCl and WHO-PCDD/F-TEQ (R ² = 0.59) whereas no correlation was found between ash insoluble in HCl and WHO-PCB-TEQ (R ² = 0.06).     

Survey of dioxins, dioxin-like PCBs and marker PCBs in German feeds of plant origin

Within a representative survey the levels of dioxins (PCDD/PCDF), dioxin-like PCBs and marker PCBs in 206 German feed samples were analysed in the years 2004/2005. The sampling plan included compound feed (N = 115) and roughage and succulent feed (N = 91) and reflected the representative feeding situation in Germany. The median content of WHO-PCB-TEQ in analysed feed samples was 0.017 ng/kg [88% dry matter (d.m.)] and consequently more than a factor of 10 below the action level of 0.35 ng/kg (88% d.m.). A differentiation between compound feed and roughage and succulent feed showed that compound feed [median 0.007 ng/kg (88% d.m.)] were significantly lower contaminated with dioxin-like PCBs than roughage and succulent feed [median 0.058 ng/kg (88% d.m.)]. The median sum contents of the six marker PCBs were 0.16 μg/kg (88% d.m.) for compound feed and 0.56 μg/kg (88% d.m.) for roughage and succulent feed. The median of the WHO-PCDD/F-TEQ was 0.03 ng/kg (88% d.m.), the maximum level of 0.75 ng/kg (88% d.m.) was not exceeded. The median of the WHO-PCDD/F-PCB-TEQ was 0.05 ng/kg (88% d.m.) and consequently a factor of 25 below the maximum level of 1.25 ng/kg. Additionally the samples of roughage and succulent feed were analysed according to their contents of ash insoluble in HCl, representing a degree of the proportion of earthy components in feed. A slight correlation was found between ash insoluble in HCl and WHO-PCDD/F-TEQ (R ² = 0.59) whereas no correlation was found between ash insoluble in HCl and WHO-PCB-TEQ (R ² = 0.06).     

Nitrous oxide fluxes in three experimental boreal forest reservoirs

Global atmospheric concentrations of nitrous oxide (N2O), a powerful greenhouse gas, continue to increase. While many sources and sinks have been identified, there is little known about how existing and newly constructed reservoirs, such as those created for hydroelectric production, impact current atmospheric N2O concentrations. We hypothesized that N2O fluxes to the atmosphere would increase because enhanced nutrient availability and increased soil respiration following the flooding of soils during reservoir creation would favor denitrification. Furthermore, we hypothesized that emissions would be linked to the amount of organic carbon contained in the flooded landscape. These hypotheses were tested by creating three experimental reservoirs over boreal upland subcatchments that ranged in the amount of organic carbon stored in soils and vegetation. Diffusive surface N2O fluxes within each reservoir were estimated using surface water concentrations of N2O and the thin boundary layer method. Surface fluxes ranged from -1.0 to -3.5 microg N2O m(-2) d(-1), and water column N2O concentrations indicated that contrary to expectations, the reservoirs were acting as slight sinks for atmospheric N2O. This net consumption of N2O was likely related to an excess of labile carbon and low concentrations of oxygen (O2) and nitrate (NO3-) in the flooded soils. Therefore, it is postulated that reservoir creation by flooding boreal soils will likely have little or no net effect of adding additional N2O to the current greenhouse gas (GHG) atmospheric burden, at least over the short term.     

Accumulation of trifluoroacetate in seasonal wetlands in California

Trifluoroacetate (TFA, CF3COO-) is a stable and mildly phytotoxic breakdown product of several fluorinated organic compounds including the hydro(chloro)fluorocarbons (HFC/HCFCs) that have largely replaced the stratospheric ozone-depleting chlorofluorocarbons (CFCs). TFA enters aquatic ecosystems primarily through precipitation and has the potential to accumulate in water bodies with little or no outflow to the point where toxic concentrations could be achieved. This study demonstrated that seasonal wetlands lacking outflow concentrated TFA as they evaporated during the dry season. In addition, the TFA within the pools was retained between years, which may result in long-term TFA accumulation. Since plants acquire TFA from their growing media, the plants exposed to high aqueous concentrations of TFA within the pools had elevated TFA concentrations with a median concentration of 279 ng/g dry weight in their tissues as compared to 33 ng/g for species growing outside the pools. The highest TFA concentrations in water, which occurred just prior to the pools drying up, were in the 2-10 micrograms/L range. These concentrations are approximately 190 or less than reported toxic concentrations for the most sensitive species tested, but our evidence suggests that these concentrations will increase with continued TFA deposition into the pools.     

Uptake and storage of PCBs by plant cuticles

The uptake kinetics and storage of PCBs by isolated cuticles and cuticular waxes from Hedera helix, Prunus laurocerasus, and Ilex aquifolium were studied. Small chambers were used, allowing variation in plant uptake parameters to be studied by having the same air boundary layer in each chamber. During the 64 day study tri- and tetrachlorinated biphenyls generally reached equilibrium in waxes but not in whole cuticles. Differences between species were observed. Higher chlorinated PCB congeners did not approach equilibrium in either sample type. Although PCBs showed higher affinity for waxes than whole cuticles, the latter dominated the total uptake capacity on a surface area basis, because of the large amount of nonwax cuticular components. Mass transfer coefficients (MTCs) for PCB uptake (into both cuticles and waxes) indicated partition dependence up to log octanol/air partition coefficients (K(OA)) of 8.5-10, depending on species and sample type. For cuticles, higher MTCs occurred at the beginning of the experiment than later. This was not seen in reconstituted waxes, a difference which may be explained by the dispersion of intracuticular waxes within cuticles. For more lipophilic compounds, uptake appeared to be limited by diffusion processes, which may be influenced by plant physiology. Leaf surface area is, therefore, likely to control the ability of vegetation to scavenge these compounds from the air in many field situations.     

Distribution and spatial trends of PCBs in commercial scallops from Galician littoral (NW, Spain). Possible influence of biometric parameters

Levels and profiles of 10 individual congeners of polychlorinated biphenyls (PCBs) were studied in 3 species of commercial scallops (Pecten maximus, Chlamys varia, and Chlamys opercularis) from several Rías in Galician littoral (NW, Spain). ΣPCBs levels ranged from 2.21 to 41.0 ng/g wet weight for P. maximus, from 13.9 to 24.9 ng/g wet weight for C. varia, and from 1.58 to 24.3 ng/g wet weight for C. opercularis. The possible influence between biometric parameters (lipid content, condition index, and shell size) and PCBs levels were studied using statistical analysis (ANOVA). No relationship between biometric parameters could be established in the studied samples. Multivariate analysis showed there were differences in bioaccumulation of some PCBs congeners. Principal component analysis classifies clearly the 3 studied Rías (Ría de Ferrol, Ría de Arousa, and Ría de Vigo) taking into account PCBs levels found in the shellfish. PRACTICAL APPLICATIONS: We investigated levels and profiles of 10 congeners of PCBs in 3 commercial scallop species from the Galician littoral zone. The influence of 3 biometric parameters on polychlorinated biphenyls (PCBs) levels was also studied in order to assess results from the monitoring programs of production areas. According to PCBs levels, geographical differences were observed in commercial scallops from the 3 studied estuarine bays (Ría de Ferrol, Ría de Arousa, and Ría de Vigo).     

Time horizon dependent characterization factors for acidification in life-cycle assessment based on forest plant species occurrence in Europe

This paper describes a new approach in life-cycle impact assessment to derive characterization factors for acidification in European forests. Time horizon dependent characterization factors for acidification were calculated, whereas before only steady-state factors were available. The characterization factors indicate the change in the potential occurrence of plant species due to a change in emission, and they consist of a fate and an effect factor. The fate factor combines the results of an atmospheric deposition model and a dynamic soil acidification model. The change in base saturation in soil due to an atmospheric emission change was derived for 20, 50, 100, and 500 year time horizons. The effect factor was based on a dose-response curve of the potential occurrence of plant species, derived from multiple regression equations per plant species. The results showed that characterization factors for acidification increase up to a factor of 13 from a 20 years to a 500 years time horizon. Characterization factors for ammonia are 4.0-4.3 times greater than those for nitrogen oxides (NO(x)), and characterization factors for sulfur dioxide are 1.4-2.0 times greater than those for NO(x). Aggregation of damage due to acidification with other impact categories on the European scale becomes feasible with the applied approach.     

Accumulation of atmospheric and sedimentary PCBs and toxaphene in a Lake Michigan food web

Seston, sediment, settling organic matter, and food web members were collected from Grand Traverse Bay, Lake Michigan, between April 1997 and September 1998 to examine PCB and toxaphene biomagnification. Stable isotopes of nitrogen and carbon were analyzed in samples and used to establish trophic structure of the food web and to determine the importance of atmospheric versus sedimentary sources in delivering PCBs to the food web. Nitrogen isotopes were confounded by multiple variables in this system, particularly seasonal variation, and did not display a simple pattern of enrichment among trophic levels. However, delta13C displayed little seasonal variation and was positively correlated with PCB concentrations among food web members (r2 = 0.69). Plots of delta13C vs PCBs separate food web members into three distinct groupings comprised of invertebrates, primary forage fish, and predatory fish. Stable isotope values of the primary organic sources indicate that the atmosphere, and not the sediment, is the most likely source of PCBs to the food web of Lake Michigan. Additionally, we suggest that seston may be important in delivering PCBs to pelagic food web members and species that receive a majority of their nutrition through pelagic sources. In contrast, settling particles are implicated in delivering PCBs to benthic organisms and Mysis relicta.     

Accumulation of persistent organic pollutants in canopies of different forest types: role of species composition and altitudinal-temperature gradient

Leaves from the dominant tree species in three different alpine forests were sampled along an altitudinal gradient and analyzed for HCB, alpha- and gamma-HCH, and PCBs. The mean canopy concentration was calculated, considering the relative abundance of each species in the respective forest. Compound fractionation occurred in the vegetation along the altitudinal/temperature gradient. Results were compared with air concentrations and in-field plant/air partition coefficients (K(PA)) were calculated for each species; this showed differences between broadleaves and needles. The mean canopy/air partition coefficient (K(CA)) was also calculated by averaging results from single species. The variability of persistent organic pollutants distribution in canopies is discussed considering two main factors, the altitudinal/temperature gradient and the species composition. The latter is responsible for most of the concentration variability of the more volatile compounds. A model to calculate dry gaseous deposition to different forest canopies is presented.     

Forestry practices increase mercury and methyl mercury output from boreal forest catchments

We observed significant increases in the runoff output of total mercury (TotHg) and methyl mercury (MeHg) from a small spruce forest catchment (0.071 km2) after clear-cutting and soil treatment. Here we show that forest regeneration practices may act as an important additional source of TotHg and MeHg to forest lakes. TotHg and MeHg in runoff from two small forested catchments were monitored during the period 1994 to 2001. In the autumn of 1997, one of the catchments was clear-cut Soil preparation (mounding) was carried out in the autumn of 1998 and replanting in the summer of 1999. During the 3 years after the silvicultural treatment, medians of monthly flow-weighted TotHg and MeHg concentrations (12.02 ng L(-1) and 0.35 ng L(-1), respectively) and output loads (0.80-0.97 g km(-2) a(-1) and 0.011-0.036 g km(-2) a(-1), respectively) increased significantly compared to the 3 years calibration period (8.13 ng L(-1) and 0.15 ng 1(-1); 2.0-5.3 g km(-2) a(-1) and 0.11-0.16 g km(-2) a(-1), respectively). These results indicate that clear-cutting and/or soil treatment significantly increases the mobility of TotHg and MeHg accumulated in forest soil and may thus be an important factor for the total input of Hg to boreal freshwater ecosystems.     

Radiative forcing impacts of boreal forest biofuels: a scenario study for Norway in light of albedo

Radiative forcing impacts due to increased harvesting of boreal forests for use as transportation biofuel in Norway are quantified using simple climate models together with life cycle emission data, MODIS surface albedo data, and a dynamic land use model tracking carbon flux and clear-cut area changes within productive forests over a 100-year management period. We approximate the magnitude of radiative forcing due to albedo changes and compare it to the forcing due to changes in the carbon cycle for purposes of attributing the net result, along with changes in fossil fuel emissions, to the combined anthropogenic land use plus transport fuel system. Depending on albedo uncertainty and uncertainty about the geographic distribution of future logging activity, we report a range of results, thus only general conclusions about the magnitude of the carbon offset potential due to changes in surface albedo can be drawn. Nevertheless, our results have important implications for how forests might be managed for mitigating climate change in light of this additional biophysical criterion, and in particular, on future biofuel policies throughout the region. Future research efforts should be directed at understanding the relationships between the physical properties of managed forests and albedo, and how albedo changes in time as a result of specific management interventions.     

Emission and long-range transport of gaseous mercury from a large-scale Canadian boreal forest fire

Field observations made at Harvard Forest [Petersham, MA, U.S.A. (42 degrees 54' N, 72 degrees 18' W)] during early July 2002 show clear evidence of long-range transport of gaseous mercury (Hg) in a smoke plume from a series of boreal forest fires in northern Quebec. These measurements indicated significant and highly correlated increases in Hg and CO during the plume event. The Hg:CO emissions ratio determined from the data (8.61 x 10(-8) mol mol(-1)) was combined with previously published information on CO emissions and biomass burned to determine a mean area-based Hg emission flux density for boreal forest fires (1.5 g Hg ha(-1)), annual Hg emissions from Canadian forest fires (3.5 tonnes), and annual global Hg emissions from boreal forest fires (22.5 tonnes). Annual Hg emissions from boreal fires in Canada may equal 30% of annual Canadian anthropogenic emissions in an average fire year and could be as high as 100% during years of intense burning. The Hg:CO emissions ratio of this study was much lower than those reported for a temperate forest in Ontario and a pine/shrub vegetation in South Africa, suggesting that fire emission is dependent on biome/species and that any extrapolation from a single fire event to determine the global fire emission is speculative.     

Using passive air samplers to assess urban-rural trends for persistent organic pollutants and polycyclic aromatic hydrocarbons. 2. Seasonal trends for PAHs, PCBs, and organochlorine pesticides

This is the second of two papers demonstrating the feasibility of using passive air samplers to investigate persistent organic pollutants along an urban-rural transect in Toronto. The first paper investigated spatial trends for polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). This second paper investigates the seasonality of air concentrations for polycyclic aromatic hydrocarbons (PAHs), PCBs, and OCPs along this transect. Air samplers, consisting of polyurethane foam (PUF) disks housed in stainless steel domed chambers, were deployed for three 4-month integration periods from June 2000 to July 2001. The seasonal variations of derived air concentrations for PAHs, PCBs, and OCPs reflected the different source characteristics for these compounds. PAHs showed a strong urban-rural gradient with maximum concentrations at urban sites during the summer period (July-October). These high summer values in Toronto were attributed to increases in evaporative emissions from petroleum products such as asphalt. PCBs also exhibited a strong urban-rural gradient with maximum air concentrations (approximately 2-3 times higher) during the spring period (April-June). This was attributed to increased surface-air exchange of PCBs that had accumulated in the surface layer over the winter. alpha-HCH was fairly uniformly distributed, spatially and temporally, as expected. This pattern and the derived air concentration of approximately 35 to approximately 100 pg m(-3) agreed well with high volume air data from this region, adding confidence to the operation of the passive samplers and showing that site-to-site differences in sampling rates was not an issue. For other OCPs, highest concentrations were observed during the spring period. This was associated with either (i) their local and/or regional application (gamma-HCH, endosulfan) and (ii) their revolatilization (chlordanes, DDT isomers, dieldrin, and toxaphene). Principal component analysis resulted in clusters for the different target chemicals according to their chemical class/source type. The results of this study demonstrate how such a simple sampling technique can provide both spatial and seasonal information. These data, integrated over seasons, can be used to evaluate contaminant trends and the potential role of large urban centers as sources of some semivolatile compounds to the regional environment, including the Great Lakes ecosystem.     

Response of key soil parameters during compost-assisted phytostabilization in extremely acidic tailings: effect of plant species

Phytostabilization of mine tailings acts to mitigate both eolian dispersion and water erosion events which can disseminate barren tailings over large distances. This technology uses plants to establish a vegetative cover to permanently immobilize contaminants in the rooting zone, often requiring addition of an amendment to assist plant growth. Here we report the results of a greenhouse study that evaluated the ability of six native plant species to grow in extremely acidic (pH ～ 2.5) metalliferous (As, Pb, Zn: 2000-3000 mg kg(-1)) mine tailings from Iron King Mine Humboldt Smelter Superfund site when amended with a range of compost concentrations. Results revealed that three of the six plant species tested (buffalo grass, mesquite, and catclaw acacia) are good candidates for phytostabilization at an optimum level of 15% compost (w/w) amendment showing good growth and minimal shoot accumulation of metal(loid)s. A fourth candidate, quailbush, also met all criteria except for exceeding the domestic animal toxicity limit for shoot accumulation of zinc. A key finding of this study was that the plant species that grew most successfully on these tailings significantly influenced key tailings parameters; direct correlations between plant biomass and both increased tailings pH and neutrophilic heterotrophic bacterial counts were observed. We also observed decreased iron oxidizer counts and decreased bioavailability of metal(loid)s mainly as a result of compost amendment. Taken together, these results suggest that the phytostabilization process reduced tailings toxicity as well as the potential for metal(loid) mobilization. This study provides practical information on plant and tailings characteristics that is critically needed for successful implementation of assisted phytostabilization on acidic, metalliferous mine tailings sites.     

Genetic parameters and trends in the Chilean multibreed dairy cattle population

Estimates of additive and nonadditive multibreed co-variance components, genetic parameters, and predicted genetic values for first lactation 305-d mature equivalent (ME) milk yield, fat yield, and protein yield were computed using data from a sample of 3316 cows from the Chilean Holstein-other breeds multibreed population. Variances and covariances were estimated by 2-trait REML analyses using a Generalized Expectation-Maximization algorithm applied to multibreed populations. Multiple estimates of additive genetic, nonadditive genetic, and environmental variances from 2-trait analyses were averaged to yield a single variance estimate for each trait and effect. Heritabilities were moderate for all traits in Holstein, other, and Holstein x other crossbred groups. Interbreed interactibilities (ratio of nonadditive genetic to phenotypic variances) were all near zero. Multibreed additive, nonadditive, and total genetic trends were estimated using the complete dataset (56,277 cows). Upward trends between 1990 and 2000 existed for all traits, genetic effects, and breed groups, except for 305-d ME protein yield in 1/4 Holstein, indicating that Chilean dairy producers were successful in choosing progressively better semen and sires from imported and local sources over time.     

Incidence and seasonal variation of Listeria species in bulk tank goat's milk

Four hundred and fifty raw goat's milk samples obtained from the bulk tanks of 39 goat farms were analyzed for Listeria spp. over a 1-year period. Modified versions of the U.S. Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) and Food and Drug Administration (FDA) protocols were used for recovery of Listeria. Overall, 35 (7.8%) samples yielded Listeria spp. with Listeria monocytogenes identified in 17 of the 35 (3.8%) Listeria-positive samples. Listeria innocua was detected in 26 (5.8%) samples. Eight milk samples contained both L. monocytogenes and L. innocua. Milk samples from 18 of the 39 (46.2%) farms were positive for Listeria at least once during this 1-year study. The modified USDA-FSIS method, which used Listeria repair broth rather than University of Vermont (UVM) broth for primary enrichment followed by a 4-h nonselective incubation period, yielded more Listeria-positive samples (77.1%) than the FDA method (51.4%). All L. monocytogenes isolates belonged to serotypes 1 (62.6%) or 4 (37.4%). Moreover, five different Listeria ribotypes were identified from 34 selected L. monocytogenes isolates, 2 of which were deemed to be of clinical importance. Listeria isolation rates were markedly higher during winter (14.3%) and spring (10.4%) as compared to autumn (5.3%) and summer (0.9%) with these trends similar to those previously reported for cow's milk.     

PCBs and selected organochlorine compounds in Italian mountain air: the influence of altitude and forest ecosystem type

Passive air samplers (polyurethane foam disks) were deployed on an altitudinal transect in the rural Italian Alps to investigate the potential influence of forest cover on air concentrations. Samplers were exposed overtwo periods, each of several weeks, either in clearings or in forests. In the first period, there was high leaf coverage (high leaf area index, LAI); in the second, the LAI was low after the autumnal leaf fall. PCBs sequestered in the PUF generally declined with altitude, for example, in the clearings PCBs-28, 52, 90/101, 118, and 138, all showed statistically significant declines (p < 0.05). The mass of HCB sequestered increased with altitude, evidence of cold condensation. Ratios of the forest:clearing concentrations were calculated; this ratio expresses the filtering ability of forests to deplete air concentrations compared to the adjacent clearings. During the high LAI sampling period, these depletion factors ranged between 0.93 and 0.54 and were inversely correlated with temperature-corrected log K0A. This relationship was notobserved during the low LAI sampling period. The depletion factors were normalized using the LAI to give a density independent depletion factor (DIDF). The slopes of the correlations with K0A were comparable for broadleaf or coniferous forests at different altitudes, suggesting that leaf surfaces determine the exchanges with air. Broadleaf forests at 1000 and 1400 m showed similar behavior, while a conifer forest at 1800 m gave depletion factors which were higher by about a factor of 2. It is suggested that DIDF can be used in regional environmental fate models to estimate the contribution of forests to contaminant fate.     

Polychlorinated biphenyls (PCBs) in air and seawater of the Atlantic Ocean: sources, trends and processes

Air and seawater samples were collected on board the RV Polarstern during a cruise from Bremerhaven, Germany to Cape Town, South Africa from October-November 2005. Broad latitudinal trends were observed with the lowest sigma27PCB air concentration (approximately 10 pg m(-3)) in the South Atlantic and the highest (approximately 1000 pg m(-3)) off the west coast of Africa. Sigma(ICES)PCBs ranged from 3.7 to 220 pg m(-3) in air samples and from 0.071 to 1.7 pg L(-1) in the dissolved phase seawater samples. Comparison with other data from cruises in the Atlantic Ocean since 1990 indicate little change in air concentrations over the remote open ocean. The relationship of gas-phase partial pressure with temperature was examined using the Clausius-Clapeyron equation; significant temperature dependencies were found for all PCBs over the South Atlantic, indicative of close air-water coupling. There was no temperature dependence for atmospheric PCBs overthe North Atlantic, where concentrations were controlled by advection of contaminated air masses. Due to large uncertainties in the Henry's Law Constant (HLC), fugacity fractions and air-water exchange fluxes were estimated using different HLCs reported in the literature. These suggest that conditions are close to air-water equilibrium for most of the ocean, but net deposition is dominating over volatilization in parts of the transect. Generally, the tri- and tetrachlorinated homologues dominated the total flux (> 70%). Total PCB fluxes (28, 52, 118, 138, and 153) ranged from -7 to 0.02 ng m(-2) day(-1).