Are there other persistent organic pollutants? A challenge for environmental chemists

The past 5 years have seen some major successes in terms of global measurement and regulation of persistent, bioaccumulative, and toxic (PB&T) chemicals and persistent organic pollutants (POPs). The Stockholm Convention, a global agreement on POPs, came into force in 2004. There has been a major expansion of measurements and risk assessments of new chemical contaminants in the global environment, particularly brominated diphenyl ethers and perfluorinated alkyl acids. However, the list of chemicals measured represents only a small fraction of the approximately 30,000 chemicals widely used in commerce (>1 t/y). The vast majority of existing and new chemical substances in commerce are not monitored in environmental media. Assessment and screening of thousands of existing chemicals in commerce in the United States, Europe, and Canada have yielded lists of potentially persistent and bioaccumulative chemicals. Here we review recent screening and categorization studies of chemicals in commerce and address the question of whether there is now sufficient information to permit a broader array of chemicals to be determined in environmental matrices. For example, Environment Canada's recent categorization of the Domestic (existing) Substances list, using a wide array of quantitative structure activity relationships for PB&T characteristics, has identified about 5.5% of 11,317 substances as meeting P & B criteria. Using data from the Environment Canada categorization, we have listed, for discussion purposes, 30 chemicals with high predicted bioconcentration and low rate of biodegradation and 28 with long range atmospheric transport potential based on predicted atmospheric oxidation half-lives >2 days and log air-water partition coefficients > or =5 and < or =1. These chemicals are a diverse group including halogenated organics, cyclic siloxanes, and substituted aromatics. Some of these chemicals and their transformation products may be candidates for future environmental monitoring. However, to improve these predictions data on emissions from end use are needed to refine environmental fate predictions, and analytical methods may need to be developed.     

Has the burden and distribution of PCBs and PBDEs changed in European background soils between 1998 and 2008? Implications for sources and processes

Background soils were collected from 70 locations on a latitudinal transect in the United Kingdom and Norway in 2008, ten years after they had first been sampled in 1998. The soils were analyzed for polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCs), to see whether there had been any change in the loadings or distributions of these persistent organic pollutants (POPs). The same transect has also been used to sample air between the mid-1990s and the present, so the air and soil spatial and temporal trends provide information on air-soil transfers, source-receptor relationships, long-range atmospheric transport (LRAT), and recycling phenomena. Comparisons of the 2008 and 1998 data sets show a general decline for PBDEs in surface soil, and a smaller averaged net decline of PCBs. Changes between the years were observed for total POP concentrations in soil and also for correlations with site and sample characteristics assumed to affect those concentrations. POP concentrations were correlated to distance and strength of possible sources, a relationship that became weaker in the 2008 data. Fractionation, a commonly discussed process for the global cycling of POPs was also lost in the 2008 data. As in 1998, soil organic matter content continues to have a strong influence on the loadings of POPs in surface soils, but changes in the PCB loads were noted. These factors indicate an approach to air-surface soil equilibrium and a lessening of the influence of primary sources on POP concentrations in soil between 1998 and 2008.     

Sediment record and atmospheric deposition of brominated flame retardants and organochlorine compounds in Lake Thun, Switzerland: lessons from the past and evaluation of the present

Chronology of brominated fame retardants (BFRs), a class of currentlywidely used chemicals, was compared to the respective historical profiles of legacy organochlorine compounds in three dated sediment cores from a prealpine lake (Lake Thun, Switzerland). Concentrations of polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs) started to increase in the 1980s-1990s. In the more recent sediment layers, PBDEs still had steady or increasing concentrations, whereas for HBCDs one sediment core revealed a decreasing trend. In contrast to the contemporary BFRs, concentrations of legacy organochlorines, such as polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), and dichlorodiphenyl trichloroethane (DDT), peaked in deeper sediment layers deposited some decades ago. Measurements of atmospheric deposition and evaluation of wastewater discharges pointtoward deposition on the lake surface as a relevant input pathway and wastewater as a minor source of POPs in Lake Thun. The effect of the environmental awareness and the regulations taken in the 1970s to reduce environmental pollution of organochlorines is well reflected in the analyzed sediment cores. The sediment burden closely follows estimated time trends of consumption and emission of PCBs and DDT. The current residues in sediment of BFRs are still lower than the historical peak levels of organochlorines. However, current atmospheric deposition of BFRs is similar to deposition of PCBs. Considering the high amount of BFRs presently stocked in the anthroposphere in flame proofed materials, further measures to reduce emissions during BFRs life cycle are recommended to prevent high environmental pollution as it occurred for the organochlorine compounds.     

Spatial and temporal trends of POPs in Norwegian and UK background air: implications for global cycling

Data are presented for PCBs and HCB measured by passive air samplers (SPMDs) along a latitudinal transect from the south of the UK to the north of Norway during 1998-2000. This work is part of an ongoing air sampling campaign in which data were previously gathered for 1994-1996. Comparisons of the masses of chemicals sequestered by the SPMDs during these different time intervals are used to investigate spatial and temporal trends. Results are discussed in the context of sources, long-range atmospheric transport, fractionation/cold condensation, and global clearance processes controlling ambient levels of POPs. Spatial trends show a decrease in absolute sequestered amounts of PCBs with increasing latitude i.e., with increasing distance from the source area. However, relative sequestered amounts of the homologue groups (expressed as a ratio to penta-PCB) show a clear latitudinal trend, with the relative contribution of the lighter congeners increasing with increasing latitude, providing evidence of latitudinal fractionation. Absolute amounts of HCB increase with latitude, suggesting this compound is undergoing cold condensation. Sequestered amounts of PCBs generally decreased between the two sampling periods by a factor 2-5 over 4 years, suggesting half-lives on the order of 1.7-4 years. The relative rates of decline (1998-2000 data as a percentage of the 1994-1996 data) were compared for different congeners and latitudes. No clear latitudinal trends were found, with all sites/congeners showing a similar marked decline over time to ca. 30% of the former value. We discuss the interpretation of these observations and conclude they imply that the underlying trends of current ambient levels of PCBs in European background air are still largely controlled by primary emissions, rather than recycling/secondary emissions from the major environmental repositories such as soils or water bodies.     

The influence of vertical sorbed phase transport on the fate of organic chemicals in surface soils

Gaseous exchange between surface soil and the atmosphere is an important process in the environmental fate of many chemicals. It was hypothesized that this process is influenced by vertical transport of chemicals sorbed to soil particles. Vertical sorbed phase transport in surface soils occurs by many processes such as bioturbation, cryoturbation, and erosion into cracks formed by soil drying. The solution of the advection/diffusion equation proposed by Jury et al. to describe organic chemical fate in a uniformly contaminated surface soil was modified to include vertical sorbed phase transport This process was modeled using a sorbed phase diffusion coefficient, the value of which was derived from soil carbon mass balances in the literature. The effective diffusivity of the chemical in a typical soil was greater in the modified model than in the model without sorbed phase transport for compounds with log K(OW) > 2 and log K(OA) > 6. Within this chemical partitioning space, the rate of volatilization from the surface soil was larger in the modified model than in the original model by up to a factor of 65. The volatilization rate was insensitive to the value of the sorbed phase diffusion coefficient throughout much of this chemical partitioning space, indicating that the surface soil layer was essentially well-mixed and that the mass transfer coefficient was determined by diffusion through the atmospheric boundary layer only. When this process was included in a non-steady-state regional multimedia chemical fate model running with a generic emissions scenario to air, the predicted soil concentrations increased by upto a factor of 25,whilethe air concentrations decreased by as much as a factor of approximately 3. Vertical sorbed phase transport in the soil thus has a major impact on predicted air and soil concentrations, the state of equilibrium, and the direction and magnitude of the chemical flux between air and soil. It is a key process influencing the environmental fate of persistent organic pollutants (POPs).     

PCBs and OCPs in sediment cores from the Lower St. Lawrence Estuary, Canada: evidence of fluvial inputs and time lag in delivery to coring sites

Three sediment cores were collected along the longitudinal axis of the Laurentian Trough in the Lower St. Lawrence Estuary (LSLE) and an additional one at the junction of the Estuary and the Gulf of St. Lawrence. After core-slicing, each sediment layer was analyzed for polychlorinated biphenyls (PCBs) and some organochlorine pesticides (OCPs) including p,p'-dichlorodiphenyltrichloroethane (DDT) and its metabolites, hexachlorobenzene (HCB) and Mirex. 210Pb activity was also measured in these sediments, which allowed us to confirm that these cores were too much affected by the overall impact of surface mixing to be dated. Nevertheless, POP sedimentary profiles in cores from the LSLE upstream stations showed well-defined subsurface peak concentrations. Apparently, the peak inputs of POPs to these sediment cores had occurred after the years of maximum sales and production of these chemicals in North America, suggesting a time lag in the delivery of POPs to the LSLE sediments. Concentrations of POPs in the LSLE surface sediments as well as POP inventories in sediment cores decreased in the seaward direction, confirming that the head of the LSLE acts as a sink for sediments and associated constituents. Surface concentrations of sigmaPCBs, sigmaDDTs, and HCB in the most upstream core were on average similar to those reported in two fluvial lakes of the St. Lawrence River but were between 12 and 39 times lower than those from Lake Ontario. For Mirex, the surface concentration in that core was 5 and 130 times lower than the average values found in the fluvial lakes and Lake Ontario, respectively. Differences between Lake Ontario sediment cores and the most upstream core from the LSLE were much smaller on the basis of POP inventories than surface concentrations of POPs, but were still important. The total burdens of POPs in LSLE sediments below the 200 m isobath were 8704 kg for sigmaPCBs, 1825 kg for sigmaDDTs, 319 kg for HCB, and 27.5 kg for Mirex. These values represent between 1% and 10% of the total burdens of these POPs in Lake Ontario sediments. The estimated contribution of POPs by direct atmospheric deposition into the water column area of the LSLE represented at most 30% of the total sediment burdens of POPs in the LSLE, illustrating the importance of fluvial inputs.     

Bottlenose dolphins as indicators of persistent organic pollutants in the western North Atlantic Ocean and northern Gulf of Mexico

Persistent organic pollutants (POPs) including legacy POPs (PCBs, chlordanes, mirex, DDTs, HCB, and dieldrin) and polybrominated diphenyl ether (PBDE) flame retardants were determined in 300 blubber biopsy samples from coastal and near shore/estuarine male bottlenose dolphins (Tursiops truncatus) sampled along the U.S. East and Gulf of Mexico coasts and Bermuda. Samples were from 14 locations including urban and rural estuaries and near a Superfund site (Brunswick, Georgia) contaminated with the PCB formulation Aroclor 1268. All classes of legacy POPs in estuarine stocks varied significantly (p < 0.05) among sampling locations. POP profiles in blubber varied by location with the most characteristic profile observed in bottlenose dolphins sampled near the Brunswick and Sapelo estuaries along the Georgia coast which differed significantly (p < 0.001) from other sites. Here and in Sapelo, PCB congeners from Aroclor 1268 dominated indicating widespread food web contamination by this PCB mixture. PCB 153, which is associated with non-Aroclor 1268 PCB formulations, correlated significantly to human population indicating contamination from a general urban PCB source. Factors influencing regional differences of other POPs were less clear and warrant further study. This work puts into geographical context POP contamination in dolphins to help prioritize efforts examining health effects from POP exposure in bottlenose dolphins.     

Modeling semivolatile organic aerosol mass emissions from combustion systems

Experimental measurements of gas-particle partitioning and organic aerosol mass in diluted diesel and wood combustion exhaust are interpreted using a two-component absorptive-partitioning model. The model parameters are determined by fitting the experimental data. The changes in partitioning with dilution of both wood smoke and diesel exhaust can be described by two lumped compounds in roughly equal abundance with effective saturation concentrations of approximately 1600 microg m(-3) and approximately 20 microg m(-3). The model is used to investigate gas-particle partitioning of emissions across a wide range of atmospheric conditions. Under the highly dilute conditions found in the atmosphere, the partitioning of the emissions is strongly influenced by the ambient temperature and the background organic aerosol concentration. The model predicts large changes in primary organic aerosol mass with varying atmospheric conditions, indicating that it is not possible to specify a single value for the organic aerosol emissions. Since atmospheric conditions vary in both space and time, air quality models need to treat primary organic aerosol emissions as semivolatile. Dilution samplers provide useful information about organic aerosol emissions; however, the measurements can be biased relative to atmospheric conditions and constraining predictions of absorptive-partitioning models requires emissions data across the entire range of atmospherically relevant concentrations.     

Contribution of volatile precursor substances to the flux of perfluorooctanoate to the Arctic

Perfluorooctanoate (PFO) has recently been found in remote ocean water and Arctic samples, despite not having been used in significant quantities in remote areas. Two main scenarios for the contamination of the Arctic by PFO have been suggested: (i) direct emissions of PFO and oceanic transport to the Arctic and (ii) emissions of volatile precursor substances that are transported and oxidized in the atmosphere to form PFO, which is subsequently deposited to the Arctic. Focusing on the atmospheric transport pathway, we compare the importance of fluorotelomer alcohols (FTOHs) and perfluorooctyl sulfonamidoethanols (FOSEs) for PFO deposition to the Arctic. Using a global scale multispecies mass balance model, we simultaneously calculate the transport, degradation, partitioning, and deposition of precursor substances, intermediate degradation products, and PFO and compare model results to field measurements. Prior to 2002, the modeled deposition fluxes of PFO to the Arctic originating from FOSEs and FTOHs are of a similar magnitude, and total estimated deposition compares well with deposition measurements for Arctic ice cores. However, the model underpredicts recent measurements of FOSEs in Arctic air, indicating that there may be additional emissions not taken into account. Using Monte Carlo calculations we quantify the uncertainties in our model results and identify that emission estimates, degradation yields, and degradation rate constants are the most influential input parameters controlling the estimated deposition of PFO to the Arctic.     

Estimation of the production, consumption, and atmospheric emissions of pentabrominated diphenyl ether in Europe between 1970 and 2000

A European consumption and atmospheric emissions inventory for pentabrominated diphenyl ethers (PeBDEs) is derived for the period 1970-2000. This time frame has seen a rise in the widespread usage of PeBDE, followed by more recent restrictions/bans. It is estimated that a total of 3000-5000 t of PeBDEs was produced in Europe during this period, with a further 9000-10,000 t imported in finished articles. The main uses for PeBDE are to flame retard consumer products as well as in packaging and solid elastomers. Their major stocks are predicted to be in polyurethane (flexible) foams with up to 30% in cars; more than 10% in furniture foam; and the rest in textiles, building material, packaging, and solid applications. Release of PeBDEs from treated products into environmental media are estimated with a focus on atmospheric inputs via volatilization from their use in cars, upholstered furniture, textiles, television sets, personal computers, and other recycled material. Different emission factors are used to derive different emission scenarios. A peak in atmospheric emissions of between 22 and 31 t of BDE-47 is estimated to have occurred around 1997, with a decline of approximately 20% in 2000. Comparisons with long-term environmental monitoring data revealed that the time trends of human blood and milk concentrations follow similar patterns to the generated emissions, while sediment core levels increase more slowly, probably because they respond to a mix of atmospheric and catchment inputs. The emissions data derived here can be used in a spatially and temporally resolved form as input data for multi-media environmental fate modeling.     

PAH molecular diagnostic ratios applied to atmospheric sources: a critical evaluation using two decades of source inventory and air concentration data from the UK

Molecular diagnostic ratios (MDRs)-the ratios of defined pairs of individual compounds-have been widely used as markers of different source categories of polycyclic aromatic hydrocarbons (PAHs). However, it is well-known that variations in combustion conditions and environmental degradation processes can cause substantial variability in the emission and degradation of individual compounds, potentially undermining the application of MDRs as reliable source apportionment tools. The United Kingdom produces a national inventory of atmospheric emissions of PAHs, and has an ambient air monitoring program at a range of rural, semirural, urban, and industrial sites. The inventory and the monitoring data are available over the past 20 years (1990-2010), a time frame that has seen known changes in combustion type and source. Here we assess 5 MDRs that have been used in the literature as source markers. We examine the spatial and temporal variability in the ratios and consider whether they are responsive to known differences in source strength and types between sites (on rural-urban gradients) and to underlying changes in national emissions since 1990. We conclude that the use of these 5 MDRs produces contradictory results and that they do not respond to known differences (in time and space) in atmospheric emission sources. For example, at a site near a motorway and far from other evident emission sources, the use of MDRs suggests "non-traffic" emissions. The ANT/(ANT + PHE) ratio is strongly seasonal at some sites; it is the most susceptible MDR to atmospheric processes, so these results illustrate how weathering in the environment will undermine the effectiveness of MDRs as markers of source(s). We conclude that PAH MDRs can exhibit spatial and temporal differences, but they are not valid markers of known differences in source categories and type. Atmospheric sources of PAHs in the UK are probably not dominated by any single clear and strong source type, so the mixture of PAHs in air is quickly "blended" away from the influence of the few major point sources which exist and further weathered in the environment by atmospheric reactions and selective loss processes.     

Modeling persistent organic pollutant (POP) partitioning between tree bark and air and its application to spatial monitoring of atmospheric POPs in mainland China

A mathematical model describing the bark/air partitioning of persistent organic pollutants (POPs) was established taking into consideration the accumulation processes of POPs from air into bark and compound-, species-, and site-specific air-to-bark accumulation factors. It allows the assessment of the concentrations of atmospheric POPs based on those recorded in tree bark. The spatial distribution of atmospheric POPs including 18 polycyclic aromatic hydrocarbons (Sigma18PAHs), 5 organic chlorinated pesticides (Sigma5OCPs), 10 polychlorinated biphenyls (Sigma10PCBs), and 17 brominated flame retardants (Sigma17BFRs) were investigated by analyzing 163 bark samples from 68 sites across mainland China. The atmospheric POPs were estimated to be 4.1-399 ng/m3 air, and 11.3-553, 4.5-130, and 0.9-624 pg/m3 air with geometric means of 71 ng/m3 air, and 99,26, and 25 pg/m3 airfor Sigma18PAHs, Sigma5OCPs, Sigma10PCBs, and Sigma17BFRs, respectively, based on those recorded in the tree barks of 5.1-1770, 0.05-12.9, 0.21-21.6, and 0.02-48.3 ng/g bark on dry weight basis, with geometric means of 295, 1.47, 3.12, and 2.79 ng/g bark. These results generally indicated that contamination by atmospheric POPs is more serious in eastern and mid China than that in western China.     

Bioaccumulation potential of persistent organic chemicals in humans

A model was used to explore the influence of physicalchemical properties on the potential of organic chemicals to bioaccumulate in humans. ACC-HUMAN, a model of organic chemical bioaccumulation through the agricultural and aquatic food chains to humans, was linked to a level I unit world model of chemical fate in the physical environment and parametrized for conditions in southern Sweden. Hypothetical, fully persistent chemicals with varying physical-chemical properties were distributed in the environment, and their bioaccumulation to humans was calculated. The results were evaluated using the environmental bioaccumulation potential (EBAP), defined as the quotient of the chemical quantity in a human divided by the quantity of chemical in the whole environment. Since the latter is closely related to emissions, EBAP is potentially a more useful tool for comparative risk assessment of chemicals than currently used medium-specific measures such as the fish-water bioaccumulation factor. A high environmental bioaccumulation potential, defined as > 10% of the maximum EBAP, was found for chemicals with 2 < log KOW < 11 and 6 < log KOA < 12. While these chemical partitioning properties clearly influenced bioaccumulation at each trophic level, these effects tended to equalize over the food web. The fact that the transfer from the environment as a whole to humans was quite uniform over a large chemical partitioning space suggests that these partitioning properties are relatively unimportant determinants of human exposure compared to other factors such as the substance's persistence in the environment and in the food web.     

Persistent organic pollutants in the equatorial atmosphere over the open Indian Ocean

Twelve air samples collected over the Indian Ocean by a high volume air sampler between August 2004 and August 2005 were analyzed for selected polychlorinated biphenyl (PCB) congeners and organochlorine pesticides. The region of the Indian Ocean and adjacent countries is likely to be acting as a source of selected POPs to the global environment. Data were compared with those reported for the last 30 years to examine historical trends of selected persistent organic pollutants (POPs) over the Indian Ocean. Compound concentrations were influenced by the proximity to land and air mass origins. Higher concentrations of atmospheric sigmaPCBs (50-114 pg m(-3)) were found on the remote islands of Chagos Archipelago and Gan, Maldives, and in the proximity of Jakarta, Indonesia, and Singapore. Military activities and unregulated waste combustion were identified as possible sources for atmospheric PCB contaminations at the more remote areas. The highest concentrations of organochlorine pesticides were found adjacent to the coastline of Sumatra and Singapore, where sigmaDDTs (dichlorodiphenyltrichloroethane) and sigmaHCHs (hexacyclohexanes) were as high as 30 and 100 pg m(-3), respectively. A comparison study for the last 30 years over six regions of the Indian Ocean showed that the concentrations of organochlorine pesticides have declined significantly, by a magnitude of two, since the mid 1970s, but were highest at the beginning of the 1990s. The time trend of PCB contamination in the atmosphere over the Indian Ocean is less apparent. The decline of atmospheric POPs over the Indian Ocean may be due to international regulation of the use of these compounds.     

Source elucidation of perfluorinated carboxylic acids in remote alpine lake sediment cores

Atmospheric deposition of perfluorinated carboxylic acids (PFCAs) in remote regions might arise from transport and degradation of precursors (e.g., perfluorooctanesulfonyl fluoride (PFOSF)-based products or fluorotelomer alcohols (FTOHs)) or direct transport (e.g., PFCAs in the vapor phase or on particles). To probe the dominant atmospheric source of PFCAs, historical trends in environmental FTOH, PFOSF, and direct perfluorooctanoate (PFOA) emissions were compared to the flux of PFCAs (sum of C7-C13 perfluoroalkyl chain lengths) and PFCA isomer signatures in dated sediment cores from two remote alpine lakes in the Canadian Rocky Mountains. Contributions from PFOSF-based substances and direct transport of PFOA were ruled to be minimal because no branched isomers were detected in either core and temporal trends for direct emission of PFOA did not match the flux measurements. PFCA flux to Lake Opabin sediment agreed well with reported FTOH emissions, including a peak in mid-2003 and subsequent decline. In Lake Oesa, agreement between PFCA flux and FTOH emissions was also good up to 2004, but a subsequent decline was only detected for some PFCA congeners through 2008, while others continued to increase. Overall, both the isomer profiles and the temporal trend data suggest that FTOH oxidation is the dominant atmospheric source of PFCAs to these high alpine lakes. The efficacy of recent industry phase-out initiatives was difficult to assess due to the divergent temporal trends in samples after 2003; thus, continued monitoring is suggested at remote sites such as these.     

Oceanic biogeochemical controls on global dynamics of persistent organic pollutants

Understanding and quantifying the global dynamics and sinks of persistent organic pollutants (POPs) is important to assess their environmental impact and fate. Air-surface exchange processes, where temperature plays a central role in controlling volatilization and deposition, are of key importance in controlling global POP dynamics. The present study is an assessment of the role of oceanic biogeochemical processes, notably phytoplankton uptake and vertical fluxes of particles, on the global dynamics of POPs. Field measurements of atmospheric polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs), and furans (PCDFs) are combined with remote sensing estimations of oceanic temperature, wind speed, and chlorophyll, to model the interactions between air-water exchange, phytoplankton uptake, and export of organic matter and POPs out of the mixed surface ocean layer. Deposition is enhanced in the mid-high latitudes and is driven by sinking marine particulate matter, rather than by a cold condensation effect. However, the relative contribution of the biological pump is a function of the physical-chemical properties of POPs. It is concluded that oceanic biogeochemical processes play a critical role in controlling the global dynamics and the ultimate sink of POPs.     

Persistent organic pollutants in British Columbia grizzly bears: consequence of divergent diets

Nitrogen and carbon stable isotope signatures in growing hair reveal that while some British Columbia grizzly bears (Ursus arctos horribilis) rely entirely on terrestrial foods, others switch in late summer to returning Pacific salmon (Oncorynchus spp.). Implications for persistent organic pollutant (POP) concentrations and patterns measured in the two feeding groups of grizzly bears were profound. While the bears consuming a higher proportion of terrestrial vegetation ("interior" grizzlies) exhibited POP patterns dominated bythe more volatile organochlorine (OC) pesticides and the heavier polybrominated diphenyl ethers (PBDEs: e.g., BDE-209), the bears consuming salmon were dominated by the more bioaccumulative POPs (e.g., DDT, chlordanes, and BDE-47). The ocean-salmon-bear pathway appeared to preferentially select for those contaminants with intermediate partitioning strength from water into lipid (log Kow approximately 6.5). This pattern reflects an optimum contaminant log Kow range for atmospheric transport, deposition into the marine environment, uptake into marine biota, accumulation through the food web, and retention in the bear tissues. We estimate that salmon deliver 70% of all OC pesticides, up to 85% of the lower brominated PBDE congeners, and 90% of PCBs found in salmon-eating grizzly bears, thereby inextricably linking these terrestrial predators to contaminants from the North Pacific Ocean.     

Temporal trends and controlling factors for polychlorinated biphenyls in the UK atmosphere (1991-2008)

Long-term air monitoring data sets are needed for persistent organic pollutants (POPs), to assess the effectiveness of source abatement measures and the factors controlling ambient levels. The Toxic Organic Micro-Pollutants (TOMPS) program in the United Kingdom started in 1991, generating a data set for polychlorinated biphenyls (PCBs). The history and volumes of production, usage, and subsequent restrictions on PCBs in the UK are well-characterized relative to many countries, providing a valuable case study on the effectiveness of controls and the factors influencing ambient levels and trends of these "model POPs". PCB air concentrations (congeners PCB 28, 52, 90/101, 118, 138, 153, and 180) from six rural and urban monitoring sites are presented. Most show a statistically significant decrease in PCBs levels over time, consistent with estimates of emissions, helping to validate emissions inventories. Times for a 50% decline in concentrations (sometimes called clearance rates) averaged 4.7 ± 1.6 years for all congeners at all sites. The trends at different sites and for different congeners were not statistically different from each other. Concentration differences between sites are correlated with local population density (i.e., the degree of urbanization), which supports approaches to modeling of primary emissions on the national and regional scale. The data set indicates that ambient levels and underlying trends of PCBs continue to reflect the controlling influence of diffuse primary sources from the ongoing stock of PCBs in urban environments. Production and use restrictions came into force in the UK over 40 years ago; trends since monitoring began in the early 1990s should be seen as part of a continuing decline in ambient levels since that time.