Crispin J. Halsall

Contaminants in the Canadian Arctic: 5 years of progress in understanding sources, occurrence and pathways

Recent studies of contaminants under the Canadian Northern Contaminants Program (NCP) have substantially enhanced our understanding of the pathways by which contaminants enter Canadas Arctic and move through terrestrial and marine ecosystems there. Building on a previous review (Barrie et al., Arctic contaminants: sources, occurrence and pathways. Sci Total Environ 1992:1-74), we highlight new knowledge developed under the NCP on the sources, occurrence and pathways of contaminants (organochlorines, Hg, Pb and Cd, PAHs, artificial radionuclides). Starting from the global scale, we examine emission histories and sources for selected contaminants focussing especially on the organochlorines. Physical and chemical properties, transport processes in the environment (e.g. winds, currents, partitioning), and models are then used to identify, understand and illustrate the connection between the contaminant sources in industrial and agricultural regions to the south and the eventual arrival of contaminants in remote regions of the Arctic. Within the Arctic, we examine how contaminants impinge on marine and terrestrial pathways and how they are subsequently either removed to sinks or remain where they can enter the biosphere. As a way to focus this synthesis on key concerns of northern residents, a number of special topics are examined including: a mass balance for HCH and toxaphene (CHBs) in the Arctic Ocean; a comparison of PCB sources within Canadas Arctic (Dew Line Sites) with PCBs imported through long-range transport; an evaluation of concerns posed by three priority metals--Hg, Pb and Cd; an evaluation of the risks from artificial radionuclides in the ocean; a review of what is known about new-generation pesticides that are replacing the organochlorines; and a comparison of natural vs. anthropogenic sources of PAH in the Arctic. The research and syntheses provide compelling evidence for close connectivity between the global emission of contaminants from industrial and agricultural activities and the Arctic. For semi-volatile compounds that partition strongly into cold water (e.g. HCH) we have seen an inevitable loading of Arctic aquatic reservoirs. Drastic HCH emission reductions have been rapidly followed by reduced atmospheric burdens with the result that the major reservoir and transport agent has become the ocean. In the Arctic, it will take decades for the upper ocean to clear itself of HCH. For compounds that partition strongly onto particles, and for which the soil reservoir is most important (e.g. PCBs), we have seen a delay in their arrival in the Arctic and some fractionation toward more volatile compounds (e.g. lower-chlorinated PCBs). Despite banning the production of PCB in the 1970s, and despite decreases of PCBs in environmental compartments in temperate regions, the Arctic presently shows little evidence of reduced PCB loadings. We anticipate a delay in PCB reductions in the Arctic and environmental lifetimes measured in decades. Although artificial radionuclides have caused great concern due to their direct disposal on Russian Shelves, they are found to pose little threat to Canadian waters and, indeed, much of the radionuclide inventory can be explained as remnant global fallout, which was sharply curtailed in the 1960s, and waste emissions released under license by the European reprocessing plants. Although Cd poses a human dietary concern both for terrestrial and marine mammals, we find little evidence that Cd in marine systems has been impacted by human activities. There is evidence of contaminant Pb in the Arctic, but loadings appear presently to be decreasing due to source controls (e.g. removal of Pb from gasoline) in Europe and North America. Of the metals, Hg provokes the greatest concern; loadings appear to be increasing in the Arctic due to global human activities, but such loadings are not evenly distributed nor are the pathways by which they enter and move within the Arctic well understood.

Polychlorinated biphenyls (PCBs) in the British environment: Sinks, sources and temporal trends

This paper estimates the present UK environmental loading of polychlorinated biphenyls (PCBs). Of the estimated approximately 40,000 t SigmaPCB sold in the UK since 1954, only an estimated 1% (400 t) are now present in the UK environment. Comparisons of estimated production and current environmental loadings of congeners 28, 52, 101, 138, 153 and 180 suggest that PCB persistence broadly increases with increasing chlorination. Those PCBs that are not now present in the UK environment are considered to have been destroyed--by natural or anthropogenic mechanisms, to be still in use, to reside in landfills or to have undergone atmospheric and/or pelagic transport from the UK. The dramatic fall in PCB levels in archived UK soils and vegetation between the mid-1960s and the present is evidence that the latter mechanism is the most important and that a significant proportion of PCBs released into the UK environment in the 1960s have subsequently undergone environmental transport away from the UK. The bulk (93.1%) of the estimated contemporary UK environmental burden of SigmaPCBs is associated with soils, with the rest found in seawater (3.5%) and marine sediments (2.1%). Freshwater sediments, vegetation, humans and sewage sludge combined account for 1.4% of the present burden, whilst PCB loadings in air and freshwater are insignificant. Although consideration of individual congeners does not reveal any major deviations from the relative partitioning of Sigma PCBs, the importance of sinks other than soils is enhanced for individual congeners, particularly 138 and 180. In particular, around 2% of the total UK burden of congener 180 is present in humans, implying that biodata as a whole may constitute an important sink for the higher chlorinated congeners. The contemporary flux of SigmaPCBs to the UK surface is estimated at 19 t yr(-1), compared with an estimated annual flux to the atmosphere of 44-46 t. This implies that the major sources of PCBs to the UK atmosphere have been identified and that there is currently a net loss of these compounds from the UK. These sources are: volatilisation from soils (88.1%), leaks from large capacitors (8.5%), the production of refuse-derived fuel (RDF) (2.2%), leaks from transformers (0.6%), the recovery of contaminated scrap metal (0.5%) and volatilisation from sewage sludge-amended land (0.2%). Interestingly, whilst large excesses of estimated annual fluxes to the atmosphere over deposition fluxes for individual congeners exist for congeners 28, 52 and 101, estimates of fluxes in both directions across the soil-atmosphere interface agree closely for congeners 138, 153 and 180. This suggests that lower chlorinated congeners are more susceptible to both long-range environmental transport beyond the UK and to atmospheric degradation. Retrospective analysis of dated sediment cores, vegetation and soils indicates that environmental transport from North America and continental Europe introduced PCBs into the British environment well before the onset of their commercial production in the UK in 1954. Since that time, the input of PCBs to the UK environment has essentially reflected temporal trends in UK use. After peaking in the 1960s they declined rapidly through the 1970s following restrictions on PCB use. Recent evidence, however, is that the rate of decrease has diminished and that further significant reductions in fresh environmental input will take some time to occur. Such reductions will be especially slow for humans and other biota with long life-spans. This stems partly from cross-generational transfer from parents to offspring and also because the persistence of PCBs in biota means that present body burdens will reflect past as well as current exposure.

Polycyclic aromatic hydrocarbons in U.K. urban air

Polycyclic aromatic hydrocarbon (PAH) data for the first two years (January 1991-December 1992) of a national urban air monitoring scheme in the U.K. are presented. Urban sample sites were operated in the cities of London, Manchester, and Cardiff and in the light industrial town of Stevenage. Both the particulate and vapor phases of 15 PAHs were sampled using high-volume air samplers at roof-top level (approximately 25 m). London, the largest urban center, had the highest annual mean [Sigma]PAH concentrations of 166 ng/m[sup 3] in 1991. Phenanthrene and fluorene dominated the total PAH at each site and were present predominantly in the vapor phase throughout the year. The heavier PAHs (MW > 250) were present on the collected particulate and showed a distinct seasonal variation (winter > summer). PAH profiles were similar at each site, even though the conurbations were different in size, indicating sources common to each site. Specific atmospheric contamination episodes, associated with particular meteorological conditions, were identified throughout the 2-year period. NO[sub 2] concentrations were obtained for the Manchester site for 1991. Weak correlations (P [le] 0.05) were found to exist between elevated NO[sub 2] concentrations and particulate-benzo[a]pyrene and [Sigma]PAH concentrations. 40 refs., 4 figs., 3 tabs.

Multi-year observations of organohalogen pesticides in the Arctic atmosphere

Atmospheric measurements of organohalogen pesticides (OCs) have been made in both the Canadian and Russian Arctic. A full quality-controlled database of weekly samples is now available for the years 1992–94. Hexachlorobenzene (HCB) and the hexachlorocyclohexanes (HCHs) were the most predominant compounds in the atmosphere, followed by the chlordanes and endosulfan. Evidence of a seasonality in air concentrations was apparent particularly for the pesticide metabolites, compounds such as oxychlordane, heptachlor epoxide and dieldrin showing a significant positive correlation with temperature (p<0.01). An exception to this was p, p′-DDE which showed elevated levels during the winter. Large spatial differences in mean annual concentrations of most OCs were not evident; however, spatial differences were apparent in α/γ-HCH ratios between the high Arctic site of Alert and the Yukon site of Tagish. The influence of both the European sector and the regional effect of the Arctic Ocean on the high Arctic probably accounted for this difference. A decline in the trans-chlordane/cis-chlordane ratio compared to studies during the 1980s may indicate a more weathered source of chlordane to be present in the Arctic by the mid-1990s. Slopes generated from plots of partial pressure (ln P) versus 1/T for selected compounds were considerably less steep than those derived from temperate studies. It is inferred here that long-range transport has a large influence on contaminant levels in the arctic atmosphere.

Atmospheric organochlorine pesticides in the western Canadian Arctic : evidence of transpacific transport

Concentrations of hexachlorocyclohexanes (HCHs), chlordane, and dichlorodiphenyltrichloroethane (DDT) were measured in ambient air samples on a weekly basis between December 1992 and January 1995 at Tagish Yukon, Canada. In winter, unusually high air concentrations of HCHs, DDT, and chlordanes at Tagish were predominantly influenced by transpacific long-range atmospheric transport from eastern Asia that generally occurred within 5 days. HCH and heptachlor epoxide concentrations were correlated with the time that air spent over eastern Asia prior to arrival at Tagish. Chlordane and DDT, which also increase with transpacific transport, do not show a correlation with the time the upwind airshed included Asia as the composition of these pesticides in the atmosphere is affected by differences in usage patterns, application methods, variable composition of parent pesticides and metabolites in the soil, and rates of volatilization. Air masses originating from North America had the highest concentrations of HCHs and chlordanes when the 5-day upwind airshed included the western United States. Concentrations of HCHs may also be influenced by lindane usage in Canada.

PCBs in U.K. Urban Air

Atmospheric PCB concentrations were routinely monitored every other week over a 2-year period (1991-1992) in four U.K. urban centers. These sites included the major cities of London, Manchester, and Cardiff and the light industrial town of Stevenage, located ∼60 km north of London. Eight major congeners were measured at all of the sites with a further 22 included at the Manchester and Cardiff sites. Atmospheric ΣPCB (eight congeners) concentrations ranged from 112 to 3850 pg m -3 at the four sites, with the mean in London the highest. Clear seasonal cycling was observed in the urban atmospheres with summer concentrations being higher than winter for all congeners. The relative amplitude change in this cycling pattern was greatest for the higher chlorinated congeners ; summer :winter ratios were 2.0, 1.7, 3.2, and 5.0 for congeners 28, 52, 153, and 180, respectively. A simple box model developed by Pankow (1) was applied to the surface area of Manchester to predict the vapor-phase concentration of the tetra-CB, congener 52. Desorption from various compartments such as vegetation, soil, and urban dust were considered. The release from building air was also estimated. The predicted gas-phase concentrations show the seasonal cycling observed in the ambient air concentrations. The model fit for the three considered compartments (veg/soil/dust) was lower than the observed city air concentrations. The model data reflect background rural concentrations more accurately, perhaps suggesting that elevated concentrations of the vapor-phase component in city air are derived from building air and/or a series of point sources. Even today, many years after restrictions of PCB manufacture and use were introduced in the U.K., cities continue to act as sources of airborne PCBs to surrounding areas.

Monoterpene emissions from soil in a Sitka spruce forest

A dynamic soil enclosure was used to characterise monoterpene emissions from 3 soil depths within a Picea sitchensis (Sitka spruce) forest. In addition, a dynamic branch enclosure was used to provide comparative emissions data from foliage. In all cases, limonene and α-pinene dominated monoterpene soil emissions, whilst camphene, β-pinene and myrcene were also present in significant quantities. α-Phellandrene, 3-carene and α-terpinene were occasionally emitted in quantifiable amounts whilst cymene and cineole, although tentatively identified, were always non-quantifiable. Total daily mean monoterpene emission rates, normalised to 30°C, varied considerably between soil depths from 33.6 μg m−2 h−1 (range 28.3–38.4) for undisturbed soil, to 13.0 μg m−2 h−1 (8.97–16.4) with uppermost layer removed, to 199 μg m−2 h−1 (157–216) with partially decayed layer removed, suggesting that the surface needle litter was the most likely source of soil emissions to the atmosphere. Relative monoterpene ratios did not vary significantly between layers. Foliar monoterpenes exhibited a similar emission profile to soils with the exceptions of camphene and 3-carene whose contributions decreased and increased, respectively. Emission rates from foliage, normalised to 30°C were found to have a daily mean of 625 ng g−1 dw h−1 (299–1360). On a land area basis however, total soil emissions were demonstrated to be relatively insignificant to total emissions from the forest ecosystem.

Atmospheric deposition of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) in two UK cities

As part of the Toxic Organic Micropollutants Survey (TOMPS) bulk (wet and dry) deposition fluxes of PAHs and PCDD/Fs for 1991/92 are presented for the UK cities of Manchester and Cardiff. The median annual flux for ΣPAH was 5.2 and 4.1 μg/m2/day for Manchester and Cardiff respectively, with an annual ΣPCDD/F flux of 1.4 and 1.0 ng/m2/d. These fluxes were comparable with deposition fluxes reported from other studies and add to the growing international database on deposition measurements. Fluxes were highly variable at both urban sites, with PAH and PCDD/F ranging over an order of magnitude within one season. Seasonality was most apparent for the PCDD/Fs, which showed higher fluxes during the winter months. Simple air to surface transfer velocities (cm/s) were calculated using air concentrations from the same sampling programme.

Contamination of Environmental Samples Prepared for PCB Analysis

Archived air-dried soil that had been collected, stored, and sealed in 1914, before the commercial manufacture of PCBs, together with wet freshly sampled ancient peat, which contained little or no PCBs, were exposed to contemporary air in a laboratory. Measurable increases in the concentration of PCBs, particularly the low molecular weight congeners, were detectable after exposure for as little as a few hours. Concentrations after a few days exposure to laboratory air were similar to those measured in contemporary field surface soils (-20-30 pg of CPCB kgl). Laboratory air concentrations ranged between 4.7 and 8.2 ng of CPCB m-3 during the period of exposure, markedly higher than routinely detected in outdoor U.K. urban air. The calculated average net dry deposition flux from air-soil in the laboratory over 25 days was 5 pg of CPCB m-2 day1. Indoor air concentrations might be expected to be higher than those routinely measured outside, exacerbating the potential problems of sample contamination. Extreme caution is needed in the preparation and handling of samples which contain inherently low concentrations of PCBs and before ascribing the presence of these compounds in certain samples to ‘natural production’ mechanisms.

Temperature dependence of PCBs in the UK atmosphere.

A thermodynamic approach was taken to assess the state of equilibrium between air and the Earth’s surface for PCBs at a variety of sites located in urban and rural areas. The Clausius–Clapeyron equation was applied to atmospheric PCB data, relating PCB partial vapour pressure (ln P) to inverse temperature (1/K); essentially representing the temperature controlled transition between condensed phases and the atmospheric gas phase. The slopes of the resulting plots ranged from −3100 to −8272 for a range of congeners at two city sites, significantly steeper than those generated at two rural locations, where there was little or no correlation between ln P and temperature. It was inferred that advection and variable meteorological conditions mask any localised, temperature dependent, air–surface exchange at these rural locations when weekly or two weekly integrated samples were taken. At a third rural site, close to Lancaster University, an intensive highly time-resolved sampling regime, carried out during very stable meteorological conditions resulted in highly correlated plots (r2>0.6), with slopes ranging from −7151 to −14 148 for different congeners. By reducing meteorological variables in this manner localised temperature controlled air–surface exchange became evident. Enthalpies of phase change generated from the temperature coefficients were similar to literature values for the enthalpy of vapourisation and the enthalpy of phase change from octanol to air. This suggests that, under these stable conditions, equilibrium was achieved as a function of either vapour pressure (P°L) or the octanol–air partition coefficient (KOA).