Utilization of bis-MPA Dendrimers for the Calibration of Ion Mobility Collision Cross Section Calculations.

Ion mobility-mass spectrometry (IM-MS) has become increasingly popular with the rapid expansion of available techniques and instrumentation. To enable accuracy, standardization, and repeatability of IM-MS measurements, the community requires reliable and well-defined reference materials for calibration and tuning of the equipment. To address this need, synthetic dendrimers of high chemical and structural purity were tested on three ion mobility platforms as potential calibrants. First, synthesized dendrimers were characterized by drift tube ion mobility (DTIMS), using an Agilent 6560 IM-qTOF-MS to assess their drift tube collision cross section (DTCCS) values. Then, assessment of obtained CCS values on trapped ion mobility (TIMS) and traveling wave ion mobility (TWIMS) ion mobility platforms were compared to those found by DTIMS. Across all three systems, dendrimers were found to have high potential for m/z and ion mobility calibration in the CCS range of 160-1700 Å2. To further validate their use as calibrants, drift tube calculated CCS values for dendrimers were utilized to calibrate calculations of CCS for known standards including Agilent Tuning mix, the CCS Major mix from Waters, and SPLASH LIPIDOMIX. Additionally, structures of sodiated dendrimers were computated along with theoretical CCS values which showed good agreement with the experimental CCS values. On the basis of the results presented, we recommend the use of dendrimers as alternatives and/or complementary compounds to commonly used calibrants for ion mobility platforms.

Main sources controlling atmospheric burdens of persistent organic pollutants on a national scale.

National long-term monitoring programs on persistent organic pollutants (POPs) in background air have traditionally relied on active air sampling techniques. Due to limited spatial coverage of active air samplers, questions remain (i) whether active air sampler monitoring sites are representative for atmospheric burdens within the larger geographical area targeted by the monitoring programs, and thus (ii) if the main sources affecting POPs in background air across a nation are understood. The main objective of this study was to explore the utility of spatial and temporal trends in concert with multiple modelling approaches to understand the main sources affecting polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in background air across a nation. For this purpose, a comprehensive campaign was carried out in summer 2016, measuring POPs in background air across Norway using passive air sampling. Results were compared to a similar campaign in 2006 to assess possible changes over one decade. We furthermore used the Global EMEP Multi-media Modeling System (GLEMOS) and the Flexible Particle dispersion model (FLEXPART) to predict and evaluate the relative importance of primary emissions, secondary emissions, long-range atmospheric transport (LRAT) and national emissions in controlling atmospheric burdens of PCB-153 on a national scale. The concentrations in air of both PCBs and most of the targeted OCPs were generally low, with the exception of hexachlorobenzene (HCB). A limited spatial variability for all POPs in this study, together with predictions by both models, suggest that LRAT dominates atmospheric burdens across Norway. Model predictions by the GLEMOS model, as well as measured isomeric ratios, further suggest that LRAT of some POPs are dictated by secondary emissions. Our results illustrate the utility of combining observations and mechanistic modelling approaches to help identify the main factors affecting atmospheric burdens of POPs across a nation, which, in turn, may be used to inform both national monitoring and control strategies.

Soil pollution at a major West African E-waste recycling site: Contamination pathways and implications for potential mitigation strategies.

Organic contaminants (polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and chlorinated paraffins (CPs)) and heavy metals and metalloids (Ag, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, Zn) were analysed in surface soil samples from the Agbogbloshie e-waste processing and dumping site in Accra (Ghana). In order to identify which of the pollutants are likely to be linked specifically to handling of e-waste, samples were also collected from the Kingtom general waste site in Freetown (Sierra Leone). The results were compared using principal component analyses (PCA). PBDE congeners found in technical octa-BDE mixtures, highly chlorinated PCBs and several heavy metals (Cu, Pb, Ni, Cd, Ag and Hg) showed elevated concentrations in the soils that are likely due to contamination by e-waste. PCAs associated those compounds with pyrogenic PAHs, suggesting that burning of e-waste, a common practice to isolate valuable metals, may cause this contamination. Moreover, other contamination pathways, especially incorporation of waste fragments into the soil, also appeared to play an important role in determining concentrations of some of the pollutants in the soil. Concentrations of several of these compounds were extremely high (especially PBDEs, heavy metals and SCCPs) and in some cases exceeded action guideline levels for soil. This indicates that exposure to these contaminants via the soil alone is potentially harmful to the recyclers and their families living on waste sites. Many organic contaminants and other exposure pathways such as inhalation are not yet included in such guidelines but may also be significant, given that deposition from the air following waste burning was identified as a major pollutant source.

An alternative approach to risk rank chemicals on the threat they pose to the aquatic environment.

This work presents a new and unbiased method of risk ranking chemicals based on the threat they pose to the aquatic environment. The study ranked 12 metals, 23 pesticides, 11 other persistent organic pollutants (POPs), 13 pharmaceuticals, 10 surfactants and similar compounds and 2 nanoparticles (total of 71) of concern against one another by comparing their median UK river water and median ecotoxicity effect concentrations. To complement this, by giving an assessment on potential wildlife impacts, risk ranking was also carried out by comparing the lowest 10th percentile of the effects data with the highest 90th percentile of the exposure data. In other words, risk was pared down to just toxicity versus exposure. Further modifications included incorporating bioconcentration factors, using only recent water measurements and excluding either lethal or sub-lethal effects. The top ten chemicals, based on the medians, which emerged as having the highest risk to organisms in UK surface waters using all the ecotoxicity data were copper, aluminium, zinc, ethinylestradiol (EE2), linear alkylbenzene sulfonate (LAS), triclosan, manganese, iron, methomyl and chlorpyrifos. By way of contrast, using current UK environmental quality standards as the comparator to median UK river water concentrations would have selected 6 different chemicals in the top ten. This approach revealed big differences in relative risk; for example, zinc presented a million times greater risk then metoprolol and LAS 550 times greater risk than nanosilver. With the exception of EE2, most pharmaceuticals were ranked as having a relatively low risk.

Environmental monitoring of organo-halogenated contaminants (OHCs) in surface soils from Pakistan.

Extensive monitoring of organo-halogenated contaminants (OHCs) from surface soils of different land-use types from Pakistan was carried out during 2010. The concentrations (ng g(-1); dry weight) and profiles clearly indicated the dominance of ∑DDT contaminants followed by the ∑HCHs, ∑30PCBs, chlordanes, and ∑10PBDEs in descending order. Concerning the spatial patterns of occurrence, industrial soils exhibited relatively higher concentration of DDTs, heavy PCBs, and PBDEs (noticeably BDE-47 and -99 congeners), while the urban soils were characterized by high total PCBs (with relatively higher levels of light PCBs), following the agricultural soils. Compared to available criterion guidelines, the current results suggested that 10% of soil samples from industrial sites exhibited slightly higher levels (>50 ng g(-1)) of DDTs. The ∑TEQ levels for mono-ortho DL-PCBs ranged from 0.7 to 5.65 (1.9) pgTEQg(-1) dw in all the studied samples and PCB-118 contributed significantly towards the total calculated TEQs. The results of this study will contribute to the environmental management of OHCs contaminated areas of Pakistan.

Using risk-ranking of metals to identify which poses the greatest threat to freshwater organisms in the UK.

Freshwater aquatic organisms face the challenge of being exposed to a multitude of chemicals discharged by the human population. The objective of this study was to rank metals according to the threat they pose to aquatic organisms. This will contribute to a wider Chemical Strategy for freshwater which will risk-rank all chemicals based on their potential risk to wildlife in a UK setting. The method involved comparing information on ecotoxicological thresholds with measured concentrations in rivers. The bioconcentration factor was also considered as a ranking method. The metals; Ag, Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn, were analysed using this approach. Triclosan and lindane were used as comparative organic pollutants. Using a range of ranking techniques, Cu, Al and Zn came top of the list of concern, with Cu coming first.

Organo-halogenated contaminants (OHCs) in the sediments from the Soan River, Pakistan: OHCs(adsorbed TOC) burial flux, status and risk assessment.

In this study, regression analysis revealed that TOC is the principal factor in controlling the fate of organo-halogenated contaminants (OHCs: PCBs, PBDEs, OCPs) in Soan River, Pakistan. The OHCs(adsorbed TOC) burial flux (OHCs(adsorbed TOC)Bf; mg/cm(2)·yr) was calculated in the following ranges: ∑PCBs (0.07-0.31), ∑PBDEs (0.005-0.029), ∑HCHs (0.015-0.046) and ∑DDTs (0.007-0.039). Apart from OHCs(adsorbed TOC)Bf, the levels of OHCs were in the following order: PCBs>DDTs>PBDEs>HCH>Chlordane>HCB. PBDEs and PCB congener patterns showed following order respectively: BDE-149>-153>-18>-138>-44 and PCB-149>-153>-18>-138>-44. DDT isomers and metabolites' pattern were p,p'-DDT>p,p'-DDD>p,p'-DDE>o,p'-DDT>o,p'-DDD>o,p'-DDE and HCHs were ß-HCH>α-HCH>γ-HCH>δ-HCH. PBDE composition had similarities to penta-BDE and DE-71 mixtures and PCBs with commercial products Aroclor-1254 and -1260. (DDE+DDD)/∑DDTs and p,p'-DDT/p,p'-DDE suggested the recent input of DDTs in sediments while α/γ-HCH indicated past usage of lindane and technical mixtures. Risk assessment suggested that Soan River and its tributaries are potentially at risk against most of the OHCs.

Relationship between the concentrations of dissolved organic matter and polycyclic aromatic hydrocarbons in a typical U.K. upland stream.

Concentrations of total and freely dissolved polycyclic aromatic hydrocarbons (PAHs) and dissolved organic carbon (DOC) were measured in water collected during four sampling events at five sites from the River Wyre. The sites are typical of streams draining upland organically rich soils in northwest U.K. Freely dissolved PAHs were separated from those associated with DOC using a flocculation method. The sum of concentrations of the total and freely dissolved PAHs analyzed ranged from 2.71 to 18.9 ng/L and 2.61 to 16.8 ng/L, respectively. PAH concentrations and PAH fluxes derived from concentrations and water flow rates generally increased downstream, the trend in the latter being more pronounced. The concentration of individual PAHs containing five or more aromatic rings was found to be strongly correlated to the DOC concentration (p < 0.0001), suggesting common terrestrial sources and hydrological pathways. In contrast, no significant relationships were observed between concentrations of PAHs with four or fewer rings and DOC. Concentrations of PAHs with more than four rings showed similar seasonal variation as DOC concentration (peaking in the late summer), while variation in two or three ring PAHs was out of phase with DOC (peaking in the winter). As the PAH-DOC relationship appeared partly dependent on the molecular weight of the PAHs, a linear regression function that included an interaction between this variable and DOC concentration was used to model PAH concentrations over a 2 year period to estimate annual fluxes. The relationship identified between PAH concentrations and DOC should help to enhance interpretation of PAH monitoring data that are currently sparse both spatially and temporally and, thus, enable more robust assessments of the potential risks of these environmental pollutants to sensitive aquatic organisms and human water supplies.

Alterations in the infrared spectral signature of avian feathers reflect potential chemical exposure: a pilot study comparing two sites in Pakistan.

Chemical contamination of ecosystems is a global issue with evidence that pollutants impact on living organisms in a harmful fashion. Developing sensor approaches that would allow the derivation of biomarkers or signatures of effect in target sentinel organisms and monitor environmental chemical contamination in a high throughput manner is of utmost importance. As biomolecules absorb infrared (IR), signature vibrational spectra related to structure and function can be derived. In light of this, we tested the notion that IR spectra of bird feathers might reflect environmental chemical contaminant exposure patterns. Feathers were collected from monospecific heronries of cattle egret based in two independent locations (Trimu vs. Mailsi) in the Punjab province of Pakistan; these sites were found to differ in their chemical contamination patterns. Feather samples were chemically analyzed for polychlorinated biphenyls, polybrominated diphenyl ethers, organochlorines and heavy metals. Attenuated total reflection Fourier-transform IR (ATR-FTIR) spectroscopy was employed to derive a spectral signature of individual feathers. Resultant IR spectra were then subjected to canonical correspondence analysis (CAA) to determine whether feather spectral signatures correlate to chemical exposure. Additionally, we explored if principal component analysis (PCA) and linear discriminant analysis (LDA) could be applied to distinguish site-specific differences; linear discriminant function (LDF) was also applied to classify sites. The sampled feathers varied in their chemical exposure patterns depending on whether they were sourced from one site associated with heavy metal exposure or the other which suggested high organic pollutant exposures. CCA of chemical and spectral data showed a correlation between spectral signatures and chemical exposure. PCA-LDA readily distinguished feathers from the two different sites. Discriminating alterations were identified and these were associated with protein and lipid regions in IR spectra. Additionally, LDF showed that the classification rate of spectral categories correlated well with the two chemical exposure patterns (93.6% for Trimu feathers and 91.77% for Mailsi feathers). This pilot study suggests that IR spectra derived from feathers reflect background chemical exposure and points to a novel monitoring tool for contamination.

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.

Polybrominated diphenyl ethers (PBDEs) in feathers of colonial water-bird species from Pakistan.

Feathers of two colonial water-birds species (Bubulcus ibis, Egretta garzetta) from four heronries in the Punjab province, Pakistan were analysed for 28 Polybrominated Diphenyl Ethers (PBDEs) congeners. Median concentrations of ∑PBDEs were 2.41 and 1.91 ng/g in little and cattle egrets. PBDE-47, -100, -138, -153 were abundant and detected in >70% of feather samples in both species. Species-specific differences based on dietary preferences indicated higher concentration of PBDE-47, -66, -75, -100, -153, -154, and -183 in fish eating little egret. BDE-47 and -100 were more frequent in little egrets and BDE-99 was more dominant in cattle egret which feed on terrestrial habitat. Higher ∑hexa- and hepta-BDEs congeners showed larger concentrations in feathers from heronries close to water bodies which receive urban and industrial effluents whereas lower-brominated congeners (BDE-47-BDE-100) dominated in rural/agricultural regions. Hazard quotients (HQs) indicated that measured ∑PBDEs pose no risk to egret population.

Ubiquitous net volatilization of polycyclic aromatic hydrocarbons from soils and parameters influencing their soil-air partitioning.

Soils are a major reservoir of organic pollutants, and soil-air partitioning and exchange are key processes controlling the regional fate of pollutants. Here, we report and discuss the soil concentrations of polycyclic aromatic hydrocarbons (PAHs), their soil fugacities, the soil-air partition coefficients (K(SA)) and soil-air gradients for rural and semirural soils, in background areas of N-NE Spain and N-NW England. Different sampling campaigns were carried out to assess seasonal variability and differences between sampling sites. K(SA) values were dependent on soil temperature and soil organic quantity and type. Soil fugacities of phenanthrene and its alkyl homologues were 1-2 orders of magnitude higher than their ambient air fugacities for all sampling sites and periods. The soil to air fugacity ratio was correlated with soil temperature and soil redox potential. Similar trends for other PAHs were found but with lower fugacity ratios. The ubiquitous source of PAHs from background soils to the atmosphere found in all temperate regions in different seasons provides an indirect evidence of potential in situ generation of two to four ring PAHs and their alkyl homologues in the surface soil. We discuss this hypothetical biogenic source and other potential processes that could drive the high soil to air fugacity ratios of some PAHs.

Factors influencing the soil-air partitioning and the strength of soils as a secondary source of polychlorinated biphenyls to the atmosphere.

Soils are a major reservoir of persistent organic pollutants, and soil-air partitioning and exchange are key processes controlling the atmospheric concentrations and regional fate of pollutants. Here, we report and discuss the concentrations of polychlorinated biphenyls (PCBs) in soils, their measured fugacities in soil, the soil-air partition coefficients (K(SA)) and soil-air fugacity gradients in rural background areas of N-NE Spain and N-NW England. Four sampling campaigns were carried out to assess seasonal and daily variability and differences between sampling sites. K(SA) values were significantly dependent on soil temperature and soil organic matter quantity, and to a minor extent organic matter type. All the PCB congeners in the soil are close to equilibrium with the atmosphere at rural Ebro sites, but soil fugacities tend to be higher than ambient air fugacities in early and late summer, consistent with the influence of temperature on soil-air partitioning. Therefore, during warm periods, soils increment their strength as secondary sources to the atmosphere. The mixture of PCBs found in the atmosphere is clearly strongly influenced by the mixture of PCBs which escape from soil, with significant correlations between them (R(2) ranging between 0.35 and 0.74 and p-level <0.001 for the Ebro sampling sites). Conversely, the close-to-equilibrium to net sink status of rural UK sites, suggest a close coupling of air and soil concentrations, but it is not possible to elucidate the importance of these soils as secondary sources yet, and presumably there are still significant primary sources to the regional/global environment.

Intrinsic human elimination half-lives of polychlorinated biphenyls derived from the temporal evolution of cross-sectional biomonitoring data from the United Kingdom.

BACKGROUND: Most empirical estimates of human elimination kinetics for persistent chemicals reflect apparent elimination half-lives that represent the aggregated effect of intrinsic elimination, ongoing exposure, and changes in body weight. However, estimates of intrinsic elimination at background levels are required for risk assessments for the general population. OBJECTIVE: To estimate intrinsic human elimination half-lives at background levels for nine polychlorinated biphenyl (PCB) congeners, we used a novel approach based on population data. METHODS: We used a population pharmacokinetic model to interpret two sets of congener-specific cross-sectional age-concentration biomonitoring data of PCB concentrations measured in lipid and blood samples that were collected from 229 individuals in 1990 and 2003. Our method is novel because it exploits information about changes in concentration in the human population along two dimensions: age and calendar time. RESULTS: Our approach extracted information about both elimination kinetics and exposure trends from biomonitoring data. The longest intrinsic human elimination half-lives estimated in this study are 15.5 years for PCB-170, 14.4 years for PCB-153, and 11.5 years for PCB-180. CONCLUSIONS: Our results are further evidence that a maximum intrinsic elimination half-life for persistent chemicals such as PCBs exists and is approximately 10-15 years. A clear conceptual distinction between apparent and intrinsic half-lives is required to reduce the uncertainty in elimination half-lives of persistent chemicals. The method presented here estimates intrinsic elimination half-lives and the exposure trends of persistent pollutants using cross-sectional data available from a large and growing number of biomonitoring programs.

Estimation of the source strength of polybrominated diphenyl ethers based on their diel variability in air in Zurich, Switzerland.

Diel (24-h) concentration variations of polybrominated diphenyl ethers (PBDEs) in air were measured in the center of Zurich, Switzerland, and on Uetliberg, a hill about 5 km from the city center. Air samples were collected simultaneously at both sites over 4 h time periods for 3 consecutive days during a stable high pressure system in August 2007. Higher PBDE concentrations in the city compared to the Uetliberg site indicate that Zurich is a likely source of PBDEs to the atmosphere. A multimedia mass balance model was used to (i) explain the diel cycling pattern of PBDE concentrations observed at both sites in terms of dominant processes and (ii) estimate emission rates of PBDEs from the city to the atmosphere. We estimate that Zurich emits 0.4, 6.2, 1.6, and 0.4 kg year(-1) of the PBDE congeners 28, 47, 99, and 100, respectively. On a per-capita basis, these estimates are within the range or somewhat above those obtained in other studies using approaches based on emission factors (EF) and PBDE production, usage, and disposal data, or concentration measurements. The present approach complements emission estimates based on the EF approach and can also be applied to source areas where EFs and PBDE material flows are poorly characterized or unknown, such as electronic waste processing plants.

Field calibration of polyurethane foam disk passive air samplers for PBDEs.

A field study was performed to derive uptake rates of airborne polybrominated diphenyl ethers (PBDEs) to polyurethane foam (PUF) disk passive air samplers (PAS) and to investigate the influence of deployment location and device design. Data are presented on the gas-particle partitioning of PBDEs, since atmospheric phase distribution was considered to be a variable which could affect sampler performance. Uptake rates for these compounds were similar to those derived previously for other classes of persistent organic pollutants (POPs) (approximately 2-6 m(3)/day), with rates higher for the higher brominated species. Whilst other compound classes (e.g. polychlorinated biphenyls) are predominantly present in the air in the gas phase, heavier PBDEs have an association with particulates in the atmosphere at ambient temperatures. In this study, the PUF disk PAS therefore sampled PBDEs present in the gas phase and on fine aerosols with a similar sampling efficiency to those which are predominantly gas phase compounds. Compounds which are exclusively on particles are sampled less efficiently. A comparison of the three most commonly used PUF deployment configurations, used by different research groups, indicated little difference in uptake rates. The ranges of derived air concentrations for BDE-47, -99, and -183 between three sampler designs were 7.5-9.8, 7.4-12.4, and 4.7-6.6 pg/m(3), respectively. This suggests the robustness of this sampler in comparisons between regional and global campaigns where these three designs are employed.

Air-boreal forest transfer and processing of polychlorinated biphenyls.

The exchange of persistent organic pollutants (POPs) between different compartments of a typical mature boreal forest was investigated. The study focused on fluxes of polychlorinated biphenyls (PCBs) between the atmosphere, vegetation and soil, and within the soil to assess whether this type of forest acts as a final sink or temporary repository for POPs. The study, at a Swedish site, suggested total PCB air-to-forest floor fluxes of 1.4 microg m(-2) year(-1). Much of this could be attributed to compounds bound to particles that may originate from needle surfaces. Degradation half-lives in soil between 6.4 and 30 years for tetra- to hepta-PCBs were obtained using a mass balance approach. This field data-based method derived degradation rates of POPs in background soils, although it may have underestimated the persistence of the heavy PCB congeners. Compounds reaching the forest soil appear to be stored efficiently and degraded slowly. As a first approximation, applying the findings from this study site to boreal forests on a global scale suggests that 2-21% (depending on the congener) of the estimated global atmospheric emission deposits to these ecosystems.

Use of depuration compounds in passive air samplers: results from active sampling-supported field deployment, potential uses, and recommendations.

Depuration compounds (DCs) are added to passive air samplers (PAS) prior to deployment to account for the wind-dependency of the sampling rate for gas-phase compounds. This correction is particularly useful for providing comparable data for samplers that are deployed in different environments and subject to different meteorological conditions such as wind speeds. Two types of PAS--the polyurethane foam (PUF) disk sampler and semipermeable membrane devices (SPMDs)--were deployed at eight heights on a 100 m tower to test whether the DC approach could yield air concentrations profiles for PCBs and organochlorine pesticides and account for the wind speed gradient with height. Average wind speeds ranged from 0.3 to 4.5 m s(-1) over the 40 day deployment, increasing with height Two low volume active air samples (AAS), one collected at 25 m and one at 73 m over the 40 day deployment showed no significant concentration differences for target compounds. As expected, the target compounds taken up by PAS reflected the wind profile with height This wind-dependency of the PAS was also reflected in the results of the DCs. A correction based on the DC approach successfully accounted for the effect of wind on PAS sampling rates, yielding a profile consistent with the AAS. Interestingly, in terms of absolute air concentrations, there were differences between the AAS and PAS-derived values for some target compounds. These were attributed to different sampling characteristics of the two approaches that may have resulted in slightly different air masses being sampled. Based on the results of this study, guidelines are presented for the use of DCs and for the calibration of PAS using AAS.

Measuring and modeling short-term variability of PCBs in air and characterization of urban source strength in Zurich, Switzerland.

Diel (24-h) variations of concentrations of polychlorinated biphenyls (PCBs) in air are reported at two sites in Zurich, Switzerland, a city surrounded by hills. One site was located in the valley near the city center and the other site was on a hill called Uetliberg, 411 m higher and about 5 km distant from the city center site. Air samples were collected simultaneously at both sites over 4-h time periods for 3 consecutive days under stable meteorological conditions during a high pressure system in August 2007. PCB concentrations at the city site were markedly higher than those at Uetliberg, indicating that the city site is influenced by urban sources of PCBs. Concentrations measured at both sites show a clear diel cycle but have opposite phases: in the city concentrations were lower during the day and higher at night, while at Uetliberg concentrations were higher during the day and lower at night. These observations are explained and interpreted using a multimedia mass balance model that includes a stable night-time inversion layer that formed over the city but below the hilltop site. At Uetliberg the concentration of PCBs is consistent with background levels and the diel concentration pattern can be explained bytemperature-mediated air-surface exchange and the influence of nearby woodland canopies. The diel pattern and concentrations in the city are attributable to volatilization from urban sources. We have developed a new method to estimate the strength of the urban PCB source using the model scenarios for the two sampling sites. Emission estimates derived from this method are in good agreement with earlier estimates derived from PCB production, consumption, and usage estimates. This study demonstrates the potential for estimating the strength of diffuse, regional sources of persistent organic pollutants (POPs) using a combined measurement and modeling approach. Such studies can provide important information to derive regional and national POPs emission inventories as required under the Stockholm Convention, and to quantify the effectiveness of actions to reduce POP emissions.

Persistent organic pollutants in boreal and montane soil profiles: distribution, evidence of processes and implications for global cycling.

The distribution of persistent organic pollutants (POPs) within background soil profiles was investigated in boreal (Norway) and montane (Italy) areas. The typical build-up of slowly mineralizing humus layers, containing high amounts of soil organic matter (SOM) makes soils of such ecosystems an important global sink for POPs released to the environment. The study focused on evidence and implications of processes influencing the fate of POPs in soil. POP deposition, interaction with SOM, volatilization, leaching, degradation, and bioturbation are discussed. Results indicate that the less volatile POPs such as hexa- and higher chlorinated biphenyls (CBs) or polybrominated diphenyl ethers are very stable in soil profiles, undergoing little translocation or (re)transfer to other environmental compartments. In contrast, more volatile compounds (e.g., tri- and tetra-CBs) were found in soil layers below those formed from vegetation ever directly exposed to airborne POPs. This suggests the occurrence of downward transport and hence limited surface-air exchange of more volatile POPs as they are removed from the top layers. Such soils may therefore be able to retain higher amounts of these compounds than just addressed by the capacity of their surface layers.