A comparison of mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) for monitoring chlorinated trace organic contaminants in Hong Kong coastal waters.

A comparison of mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) was carried out at five sites, representing a gradient of contaminant concentrations, in Hong Kong coastal waters. Mussels, originally collected from a “clean” location, were deployed along with SPMDs at each site for 30 days. Analyses for chlorinated pesticides and polychlorinated biphenyls (PCBs) indicated that SPMDs have potential as monitoring tools, and to some extent can overcome the problems associated with mussels, such as natural variability, differing age, sex, and physical condition. However, in most cases, SPMDs failed to rank the sites in the same order as mussels in terms of contaminant concentrations. Nonetheless, in localities where mussels cannot survive – as shown at Kwun Tong in the present experiment – SPMDs may be valuable in providing an indication of potentially bio-available lipophilic pollutants.     

A comparison of polycyclic aromatic hydrocarbon and petroleum hydrocarbon uptake by mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) in Hong Kong coastal waters

The ability of mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) to accumulate polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbons (PHCs) from five sites in Hong Kong's coastal waters was compared. Mussels consistently had higher levels of contaminants, but their utility was limited at one highly polluted site due to mortality. Mussels and SPMDs ranked sites differently in terms of individual contaminant levels. Although SPMDs overcome many of the disadvantages of using living organisms to measure contaminants in marine waters, they cannot be used as "mimics" due to different PAH and PHC accumulation patterns.     

Monitoring of organic pollutants in marine environment by semipermeable membrane devices and mussels: accumulation and biochemical responses

This study involves the monitoring of organic pollutants using transplanted mussels (Mytilus galloprovincialis) as bioindicator organisms and semipermeable membrane devices (SPMDs) as passive samplers. Mussels and SPMDs were deployed to marinas, shipyards and shipbreaking yards on the coastal area of Turkey and retrieved after 60 days. Polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and organochlorine pesticide (OCP) compounds were analysed with high-resolution GC-MS. Total PAH concentrations in SPMDs and mussels ranged from 200 to 4740 ng g sampler^?1 and from 7.0 to 1130 ng g^?1 in wet weight (ww). PCB and OCP concentrations in SPMDs changed between 0.04–200 and 4.0–26 ng g sampler^?1, respectively. The highest PCB (190 ng g^?1 ww) and OCP (200 ng g^?1 ww) concentrations in mussels were measured at shipyard stations. A strong correlation was observed between the PAH and PCB concentrations in SPMDs and mussels. Enzyme assays (acetylcholinesterase, ethoxyresorufin-O-deethylase, glutathione S-transferase, glutathion reductase and carboxylesterase activities) were performed as biomarkers to reveal the effects of pollution on the mussels. There was no clear relationship found between the enzyme levels and the pollutant concentrations in mussels. Integrated biomarker responses were calculated to interpret the overall effect of pollutants.

     

Use of semipermeable membrane devices (SPMDs)

Triolein-containing semipermeable membrane devices (SPMDs) were employed as passive samplers to provide data on the bioavailable fraction of organic, waterborne, organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs) in streams flowing through a highly polluted industrial area of Bitterfeld in Saxony-Anhalt, Germany. The contamination of the region with organic pollutants originates in wastewater effluents from the chemical industry, from over one-hundred years of lignite exploitation, and from chemical waste dumps. The main objective was to characterise time-integrated levels of dissolved contaminants, to use them for identification of spatial trends of contamination, and their relationship to potential pollution sources. SPMDs were deployed for 43 days in the summer of 1998 at four sampling sites. The total concentration of pollutants at sampling sites was found to range from a low of 0.8 microgram/SPMD to 25 micrograms/SPMD for PAHs, and from 0.4 microgram/SPMD to 22 micrograms/SPMD for OCPs, respectively. None of the selected PCB congeners was present at quantifiable levels at any sampling site. A point source of water pollution with OCPs and PAHs was identified in the river system considering the total contaminant concentrations and the distribution of individual compounds accumulated by SPMDs at different sampling sites. SPMD-data was also used to estimate average ambient water concentrations of the contaminants at each field site and compared with concentrations measured in bulk water extracts. The truly dissolved or bioavailable portion of contaminants at different sampling sites ranged from 4% to 86% for the PAHs, and from 8% to 18% for the OCPs included in the estimation. The fraction of individual compounds found in the freely dissolved form can be attributed to the range of their hydrophobicity. In comparison with liquid/liquid extraction of water samples, the SPMD method is more suitable for an assessment of the background concentrations of hydrophobic organic contaminants because of substantially lower method quantification limits. Moreover, contaminant residues sequestered by the SPMDs represent an estimation of the dissolved or readily bioavailable concentration of hydrophobic contaminants in water, which is not provided by most analytical approaches.     

Lipid-Filled semipermeable membrane devices and mussels as samplers of organochlorine compounds in lake water

Semipermeable membrane sampling devices (SPMDs) and caged lake mussels (Anodonta piscinalis) were simultaneously deployed at four lake watercourse sites in Central Finland four weeks in August 1992. This study was part of the regular annual monitoring of the organochlorine compounds (OCC) in pulp-mill recipient watercourses of Finland with bivalves. Chlorohydrocarbons (CHCs), chlorophenol compounds (PCPs), chloroanisoles (PCAs) and chloroveratroles (PCVs) were analyzed from lipid extract of mussels and from the synthetic triolein lipid of the SPMDs. Hexane-diethyl ether (9:1, v/v) dialysis using polyethylene membrane was applied in dean up of the SPMD lipids and, for comparison, to six sets of the mussel fat. Dialysis recovered CHCs but not PCPs from the mussel fat. CHCs, PCPs, PCAs and PCVs were all recovered in dialysis of the SPMD lipid. Handling of SPMDs in the transport and deployment operations caused significant OCC contamination for the blank SPMDs. Similar trends were revealed in the OCC profiles for mussels ans SPMDs. An exception was the lack of PCPs appearing in SPMDs that did appear in mussels and in a complementary manner the appearance of the PCAs and PCVs in SPMDs.     

Tissue distribution of polychlorinated naphthalenes (PCNs) and non-ortho chlorinated biphenyls (non-ortho CBs) in harbour porpoises (Phocoena phocoena) from Swedish waters

Polychlorinated naphthalenes (PCNs) and non-ortho chlorinated biphenyls (non-ortho CBs) were analysed in blubber, nuchal fat, liver, muscle, kidney and brain of three male harbour porpoises (Phocoena phocoena) from the west coast of Sweden. To estimate spatial variation, PCNs and non-ortho CBs were analysed in six blubber samples collected at different anatomical sites of each animal. Highest wet weight concentrations of ΣPCNs were detected in the lipid rich tissues (blubber and nuchal fat) and liver (520–730 and 520 pg/g, respectively) and lowest in brain (22 pg/g). TetraCNs were most abundant in muscle, kidney and brain, while the hexaCNs were most abundant in the lipid rich tissues and liver. The highest lipid weight concentration recorded (11 ng/g) was for the hexaCN congeners no. 66/67 in liver. These coeluting hexaCN congeners accounted for 80–100% of total hexaCNs in all tissues examined.Concentrations of Σnon-ortho CBs were highest in lipid rich tissues (220–280 pg/g wet weight). Non-ortho CB no. 77 and 169 constituted between 62–86% and 4.9–9.3%, respectively, of total Σnon-ortho CBs. No major variation of Σnon-ortho CB concentrations was found between the six different blubber sites but higher ΣPCN concentrations (wet weight) were found dorsally at the peduncle. Toxic equivalent concentrations (TEQs) showed that non-ortho CB no. 126 was the main contributor to total TEQs in all tissues, except liver in which hexaCN congener nos. 66/67 contributed to about 50% of total TEQs.     

Application of semipermeable membrane device (SPMD) to assess air genotoxicity in an occupational environment

Semipermeable membrane device (SPMD) is a passive sampler that sequesters lipophilic contaminants, mimicking the bioconcentration in the fatty tissue of organisms. This study was designed to assess the use of SPMD and biological tests (Comet assay and Ames test) for air monitoring. For this purpose an occupational environment with expected polycyclic aromatic hydrocarbons (PAHs) contamination (coke plant) was selected for a case study. The SPMDs were deployed in five occupational contaminated sites and in a control site. The SPMD dialysates were chemically analysed and examined for in vitro DNA-damaging activity in human cells (Jurkat) by Comet assay and for mutagenicity with the Ames test (TA98 strain, w/o S9). Total suspended particulates were also collected and analysed (GC–MS). No biological effect of SPMD extract was revealed in the control site. On the other hand, air samples collected with SPMDs within the coke plant showed variable degrees of genotoxic and mutagenic activity. The highest effects were associated with the highest PAH level recovered in the SPMDs extracts and in particulate samples.Results obtained support the sensitivity of biological tests associated to SPMD sampling for evaluating the health risk of potentially contaminated work environments highlighting the usefulness of SPMDs for environmental air quality monitoring.     

Experiments probing the influence of air exchange rates on secondary organic aerosols derived from indoor chemistry

Reactions between ozone and terpenes have been shown to increase the concentrations of submicron particles in indoor settings. The present study was designed to examine the influence of air exchange rates on the concentrations of these secondary organic aerosols as well as on the evolution of their particle size distributions. The experiments were performed in a manipulated office setting containing a constant source of d-limonene and an ozone generator that was remotely turned “on” or “off” at 6 h intervals. The particle number concentrations were monitored using an optical particle counter with eight-channels ranging from 0.1–0.2 to>2.0 μm diameter. The air exchange rates during the experiments were either high (working hours) or low (non-working hours) and ranged from 1.6 to>12 h⁻¹, with intermediate exchange rates. Given the emission rates of ozone and d-limonene used in these studies, at an air exchange rate of 1.6 h⁻¹ particle number concentration in the 0.1–0.2 μm size-range peaked 1.2 h after the ozone generator was switched on. In the ensuing 4.8 h particle counts increased in successive size-ranges up to the 0.5–0.7 μm diameter range. At higher air exchange rates, the resulting concentrations of total particles and particle mass (calculated from particle counts) were smaller, and at exchange rates exceeding 12 h⁻¹, no excess particle formation was detectable with the instrument used in this study. Particle size evolved through accretion and, in some cases, coagulation. There was evidence for coagulation among particles in the smallest size-range at low air exchange rates (high particle concentrations) but no evidence of coagulation was apparent at higher air exchange rates (lower particle concentrations). At higher air exchange rates the particle count or size distributions were shifted towards smaller particle diameters and less time was required to achieve the maximum concentration in each of the size-ranges where discernable particle growth occurred. These results illustrate still another way in which ventilation affects human exposures in indoor settings. However, the ultimate effects of these exposures on health and well being remain to be determined.     

Release of persistent organic contaminants from carcasses of Lake Ontario Chinook salmon (Oncorhynchus tshawytscha)

About 20,000 Chinook salmon (Oncorhynchus tshawytscha) from Lake Ontario enter the Credit River, Ontario, Canada every fall to spawn and die. In this study, samples of muscle and eggs collected from female Chinook salmon entering the Credit River contained total PCBs, DDT compounds and other organochlorine (OC) compounds at mug/kg concentrations. Semi-permeable membrane devices (SPMDs) were deployed at a reference site above the spawning grounds and at two downstream sites at intervals over a 14-month period that spanned two spawning runs. There was an increase in the concentrations of total PCBs, total DDT and other classes of OCs in the SPMDs deployed at the two downstream sites during and after both spawning runs; indicating that the decay of salmon releases contaminants into the river. Based upon the concentrations of contaminants in the salmon tissues, approximately 75 g of total PCBs and 35 g of total DDT compounds would be transported annually into the Credit River from this source.     

Why biota still accumulate high levels of PCB after removal of PCB contaminated sediments in a Norwegian fjord

Accumulation of polychlorinated biphenyls (PCBs) in blue mussels (Mytilus edulis) and semipermeable membrane devices (SPMDs) was still high after the removal of PCB contaminated sediments from a Norwegian fjord by dredging. The accumulation of low chlorinated PCB congeners with a low octanol water-partitioning coefficient (K_ow) in blue mussels and SPMDs was higher than for the highly chlorinated congeners with a high K_ow. The accumulation of low chlorinated congeners was also higher in a lightly contaminated area compared to a highly contaminated area. That dredging the contaminated sediments was unsuccessful in lowering PCB levels in the biota may be for the following reasons: (1) Due to the low solubility of PCBs in the water it is possible that a decrease in the sediment concentration of PCB would leave the water concentrations of PCB unchanged. (2) Removal of the fine organic sediments may also play an important role, since a seabed with coarse inorganic material has a lesser ability to bind PCB. (3) The dredging may whirl up fine contaminated particles that eventually settles on the seabed producing a thin contaminated sediment layer that determine the water concentration. (4) Bioaccumulation in blue mussels and in the SPMDs occurs mostly from PCB dissolved in the water column. Since the water concentration of PCB is unchanged by the dredging, the accumulation in SPMDs and mussels is the same as before dredging. Further monitoring need to be carried out to report the long-term effect of the dredging.     

Field use of semipermeable membrane devices (SPMDs) for passive air sampling of polycyclic aromatic hydrocarbons: Opportunities and limitations

Semipermeable membrane devices (SPMDs) were used for measurements in air of twelve polycyclic aromatic hydrocarbons (PAHs) in two Genoa locations, both on building roofs, distant 300 m from each other. The first, site A, was in front a dismissing steel complex and the second, site B, was in an urban area overlooking a busy thoroughfare. SPMDs were deployed contemporary at the two sites, in nine monthly samplings, from April 2007 to May 2008. The amount of sequestered PAHs, in sites A and B, ranged between 61–267 ng SPMD^?1 d^?1 and 50–535 ng SPMD^?1 d^?1, respectively.PAHs profiles highlighted seasonal differences and suggested the possible role of different PAHs sources in the two areas. In particular, the contribution of remediation works of the steel complex was observed in site A. Moreover, a naphthalene leak from a tank, into the former industrial area, and a fire broke out near site A, were registered by time-integrated measurements of SPMDs.However, the strong dependence between amount of sequestered PAHs and air temperature needs further studies to distinguish between uptake rate variability and seasonal contribution of different sources. Finally, to measure air concentrations with reasonable accuracy, it should be very important to have certified sampling rates for all individual PAHs.     

Mercury levels and trends (1993-2009) in bream (Abramis brama L.) and zebra mussels (Dreissena polymorpha) from German surface waters

Mercury concentrations have been analysed in bream (Abramis brama L.) and zebra mussels (Dreissena polymorpha) collected at 17 freshwater sites in Germany from 1993-2009 and 1994-2009, respectively, within the German Environmental Specimen programme. Mercury concentrations in bream ranged from 21 to 881 ng g⁻¹ wet weight with lowest concentrations found at the reference site Lake Belau and highest in fish from the river Elbe and its tributaries. Statistical analysis revealed site-specific differences and significant decreasing temporal trends in mercury concentrations at most of the sampling sites. The decrease in mercury levels in bream was most pronounced in fish from the river Elbe and its tributary Mulde, while in fish from the river Saale mercury levels increased. Temporal trends seem to level off in recent years. Mercury concentrations in zebra mussels were much lower than those in bream according to their lower trophic position and varied by one order of magnitude from 4.1 to 42 ng g⁻¹ wet weight (33-336 ng g⁻¹ dry weight). For zebra mussels, trend analyses were performed for seven sampling sites at the rivers Saar and Elbe of which three showed significant downward trends. There was a significant correlation of the geometric mean concentrations in bream and zebra mussel over the entire study period at each sampling site (Pearson’s correlation coefficient = 0.892, p = 0.00002). A comparison of the concentrations in bream with the environmental quality standard (EQS) of 20 ng g⁻¹ wet weight set for mercury in biota by the EU showed that not a single result was in compliance with this limit value, not even those from the reference site. Current mercury levels in bream from German rivers exceed the EQS by a factor 4.5-20. Thus, piscivorous top predators are still at risk of secondary poisoning by mercury exposure via the food chain. It was suggested focusing monitoring of mercury in forage fish (trophic level 3 or 4) for compliance checking with the EQS for biota and considering the age dependency of mercury concentrations in fish in the monitoring strategy.     

Levels of some polybrominated diphenyl ether (PBDE) flame retardants along the Dutch coast as derived from their accumulation in SPMDs and blue mussels (Mytilus edulis)

Aqueous concentrations of individual brominated diphenyl ethers (BDEs) were determined for five stations in the Scheldt estuary and the North Sea along the Dutch coast using passive sampling by semipermeable membrane devices (SPMDs). Values of 0.1-5 pg l(-1) were observed. The highest levels were found in the Scheldt estuary. Concentration differences between February and October were a factor of 4-8 for BDE209, and were smaller than a factor of 2 for the other BDEs. Bioaccumulation was studied for native mussels and for mussels that were transplanted from an uncontaminated area into the Scheldt estuary for 6 weeks. Concentrations in native mussels were higher by a factor of 10 and 2 for BDEs and PCBs, respectively. Field based bioaccumulation factors (BAFs) were higher for BDEs than for PCBs by a factor of 10. Depuration experiments showed that the larger part of the BDE209 content in mussels was associated with ingested particles, whereas no such effect was observed for the other BDEs or PCBs.     

Influence of temporally variable groundwater flow conditions on point measurements and contaminant mass flux estimations

Monitoring of contaminant concentrations, e.g., for the estimation of mass discharge or contaminant degradation rates, often is based on point measurements at observation wells. In addition to the problem, that point measurements may not be spatially representative, a further complication may arise due to the temporal dynamics of groundwater flow, which may cause a concentration measurement to be not temporally representative. This paper presents results from a numerical modeling study focusing on temporal variations of the groundwater flow direction. “Measurements” are obtained from point information representing observation wells installed along control planes using different well frequencies and configurations. Results of the scenario simulations show that temporally variable flow conditions can lead to significant temporal fluctuations of the concentration and thus are a substantial source of uncertainty for point measurements. Temporal variation of point concentration measurements may be as high as the average concentration determined, especially near the plume fringe, even when assuming a homogeneous distribution of the hydraulic conductivity. If a heterogeneous hydraulic conductivity field is present, the concentration variability due to a fluctuating groundwater flow direction varies significantly within the control plane and between the different realizations. Determination of contaminant mass fluxes is also influenced by the temporal variability of the concentration measurement, especially for large spacings of the observation wells. Passive dosimeter sampling is found to be appropriate for evaluating the stationarity of contaminant plumes as well as for estimating average concentrations over time when the plume has fully developed. Representative sampling has to be performed over several periods of groundwater flow fluctuation. For the determination of mass fluxes at heterogeneous sites, however, local fluxes, which may vary considerably along a control plane, have to be accounted for. Here, dosimeter sampling in combination with time integrated local water flux measurements can improve mass flux estimates under dynamic flow conditions.     

Passive water sampling via semipermfable membrane devices (SPMDS) in concert with bivalves in the Sacramento/San Joaquin River Delta

Freshwater clams (Corbicula fluminea) and the Huckins et al. (1) semi-permeable membrane sampling device (SPMD) were simultaneously deployed at three sites on the Sacramento and San Joaquin rivers in 1990. Both clams and the SPMDs were analyzed for sequestered pesticides and polychlorinated biphenyls (PCBs) by gas chromatography with electron capture detection (GC/ECD). Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and non-ortho PCBs were quantified by high resolution mass spectrometry (MS). In general, levels of organochlorine compounds were approximately 1.6 times higher in clams on a wet weight basis than in the SPMDs, and trends in accumulation were similar except where biofouling of the SPMD membranes decreased uptake rates. Comparisons between the normalized, average levels of PCDDs accumulated showed that while octachlorodibenzo-p-dioxin (OCDD) was most prevalent in both clams and SPMDs, much higher levels of 2,3,7,8 TCDD were found in the SPMDs than in the clams; 2,3,7,8 TCDD was 32% of the profile relative to the OCDD level for the SPMDs and <1% of the clam OCDD level. PCB levels showed the clams primarily accumulated hexachlorinated PCBs while the pentachlorinated and tetrachlorinated congeners were higher in the SPMDs. Differences in profiles for homologous series among the PCBs reveal that some congeners, especially those with 2,4,5 substitution, are more likely to bioaccumulate than those with lower chlorination or adjacent unsubstituted sites. GC/MS chromatograms indicate the SPMDs also sequestered several polyaromatic hydrocarbons. GC/ECD chromatograms indicate the presence of several unidentified, early eluting compounds in the SPMDs.     

Assessment of bioavailable PAH, PCB and OCP concentrations in water, using semipermeable membrane devices (SPMDs), sediments and caged carp

Bioavailable water concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were assessed at several freshwater sites in and around the city of Amsterdam. Carp (Cyprinus carpio) were caged for 4 weeks at 10 sites, together with semipermeable membrane devices (SPMDs). In addition, sediment samples were taken at each site. SPMDs and sediments were analysed for PAHs, PCBs and OCPs. Carp muscle tissues were analysed for PCBs and OCP, while PAH metabolites were assessed in fish bile. Contaminant concentrations in the water phase were estimated using three different methods: 1. Using fish tissue concentrations and literature bioconcentration factors (BCFs), 2. Using SPMD levels and a kinetic SPMD uptake model, and 3. Using sediment levels and literature sorption coefficients (K_ocs). Since PAH accumulation in fish is not considered an accurate indicator of PAH exposure, calculated aqueous PAH concentrations from SPMD data were compared with semiquantitatively determined biliary PAH metabolite levels. Contaminant concentrations in the water phase estimated with fish data (Cw_fish) and SPMD data (Cw_spmd) were more in line for compounds with lower K_ow than for compounds with higher K_ow values. This indicates that the assumption of fish–water sorption equilibrium was not valid. At most sites, sediment-based water levels (Cw_sed) were comparable with the Cw_spmd, although large differences were observed at certain sites. A significant correlation was observed between biliary PAH metabolite levels in fish and aqueous PAH concentrations estimated with SPMD data, suggesting that both methods may be accurate indicators of PAH exposure in aquatic ecosystems.     

Impact of dredged urban river sediment on a Saronikos Gulf dumping site (Eastern Mediterranean): sediment toxicity,contaminant levels,and biomarkers in caged mussels

Impacts of chemical contaminants associated with dumping of dredged urban river sediments at a coastal disposal area in Saronikos Gulf (Eastern Mediterranean) were investigated through a combined approach of sediment toxicity testing and active biomonitoring with caged mussels. Chemical analyses of aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), Cu, and Zn in combination with the solid phase Microtox® test were performed on sediments. Concentrations of PAHs, AHs, Cu, and Zn as well as multiple biomarkers of contaminant exposure and/or effects were measured in caged mussels. Sediments in the disposal and neighboring area showed elevated PAHs and AHs concentrations and were characterized as toxic by the solid-phase Microtox® test during and after dumping operations. Biomarker results in the caged mussels indicated sublethal effects mainly during dumping operations, concomitantly with high concentrations of PAHs and AHs in the caged mussel tissues. Cu and Zn concentrations in sediments and caged mussels were generally not elevated except for sediments at the site in the disposal area that received the major amount of dredges. High PAHs and AHs levels as well as sublethal effects in the caged mussels were not persistent after termination of operations. The combined bioassay–biomarker approach proved useful for detecting toxicological impacts of dredged river sediment disposal in sediments and the water column. Nevertheless, further research is needed to evaluate whether sediment toxicity will have long-term effects on benthic communities of the disposal area.     

Adsorption of uranium(VI) on amorphous ferric oxyhydroxide at high concentrations of dissolved carbon(IV) and sulfur(VI)

Amorphous ferric oxyhydroxide is being used to treat groundwater contaminated with uranium(VI); the compound also has potential for use as a component in in situ chemical barriers. To quantitatively evaluate its effectiveness in such applications, adsorption of uranium(VI) onto amorphous ferric oxyhydroxide was experimentally investigated under a wide range of uranium(VI) (8.40·10⁻⁷−2.10·10⁻³ mol L⁻¹; 0.2–500 mg L⁻¹), sulfur(VI) (0–0.07 mol L⁻¹; 0–2240 mg L⁻¹) and carbon(IV) (0–0.0195 mol L⁻¹; 0–234 mg L⁻¹) concentrations, and pH-values (4–9.6). The adsorption behavior of uranium(VI) (uranyl ion and its complexes) is similar to that of other cations; it exhibits a sharp rise in the extent of adsorption with increasing pH. Interactions among uranyl complexes and surface sites are interpreted using a site complexation model. Although the model does not incorporate electrostatics and includes only a single type of adsorption site, it provides a reasonable match to measured adsorption and proton exchange data. The simplicity of the model and the resulting reduction in computational demand allow its efficient incorporation into coupled reaction-transport models.     

Impact of the Saharan dust outbreaks on the ambient levels of total suspended particles (TSP) in the marine boundary layer (MBL) of the Subtropical Eastern North Atlantic Ocean

Six years (1998–2003) of measurements of ambient air concentrations of total suspended particulate (TSP) measured at a rural background monitoring station in Tenerife (Canary Islands), the El Río station (ER, 28°08′35″N, 16°39′20″W, 500 m a.s.l.) were studied. African dust outbreaks were objectively identified using a new quantitative tool, called the African Index. This index indicates the percentage of time that an air mass remained over an African region at one of three possible height intervals of the lower troposphere. After identifying these episodes, a study of the background TSP levels at the ER station and of direct and indirect (those which cause vertical deposition of dust) African air mass intrusion impacts was performed. Taking into account both direct and indirect episodes, a total of 322 days of African dust intrusion were objectively identified (a mean of 54 episodes per year) in the period 1998–2003, some of them caused by “transition episodes” or “return African air masses”. A subjective method confirmed that 256 of these days were caused by direct impacts of African dust on the ER station. A mean TSP value of 21.6 μg m⁻³ was found at the station during this period. All the episodes occurred when the TSP concentration was >28.5 μg m⁻³. The TSP background (14 μg m⁻³) can be assumed to be representative of the MBL of the Eastern North Atlantic subtropical region. The highest number of dust gravitational settlement (or indirect) episodes occurs in summer, but the highest contribution of these episodes to the TSP levels is in March with a monthly mean TSP contribution of up to 30.5 μg m⁻³.     

Passive water sampling for polynuclear aromatic hydrocarbons using lipidcontaining semipermeable membrane devices (SPMDs): Application to contaminant residence times

Lipid-containing semipermeable membrane devices are applied to the quantitative determination of the persistence of polynuclear aromatic hydrocarbons (PAH) in an irrigation water canal, a representative waterway. The uniform and reproducible sampling of the USGS design of lipid-containing SPMDs is exploited to measure PAH half-lives without requiring calculation of water concentrations. The trend in calculated PAH half-lives agrees with that expected if volatilization is a significant mechanism for loss from the canal with more volatile PAHs having shorter half-lives. The higher persistence of phenanthrene compared to anthracene is consistent with the greater stability of phenanthrene and suggests, with other physicochemical evidence, that other (reactive) mechanisms may be involved. The results of this study demonstrate the feasibility of the SPMD method for the measurement of residence times in aquatic and other compartments. Such information is essential for quantifying contaminant behavior in the environment and providing insights into contaminant fate.