Maximum capacities for adsorption of phenanthrene in the slowly and very slowly desorbing domains in nineteen soils and sediments

The maximum amounts of phenanthrene that can be taken up in both the slowly desorbing domain and the very slowly desorbing domain of 19 soils and sediments were determined by measuring the desorption of phenanthrene added at high loadings associated with equilibrium concentrations in water close to the aqueous solubility of phenanthrene. For two soils and one sediment, literature values for Langmuir phenanthrene adsorption capacities were available. These values were almost equal to the sum of the maximum amounts taken up in the slowly and in the very slowly desorbing domain. For the other soils, the range of the sum of the maximum amounts in the slowly and very slowly desorbing domains was comparable to the range for literature values of Langmuir phenanthrene adsorption capacities for soils and sediments. Results suggested that the maximum amounts determined from the desorption studies were Langmuir adsorption capacities. The correlation of maximum capacities for adsorption in both the slow desorption domain as well as the very slow desorption domain with soot content was virtually absent. In contrast, the variation of maximum amounts of phenanthrene adsorbed in either the slowly or the very slowly desorbing domains was substantially reduced by normalization to the total organic carbon content of the soils and sediments. It is suggested that adsorption in the slowly and very slowly desorbing domain took place in organic matter derived material such as kerogen, charcoal, or char.     

How quality and quantity of organic matter affect polycyclic aromatic hydrocarbon desorption from Norwegian harbor sediments

The desorption behavior of phenanthrene, pyrene, and benzo[a]pyrene was investigated for three Norwegian harbor sediments and their respective particle size fractions using the Tenax desorption method. Rate constants for rapidly, slowly, and very slowly desorbing fractions were on the order of 10(-1), 10(-2) to 10(-4), and 10(-4) to 10(-6)/h, respectively. Relatively small amounts were present in the rapidly desorbing fractions (F(rapid): < 6% for phenanthrene, 3-19% for pyrene, and 1-12% for benzo[a]pyrene). With the exception of benzo[a]pyrene, these F(rapid) values were generally lower than median F(rapid) values obtained from more than 100 literature values for native polycyclic aromatic hydrocarbons (PAHs) (22% for phenanthrene, 29% for pyrene, and 8% for benzo[a]pyrene). To understand which parameters influence PAH desorption, relations between desorption behavior and the sediment characteristics were investigated. A significant positive correlation was found between the extent of slow and very slow desorption and the ratios of black carbon to total organic carbon, as well as the temperature at which 50 and 90%, respectively, of the organic matter was oxidized, as obtained from oxidation-only Rock Eval analysis. Thus, black carbon-bound PAHs probably desorb slowly and very slowly. Furthermore, significant positive correlations between desorption behavior and the average particle size were observed, which could be explained by retarded intraparticle diffusion.     

Sorbate size-dependent maximum capacities for adsorption of organic compounds in the slowly and very slowly desorbing domains of a sediment

Maximum capacities were determined for adsorption of six polycyclic aromatic hydrocarbons, seven polychlorinated biphenyls, and five chlorobenzenes in both the slowly desorbing domain and the very slowly desorbing domain of a sediment. For separate compound classes in the two desorption domains, log-transformed maximum adsorption capacities were linearly related to the relative magnitude of the shadow of the sorbate on an imaginary planar surface. For planar compounds, the ratio of maximum adsorption capacities for the slowly desorbing domain and the very slowly desorbing domain was approximately two. This ratio was eightfold higher for strongly nonplanar polychlorinated biphenyls, which suggests that adsorption depends on sorbate thickness in the very slow desorption domain but not in the slow desorption domain. The rates of decrease of the log-transformed sum of maximum capacities for adsorption in the slow desorption domain and the very slow desorption domain with increasing relative magnitude of the shadow of the sorbate on a planar surface were similar to those derived from literature data regarding maximum capacities for adsorption onto a soil and a sediment. It is proposed that the rates of decrease for both the slow desorption domain and the very slow desorption domain may have general applicability to soils and sediments.     

Slow desorption behavior of one highly resistant aromatic amine in Lake Macatawa, Michigan, USA, sediment

The desorption behavior of benzidine from Lake Macatawa (Holland, MI, USA) sediment was investigated in this study using batch solvent extraction method. Seven solvents were tested as the extracting reagents: Deionized water (DI), calcium chloride in DI (CaCl2), sodium hydroxide in DI (NaOH), acetonitrile (ACN), a mixture of acetonitrile and ammonium acetate in DI (ACN-NH4OAc), methanol (MeOH), and hydrochloric acid in DI (HCl). These solvents are proposed to react with sediment-associated benzidine by different mechanisms (e.g., cation exchange, hydrophobic partitioning, and covalent binding). Three sets of sorption isotherm experiments were conducted separately in these seven solvents with a 7-d, three-week, and two-month contact time. The results demonstrated nonlinear isotherms with Freundlich 1/n values varying from 0.25 to 0.52. The desorption behavior of benzidine in the solvents was evaluated after the sorption of benzidine onto the sediment with same contact times of 7 d, three weeks, and two months. A two-stage model subsequently was applied to simulate the experimental data. The rapidly desorbing rate constants were on the order of one to two per day for ACN, ACN-NH4OAc, and NaOH solvents, and the slowly desorbing rate constants were on the order of 10(-5) to 10(-4)/d. Sequential desorption experiment demonstrated low total extraction efficiency of less than 40%. Both the observed sorption and desorption phenomena suggested that hysteresis and/or mass-transfer limited diffusion may result in the slow desorption behavior observed in this study.     

Temperature effects on very slow desorption of native chlorobenzenes from sediment to water

The temperature dependence of the kinetics of very slow desorption of eight chlorobenzenes was studied in laboratory batch experiments on a field-contaminated sediment from Lake Ketelmeer, The Netherlands. The observed rate constants for very slow desorption averaged (1.5 +/- 0.4) x 10(-4)/h at 10 degrees C, (2.9 +/- 1.0) x 10(-4)/h at 20 degrees C, (5.8 +/- 2.4) x 10(-4)/h at 35 degrees C, and (6.4 +/- 3.0) x 10(-4)/h at 45 degrees C over all eight compounds. Activation energies for desorption to water were close to the enthalpy for dissolution of the pure solid in water. The activation energies ranged from 18 to 53 kJ/mol with an average of 36 +/- 11 kJ/mol. These values confirm earlier reported activation energies for very slow desorption to water. They are much less than values for activation energies for desorption to the gas phase. That difference can be explained in terms of rate limiting desorption from carbonaceous adsorption sites.     

Desorption and Bioavailability of Spiked Pentabromo Diphenyl Ether and Tetrachlorodibenzo(<Emphasis Type="Italic">p</Emphasis>)dioxin in Contaminated Sediments

The relationship between desorption kinetics and bioavailability of sediment-associated 2,2',4,4,5' pentabromo diphenyl ether [(14)C] (BDE-99) and 2,3,7,8 tetrachlorodibenzo(p)dioxin [(3)H] (TCDD) was examined in the contaminated sediments. The desorption kinetics were measured in a sediment-water suspension using Tenax extraction, and bioaccumulation was examined by exposing Lumbriculus variegatus (Oligochaeta) to BDE-99 and TCDD spiked sediment in a 14-day kinetic study. Both chemicals had a high affinity to the finest particle size fraction (<20 microm) and the large, very slowly desorbing fraction (58-75%). The biota-sediment accumulation factors ranged between 1.9 and 4.4 for BDE-99 and between 1.4 and 2.8 for TCDD. The chemical outflux from the rapidly desorbing fraction and influx into organisms shows the connection between desorption and bioavailability. Despite this, normalization to the rapidly desorbing fraction was unable to reduce differences in bioavailability estimates between the chemicals. Thus, it is evident that chemical extraction in the mixed system (Tenax tubes) does not fully describe the bioavailable fraction that worms face in stagnant sediments in a similar way for all chemicals. However, when all desorbing domains were included in the calculation, the difference between the chemicals disappears. Desorbing fractions were also able to reduce variability in the biota-sediment accumulation factors between the tested sediments when organic carbon-based sediment chemical concentrations were modified by the desorbing fractions.     

Investigating the role of desorption on the bioavailability of sediment-associated 3,4,3',4'-tetrachlorobiphenyl in benthic invertebrates

Only a fraction of all sediment-associated hydrophobic organic contaminants are bioavailable, and a simple Tenax extraction procedure may estimate this fraction. Bioavailability is assumed to coincide with the rapidly and, possibly, slowly desorbing sediment-associated contaminant. River sediment was spiked with radiolabeled (14C) and nonradiolabeled (12C) 3,4,3',4'-tetrachlorobiphenyl (TCBP), and desorption kinetics using Tenax extraction were obtained at 10 degrees C and 22 degrees C. Bioaccumulation was measured in Lumbriculus variegatus, Chironomus tentans, and Hyalella azteca. Desorption of TCBP was triphasic at 22 degrees C and slowed at 10 degrees C to show only biphasic kinetics. The rapidly desorbing fractions decreased with increasing TCBP sediment concentration. The biota sediment accumulation factors, biota accumulation factors, and sediment clearance coefficients (ks) also decreased with increasing sediment TCBP concentration. The rapidly plus slowly desorbing fractions and the total TCBP desorbed when 99.9% of the rapidly desorbing fraction had desorbed were used to estimate bioavailable TCBP. These Tenax-based fractions did not explain the decreasing bioavailability with increasing TCBP load. Several factors, such as animal behavior and TCBP water solubility limitations, were evaluated to explain the concentration effect, but the most likely cause was severe diffusion limitations in whole sediment that were not predicted by the fully mixed Tenax extraction. Therefore, desorbing fractions determined by Tenax extraction overestimated the bioavailable fractions in sediments.     

A dynamic multimedia environmental and bioaccumulation model for brominated flame retardants in Lake Huron and Lake Erie, USA

Polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) may pose a worldwide pollution problem because of their persistence, long-range transport capability, and predisposition to bioaccumulate. The ubiquitous presence of PBBs and PBDEs has heightened interest in determination of their fate. We report results for a fugacity-based dynamic environmental and bioaccumulation model of the fate of hexabromobiphenyl (hexaBB) discharged into the Saginaw Bay region of Lake Huron, USA. We calculated transient fugacity profiles of hexaBB in Lake Huron and Lake Erie water and sediment during the 1970s, 1980s, and 1990s. The hexaBB concentrations in the environmental compartments were used as inputs for a dynamic bioaccumulation model of Lake Huron and Lake Erie aquatic biota. The model results indicate that the sediment compartments of Lakes Huron and Erie serve as reservoirs for the accumulation and slow transfer of hexaBB to the food web constituents of these lakes. We present bioaccumulation factors (BAFs) and compare the predicted hexaBB concentrations in lake trout from the bioaccumulation model with measurements during the period 1980 to 2000. An uncertainty analysis for this model suggests that errors associated with input parameter uncertainty can be reduced by refining estimates of the sediment degradation half-life of hexaBB. The corroborated PBB model has carryover application for modeling the fate of polybrominated diphenyl ether (PBDE) contaminants in the Great Lakes. By fitting model outputs to field measurement data using the transformed least square fit method, we report estimations of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) emission rates into the Lake Huron and Lake Erie watershed areas.     

A simple Tenax extraction method to determine the availability of sediment-sorbed organic compounds

A simple method to determine the availability of sediment-sorbed organic contaminants was developed and validated. For 10 polycyclic aromatic hydrocarbons, 4 polychlorinated biphenyls, and 9 chlorobenzenes in 6 sediments, we measured the fraction extracted by Tenax in 6 and 30 h. These fractions were compared with the rapidly desorbing fractions determined by consecutive Tenax extraction. Extraction by Tenax for 30 h completely removed the rapidly desorbing fraction plus some part of the slowly desorbing fraction. The fraction removed after 30 h was about 1.4 times the rapidly desorbing fraction. The fraction extracted by Tenax after 6 h is about 0.5 times the rapidly desorbing fraction for chlorobenzenes (CBs)/polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). The rapidly desorbing fraction probably represents the fraction of sorbed organic compound that poses actual risks for transport to (ground) water and determines the uptake by organisms and that can be microbially degraded. Extraction by Tenax for 6 h provides an easy way to address these issues more accurately than does the measurement of total concentrations.     

Screening Level of PAHs in Sediment Core from Lake Hongfeng,Southwest China

Using data from a 25-year retrospective of polycyclic aromatic hydrocarbons (PAHs) in sediment core from Lake Hongfeng, Southwest China, their possible sources and potential toxicologic significance were investigated. The total PAH concentrations (16 priority PAHs as proposed by the United States Environmental Protection Agency) in sediments ranged from 2936.1 to 5282.3 ng/g and gradually increased from the analyzed deeper sediments to surface sediments. PAHs were dominated by low molecular-weight components, especially phenanthrene (PHEN) and fluorene (FLU). However, a significantly increased number of high molecular-weight (HMW) PAHs was found in upper segments. The temporal trends of individual PAH species suggest that there may have been a change in energy use from low- to high-temperature combustion, especially after approximately 2001. PAH input to Lake Hongfeng originated mainly from domestic coal combustion and biomass burning, whereas fuel combustion characteristics have also been found in recent years. Sediment-quality assessment implied that potential adverse biologic impact could be a probability for most low-ring PAHs (including naphthalene, acenaphthylene, acenaphthylene, FLU, PHEN, and anthracene). Nevertheless, more concern should be paid to HMW PAHs in the future due to their rapidly increasing trends in upper sediments. Because only one core was analyzed in this study, more work is needed to confirm the sources and toxicity of PAHs in Lake Hongfeng.     

Spatial and temporal patterns in mercury contamination in sediments of the Laurentian Great Lakes

Data from recent sediment surveys have been collated and mapped in order to determine the spatial distribution of mercury in sediments across the entire Great Lakes basin. Information from historical surveys has also been collated in order to evaluate temporal trends. Lake Huron (2002) exhibited the lowest mercury concentrations (lakewide average concentration, 0.043 microg/g); Lakes Michigan (1994-1996) and Superior (2000) also exhibited relatively low levels (lakewide averages of 0.088 and 0.078 microg/g, respectively). The western basin of Lake Erie (1997-1998, 0.402 microg/g) and Lake Ontario (0.586 microg/g) exhibited the highest levels. Sources of mercury contamination in Lakes Erie and Ontario are primarily attributed to loadings from historical sources, including chlor-alkali production in the Detroit, St. Clair, and Niagara Rivers. The spatial distributions of mercury in sediments of Lakes Huron and Superior suggest that natural geochemical factors are an influence. Surficial sediment mercury contamination was found to have decreased markedly since the late 1960s and 1970s. Decreases in lakewide average sediment concentrations of mercury over this time period ranged from approximately 25% for Lake Ontario to 80% for Lake Huron.     

Effects of anaerobic incubation on the desorption of polycyclic aromatic hydrocarbons from contaminated soils

Incubation of field-contaminated soil under anaerobic conditions can lead to increased mobilization of polycyclic aromatic hydrocarbons (PAHs) into water. In the present study, we evaluated the effects of anaerobic incubation on the rate and extent of desorption of PAH from two field-contaminated soil samples. One was a highly contaminated soil from a former wood-preserving site that had not been subject to previous treatment; the other was a soil from a former manufactured-gas plant site that had been treated in an aerobic bioreactor. A two-site desorption model was applied to quantify the fast and slowly desorbing fractions of each PAH and the corresponding first-order rate constants for each fraction. For most of the PAHs, the total amount desorbed after 18 d from anaerobically incubated samples was significantly greater than that from their counterparts not subjected to anaerobic incubation, but the overall effect was modest. The rate constant corresponding to the slowly desorbing fraction (k(2)) was much higher for the samples incubated under active anaerobic conditions than that for the controls, implying anaerobic incubation had the greatest influence on the soil compartments controlling the slow release of PAHs. Anaerobic incubation had little to no effect on the rapidly desorbing fraction.     

Bioavailability and assimilation of sediment-associated benzo[a]pyrene by Ilyodrilus templetoni (Oligochaeta)

Benzo[a]pyrene (BaP)-amended sediment was desorbed by a sequential batch method using an isopropanol solution wash. The observed isotherm showed no evidence of desorption resistance, as indicated by increased partitioning to the solid phase at low concentrations. This was consistent with the prediction of minimal desorption resistance for highly hydrophobic compounds using a biphasic model. Bioavailability of BaP in desorbed sediments was assessed by toxicokinetic measures of uptake, bioaccumulation, and elimination in the deposit-feeding, freshwater tubificid oligochaete Ilyodrilus templetoni. Worms were exposed to sediments with BaP concentrations of approximately 26 and 11 microg/g dry weight sediment after desorption for one and three batches, respectively. The I. templetoni tissue concentration attained an apparent steady state after approximately one month and resulted in a biota-sediment accumulation factor of approximately 1.3 for both sediments. This is consistent with the paradigm that pore-water concentration predicts the uptake of organic contaminants into lipids despite the literature data showing that the major uptake route for BaP is likely from the ingestion of sediment particles. Ilyodrilus templetoni exhibited a high assimilation efficiency (80%) during a single-gut passage, a low elimination rate (k(c) = 0.0032 h(-1)), and negligible biotransformation of sediment-associated BaP.     

Influence of sorbate planarity on the magnitude of rapidly desorbing fractions of organic compounds in sediment

Organic compounds in sediments are known to distribute between rapid, slowly, and very slowly desorbing sites. This distribution is relevant to bioavailability and risk assessment of organic compounds in sediment. In this study, the fraction desorbing to Tenax in 6 h was measured for a range of organic compounds in sediment differing in their extent of planarity. The aim was to determine the influence of the extent of planarity on the distribution over the rapidly desorbing sites on the one hand and the slowly and very slowly desorbing sites on the other. The magnitude of rapidly desorbing fractions, calculated from the fractions desorbed to Tenax in 6 h, decreased with increasing extent of planarity, expressed as sorbate thickness. For a thickness of less than 5.5 to 6 A, rapidly desorbing fractions are approximately equal to those for fully planar compounds, such as polycyclic aromatic hydrocarbons, which have a thickness of about 3 A. This is in agreement with previously reported differences in sediment-water distribution coefficients between planar polycyclic aromatic hydrocarbons (PAHs) and nonplanar PCBs. The present findings suggest that simple molecular modeling of the thickness of nonplanar organic compounds enables the estimation of the affinity for rapidly desorbing sites relative to planar compounds.     

Organochlorine Contaminants in Water, Sediment and Fish of Lake Burullus, Egyptian Mediterranean Sea

Lake Burullus is one of the Delta lakes, connected with the Mediterranean Sea through El Boughaz opening. Concentrations of organochlorine contaminants were measured in water, sediments and biota of the lake because of concerns about their effects on its productivity. The concentrations of chlorinated hydrocarbons decreased in the order of PCBs > DDTs > TC > HCHs for all water samples collected from Lake Burullus during 2006. Higher concentrations were recorded during summer season, this clearly affected by higher agricultural and sewage activities. The concentrations of DDTs in water were ranged from 0.07 to 221.9 ng L(-1); 46.3-656.5 ng L(-1); 94.3-882.6 ng L(-1) and 24.8-233 ng L(-1) during winter, spring, summer and autumn, respectively. Among DDTs metabolites p,p-DDE was the most dominant with a maximum of 520.13 ng L(-1) recorded at station 10 (El Boughaz opening). In sediment samples, PCBs concentrations were ranged from 4.6 to 213.9 ng g(-1) with an average 47.2 ng g(-1); dry weight. Total pesticides were higher than PCBs for mostly all sediment samples of Lake Burullus. Concentrations of DDTs in fish tissues were ranged from 2.76 to 24.23 ng g(-1) and from 14.16 to 45.13 ng g(-1); wet weight for Oresochromus niloticus and Clarries sp., respectively.     

Principal components analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in sediments from Lake Champlain and Lake George,New York,USA

Principal-components analysis (PCA) was used to compare concentrations of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) compounds in sediments collected from two interconnected lakes, Lake Champlain and Lake George, New York, USA. Two different PCDD/PCDF congener profiles were present in surface sediment samples from Lake George. Samples collected near residential areas and power-boat marinas had elevated hepta- and octa-CDDs (1±0.3 ng/g) and tetra-octa-CDFs compared with samples collected in other areas of the lake. The PCDD/PCDF pattern in the high-level samples was similar to the PCDD/PCDF pattern in sediments from Green Lake, NY, a small lake in which atmospheric deposition is the only route for PCDD/PCDF contamination, either from local sources or from long range transportation from multiple sources in the midwest. The samples containing the higher PCDD/PCDF concentrations also contained higher lead concentrations (173±33 g/g) compared to the low-level PCDD/PCDF samples (52±25 g/g). However, the increase in lead concentrations was accompanied by increased concentrations of other trace metals. Consequently, it can be concluded that emissions from power boats are not responsible for the PCDD/PCDF contamination in Lake George. Concentrations of PCDDs/PCDFs in the low-level samples were similar to PCDD/PCDF concentrations in sediments from remote midwestern lakes where long range atmospheric deposition was the only plausible route of entry for the PCDD/PCDF compounds. However, other studies have shown that offshore sediments in Lake George have lower concentrations of organic carbon than inshore samples and, therefore, the low-level PCDD/PCDF pattern may be an artifact related to a reduced PCDD/PCDF concentration in sediments with a low organic carbon content. Surface and core sediments from Lake Champlain also partitioned into two groups, which both had PCDD/PCDF patterns differing from the high-level surface sediments collected from Lake George. The largest group of samples was characterized by the presence of high octa-CDD concentrations (3.5–18 ng/g). The second group of samples was four sections from a single core sample collected near a bleached kraft pulp and paper mill, which closed in 1970. These samples had high concentrations of tetra-CDFs (0.5–1.4 ng/g), primarily 2,3,7,8-tetra-CDF, accompanied by comparable concentrations of octa-CDD (0.9–4.4 ng/g). The presence of 2,3,7,8-tetra-CDF is consistent with results from several studies where PCDDs/PCDFs were analyzed in samples taken from various stages of the bleached kraft process. These samples were grouped in the same quadrant on a PCA plot as coal soot and pulp and paper mill sludge. However, the grouping was not close, and the PCDD/PCDF contamination in these sediments cannot be associated with either source. Five sections of a core collected near a currently operating bleached kraft pulp and paper mill also had elevated 2,3,7,8-tetra-CDF concentrations (0.3±0.05 ng/g), but these 2,3,7,8-tetra-CDF concentrations were accompanied by considerably higher octa-CDD concentrations (7.5±0.5 ng/g). Therefore, they could not be distinguished by PCA from the majority of the Lake Champlain samples.     

Effect of aging on desorption kinetics of sediment-associated pyrethroids

Pyrethroids are insecticides commonly used in both agricultural and urban environments. Residues of pyrethroids frequently are found in bed sediments of regions such as California (USA), and as such, sediment toxicity from pyrethroid contamination is an emerging concern. Pyrethroids are highly hydrophobic, and toxicity from sediment-borne pyrethroids is expected to depend closely on their desorption rate. In the present study, we evaluated the effect of aging on desorption kinetics of sediment-borne pyrethroids. Two sediments spiked with four pyrethroids were incubated for 7, 40, 100, and 200 d at room temperature. Desorption measured using sequential Tenax extractions was well described by a three-compartment model. The estimated rapid desorption fraction (F(rapid)) decreased quickly over time and was accompanied by an increase of the very slow desorption fraction. The aging effect on desorption kinetics followed a first-order model, with half-lives for the decrease in F(rapid) for all four pyrethroids in both sediments ranging from two to three months. When coupled with degradation, the estimated half-lives of the rapidly desorbing fraction (and, thus, the potentially bioavailable concentration) were two months or less for all four pyrethroids. Two field-contaminated sediments displayed distinctively different desorption kinetics. The sediment with fresh residues exhibited rapid desorption, and the sediment containing aged residues was highly resistant to desorption. The observation that desorption of pyrethroids decreased quickly over contact time implies that the bioavailability of sediment-borne pyrethroids may diminish over time and that use of nonselective extraction methods may lead to overestimating the actual sediment toxicity from pyrethroid contamination.     

Biological and Chemical Characterization of Metal Bioavailability in Sediments from Lake Roosevelt,Columbia River,Washington, USA

We studied the bioavailability and toxicity of copper, zinc, arsenic, cadmium, and lead in sediments from Lake Roosevelt (LR), a reservoir on the Columbia River in Washington, USA that receives inputs of metals from an upstream smelter facility. We characterized chronic sediment toxicity, metal bioaccumulation, and metal concentrations in sediment and pore water from eight study sites: one site upstream in the Columbia River, six sites in the reservoir, and a reference site in an uncontaminated tributary. Total recoverable metal concentrations in LR sediments generally decreased from upstream to downstream in the study area, but sediments from two sites in the reservoir had metal concentrations much lower than adjacent reservoir sites and similar to the reference site, apparently due to erosion of uncontaminated bank soils. Concentrations of acid-volatile sulfide in LR sediments were too low to provide strong controls on metal bioavailability, and selective sediment extractions indicated that metals in most LR sediments were primarily associated with iron and manganese oxides. Oligochaetes (Lumbriculus variegatus) accumulated greatest concentrations of copper from the river sediment, and greatest concentrations of arsenic, cadmium, and lead from reservoir sediments. Chronic toxic effects on amphipods (Hyalella azteca; reduced survival) and midge larvae (Chironomus dilutus; reduced growth) in whole-sediment exposures were generally consistent with predictions of metal toxicity based on empirical and equilibrium partitioning-based sediment quality guidelines. Elevated metal concentrations in pore waters of some LR sediments suggested that metals released from iron and manganese oxides under anoxic conditions contributed to metal bioaccumulation and toxicity. Results of both chemical and biological assays indicate that metals in sediments from both riverine and reservoir habitats of Lake Roosevelt are available to benthic invertebrates. These findings will be used as part of an ongoing ecological risk assessment to determine remedial actions for contaminated sediments in Lake Roosevelt.     

Tenax extraction as a tool to evaluate the availability of polybrominated diphenyl ethers, DTT, and DTT metabolites in sediments

Solid-phase extraction with Tenax is one of the most used methods for determining the fraction of a pollutant that desorbs rapidly from sediment and thus is available for living beings. In the present study, this technique has been applied to sediment contaminated in the laboratory with polybrominated diphenyl ethers (PBDEs) and dichlorodiphenyltrichloroethane, dichlorodifenyldichloroethylene, and dichlorodifenyldichloroethane (generically, DDXs). The amount of chemical retained in sediment during the time of the experiment fit well with a three-phase exponential desorption model. The ratios between the rapidly desorbing fraction and the fraction desorbed during a fixed time (6 or 24 h) were calculated. The fraction desorbed in 6 h was lower than the rapidly desorbing fraction for most of PBDEs, whereas the fraction desorbed in 24 h exceeded the rapidly desorbing fraction for both groups of compounds. However, variability of these data suggests, when possible, a long time measure of desorption in order to achieve a more accurate estimation. Both the extent and the velocity of desorption were inversely related with the bromination degree and, consistently, with hydrophobicity and molecular size. In this way, low brominated PBDEs and DDXs showed a high availability relative to high brominated PBDEs.     

Polycyclic aromatic hydrocarbons and black carbon in sediments of a remote alpine lake (Lake Planina,northwest Slovenia)

Polycyclic aromatic hydrocarbons (PAH) and black carbon (BC) were measured in alpine Lake Planina (Slovenia) sediment. Lake Planina is a remote mountain lake with almost no direct anthropogenic influence. Long-distance atmospheric deposition is a major pathway for the loading of contaminants to the sediment. The PAH were analyzed by gas chromatography coupled to mass spectrometry, whereas the BC was determined by thermal oxidation method. A flux of PAH to surface sediments of approximately 1,100 microg m(-2) year(-1) was obtained and was higher than that in other alpine lakes of the central European Alps. However, surface sediment PAH concentration, normalized to organic carbon content (OC), amounted to 5 microg PAH(pyr)/g OC and showed that Lake Planina is relatively equally exposed to atmospheric pollution compared with other lakes in the region. The BC:OC ratios ranged from 3 to 8% (w/w). In addition, a huge forest fire occurred in 1948 in the lake's surrounding area, which is recorded in the sediment. Both PAH and BC distributions were affected by the fire in 1948 in the lake's watershed, because their concentration increased remarkably. The concentration of retene, a molecular marker of coniferous wood combustion, increased to 1,000 ng/g dry weight sediment at the sediment interval corresponding to approximately the year 1950.