Effects of organic amendments on the toxicity and bioavailability of cadmium and copper in spiked formulated sediments

We evaluated the partitioning and toxicity of cadmium (Cd) and copper (Cu) spiked into formulated sediments containing two types of organic matter (OM), i.e., cellulose and humus. Amendments of cellulose up to 12.5% total organic carbon (TOC) did not affect partitioning of Cd or Cu between sediment and pore water and did not significantly affect the toxicity of spiked sediments in acute toxicity tests with the amphipod Hyalella azteca. In contrast, amendments of natural humus shifted the partitioning of hoth Cd and Cu toward greater concentrations in sediment and lesser concentrations in pore water and significantly reduced toxic effects of both metals. Thresholds for toxicity, based on measured metal concentrations in whole sediment, were greater for both Cd and Cu in sediments amended with a low level of humus (2.9% TOC) than in sediments without added OM. Amendments with a high level of humus (8.9% TOC) eliminated toxicity at the highest spike concentrations of both metals (sediment concentrations of 12.4 microg Cd/g and 493 microg Cu/g). Concentrations of Cd in pore water associated with acute toxicity were similar between sediments with and without humus amendments, suggesting that toxicity of Cd was reduced primarily by sorption to sediment OM. However, toxic effects of Cu in humus treatments were associated with greater pore-water concentrations than in controls, suggesting that toxicity of Cu was reduced both by sorption and by complexation with soluble ligands. Both sorption and complexation by OM tend to make proposed sediment quality guidelines (SQGs) based on total metal concentrations more protective for high-OM sediments. Our results suggest that the predictive ability of SQGs could be improved by models of metal interactions with natural OM in sediment and pore water.     

Ecological impacts of lead mining on Ozark streams: toxicity of sediment and pore water

We studied the toxicity of sediments downstream of lead-zinc mining areas in southeast Missouri, using chronic sediment toxicity tests with the amphipod, Hyalella azteca, and pore-water toxicity tests with the daphnid, Ceriodaphnia dubia. Tests conducted in 2002 documented reduced survival of amphipods in stream sediments collected near mining areas and reduced survival and reproduction of daphnids in most pore waters tested. Additional amphipod tests conducted in 2004 documented significant toxic effects of sediments from three streams downstream of mining areas: Strother Creek, West Fork Black River, and Bee Fork. Greatest toxicity occurred in sediments from a 6-km reach of upper Strother Creek, but significant toxic effects occurred in sediments collected at least 14 km downstream of mining in all three watersheds. Toxic effects were significantly correlated with metal concentrations (nickel, zinc, cadmium, and lead) in sediments and pore waters and were generally consistent with predictions of metal toxicity risks based on sediment quality guidelines, although ammonia and manganese may also have contributed to toxicity at a few sites. Responses of amphipods in sediment toxicity tests were significantly correlated with characteristics of benthic invertebrate communities in study streams. These results indicate that toxicity of metals associated with sediments contributes to adverse ecological effects in streams draining the Viburnum Trend mining district.     

An in situ toxicity identification evaluation method Part II: Field validation

When sediments are found to be toxic usually there is a mixture of chemicals present. Often it is important to establish which chemicals contribute to the toxicity. Establishing causality can be difficult and often requires fractionation with subsequent toxicity testing. The sample collection and manipulation process can alter chemical bioavailability and toxicity. An in situ toxicity identification evaluation (iTIE) chamber is described that was placed in sediments and fractionated pore-water chemicals into nonpolar chemicals, metals, and ammonia-type groups. This method was field tested and compared to the laboratory-based, U.S. Environmental Protection Agency (U.S. EPA) toxicity identification evaluation (TIE) method. Field studies were performed at three sites contaminated primarily with polycyclic aromatic hydrocarbons (PAHs) (Little Scioto River, OH, USA), polychlorinated biphenyls (PCBs) (Dicks Creek, OH, USA), and chlorobenzenes (Sebasticook River, ME, USA). Both the iTIE and the U.S. EPA TIE methods used Daphnia magna in 24-h exposures. Although the iTIE and TIE were conducted on sediments from the same location, there was significantly more toxicity observed in the iTIE testing. The dominant chemical classes were separated by the iTIE method and revealed which fractions contributed to toxicity. The loss of toxicity in the TIE approach did not allow for subsequent fractionation and stressor identification. Advantages of the iTIE over the TIE method were greater sensitivity and ability to detect causative toxic chemical fractions; lack of sediment collection and subsequent manipulation; and, thus, reduction in potential artifacts, more realistic exposure with slow, continual pore-water renewal in situ, ability to evaluate pore waters in sandy or rocky substrates where pore waters are difficult to collect, and a quicker phase I evaluation. Limitations of the iTIE method as compared to the TIE methods were extensive pretest assembly process, fewer phase I fractionation possibilities, and restriction to shallow waters. The results of these studies suggest that the iTIE method provides a more accurate and sensitive evaluation of pore water toxicity than the laboratory TIE method.     

Chronic sublethal sediment toxicity testing using the estuarine amphipod, Melita plumulosa (Zeidler): evaluation using metal-spiked and field-contaminated sediments

The present study describes the development of a 42-d chronic sublethal sediment toxicity test using the estuarine amphipod Melita plumulosa (Zeilder). This test was shown to predict the toxicity of metal-contaminated sediments previously found to adversely affect benthic community structure. Metals initially were tested individually by spiking reference sediment under conditions that ensured low metal concentrations in pore waters. Fertility was the most sensitive sublethal endpoint for copper- and zinc-spiked sediments, whereas cadmium-spiked sediments were not toxic to M. plumulosa, despite their high bioaccumulation of cadmium. The 42-d chronic sediment test was reproducible; however, variation between reference sediments collected from the same field location over time or from different locations did affect the reproduction of M. plumulosa. Sensitivity of M. plumulosa to metal-spiked sediments suggested that the interim sediment-quality guidelines (ISQGs) were too conservative. However, toxicity testing of sediments collected from field sites known to affect community assemblages significantly (p < 0.001) reduced the fertility of M. plumulosa, reflecting benthic community survey results and supporting the ISQGs. Bioaccumulation of cadmium and copper by M. plumulosa was elevated following chronic exposure to both laboratory and field-contaminated sediments; however, zinc bioaccumulation could be measured only in M. plumulosa exposed to field-contaminated sediments.     

Assessing sediment contamination in estuaries

Historic and ongoing sediment contamination adversely affects estuaries, among the most productive marine ecosystems in the world. However, all estuaries are not the same, and estuarine sediments cannot be treated as either fresh or marine sediments or properly assessed without understanding both seasonal and spatial estuarine variability and processes, which are reviewed. Estuaries are physicochemically unique, primarily because of their variable salinity but also because of their strong gradients in other parameters, such as temperature, pH, dissolved oxygen, redox potential, and amount and composition of particles. Salinity (overlying and interstitial) varies spatially (laterally, vertically) and temporally and is the controlling factor for partitioning of contaminants between sediments and overlying or interstitial water. Salinity also controls the distribution and types of estuarine biota. Benthic infauna are affected by interstitial salinities that can be very different than overlying salinities, resulting in large-scale seasonal species shifts in salt wedge estuaries. There are fewer estuarine species than fresh or marine species (the paradox of brackish water). Chemical, toxicological, and community-level assessment techniques for estuarine sediment are reviewed and assessed, including chemistry (grain size effects, background enrichment, bioavailability, sediment quality values, interstitial water chemistry), biological surveys, and whole sediment toxicity testing (single-species tests, potential confounding factors, community level tests, laboratory-to-field comparisons). Based on this review, there is a clear need to tailor such assessment techniques specifically for estuarine environments. For instance, bioavailability models including equilibrium partitioning may have little applicability to estuarine sediments, appropriate reference comparisons are difficult in biological surveys, and there are too few full-gradient estuarine sediment toxicity tests available. Specific recommendations are made to address these and other issues.     

Linking ecological impact to metal concentrations and speciation: a microcosm experiment using a salt marsh meiofaunal community

Microcosm experiments addressed the impact of a mixture of Cu, Cr, Cd, Pb, and Hg at three concentrations after 36 h, 12 d, and 30 d on a meiofauna-dominated salt marsh community. In addition to analyzing effects on meiofaunal abundances, the study quantified the sediment metal concentrations of all five metals and pore-water concentrations, speciation, and ligand complexation of Cu. Abundances of deposit feeders such as the polychaete Streblospio benedicti, gastropods, and bivalves were impacted at lower metal concentrations than the mainly algal-feeding copepods, ostracods, and nematodes. We suggest that this might be due to bulk ingestion of metal-contaminated sediments resulting in relatively higher metal exposure in the deposit feeders than in the other, nondeposit feeding taxa. Copepod and ostracod abundances decreased only in the highest metal treatment, where levels of inorganic Cu ([Cu']) in pore waters were similar to levels associated with both acute and subacute toxicity in published in vivo toxicity studies of marine copepods. The higher metal treatments yielded disproportionately higher pore-water [Cu] compared with sediment [Cu], suggesting saturation of sediment-associated ligands with increased additions of Cu. Similarly, the higher metal treatments appeared to reach saturation of the organic Cu ligands, with the excess pore-water [Cu] present in the more toxic, inorganic species of Cu. Acid-volatile sulfide (AVS) concentrations at sediment horizons inhabited by meiofauna were low and AVS was not considered a significant metal ligand at these depths. Since meiofauna are predominantly associated with oxic surface sediments, it is doubtful that AVS is a major factor controlling availability of free metal for exposure to these taxa.     

Assessment of Metal Toxicity in Sediment Pore Water from Lake Macquarie,Australia

Recent investigations into the level of heavy metal enrichment in the sediments of Lake Macquarie have indicated that significant contamination has occurred over the past 100 years, with elevated levels of lead, zinc, cadmium, copper, and selenium being observed in most parts of the lake. Pore water extracted from sediments showing the greatest contamination by these metals exhibited toxicity to the larval development of the sea urchin Heliocidaris tuberculata. However, an analysis of pore water metal concentrations revealed that the concentrations of these metals were too low to cause toxicity. Rather, pore water toxicity was highly correlated with manganese for the majority of sites sampled; subsequent spiking experiments confirmed manganese as a cause of toxicity. Current levels of manganese in the sediments of Lake Macquarie have arisen from natural sources and are not the result of anthropogenic activities. These results reiterate the importance of identifying the causes of toxicity in assessments of sediment contamination, particularly when testing sediment pore waters using sensitive early life stages. Received: 31 January 2002/Accepted: 5 September 2002     

Mobility and bioavailability of trace metals in sulfidic coastal sediments

High concentrations of Hg, Cd, Pb, Cu, and Zn were found in the euxinic sediment of the inner archipelago of Stockholm. In the sulfide-rich sediment, they are precipitated as metal sulfides with low dissolving capacity and bioavailability. In two experiments, the significance of acid-volatile sulfide (AVS) and dissolved sulfides for mobility, bioavailability, and toxicity of metals were studied by oxygenation of intact sediment cores. Influence of bioturbating deposit-feeding amphipods, that is, Monoporeia affinis, was examined on studied sediment processes. Results showed a low mobility of most metals except Cd and Zn. Bioturbation did not enhance mobility. Cd and Zn, released from the sediment, were not bioaccumulated in amphipods. In contrast, the less mobile metals Hg and Pb were bioaccumulated. A low toxicity of contaminated sediments, in terms of mortality and embryonic malformations of amphipods, was recorded. Results indicate that Cd, Zn, and Cu are comparatively unavailable after oxygenation of the metal sulfides. Similar results were recorded in contaminated sediments differing in redox potential, AVS, dissolved sulfides, and organic contents, suggesting that other metal ligands, in addition to AVS, are important for metal bioavailability and toxicity in anoxic and suboxic environments.     

Mobility and toxicity of metals in sandy sediments deposited on land

A times series of laboratory experiments were conducted to investigate the effect of land deposition of contaminated sediments on the bioavailability and mobility of metals. Four sandy sediments were sampled at sites expected to have elevated levels of cadmium and zinc. The physical and chemical characteristics and ecotoxicity of sediments, pore waters, and leachates were evaluated after periods ranging from 1 to 45 days of land deposition. Cd and Zn retardation and leaching potential were calculated and this simulation gave good predictions of subsequently observed Cd and Zn mobility. The mobility and leaching of Cd and Zn in the sediments increased with decreasing pH and with decreasing content of organic matter. During the deposition an increase in sediment toxicity to plants and an increase in eluate toxicity to invertebrates were observed. A high rate of water flow through the sediment resulted in a lower toxicity enhancement of the sediments and a higher toxicity enhancement of the eluates. This result suggests that water flow through the sediment reduces the actual toxicity of the upper layer of deposited sediment but at the same time intensifies the risk of groundwater contamination.     

Importance of equilibration time in the partitioning and toxicity of zinc in spiked sediment bioassays

The influences of spiked Zn concentrations (1-40 micromol/g) and equilibration time (approximately 95 d) on the partitioning of Zn between pore water (PW) and sediment were evaluated with estuarine sediments containing two levels (5 and 15 micromol/g) of acid volatile sulfides (AVS). Their influence on Zn bioavailability was also evaluated by a parallel, 10-d amphipod (Leptocheirus plumulosus) mortality test at 5, 20, and 85 d of equilibration. During the equilibration, AVS increased (up to twofold) with spiked Zn concentration ([Zn]), whereas Zn-simultaneously extracted metals ([SEM]; Zn with AVS) remained relatively constant. Concentrations of Zn in PW decreased most rapidly during the initial 30 d and by 11- to 23-fold during the whole 95-d equilibration period. The apparent partitioning coefficient (Kpw, ratio of [Zn] in SEM to PW) increased by 10- to 20-fold with time and decreased with spiked [Zn] in sediments. The decrease of PW [Zn] could be explained by a combination of changes in AVS and redistribution of Zn into more insoluble phases as the sediment aged. Amphipod mortality decreased significantly with the equilibration time, consistent with decrease in dissolved [Zn]. The median lethal concentration (LC50) value (33 microM) in the second bioassay, conducted after 20 d of equilibration, was twofold the LC50 in the initial bioassay at 5 d of equilibration, probably because of the change of dissolved Zn speciation. Sediment bioassay protocols employing a short equilibration time and high spiked metal concentrations could accentuate partitioning of metals to the dissolved phase and shift the pathway for metal exposure toward the dissolved phase.     

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.     

Effects of triclosan on marine benthic and epibenthic organisms

Triclosan is an antimicrobial compound that has been widely used in consumer products such as toothpaste, deodorant, and shampoo. Because of its widespread use, triclosan has been detected in various environmental media, including wastewater, sewage sludge, surface waters, and sediments. Triclosan is acutely toxic to numerous aquatic organisms, but very few studies have been performed on estuarine and marine benthic organisms. For whole sediment toxicity tests, the sediment-dwelling estuarine amphipod, Ampelisca abdita, and the epibenthic mysid shrimp, Americamysis bahia, are commonly used organisms. In the present study, median lethal concentration values (LC50) were obtained for both of these organisms using water-only and whole sediment exposures. Acute 96-h water-only toxicity tests resulted in LC50 values of 73.4 and 74.3 μg/L for the amphipod and mysid, respectively. For the 7-d whole sediment toxicity test, LC50 values were 303 and 257 mg/kg (dry wt) for the amphipod and mysid, respectively. Using equilibrium partitioning theory, these whole sediment values are equivalent to interstitial water LC50 values of 230 and 190 μg/L for the amphipod and mysid, respectively, which are within a threefold difference of the observed 96-h LC50 water-only values. Triclosan was found to accumulate in polychaete tissue in a 28-d bioaccumulation study with a biota-sediment accumulation factor of 0.23 kg organic carbon/kg lipid. These data provide some of the first toxicity data for triclosan with marine benthic and epibenthic species while also indicating a need to better understand the effects of other forms of sediment carbon, triclosan ionization, and organism metabolism of triclosan on the chemical's behavior and toxicity in the aquatic environment.     

Toxicity of Sediment Collected Upriver and Downriver of Major Cities Along the Lower Mississippi River

The Lower Mississippi River contributes significantly to the biodiversity and ecological stability of the alluvial valley, but agricultural, industrial, and municipal developments have historically impacted environmental quality of the river. Toxicity of sediment and sediment pore water was used to assess the current effects of major cities on sediment quality along the Lower Mississippi River. Composite sediment samples were collected from four sites upriver and four sites downriver of five major cities: Cairo, IL; Memphis, TN; Vicksburg, MS; Baton Rouge, LA; and New Orleans, LA. Acute toxicity was determined by exposing Hyalella azteca to solid-phase sediment for 10 days with two water renewals per day and to sediment pore water under static conditions for 96 h. After the initial tests, animals were exposed to ultraviolet light for 16 h. Sediments were analyzed for organics (organochlorine pesticides, PCBs, organophosphate insecticides, and PAHs) and metals (Cr, Cu, Pb, Mn, Ni, Zn). With the exception of upriver from Memphis, solid-phase sediments were not toxic to H. azteca. Pore water from sediments collected upriver of Memphis also showed slight toxicity. Exposure of H. azteca to ultraviolet light did not increase the toxicity of the sediment or pore-water samples, indicating a lack of toxicity from PAHs that are photoactivated by ultraviolet light. Chemical analyses did not reveal any contaminant levels of concern in the sediments. Based on toxicity testing and chemical analyses, quality of sediments collected from the Lower Mississippi was good, with the exception of sites sampled upriver of Memphis. Received: 3 June 1997/Accepted: 22 December 1997     

Amendment of sediments with a carbonaceous resin reduces bioavailability of polycyclic aromatic hydrocarbons

We evaluated the effectiveness of Ambersorb, a carbonaceous resin, in reducing bioavailability of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediments collected from the field. In laboratory studies, sediment pore-water concentrations of eight unsubstituted PAHs were significantly decreased after resin addition. Reduced PAH concentrations in oligochaete tissues from a laboratory bioaccumulation test, along with increased survival/reproduction and reduced photo-enhanced toxicity and sediment avoidance, also resulted from sediment treatment with Ambersorb. Resin amendment also decreased pore-water PAH concentrations in field deployed sediments but did not improve benthic invertebrate colonization. Prediction of partitioning of PAHs between solid and aqueous phases in the test sediments was complicated by the presence of coal and soot. However, accurate predictions of bioavailability were achieved based on pore-water chemistry. Overall, these studies show that the addition of high affinity sorbents effectively reduces pore-water PAH concentrations and bioavailability and suggests that sorbent addition may serve as an option for in situ remediation of some contaminated sediments.     

Sediment geochemical controls on CD, CR, and ZN assmilation by the clam Ruditapes philippinarum

Several important sediment geochemical factors (particle size, contact time, artificial sediment composition, acid volatile sulfide, and pure inorganic particles coated or uncoated with humic acid) were examined for their influences on the assimilation of Cd, Cr, and Zn in the marine clam Ruditapes philippinarum. Metal desorption and phase speciation were concurrently measured for these particles. Differences in particle size did not significantly affect metal assimilation. Increasing contact time with sediments decreased assimilation by the clams of Cr and Zn, but not of Cd. A significant positive relationship was found between the metal assimilation efficiency (AE) and the metal partitioning in the exchangeable fraction of sediments for Cd and Zn. The assimilation of metals was negatively dependent on the metal distribution in the reducible (Fe oxide) fraction, indicating that Fe oxide reduced metal bioavailability to the clams. Metal AEs measured with artificially prepared sediments were comparable to those measured with natural sediments. The AEs were significantly higher in artificial sediment without Fe oxide. Humic acid coating appeared to have no major and consistent influence on metal assimilation by the clams. The AEs measured for pure inorganic particles were much higher than those measured for sediments or artificially prepared sediments, except for the Fe oxide particles, indicating that digestion may behave differently for pure particles. Metals bound to artificially synthesized acid volatile sulfide were much less bioavailable to the clams. The AEs were as low as 4% for Cd and 7% for Zn, whereas the AE for Cr was somewhat similar to those measured for other types of particles. When all particle types (natural sediments, artificial sediment, and pure particles) were considered, a significant relationship was found between Cd AE and its desorption in seawater. This study has demonstrated that several geochemical fractions of the sediments, particularly the exchangeable, Fe oxide, and sulfide fractions, are important in determining metal bioavailability from sediments to clams.     

Influence of sediment ingestion and exposure concentration on the bioavailable fraction of sediment-associated tetrachlorobiphenyl in oligochaetes

The desorption and bioavailability of 3,3',4,4'-tetrachlorobiphenyl (PCB 77) were studied in spiked natural sediments at six concentrations. The desorption kinetics were measured in a sediment-water suspension using Tenax resin extraction, and the bioavailability was measured by exposing Lumbriculus variegatus (Oligochaeta) to PCB 77-spiked sediment in a 14-d kinetic study. In addition, freely dissolved pore-water concentrations were measured using the polyoxymethylene solid-phase extraction method. The present study examined whether bioavailability can be defined more accurately by measuring the size of desorbing fractions and the pore-water concentrations than by using the standard equilibrium partitioning approach. The importance of ingested sediment in bioaccumulation also was investigated. Our data showed a clear, decreasing trend in the rapid-desorbing fractions and in the standard biota-sediment accumulation factors (BSAF) with increasing concentration in sediment. Desorbing fractions-refined BSAFs were more uniform across the concentration treatments, and the pore-water PCB 77 concentration predicted tissue concentrations close to observed values. In the risk assessment process, pore-water concentration or desorbing fractions would lead to more precise bioavailability estimates compared with those from the traditional equilibrium partitioning approach. The result also showed, however, that sediment-ingesting worms had access to an additional bioavailable chemical fraction that was especially evident when PCB 77 pore-water concentrations most likely approached the solubility limit. Thus, feeding may modify the bioavailable fraction that cannot be explained by simple equilibrium partitioning models.     

Effects of cyclic changes in pH and salinity on metals release from sediments

The effects of dynamic changes in pH and salinity on metal speciation and release are investigated with sediments posed in a simulated estuarine environment. The release of Zn, Cd, Mn, and Fe was studied using sediment from the Anacostia River (Washington, DC, USA) spiked with freshly precipitated amorphous cadmium sulfide to increase Cd content. The sediment was exposed to salt water (high pH, ionic strength) and freshwater (neutral pH, minimal ionic strength) continuously and alternately (to mimic tidal changes) in small microcosms over 100 d. At the conclusion of the experiments, the vertical profiles of acid volatile sulfide (AVS) and simultaneously extracted metals (SEM) as well as porewater metals and anion concentrations were characterized. Acid volatile sulfide oxidation at the sediment surface led to a commensurate increase in dissolved metal species and metal release that was strongly dependent on the changes in the overlying water characteristics. Total Cd release was substantially higher during exposure to salt water, although, as a result of complexation, predicted dissolved Cd(2+) concentration in the overlying water was higher during exposure to freshwater. Total Zn release was little changed during exposure to salt water and freshwater, although the predicted dissolved Zn(2+) concentration was much higher during freshwater exposures. No significant iron was released because of the rapid oxidation of ferrous iron (Fe(2+)) in aerobic surficial sediments and overlying water. The present study suggests that cyclic changes in pH and salinity in the overlying water can dramatically influence metal release from estuarine sediments.     

Analysis of pyrethroids in sediment pore water by solid-phase microextraction

Sediment toxicity from trace contamination of pyrethroid insecticides is an emerging water quality concern. Pyrethroids are highly hydrophobic, and their sediment toxicity is related to the freely dissolved concentration in pore water. Solid-phase microextraction (SPME) was evaluated as a selective method to analyze free concentrations of eight pyrethroids in sediment pore water, and SPME measurements were compared to total pore-water concentrations measured using a conventional liquid-liquid extraction (LLE) method. Free pore-water concentrations detected by SPME (C(w-SPME)) were 4.1 to 37% of the total concentration given by LLE (C(w-LLE)) in pore water prepared from a freshwater sediment and only 3.2 to 13.3% in the pore water of a marine sediment. The difference suggested predominant partitioning of pyrethroids into the dissolved organic matter phase in pore water. The method detection limits of the SPME method were lower than the 10th percentile of the reported median lethal concentrations for aquatic organisms, with relative standard deviation <20% as determined over 200 analyses. The SPME method was further used to analyze field-contaminated sediment samples. Those analyses showed that the phase distribution of pyrethroids in sediment was influenced by sediment type and other conditions. Our results show that SPME provides a sensitive, reproducible, and practical method for screening sediment toxicity from potential pyrethroid contamination.     

A vacuum-operated pore-water extractor for estuarine and freshwater sediments

A vacuum-operated pore-water extractor for estuarine and freshwater sediments was developed and constructed from a fused-glass air stone attached with aquarium airline tubing to a 30 or 60 cc polypropylene syringe. Pore water is extracted by inserting the air stone into the sediment and creating a vacuum by retracting and bracing the syringe plunger. A hand-operated vacuum pump attached to a filtration flask was also evaluated as an alternative vacuum source. The volume and time to extract pore water varies with the number of devices and the sediment particle size. Extraction time is longer for fine sediments than for sandy sediments. Four liters of sediment generally yield between 500 and 1,500 mL of pore water. The sediment that surrounds and accumulates on the air stone acts as a filter, and, except for the first few milliliters, the collected pore water is clear. Because there is no exposure to air or avenue for escape, volatile compounds andin situ characteristics are retained in the extracted pore water.     

Predicting sediment metal toxicity using a sediment biotic ligand model: methodology and initial application

An extension of the simultaneously extracted metals/acid-volatile sulfide (SEM/AVS) procedure is presented that predicts the acute and chronic sediment metals effects concentrations. A biotic ligand model (BLM) and a pore water-sediment partitioning model are used to predict the sediment concentration that is in equilibrium with the biotic ligand effects concentration. This initial application considers only partitioning to sediment particulate organic carbon. This procedure bypasses the need to compute the details of the pore-water chemistry. Remarkably, the median lethal concentration on a sediment organic carbon (OC)-normalized basis, SEM*(x,OC), is essentially unchanged over a wide range of concentrations of pore-water hardness, salinity, dissolved organic carbon, and any other complexing or competing ligands. Only the pore-water pH is important. Both acute and chronic exposures in fresh- and saltwater sediments are compared to predictions for cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) based on the Daphnia magna BLM. The SEM*(x,OC) concentrations are similar for all the metals except cadmium. For pH = 8, the approximate values (micromol/gOC) are Cd-SEM*(xOC) approximately equal to 100, Cu-SEM*(x,OC) approximately equal to 900, Ni-SEMoc approximately equal to 1,100, Zn-SEM*(x,OC) approximately equal to 1,400, and Pb-SEM*(x,OC) approximately equal to 2,700. This similarity is the explanation for an empirically observed dose-response relationship between SEM and acute and chronic effects concentrations that had been observed previously. This initial application clearly demonstrates that BLMs can be used to predict toxic sediment concentrations without modeling the pore-water chemistry.