Assessing the Effects of Bioturbation on Metal Bioavailability in Contaminated Sediments by Diffusive Gradients in Thin Films (DGT).

The burrowing and feeding activities of benthic organisms can alter metal speciation in sediments and affect an organisms' exposure to metals. Recently, the performance of the in situ technique of diffusive gradients in thin films (DGT) for predicting metal bioavailability has been investigated in response to the increasing demand of considering contaminant bioavailability in sediment quality assessments. In this study, we test the ability of the DGT technique for predicting the metal bioavailability in clean and contaminated sediments that are being subjected to varying degrees of sediments disturbance: low bioturbation (bivalve Tellina deltoidalis alone) and high bioturbation (bivalve and actively burrowing amphipod, Victoriopisa australiensis). Significant release of DGT-labile Cd, Ni, Pb, and Zn, but lower Cu and Fe, occurred in the pore and overlying waters of sediments exposed to high bioturbation conditions, resulting in higher bioaccumulation of zinc in bivalves. Strong relationships were found between bioaccumulation of Pb and Zn and time-integrated DGT-metal fluxes, whereas poor relationships were obtained using total or dilute-acid extractable metal concentrations. This results demonstrate that DGT is a useful tool for assessing metal bioavailability in sediments and can provide useful predictions of metal bioavailable to benthic organisms in dynamic sediment environments.

Metal Fluxes from Porewaters and Labile Sediment Phases for Predicting Metal Exposure and Bioaccumulation in Benthic Invertebrates.

The use of diffusive gradients in thin films (DGT) for predicting metal bioavailability was investigated by exposing the bivalve Tellina deltoidalis to an identical series of metal-contaminated sediments deployed simultaneously in the field and laboratory. To understand the differences in metal exposure occurring between laboratory- and field-based bioassays, we investigated changes in metal fluxes to DGT probes in sediments and in metal concentrations and partitioning to porewaters and overlying waters. DGT-metal fluxes (Cu, Pb, and Zn) were lower in the overlying waters of most field bioassays compared to the laboratory, causing differences in Pb and Zn bioaccumulation between bivalves exposed to laboratory and field conditions. Overall, DGT-metal fluxes provided predictions of metal bioaccumulation similar to those obtained using dilute-acid extractable metal measurements. This study demonstrates that, irrespective of the physicochemical properties of the sediment and type of exposure (laboratory or field), sediments pose a significant risk of bioaccumulation by T. deltoidalis when the Cu, Pb, and Zn DGT flux exceeds 3.5, 1.3, and 156 µg/h/m(2), respectively. The results presented here support the use of the DGT technique for sediment quality assessment and the hypothesis that DGT-metal fluxes may potentially be useful surrogates for the lability of metals for all exposure routes.

Diffusive gradients in thin films technique provide robust prediction of metal bioavailability and toxicity in estuarine sediments.

Many sediment quality assessment frameworks incorporate contaminant bioavailability as a critical factor regulating toxicity in aquatic ecosystems. However, current approaches do not always adequately predict metal bioavailability to organisms living in the oxidized sediment surface layers. The deployment of the diffusive gradients in thin films (DGT) probes in sediments allows labile metals present in pore waters and weakly bound to the particulate phase to be assessed in a time-integrated manner in situ. In this study, relationships between DGT-labile metal fluxes within 5 mm of the sediment-water interface and lethal and sublethal effects to the amphipod Melita plumulosa were assessed in a range of contaminated estuarine sediments during 10-day laboratory-based bioassays. To account for differing toxicities of metals, DGT fluxes were normalized to water (WQG) or sediment quality guidelines or toxicity thresholds specific for the amphipod. The better dose-response relationship appeared to be the one based on WQG-normalized DGT fluxes, which successfully predicted toxicity despite the wide range of metals and large variations in sediment properties. The study indicated that the labile fraction of metals measured by DGT is useful for predicting metal toxicity to benthic invertebrates, supporting the applicability of this technique as a rapid monitoring tool for sediments quality assessments.

Making waves: Xanthates on the radar - Environmental risks and water quality impact.

Xanthates, derivatives of xanthic acid, are widely utilized across industries such as agrochemicals, rubber processing, pharmaceuticals, metallurgical, paper and mining to help separate metals from ore. Despite their prevalent use, many registered xanthates lack comprehensive information on potential risks to human health and the environment. The mining sector, a significant consumer of xanthates, drives demand. However, emissions into the environment remain poorly understood, especially concerning water quality. A recent EU parliamentary voting on water legislation highlights the urgency to address water pollution and the potential toxicity of xanthates. While limited data exist on xanthate presence in the environment, existing studies indicate their toxicity and contribution to environmental pollution, primarily due to carbon disulfide, a decomposition product. Concerns are mounting over the release of xanthates and carbon disulfide, particularly in mining areas near populated regions and river tributaries, raising questions about downstream impacts and public health risks. Proposed expansions of xanthate-reliant mining activities in Europe, heighten concerns about emissions and water quality impacts. Current databases lack xanthate-related monitoring data, hindering environmental and health risk assessments. Addressing this gap requires water sampling and chemical analysis and investigations into the use, occurrence, and potential impacts of xanthates from industrial activities on water bodies, including those used for drinking water production is imperative.

Field application of a novel active-passive sampling technique for the simultaneous measurement of a wide range of contaminants in water.

A first test of the field capabilities of a novel in situ sampling technique combining active and passive sampling (APS) was conducted in the sea. The proof-of-concept device uses a pump to draw water into a diffusion cell where dissolved target substances are accumulated onto sorbents which are selective for different classes of contaminants (i.e., metal cations, polar and non-polar organic compounds), simultaneously. A controlled laminar flow established in the diffusion cell enables measurements of contaminant concentrations that are fully independent from the hydrodynamic conditions in the bulk solution. APS measurements were consistent with those obtained using conventional passive sampling techniques such as organic diffusive gradients in thin films (o-DGT) and silicone rubber (SR) samplers (generally < 40% difference), taking into account the prevailing hydrodynamic conditions. The use of performance reference compounds (PRC) for hydrophobic contaminants provided additional information. Field measurements of metal ions in seawater showed large variability due to issues related to the device configuration. An improved field set-up deployed in supplementary freshwater mesocosm experiments provided metal speciation data that was consistent with passive sampling measurements (DGT), taking into account the hydrodynamic conditions. Overall, the results indicate that the APS technique provides a promising approach for the determination of a wide range of contaminants simultaneously, and independently from the hydrodynamic conditions in the bulk solution.

Characterization of the accumulation of metals and organic contaminants on a novel active-passive sampling device under controlled water flow conditions.

Recently, a new sampling device combining active and passive sampling (APS) was developed for the measurement of time-averaged concentrations of metal species and both polar and non-polar organic contaminants in water. By coupling a diffusion cell (loaded with a set of sorbents selective for different substances) with a small pump and a flow meter, the APS device is able to perform in situ measurements that are independent of the hydrodynamic conditions in the exposure medium. In the present study, the diffusion layer thickness (δ) at the sorbent/solution interface within the diffusion cell was characterised under controlled flow conditions. Laboratory tests indicated that, in the range of flow rates investigated, the average diffusion layer thickness (δ¯) varied from ∼60 to ∼110 µm, depending on the type of substance measured and the position of the sorbent with respect to the flow direction. Due to its ability to maintain an approximately constant δ¯, good to excellent agreement was found between measurements performed with the APS device in non-complexing media and concentrations measured in discrete water samples for all the substances investigated. These results suggest that the APS device could overcome issues affecting the quantitative interpretation of measurements by conventional passive sampling devices and serve as a useful tool for simultaneously monitoring a wide range of contaminants in water.

Field and laboratory evaluation of DGT for predicting metal bioaccumulation and toxicity in the freshwater bivalve Hyridella australis exposed to contaminated sediments.

The diffusive gradients in thin films (DGT) technique has shown to be a useful tool for predicting metal bioavailability and toxicity in sediments, however, links between DGT measurements and biological responses have often relied on laboratory-based exposures and further field evaluations are required. In this study, DGT probes were deployed in metal-contaminated (Cd, Pb, Zn) sediments to evaluate relationships between bioaccumulation by the freshwater bivalve Hyridella australis and DGT-metal fluxes under both laboratory and field conditions. The DGT-metal flux measured across the sediment/water interface (±1 cm) was useful for predicting significant cadmium and zinc bioaccumulation, irrespective of the type of sediment and exposure. A greater DGT-Zn flux measured in the field was consistent with significantly higher zinc bioaccumulation, highlighting the importance of performing metal bioavailability assessments in situ. In addition, DGT fluxes were useful for predicting the potential risk of sub-lethal toxicity (i.e., lipid peroxidation and lysosomal membrane damage). Due to its ability to account for multiple metal exposures, DGT better predicted bioaccumulation and toxicity than particulate metal concentrations in sediments. These results provide further evidence supporting the applicability of the DGT technique as a monitoring tool for sediment quality assessment.

A novel active-passive sampling approach for measuring time-averaged concentrations of pollutants in water.

Passive sampling with in situ devices offers several advantages over traditional sampling methods (i.e., discrete spot sampling), however, data interpretation from conventional passive samplers is hampered by difficulties in estimating the thickness of the diffusion layer at the sampler/medium interface (δ), often leading to inaccurate determinations of target analyte concentrations. In this study, the performance of a novel device combining active and passive sampling was investigated in the laboratory. The active-passive sampling (APS) device is comprised of a diffusion cell fitted with a pump and a flowmeter. Three receiving phases traditionally used in passive sampling devices (i.e., chelex resin, Oasis HLB, and silicone rubber), were incorporated in the diffusion cell and allowed the simultaneous accumulation of cationic metals, polar, and non-polar organic compounds, respectively. The flow within the diffusion cell was accurately controlled and monitored, and, combined with diffusion coefficients measurements, enabled the average δ to be estimated. Strong agreement between APS and time-averaged total concentrations measured in discrete water samples was found for most of the substances investigated. Accuracies for metals ranged between 87 and 116%, except Cu and Pb (∼50%), whilst accuracies between 64 and 101%, and 92 and 151% were achieved for polar and non-polar organic compounds, respectively. These results indicate that, via a well-defined in situ preconcentration step, the proposed APS approach shows promise for monitoring the concentration of a range of pollutants in water.

The impact of sediment bioturbation by secondary organisms on metal bioavailability, bioaccumulation and toxicity to target organisms in benthic bioassays: Implications for sediment quality assessment.

Bioturbation alters the properties of sediments and modifies contaminant bioavailability to benthic organisms. These naturally occurring disturbances are seldom considered during the assessment of sediment quality. We investigated how the presence (High bioturbation) and absence (Low bioturbation) of a strongly bioturbating amphipod within three different sediments influenced metal bioavailability, survival and bioaccumulation of metals to the bivalve Tellina deltoidalis. The concentrations of dissolved copper decreased and manganese increased with increased bioturbation. For copper a strong correlation was observed between increased bivalve survival (53-100%) and dissolved concentrations in the overlying water. Increased bioturbation intensity resulted in greater tissue concentrations for chromium and zinc in some test sediments. Overall, the results highlight the strong influence that the natural bioturbation activities from one organism may have on the risk contaminants pose to other organisms within the local environment. The characterisation of field-based exposure conditions concerning the biotic or abiotic resuspension of sediments and the rate of attenuation of released contaminants through dilution or readsorption may enable laboratory-based bioassay designs to be adapted to better match those of the assessed environment.

The mismatch between bioaccumulation in field and laboratory environments: Interpreting the differences for metals in benthic bivalves.

Laboratory-based bioaccumulation and toxicity bioassays are frequently used to predict the ecological risk of contaminated sediments in the field. This study investigates the bioassay conditions most relevant to achieving environmentally relevant field exposures. An identical series of metal-contaminated marine sediments were deployed in the field and laboratory over 31 days. Changes in metal concentrations and partitioning in both sediments and waters were used to interpret differences in metal exposure and bioaccumulation to the benthic bivalve Tellina deltoidalis. Loss of resuspended sediments and deposition of suspended particulate matter from the overlying water resulted in the concentrations of Cu, Pb and Zn (major contaminants) becoming lower in the 1-cm surface layer of field-deployed sediments. Lower exchange rates of overlying waters in the laboratory resulted in higher dissolved metal exposures. The prediction of metal bioaccumulation by the bivalves in field and laboratory was improved by considering the metal partitioning within the surface sediments.