Trace metal behaviour in estuarine and riverine floodplain soils and sediments: A review

Bio-electrochemical systems (BESs) have recently emerged as an exciting technology. In a BES, bacteria interact with electrodes using electrons, which are either removed or supplied through an electrical circuit. The most-described type of BES is microbial fuel cells (MFCs), in which useful power is generated from electron donors as, for example, present in wastewater. This form of charge transport, known as extracellular electron transfer, was previously extensively described with respect to metals such as iron and manganese. The importance of these interactions in global biogeochemical cycles is essentially undisputed. A wide variety of bacteria can participate in extracellular electron transfer, and this phenomenon is far more widespread than previously thought. The use of BESs in diverse research projects is helping elucidate the mechanism by which bacteria shuttle electrons externally. New forms of interactions between bacteria have been discovered demonstrating how multiple populations within microbial communities can co-operate to achieve energy generation. New environmental processes that were difficult to observe or study previously can now be simulated and improved via BESs. Whereas pure culture studies make up the majority of the studies performed thus far, even greater contributions of BESs are expected to occur in natural environments and with mixed microbial communities. Owing to their versatility, unmatched level of control and capacity to sustain novel processes, BESs might well serve as the foundation of a new environmental biotechnology. While highlighting some of the major breakthroughs and addressing only recently obtained data, this review points out that despite rapid progress, many questions remain unanswered.

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Microbial ecology meets electrochemistry: electricity-driven and driving communities.

The science of sediment toxicology essentially began in the late 1970s. It was largely a product of dredging concerns and recognition of widespread contamination of sediments. During the past few years, sediment toxicity research activity has increased dramatically. Currently, most tests are of an acute nature with fewer available for determining sublethal endpoints of chronic toxicity. Test systems of single and multiple species have included most levels of biological organization in aquatic ecosystems and have been conducted in the laboratory on whole sediments, interstitial waters, elutriates, or other extractable fractions under a wide variety of conditions. Evaluations of methodological effects and comparisons with in situ toxicity using surrogate test species and indigenous communities have, on occasion, shown significant differences in test responses. These differences may be attributed to laboratory-controlled parameters (e.g., light, species, life stage, exposure conditions, test phase, spiking method); sampling and laboratory-induced disruption of sediment integrity; alteration of toxicant partitioning due to manipulations and temporal effects; and failure to recognize other influencing ecosystem variables (e.g., organism niche and life cycle, sediment partitioning and gradient dynamics, physicochemical and biological process integration, biotic and abiotic disturbances, micro- and macrobiota patches, food-web interactions). Optimizing and standardizing test methods will require further studies of these variables to improve inter-laboratory comparisons and ecosystem validity. Despite the many unknowns that exist, a variety of sediment toxicity tests have been effectively used in assessing toxicant contamination by measuring the bioavailable fraction of the in-place pollutants. The optimal assays vary with the study and its objectives. Intergrative studies using several chemical, community, and toxicity measures are currently the most effective at defining ecosystem perturbations.

https://setac.onlinelibrary.wiley.com/doi/pdf/10.1002/etc.5620101204

Assessing the toxicity of freshwater sediments

Contaminants in sediments: remobilisation and demobilisation.

Metal accumulation within salt marsh environments: A review

This review article covers the processes affecting trace metals in deposited sediments The sediment-water system can be divided in three parts: the oxic layer, the anoxic layer and the oxic-anoxic interface Available data show that trace metals like Cu, Zn and Cd occur as sulphides in marine and estuarine anoxic sediments Calculations show that organic complexation is unlikely and the dominant species are sulphide and bisulphide complexes Chromium and arsenic are probably present as adsorbed species on the sediments; their concentrations in the pore waters, therefore depend on the concentrations in the sediments The oxic-anoxic interface plays the major role in the potential flux of trace metals from the sediments, however this interface is not well studied at present Changes from an anoxic to an oxic environment as occurs during dredging and land disposal of contaminanted sediments may cause a remobilization of some trace metals

Sediments as a source for contaminants

Summary The migration of the heavy metals Cd, Zn, Cu, Cr and As from harbour sludge dumps into an underlying soil‐groundwater system can be calculated with the chemical model CHARON. This model is described briefly. The processes with respect to heavy metals are treated with some more detail. The results of two case studies show, that the behaviour of the metals may vary to a large extent from one case to another, mainly dependent on the hydrological, geological and geochemical characteristics of the soil‐groundwater system. Despite inevitable inaccuracies in model inputs CHARON has proved to be a useful tool for the assessment of groundwater pollution.

Modeling heavy metals in groundwater near harbour sludge disposal sites

The behaviour and concentrations of the heavy metals Cd, Zn and As in the topsoil of a harbour sludge depot have been modelled with the chemical model CHARON. This model is described briefly. The chemical processes with respect to the heavy metals are treated with some more detail. Two calculations were performed: One with a topsoil of ripening harbour sludge and one with a top-soil of sand. The results of the two calculations show, that the application of a top layer of relatively clean sand does lead to an appreciable lowering of the concentrations of the metals in the pore water, especially in the unsaturated zone. The calculated concentrations of the heavy metals in the unsaturated zone of a harbour sludge topsoil are much higher than in the reduced zone of the profile, whereas the concentrations in the unsaturated zone of sandy topsoil are lower than the concentrations in the reduced zone.

Modeling Heavy Metals in the Top Soil of a Harbour Sludge Depot

Methodology for determinations of heavy metal standards for soil

The surface water quality of Lake Heenvliet has been modelled in relation to planned disposal of polluted harbor sludge in the lake. Lake Heenvliet is a small lake situated near the Rotterdam harbor area, from which the sludge is dredged.

J. Bril

Papers

Sediments as a source for contaminants

Modeling heavy metals in groundwater near harbour sludge disposal sites

Modeling Heavy Metals in the Top Soil of a Harbour Sludge Depot

Methodology for determinations of heavy metal standards for soil

Modelling Water Quality of Lake Heenvliet in Relation to Planned Disposal of Harbor Sludge