Changes In Metal Speciation Research Articles

The potential of ferrihydrite-synthetic humic-like acid composite as a soil amendment for metal-contaminated agricultural soil: Immobilization mechanisms by combining abiotic and biotic perspectives

In-situ passivation technique has attracted increasing attention for metal-contaminated agricultural soil remediation. However, metal immobilization mechanisms are mostly illustrated based on metal speciation changes and alterations in soil physicochemical properties from a macroscopic and abiotic perspective. In this study, a ferrihydrite-synthetic humic-like acid composite (FH-SHLA) was fabricated and applied as a passivator for a 90-day soil incubation. The heavy metals immobilization mechanisms of FH-SHLA were investigated by combining both abiotic and biotic perspectives. Effects of FH-SHLA application on soil micro-ecology were also evaluated. The results showed that the 5%FH-SHLA treatment significantly decreased the DTPA-extractable Pb, Cd and Zn by 80.75%, 46.82% and 63.63% after 90 days of incubation (P < 0.05), respectively. Besides, 5% FH-SHLA addition significantly increased soil pH, soil organic matter content and cation exchange capacity (P < 0.05). The SEM, FTIR, and XPS characterizations revealed that the abiotic metal immobilization mechanisms by FH-SHLA included surface complexation, precipitation, electrostatic attraction, and cation-π interactions. For biotic perspective, in-situ microorganisms synergistically participated in the immobilization process via sulfide precipitation and Fe mineral production. FH-SHLA significantly altered the diversity and composition of the soil microbial community, and enhanced the intensity and complexity of the microbial co-occurrence network. Both metal bioavailability and soil physiochemical parameters played a vital role in shaping microbial communities, while the former contributed more. Overall, this study provides new insight into the heavy metal passivation mechanism and demonstrates that FH-SHLA is a promising and environmentally friendly amendment for metal-contaminated soil remediation.

Trace metal partitioning in the parnaíba delta in dry season, equatorial coast of Brazil

Trace metal concentrations in the particulate fractions (MP), dissolved fractions (MD) and sediments (MS), such as Ba, Cu, Co, Cr, Pb, Ni and Zn, were determined during the dry season of the largest open sea delta of Americas, the Parnaíba River Delta (Brazil). This study aimed to comprehend the distribution, dynamic changes of metal speciation and environmental quality index of trace metals in the particulate fractions and subsurface sediments in scenario of major marine influence over the delta. The trace metals bound to suspended particulate material (SPM) from weathering the drainage basin exhibited a removal trend under increases in salinity and pH. Desorption influenced the partitioning of BaMP, ZnMP, NiMP, CoMP, CuMP, and the adsorption and precipitation of PbMP and CrMP to the surface sediments. The organic matter contents in the sediments acts as an important geochemical carrier of these contaminants, and the dissolved organic carbon influences the binding of PbMD in the subsurface waters. The geoaccumulation index (Igeo) plays a crucial role in revealing potential contamination with ZnMP contents and weak association to this fraction. These results make possible the assessment of ecological risk by metal contamination and global pollution mitigation in coastal tidal estuaries under intensive physical mixing along the equatorial coast.

Investigating Nanoscale Electron Transfer Processes at the Cell-Mineral Interface in Cobalt-Doped Ferrihydrite Using Geobacter sulfurreducens: A Multi-Technique Approach

Cobalt is an essential element for life and plays a crucial role in supporting the drive to clean energy, due to its importance in rechargeable batteries. Co is often associated with Fe in the environment, but the fate of Co in Fe-rich biogeochemically-active environments is poorly understood. To address this, synchrotron-based scanning X-ray microscopy (SXM) was used investigate the behaviour of cobalt at the nanoscale in Co-Fe(III)-oxyhydroxides undergoing microbial reduction. SXM can assess spatial changes in metal speciation and organic compounds helping to elucidate the electron transfer processes occurring at the cell-mineral interface and inform on the fate of cobalt in redox horizons. G. sulfurreducens was used to reduce synthetic Co-ferrihydrite as an analogue of natural cobalt-iron-oxides. Magnetite [Fe(II)/Fe(III)3O4] production was confirmed by powder X-ray diffraction (XRD), SXM and X-ray magnetic circular dichroism (XMCD) data, where best fits of the latter suggested Co-bearing magnetite. Macro-scale XAS techniques suggested Co(III) reduction occurred and complementary SXM at the nanoscale, coupled with imaging, found localised biogenic Co(III) reduction at the cell-mineral interface via direct contact with outer membrane cytochromes. No discernible localised changes in Fe speciation were detected in the reordered cobalt-iron-oxides that were formed and at the end point of the experiment only 11% Co and 1.5% Fe had been solubilised. The solid phase retention, alongside the highly localised and preferential cobalt bioreduction observed at the nanoscale is consistent with retention of Co in redox zones. This work improves our fundamental molecular-scale understanding of the fate of Co in complex environmental systems and supports the development of biogenic Co-doped magnetite for industrial applications from drug delivery systems to magnetic recording media.

Extraction and purification of glomalin-related soil protein (GRSP) to determine the associated trace metal(loid)s

Glomalin-related soil protein (GRSP) is recalcitrant compound in the soil and sediment and plays a crucial role in metal transportation. However, potential metal speciation changes during GRSP extraction remain unreported. Here, a feasible GRSP extraction and purification procotol is described for robust determination of GRSP-bound metal(loid)s. Several spectrum patterns measured before and after GRSP extraction indicate that the GRSP extraction process does not significantly affect the mineral state of the samples. Potential bias generated by simultaneous metal release during GRSP extraction can be effectively eliminated by applying complete and independent dialysis.•Na signal appeared in the X-ray photoelectron survey spectrum after GRSP extraction, suggesting that Na exchange may be a critical process in releasing metal(loid)s.•Element maps obtained using secondary ion mass spectroscopy exhibited different distribution of C-N and Fe after GRSP extraction, thus suggesting that uncoupling of the Fe-organic framework occurred during GRSP extraction, which could result in the release of organic matter and metal(loid)s.•European Community Bureau of Reference (BCR) subsequent extraction reveals that most of the metal(loid)s were extracted from the acid-exchangeable and residual fraction during GRSP extraction. Remarkable differences in the GRSP-bound metal content before and after dialysis implied that the dialysis could remove most metal(loid)s.

Role of plant growth promoting bacteria in driving speciation gradients across soil-rhizosphere-plant interfaces in zinc-contaminated soils.

Inoculation of soil or seeds with plant growth promoting bacteria ameliorates metal toxicity to plants by changing metal speciation in plant tissues but the exact location of these changes remains unknown. Knowing where the changes occur is a critical first step to establish whether metal speciation changes are driven by microbial metabolism or by plant responses. Since bacteria concentrate in the rhizosphere, we hypothesised steep changes in metal speciation across the rhizosphere. We tested this by comparing speciation of zinc (Zn) in roots of Brassica juncea plants grown in soil contaminated with 600mgkg-1 of Zn with that of bulk and rhizospheric soil using synchrotron X-ray absorption spectroscopy (XAS). Seeds were either uninoculated or inoculated with Rhizobium leguminosarum bv. trifolii and Zn was supplied in the form of sulfide (ZnS nanoparticles) and sulfate (ZnSO4). Consistent with previous studies, Zn toxicity, as assessed by plant growth parameters, was alleviated in B.juncea inoculated with Rhizobium leguminosarum. XAS results showed that in both ZnS and ZnSO4 treatments, the most significant changes in speciation occurred between the rhizosphere and the root, and involved an increase in the proportion of organic acids and thiol complexes. In ZnS treatments, Zn phytate and Zn citrate were the dominant organic acid complexes, whilst Zn histidine also appeared in roots exposed to ZnSO4. Inoculation with bacteria was associated with the appearance of Zn cysteine and Zn formate in roots, suggesting that these two forms are driven by bacterial metabolism. In contrast, Zn complexation with phytate, citrate and histidine is attributed to plant responses, perhaps in the form of exudates, some with long range influence into the bulk soil, leading to shallower speciation gradients.

The effect of increasing water content on transition metal speciation in deep eutectic solvents

A move towards the use of green solvents in metal recovery processes is going to be necessary for the development of a sustainable circular economy. This paper determines the effect of adding water to choline chloride based deep eutectic solvents on transition metal speciation, a common method for reducing their viscosity, using UV/Vis absorption spectroscopy. Even small amounts of water (< 5 %) were seen to cause a hypsochromic shift in UV/Vis spectra, indicating a change in metal speciation. In the choline chloride – urea solvent, the hydrolysis of the studied metals (V3+, Fe3+, Ni2+, Co2+, Cu2+) was observed. In the ethylene glycol and malonic acid systems precipitation was not observed, and Mx+ − H2O interactions were generally seen to dominate above ca. 30 % H2O. The presented results will impact metal recovery process design, where water additions to deep eutectic solvents to lower viscosity must be balanced with changes in metal speciation. This will allow for optimization of pumping systems whilst maintaining an effective process.

Transformation of pig manure by passage through the gut of black soldier fly larvae (Hermetia illucens): Metal speciation, potential pathogens and metal-related functional profiling

Black soldier fly larvae (BSFL) have great potential in livestock manure disposal. However, the changes in metal speciation, microbial communities, potential pathogens during the manure transformation process by BSFL is still largely uncharacterized, as well as the underlying metal tolerance mechanism of larval gut microbiome. Here we used BSFL to convert pig manure (PM) into larval feces (BF), and investigated the metal and microbial changes in the conversion process. Physicochemical parameters (e.g. pH, electrical conductivity, total nitrogen, total phosphorus and total potassium) in PM were significantly altered compared to BF. After conversion, less than 10% of Cu and Zn were accumulated in larval bodies. The bioavailable fraction of Cu (88.3%–86.2%) and Zn (80.6%–82.3%) occupied as the primary form in PM and BF. Genera Enterococcus, Clostridium_sensu_stricto_1, Terrisporobacter and Romboutsia were substantially enriched in the final BSFL gut (GF) compared with initial gut (GI). BSFL transformation substantially reduced pathogen abundances (decreased by 89%) derived from pig manure. Functional genes involved in metal homeostasis and resistance (e.g. CutC, pcoC, cusR, zurR and zntB) were obviously strengthened (by 2.3–7.7 folds) in GF than in GI, which might partly explain the metal tolerance ability of BSFL during the livestock manure transformation process.

Ecodynamics and bioavailability of metal contaminants in a constructed wetland within an agricultural drained catchment

Constructed wetlands are designed to mitigate nutrient and pesticide fluxes from agricultural catchments. Nevertheless, information on their efficiency in removing non-degradable contaminants such as metals is still scarce. This study aimed to explore the metallic signature and fate of metals within the Rampillon wetland (France) receiving water from a drained 355-ha catchment under intensive agriculture. Original monitoring coupling classic, time-integrated and bioaccumulation-based tools was achieved to characterise spatiotemporal dynamics of various metals (As, Cd, Cr, Co, Cu, Mn, Ni, Pb, Sb, Se and Zn). To assess metal inflows and mitigation, samples of dissolved and particulate metals were collected bimonthly at the inlet and outlet of the wetland over 3 months. Simultaneously, time-integrated (sediment traps and passive samplers) and bioaccumulation-based (caged gammarids and biofilms) tools were deployed to monitor temporal changes in metal speciation and bioavailability. To gain insight into the spatial distribution of metals between abiotic and biotic matrices, sediments and indigenous invertebrates with contrasted ecologies were sampled in different cells of the wetland. The results showed time-integrated tools were more suitable than bimonthly samples to quantify metal mitigations because of temporal fluctuations and low contamination levels. Significant mitigations were thus observed in trapped sediments for all metals (ranged 11–23%, except Mn) as well as in the DGT-labile fraction for Cd, Cr, Co, Mn and Ni (ranged 13–51%). Bioaccumulation levels in biofilms also revealed a decrease in metal bioavailability at the outlet. Furthermore, the spatial survey supported the central role of sediments in metal trapping and the beneficial effect of this wetland for local biodiversity in terms of exposure. To conclude, this study provides valuable information on the ecodynamics and bioavailability of metals required for sustainable management of such artificial ecosystems and furthermore, of agricultural areas.

Chemical Conditions in the Boundary Layer Surrounding Phytoplankton Cells Modify Cadmium Bioavailability.

In this study we tested the hypothesis that metal uptake by unicellular algae may be affected by changes in metal speciation in the boundary layer surrounding the algal cells. The freshwater alga Chlamydomonas reinhardtii was preacclimated to different N nutrition regimes; changes in N nutrition are known to change the nature of extracellular metabolites (e.g., reactive oxygen species "ROS", and OH-) and thus boundary layer chemical conditions. Specifically, at a constant bulk free Cd2+ concentration, Cd uptake by N-starved algae in cysteine-buffered solution was significantly higher than that in NTA-buffered solution. This enhancement was likely due to an increase of the free Cd2+ concentration in the boundary layer, resulting from localized cysteine oxidation by ROS released from these algae. On the other hand, Cd uptake was markedly lower when the free Cd2+ concentration near cell surface decreased as a result of an increase in the boundary layer pH of nitrate-acclimated algae or enhanced localized metal complexation. The results imply that redox, acid-base and metal complexation processes in the boundary layer differ from those in bulk water, even under chemically stable bulk conditions, and the boundary layer effect may well be of significance to phytoplankton acquisition of other trace metals.

Use of earthworms Eisenia andrei on the bioremediation of contaminated area in north of Tunisia and microbial soil enzymes as bioindicator of change on heavy metals speciation

A better understanding is required of the potential of soil biota in controlling the availability and mobility of heavy metals and ascertaining their toxicity. The objectives of this work are to assess, first, the modification of heavy metal speciation induced by earthworms Eisenia andrei and, second, the consequence of this metal speciation change on soil enzyme activities as an easy bioindicator of stress. The experiment was conducted on six sites from Jebel Ressas Mines, which are characterized by a gradient heavy metal contamination (Pb, Zn, and Cd). Earthworms E. andrei were introduced in these six soils for 60 days. We had performed heavy metal speciation both in the presence and absence of worms. Modifications of activities of seven enzymes implicated in C, N, and P biochemical cycles were used as a bioindicator of metal stress. We had used the co-inertia statistical method to evaluate the correlation between change in heavy metal speciation induced by earthworms and the enzyme activities in soils. Our results suggested that earthworms modified the heavy metal dynamic and speciation. They decrease the amount of metal associated with the most available fraction, such as exchangeable one, and increase the amount of metal bound to the more stable fraction, like Mn and Fe oxide ones. On the same hand, enzyme activities increased in majority of the soils, following earthworm activity, but this effect is dependent on the amount of soil contamination. Moreover, the co-inertia results denote that change in heavy metal speciation significantly influences the soil enzyme activities in Jebel Ressas soils, especially β-glucosidase, urease, deshydrogenase, and fluorescein diacetate hydrolysis (FDA), and can be considered as bioindicators of metal toxicity and biological quality in the contaminated area. By reducing the availability of heavy metals, the earthworms are useful in the bioremediation of heavy metal contaminated soils. Soil enzymes β- glucosidase, urease, deshydrogenase, and FDA can be used to assess the changes in metal speciation and can let us, therefore, predict if the soils are bioremediated.

Geomycology: fungi as agents of biogeochemical change

Geomycology is the study of the roles of fungi in geological processes. The biogeochemical importance of fungi is significant in several areas, including nutrient and element cycling, rock, mineral and metal transformations, bioweathering and mycogenic biomineral formation. Such processes can occur in aquatic and terrestrial habitats, but it is the terrestrial environment where fungi probably have the greatest geochemical influence. Of special significance are the mutualistic relationships with phototrophic organisms: lichens (algae, cyanobacteria) and mycorrhizas (plants). Central to many geomycological processes are transformations of metals and minerals, and fungi possess many properties that effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Some fungal transformations have potential applications in environmental biotechnology, e.g. metal and radionuclide leaching, recovery, detoxification and bioremediation, and in the production or deposition of biominerals or metallic elements with catalytic or other properties. Metal and mineral transformations may also result in adverse effects when these processes result in spoilage and destruction of natural and synthetic materials, rock and mineral-based building materials (e.g. concrete), biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment.

Changes in metal speciation and mobility during electrokinetic treatment of industrial wastes: Implications for remediation and resource recovery

Industrial waste deposits contain substantial quantities of valuable metals and other resources, although often in a recalcitrant form that hinders their recovery. This paper reports an experimental programme on the application of electrokinetic (EK) processing to two different waste materials (a mine tailings deposit and a metallurgical furnace dust), with the aim of exploring the effect of EK on metal speciation and extractability, with a focus on Pb and Zn due to their prevalence in these materials. The speciation of metals within the waste was determined based on a selective sequential extraction (SSE) procedure which was applied to the materials before, during and after the application of the EK treatment. The results demonstrate the generation of an acidic front in the mine tailings, which enhanced the transport of ions associated with the more labile fractions, a behaviour typical of materials characterized by a lower buffering capacity. The application of the EK in the furnace dust showed much less effect due to a very high starting pH (10) with the higher buffering capacity posing an obstacle to transport. It is shown that EK has altered the geochemical speciation of the metals in both materials, typically redistributing them from less available SSE fractions to the more labile fractions. Zn was redistributed with the SSE fractions and mobilised to a greater extent than Pb in both samples. The changes in pH and redox potential arising as a result of the application of an electric field are likely to be the main causes of the changes in speciation of both Zn and Pb. The considerable changes in metal fractionation, including removal from more recalcitrant fractions, suggest that EK may facilitate metal recovery processes. This, combined with its applicability to fine grained materials and heterogeneous environments, demonstrates that the technique may be particularly suited to both remediation of, and in-situ resource recovery from, such materials.

TiO2 nanoparticles in sediments: Effect on the bioavailability of heavy metals in the freshwater bivalve Corbicula fluminea

Most studies investigating the influence of TiO2 NPs on heavy metal bioavailability have focused on the aqueous phase; however, few have examined the sediments containing more nanoparticles. Here, we investigated the effects of TiO2 NPs on heavy metal bioavailability in C. fluminea in sediments. The interactions between the TiO2 NPs and metals in sediments, the influence of TiO2 NPs on metals levels in aqueous phase and geochemical speciation were also explored. The results indicated the large adsorption capacity of TiO2 NPs and the strong adsorption affinity to metals caused the metals adsorbed on nanoparticles, which decreased the metals concentrations in water phase. Changes in metal speciation caused by metals in EXC, CAR, and IMO partly transported from sediments to TiO2 NPs during the aging of sediments. Heavy metals contents in C. fluminea tissues were in the order of gill>visceral mass>mantle>foot and increased with the increasing TiO2 NPs contents in sediments. TiO2 NPs enhanced the bioavailability of metals in the speciation of EXC, CAR, and IMO in sediments by the Trojan horse effects. The results can facilitate a more realistic evaluation of the environmental risks of TiO2 NPs to benthic organisms in heavy metal-contaminated sediments.

Key parameters influencing metallic element mobility associated with sediments in a daily-managed reservoir

In a hydroelectric reservoir, sediments are subject to remobilization events, water-level fluctuations and physicochemical changes. Depending on their associated metallic content, surficial oxic to suboxic sediments could constitute a major source of metals. To identify the key parameters that control metallic elements in terms of their mobility and sensitivity to reservoir management, sediments were subject to resuspension and drying/wetting cycle experiments over a wide range of pH values, solid/liquid ratios (S/L) and redox (Eh) conditions. During these tests, special attention was also paid to the influence of pretreatments on samples, i.e., drying, aeration and the leachate composition (ultrapure water vs. natural water); on the preservation of the sediment characteristics; and especially on metallic element release. The results of this study show that the pH, S/L ratio and Eh parameters are key variables in metal solubilization; the pH influences metal mobility primarily through sorption-desorption phenomena as well as the dissolution of metallic-bearing phases, the S/L ratio modifies the sorption-desorption equilibria, and the Eh primarily affects the reducible sensitive phases and associated metallic elements through dissolution-precipitation processes. Under environmental conditions, evolution of these parameters can lead to a >20% solubilization of the most mobile elements, i.e., As and Cd. These results are influenced by the sample pretreatment and experimental conditions. In fact, even if the solubilization patterns show no significant differences between dry and wet sediment depending on the physicochemical conditions, the magnitude of their release is significantly affected. Drying pretreatment induces changes in metal speciation, notably altering the distribution of the most weakly bound elements; there is almost half the amount of metallic elements associated with the exchangeable fraction in dry compared to wet sediments. The solubilization percentages were higher in the ultrapure phase than in reservoir water primarily due to the low pH, which influenced the sorption equilibria.

Effects of trace metal deficiency and supplementation on a submerged anaerobic membrane bioreactor

This study examined the effects of a deficiency in trace metals (TMs) on the performance of a submerged anaerobic membrane bioreactor (SAMBR). When trace metals were excluded from the feed to the SAMBR, COD removal and methane yield reduced while VFAs in the effluent increased. A reduction of up to 37.48% in the total metal content in the reactor was observed, while the less bioavailable fractions increased up to 13.29%. Pulse addition of trace metals for 7 days at 5-times the daily metal loading was effective in improving the performance of the SAMBR by increasing the amount of trace metals in the bioavailable fractions from 2.12% to 11.92%, with up to 87.7% of added metals retained in the reactor within 24h. However, the second and third pulse at 5 and 10-times daily metal loading did not result in similar changes in metal speciation and might have inhibited the methanogens.

The Geomycology of Elemental Cycling and Transformations in the Environment.

Geomicrobiology addresses the roles of microorganisms in geological and geochemical processes, and geomycology is a part of this topic focusing on the fungi. Geoactive roles of fungi include organic and inorganic transformations important in nutrient and element cycling, rock and mineral bioweathering, mycogenic biomineral formation, and metal-fungal interactions. Lichens and mycorrhizas are significant geoactive agents. Organic matter decomposition is important for cycling of major biomass-associated elements, e.g., C, H, N, O, P, and S, as well as all other elements found in lower concentrations. Transformations of metals and minerals are central to geomicrobiology, and fungi affect changes in metal speciation, as well as mediate mineral formation or dissolution. Such mechanisms are components of biogeochemical cycles for metals as well as associated elements in biomass, soil, rocks, and minerals, e.g., S, P, and metalloids. Fungi may have the greatest geochemical influence within the terrestrial environment. However, they are also important in the aquatic environment and are significant components of the deep subsurface, extreme environments, and habitats polluted by xenobiotics, metals, and radionuclides. Applications of geomycology include metal and radionuclide bioleaching, biorecovery, detoxification, bioremediation, and the production of biominerals or metal(loid) elements with catalytic or other properties. Adverse effects include biodeterioration of natural and synthetic materials, rock and mineral-based building materials (e.g., concrete), cultural heritage, metals, alloys, and related substances and adverse effects on radionuclide mobility and containment. The ubiquity and importance of fungi in the biosphere underline the importance of geomycology as a conceptual framework encompassing the environmental activities of fungi.

Leaching and redistribution of Cu and Pb due to simulated road runoff assessed by column leaching test, chemical analysis, and PHREEQC modeling

In this study, column leaching with artificial road runoff experiments was conducted for 30 days under intermittent leaching. The heavy metal content and partitioning in the soil used in columns were characterized before and after the leaching experiments. A leaching model, PHREEQC, was used to simulate the metal speciation changes during leaching. A large portion of Cu and Pb were leached out with ARR at the early leaching stage and a slow decrease then occurred of the metal leaching toward the end of leaching period. The content of Cu and Pb associated with the oxidizable fraction (organic and sulfide bound metals) was decreased, while the content of metals associated with carbonate fraction increased by about twofold for Pb and threefold for Cu. Geochemical modeling demonstrated that Pb speciation may be dominated by carbonate in the leached soil. Geochemical modeling also indicated that the solution was under saturated with respect to the alite, calcite, and huntite mineral phases, while carbonate minerals such as annite and cerussite, and muscovite controlled the leachability of the metals.

Lead Bioprecipitation by Yeasts Utilizing Organic Phosphorus Substrates

ABSTRACTYeasts can exhibit various mechanisms that effect changes in metal speciation, toxicity and mobility. This research has examined the role of yeast phosphatases in lead bioprecipitation when utilizing an organic phosphorus-containing substrate as the sole phosphorus source. The formation of lead-containing biominerals after growth with organic phosphorus sources (glycerol 2-phosphate, phytic acid) was demonstrated and it was found that test yeasts were capable of mediating precipitation of lead phosphate (Pb3(PO4)2), pyromorphite (Pb5(PO4)3Cl), anglesite (PbSO4), and the lead oxides massicot and litharge (PbO), with variations in the mineral types produced between the different species. All test yeasts produced pyromorphite, and most produced anglesite. Lead oxides were only detected with Pichia acacia. Lead-containing precipitates were also formed if yeast cells were pre-grown in organic-phosphorus-containing media and subsequently exposed to Pb(NO3)2. The role of phosphatases in mediating the formation of lead-containing minerals has provided further understanding of potential fungal roles in metal and mineral biogeochemistry as well as the possible significance of these mechanisms for element biorecovery or bioremediation.

Toxicological effects of short-term resuspension of metal-contaminated freshwater and marine sediments.

Sediments in navigation-dominated waterways frequently are contaminated with a variety of particle-associated pollutants and are subject to frequent short-term resuspension events. There is little information documenting whether resuspension of metal-contaminated sediments has adverse ecological effects on resident aquatic organisms. Using a novel laboratory approach, the authors examined the mobilization of Zn, Cu, Cd, Pb, Ni, and Cr during resuspension of 1 freshwater and 2 coastal marine sediments and whether resuspension and redeposition resulted in toxicity to model organisms. Sediment flux exposure chambers were used to resuspend metal-contaminated sediments from 1 site in Lake DePue, Illinois (USA), and 2 sites in Portsmouth Naval Shipyard, Maine (USA). Short-term (4-h) resuspension of sediment at environmentally relevant suspended particulate matter concentrations (<1 g/L) resulted in metal mobilization to water that was sediment and metal specific. Overall, the net release of metals from suspended particles was limited, likely because of scavenging by organic matter and Fe oxides that formed during sediment interaction with oxic water. Minimal toxicity to organisms (survival of Hyalella azteca and Daphnia magna; survival, growth, and tissue metal concentration of Neanthes arenaceodentata; bioluminescence of Pyrocystis lunula) was observed during 4-h exposure to resuspended sediments and during 4-d to 10-d post-exposure recovery periods in uncontaminated water. Redeposited suspended particles exhibited increased metal bioavailability and toxicity to H. azteca, highlighting the potential for adverse ecological impacts because of changes in metal speciation. It is important to consider interactions between organisms' life histories and sediment disturbance regimes when assessing risks to ecosystems.

Assessing Methods of Removing Metals from Wastewater: The Effect of Ferric Chloride Addition on Metal Speciation and Removal

The presence of cationic pollutant metals in municipal wastewater effluent is a concern because stringent discharge requirements cannot always be met with conventional treatment methods. Attempts to improve metal removal are often unsuccessful because a significant fraction of the cationic metals are complexed by the synthetic chelating agent ethylenediamine tetraacetic acid (EDTA). To identify practical approaches for improving metal removal, an analytical method for measuring metal-EDTA complexes was used to survey metal speciation at a series of wastewater treatment plants. Following these analyses, bench-scale experiments were conducted. The survey data indicated that pollutant metal-EDTA complexes account for a significant fraction of the dissolved metals in wastewater. The bench-scale studies indicated that ferric chloride addition improves the removal of copper and zinc by approximately 20%. To test the results of the bench-scale experiments, a full-scale experiment was conducted by interrupting chemical addition at a municipal wastewater treatment plant that normally adds ferric chloride during primary treatment. Results indicated that ferric chloride addition had a slight impact on metal speciation but no effect on metals removal. The lack of an effect was attributed to changes in metal speciation that occurred during primary treatment irrespective of ferric chloride addition. This title belongs to WERF Research Report Series ISBN: 9781843396949 (Print) ISBN: 9781780404387 (eBook)