Changes In Metal Speciation Research Articles

Metal solubility and speciation under the influence of waterlogged condition and the presence of wetland plants

The effect of wetland plants on metal status in the rhizosphere is species specific. The present study aimed to address the effects of different chemical speciations on metal redistribution and verify changes in metal speciation in the rhizosphere caused by wetland plants based on different radial oxygen losses. The presence of wetland plants increased the redox potential and led to the redistribution of metals in the rhizosphere across different chemical speciations. Associated metals such as Pb and Zn were correspondingly released or co-precipitated, influencing their solubility. The higher the root oxidisation ability of the plant, the greater the effect. However, the presence of wetland plants also transformed metals (Pb and Zn) to a more stable fraction (residual), leading to a lower potential metal bioavailability and leaching process in the long run. Knowledge of these variables and the time-dependent metal behaviour revealed by this study is crucial for the remediation of mine tailings using wetland plants.

Metal partitioning and availability in estuarine surface sediments: Changes promoted by feeding activity of Scrobicularia plana and Liza ramada

Several works have evidenced in the past the importance and influence of plants and terrestrial invertebrates in metal availability in soils and sediments through changes in metal speciation. In contrast, the impact of estuarine invertebrates and fishes in this process has been poorly explored. The partition of metals in estuarine surface sediments was studied in a controlled environment according to four operationally defined fractions. Sediments were analyzed before and after the passage through the gut of two detritivorous species. Scrobicularia plana feeds on the bottom and suspended sediment particles through the inhalant siphon. Liza ramada is an interface feeder, filtering the superficial layer of the sediment and suspended particles in the water column. Cd, Cu and Ni bound to carbonates increased in the pellets of S. plana, compared with the ingested sediment, as did exchangeable Zn. Similarly, Cd and Zn bound to carbonates have also increased in the pellets of L. ramada; on the contrary, a decrease of Ni was observable in the pellets of this fish. The outcome of the controlled experiments pointed to a potential increase in some metals' availability in the estuarine environment, as a result of the more mobile metal forms in the excreted fecal pellets. This draws the attention to a relevant impact of the trophic activity of both species, alongside with the potential enhancement brought to it by the bioturbation promoted by them, in the role that the estuary itself has as a contaminants' buffer.

Speciation of Cu and Zn in Two Colored Oyster Species Determined by X-ray Absorption Spectroscopy.

In oysters, Cu and Zn concentration can reach extraordinarily high (1-2% of tissue dry weights), leading to intense green or blue colors in oyster tissues. It is thus puzzling how oysters detoxify the excessively accumulated metals. Here, we used X-ray absorption spectroscopy to examine the Cu and Zn speciation in two "colored" oysters (Crassostrea hongkongensis and Crassostrea sikamea) collected from a severely metal-contaminated estuary. In contaminated oysters, we found a much higher proportion of tissue Cu and Zn as oxygen- or nitrogen-bonded species, contrasting to the sulfur-bonded (thiolate) species in normal oysters. Speciation of Cu and Zn in mantle was similar to that in gills, both of which were different from that in the digestive gland. In C. sikamea, the difference of metal speciation between normal and contaminated individuals was of similar pattern but less pronounced than that in C. hongkongensis. In normal oysters, Cu existed mainly as Cu(I) bound to sulfur, whereas in contaminated oysters mainly as Cu(II) bound to oxygen or nitrogen. Our study provided direct and semiquantitative information on the changes of metal speciation in contaminated oysters, indicating that oysters could efficiently detoxify the excessively accumulated Cu and Zn by storing them in oxygen- and nitrogen-bonded complexes in metal-rich environments.

Metal speciation and potential bioavailability changes during discharge and neutralisation of acidic drainage water

The discharge of acid drainage from the farm irrigation areas to the Murray River in South Australia represents a potential risk to water quality. The drainage waters have low pH (2.9–5.7), high acidity (up to 1190mgL−1 CaCO3), high dissolved organic carbon (10–40mgL−1), and high dissolved Al, Co, Ni and Zn (up to 55, 1.25, 1.30 and 1.10mgL−1, respectively) that represent the greatest concern relative to water quality guidelines (WQGs). To provide information on bioavailability, changes in metal speciation were assessed during mixing experiments using filtration (colloidal metals) and Chelex-lability (free metal ions and weak inorganic metal complexes) methods. Following mixing of drainage and river water, much of the dissolved aluminium and iron precipitated. The concentrations of other metals generally decreased conservatively in proportion to the dilution initially, but longer mixing periods caused increased precipitation or adsorption to particulate phases. Dissolved Co, Mn and Zn were typically 95–100% present in Chelex-labile forms, whereas 40–70% of the dissolved nickel was Chelex-labile and the remaining non-labile fraction of dissolved nickel was associated with fine colloids or complexed by organic ligands that increased with time. Despite the different kinetics of precipitation, adsorption and complexation reactions, the dissolved metal concentrations were generally highly correlated for the pooled data sets, indicating that the major factors controlling the concentrations were similar for each metal (pH, dilution, and time following mixing). For dilutions of the drainage waters of less than 1% with Murray River water, none of the metals should exceed the WQGs. However, the high concentrations of metals associated with fine precipitates within the receiving waters may represent a risk to some aquatic organisms.

Effects of Chemical Amendments on the Lability and Speciation of Metals in Anaerobically Digested Biosolids

The interaction of inorganic contaminants present in biosolids with iron, aluminum, and manganese oxy/hydroxides has been advocated as a key mechanism limiting their bioavailability. In this study, we investigated whether this is indeed the case, and further, whether it can be exploited to produce optimized biosolids products through the addition of chemical additives during sewage sludge processing. Experiments were conducted to investigate whether the addition of iron- and aluminum-based amendments (at 5 different rates) during the anaerobic digestion phase of wastewater treatment can effectively change the speciation or lability of contaminant metals (copper, zinc and cadmium) in biosolids destined for use in agriculture. The performance of the bioreactors was monitored throughout and the speciation and lability were determined in both fresh and 3-month aged biosolids using X-ray absorption spectroscopy (Cu, Zn) and isotopic dilution ((65)Cu, (65)Zn, (109)Cd). The tested amendments (FeCl3, Al2(SO4)3, and Al-rich water treatment residual) did not cause significant changes in metal speciation and were of limited use for reducing the lability of contaminant metals in good quality biosolids (suitable for use in agriculture), suggesting that high affinity binding sites were already in excess in these materials. However, the use of chemical amendments may offer advantages in terms of treatment process optimization and may also be beneficial when biosolids are used for contaminated site remediation.

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 photo trop hie 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.

Ocean acidification increases the toxicity of contaminated sediments

Ocean acidification (OA) may alter the behaviour of sediment-bound metals, modifying their bioavailability and thus toxicity. We provide the first experimental test of this hypothesis with the amphipod Corophium volutator. Amphipods were exposed to two test sediments, one with relatively high metals concentrations (Σmetals 239 mg kg(-1) ) and a reference sediment with lower contamination (Σmetals 82 mg kg(-1) ) under conditions that mimic current and projected conditions of OA (390-1140 μatm pCO2 ). Survival and DNA damage was measured in the amphipods, whereas the flux of labile metals was measured in the sediment and water column (WC) using Diffusive Gradients in Thin-films. The contaminated sediments became more acutely toxic to C. volutator under elevated pCO2 (1140 μatm). There was also a 2.7-fold increase in DNA damage in amphipods exposed to the contaminated sediment at 750 μatm pCO2 , as well as increased DNA damage in organisms exposed to the reference sediment, but only at 1140 μatm pCO2 . The projected pCO2 concentrations increased the flux of nickel and zinc to labile states in the WC and pore water. However, the increase in metal flux at elevated pCO2 was equal between the reference and contaminated sediments or, occasionally, greater from reference sediments. Hence, the toxicological interaction between OA and contaminants could not be explained by e ffects of pH on metal speciation. We propose that the additive physiological effects of OA and contaminants will be more important than changes in metal speciation in determining the responses of benthos to contaminated sediments under OA. Our data demonstrate clear potential for near-future OA to increase the susceptibility of benthic ecosystems to contaminants. Environmental policy should consider contaminants within the context of changing environmental conditions. Specifically, sediment metals guidelines may need to be reevaluated to afford appropriate environmental protection under future conditions of OA.

Impacts of pH-dependent metal speciation on the decomposition of triclosan by sulfate radicals

The presence of triclosan (TCS) in water resources has drawn significant attention due to its endocrine disruption potential. Sulfate radicals (SRs), generated particularly by the metal-mediated activation of peroxymonosulfate (PMS), have been proposed to effectively decompose TCS and many other pharmaceuticals and personal care products. In spite of its significance for understanding the efficiency of SR generation and catalytic/non-catalytic nature of the oxidation reaction, metal speciation has not been adequately highlighted in previous studies. This study investigated the detailed changes in metal speciation in cobalt/PMS and iron/PMS systems and correlated it with TCS decomposition under different pH conditions. A rapid oxidation of Co2+ to Co3+ and Fe2+ to Fe3+ generally corresponded with pseudo-steady state decomposition kinetics of TCS after its initial fast decomposition. The presence of potential threshold concentrations of metals to effectively activate PMS was found. A strong catalytic activity was observed for Co/PMS system at pH 3, where most of Co was present in the form of dissolved Co2+. The pH impacts were different for Co/PMS and Fe/PMS. TCS oxidation was fast at pH 5 for Co and pH 3 for Fe. However, long-term mineralization of TCS seemed less dependent on pH.

Low frequency ultrasound-assisted leaching of sewage sludge for toxic metal removal, dewatering and fertilizing properties preservation

The aim of this research was to evaluate the efficiency of an ultrasonication process in combination with METIX-AC technology, a chemical process, for metal removal and dewatering ability, with preservation of fertilizing properties of sewage sludge. Waste activated sludge samples having a total solids concentration of 4 and 20gL−1, were enriched with Cu and Zn in order to exceed the limiting values recommended by Québec regulation for sludge valorization. Ultrasonication was applied at low frequency (22kHz) at specific energies ranging from 180 to 66,000kJkg−1 of dry sludge. Ultrasound-assisted leaching rates and yields were similar to chemical leaching alone for Zn, whereas solubilisation was reduced for Cu, regardless the specific energy. Fertilizing properties preservation and dewatering ability were similar in ultrasound-assisted leaching, compared to chemical leaching alone. These trends were mainly attributed to the changes of metal speciation, particle size and morphology during ultrasonication, in addition to untreated sludge properties.

Phytotoxicity and speciation of copper and nickel in composted sewage sludge

In recent years, sewage sludge production in Poland has increased sharply. Composting is one of the most preferable methods for sewage sludge utilization. Compost can improve the physical and chemical properties of soil. However, the quality of sewage sludge composts should be assessed before soil application by using biological and chemical methods. A germination test is used as a biological index to determine the possible phytotoxic effect of composts. Chemical methods are helpful in assessment of availability of metals to plants. This study has been conducted to validate the effect of composting process on phytotoxicty, speciation and availability of copper and nickel in sewage sludge composted with sawdust and wheat straw. The composting process of organic wastes was carried out in chambers of a bioreactor for 28 days; afterwards each chamber was emptied and the content was stored in a closed room for 3 months to allow the maturation process to complete. Samples for analysis were collected at three characteristic phases of the composting process: mesophilic, thermophilic and mature compost. Determinations of the changes in metal speciation as well as metal bioavailability were achieved, respectively, with the technique of BCR sequential analysis and single extraction method using DTPA. Phytotoxicity of the analyzed composts was evaluated with the germination index using cress seeds. It was found that an increasing proportion of sewage sludge in composted mixtures increased copper and nickel content in compost fractions as well as bioavailable quantities of these metals. The germination index increased only during the composting process of a mixture containing 30% of sewage sludge. The compost with 75% share of sewage sludge strongly inhibited germination of cress seeds. The process of compost maturation resulted in an increase of copper in fractions I and III. However, the smallest amounts of copper were determined in exchangeable bonds and the highest ones were determined in bonds with organic matter and sulphides. Composting sewage sludge with sawdust and wheat

Geomycology: metals, actinides and biominerals

Geomycology can be simply defined as 'the scientific study of the roles of fungi in processes of fundamental importance to geology' and the biogeochemical importance of fungi is significant in several key areas. These include nutrient and element cycling, rock and mineral transformations, bioweathering, mycogenic biomineral formation and interactions of fungi with clay minerals and metals. Such processes can occur in aquatic and terrestrial habitats, but it is in 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 a variety of properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Some fungal transformations have beneficial applications in environmental biotechnology, e.g. in 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), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment. The ubiquity and importance of fungi in biosphere processes underlines the importance of geomycology as an interdisciplinary subject area within microbiology and mycology.

Influence of soil ageing on bioavailability and ecotoxicity of lead carried by process waste metallic ultrafine particles

Ultrafine particulate matters enriched with metals are emitted into the atmosphere by industrial activities and can impact terrestrial and aquatic ecosystems. Thus, this study investigated the environmental effects of process particles from a lead-recycling facility after atmospheric deposition on soils and potential run-off to surface waters. The toxicity of lead-enriched PM for ecosystems was investigated on lettuce and bacteria by (i) germination tests, growth assays, lead transfer to plant tissues determination and (ii) Microtox analysis. The influence of ageing and soil properties on metal transfer and ecotoxicity was studied using three different soils and comparing various aged, spiked or historically long-term polluted soils. Finally, lead availability was assessed by 0.01 M CaCl 2 soil extraction. The results showed that process PM have a toxic effect on lettuce seedling growth and on Vibrio fischeri metabolism. Soil–PM interactions significantly influence PM ecotoxicity and bioavailability; the effect is complex and depends on the duration of ageing. Solubilisation or stabilisation processes with metal speciation changes could be involved. Finally, Microtox and phytotoxicity tests are sensitive and complementary tools for studying process PM ecotoxicity.

Deciphering the weathering processes using environmental mineralogy and geochemistry: Towards an integrated model of laterite and podzol genesis in the Upper Amazon Basin

This article reports major results from collaborative research between France and Brazil on soil and water systems, carried out in the Upper Amazon Basin. It reveals the weathering processes acting in the partly inundated, low elevation plateaus of the Basin, mostly covered by evergreen forest. Our findings are based on geochemical data and mineral spectroscopy that probe the crystal chemistry of Fe and Al in mineral phases (mainly kaolinite, Al- and Fe-(hydr)oxides) of tropical soils (laterites). These techniques reveal crystal alterations in mineral populations of different ages and changes of metal speciation associated with mineral or organic phases. These results provide an integrated model of soil formation and changes (from laterites to podzols) in distinct hydrological compartments of the Amazon landscapes and under altered water regimes.

Behavior of metals (Cu, Zn and Cd) in the initial stage of water system contamination: Effect of pH and suspended particles

The fate of potentially harmful metals (PHM) after their entry into an unpolluted fresh water body depends on the physicochemical and biological parameters of the aquatic ecosystem. This paper considers the effect of pH and suspended particles (SP) on the behavior of Cu, Zn and Cd when they enter a fresh water reservoir. In a field experiment, four mesocosms were constructed in the Novosibirskoye Reservoir to allow systematic variation of SP concentration (15 or 250 mg/L) and pH (8.5 or 6.5). The initial concentrations of Cu, Zn and Cd in the mesocosms were 1000, 1000 and 200 μg/L, respectively. Natural bottom sediments were used to provide additional mineral SP, and water hyacinth was used as a floating plant species. Over 11 days, measurements were made of several indicators: residual metal concentration in solution ([PHM] w ); metal concentration in SP ([PHM] s ); primary productivity of the phytoplankton community; mass of settled SP; PHM concentration in settled SP; and PHM bioaccumulation by water hyacinth. The ratio [PHM] w /[PHM] s in the water varied in the order Cu < Zn < Cd and was higher at pH 6.5 than at pH 8.5. This observation reflects different PHM sorption (Cu > Zn > Cd) onto mineral SP and PHM biosorption by planktonic organisms. Phytoplankton acts as a renewable source of organic SP and plays an important role in metal removal from the water in the mesocosms. After 11 days the residual concentrations of Cu, Zn and Cd in the mesocosm without SP addition (initial SP concentration was 15 mg/L) were 272, 355 and 84 μg/L, respectively. The residual concentrations of Cu, Zn and Cd in mesocosms with SP addition were 57, 100 and 14 μg/L at pH 8.5 and 80, 172 and 20 μg/L at pH 6.5, respectively. Therefore, addition of SP resulted in faster and more complete removal of metals into the bottom sediments. Floating plants (water hyacinth) accumulated PHM (Cu > Zn > Cd) more effectively at pH 8.5 than at pH 6.5, and PHM concentrations in the roots were higher than in settling SP. The general trends of PHM removal from contaminated water via sedimentation and bioaccumulation are compared with changes of metal speciation in solution.

Effects of airborne contaminant exposure on the physical properties and filtration performance of activated, impregnated carbon

The effects of airborne contaminant exposure in humid air on the physical properties and filtration capabilities of a copper/zinc/molybdenum impregnated carbon were investigated. The impregnated carbon was exposed individually to CO2, NH3 and NO2 in humid air, then evaluated for changes in metal speciation, metal distribution, porosity and water-uptake. The exposed impregnated carbon was further evaluated for changes in its ability to remove SO2 and cyclohexane from air streams. Exposure to CO2 did not impact the physical properties of the impregnated carbon, with changes in filtration performance were not evident. NH3 exposure resulted in the formation of metal amine complexes, which led to a migration of impregnants from within the pores of the carbon granule to the external surface. NH3 exposure increased SO2 filtration while decreasing cyclohexane filtration. The decrease in cyclohexane filtration was attributed to an increase in water uptake and a decrease in porosity. NO2 exposure significantly decreased the porosity of the carbon substrate while increasing the amount of surface oxygen. The increased surface oxygen greatly increased water uptake. NO2 exposure greatly reduced the SO2 breakthrough time and the ability of the material to remove cyclohexane.

Metals, minerals and microbes: geomicrobiology and bioremediation

Microbes play key geoactive roles in the biosphere, particularly in the areas of element biotransformations and biogeochemical cycling, metal and mineral transformations, decomposition, bioweathering, and soil and sediment formation. All kinds of microbes, including prokaryotes and eukaryotes and their symbiotic associations with each other and 'higher organisms', can contribute actively to geological phenomena, and central to many such geomicrobial processes are transformations of metals and minerals. Microbes have a variety of properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Such mechanisms are important components of natural biogeochemical cycles for metals as well as associated elements in biomass, soil, rocks and minerals, e.g. sulfur and phosphorus, and metalloids, actinides and metal radionuclides. Apart from being important in natural biosphere processes, metal and mineral transformations can have beneficial or detrimental consequences in a human context. Bioremediation is the application of biological systems to the clean-up of organic and inorganic pollution, with bacteria and fungi being the most important organisms for reclamation, immobilization or detoxification of metallic and radionuclide pollutants. Some biominerals or metallic elements deposited by microbes have catalytic and other properties in nanoparticle, crystalline or colloidal forms, and these are relevant to the development of novel biomaterials for technological and antimicrobial purposes. On the negative side, metal and mineral transformations by microbes may result in spoilage and destruction of natural and synthetic materials, rock and mineral-based building materials (e.g. concrete), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment, all with immense social and economic consequences. The ubiquity and importance of microbes in biosphere processes make geomicrobiology one of the most important concepts within microbiology, and one requiring an interdisciplinary approach to define environmental and applied significance and underpin exploitation in biotechnology.

Effect of pH, EDTA, and Anions on Heavy Metal Toxicity Toward a Bioluminescent Cyanobacterial Bioreporter

The bioavailability and therefore toxicity of a metal depends on the chemical species present in a particular environment. We evaluated the effect of a series of factors that could potentially modify metal speciation on the toxicity of Hg, Cu, Zn, and Cd toward a recombinant strain of the freshwater cyanobacterium Anabaena sp. PCC 7120 with cloned lux operon of luminescent terrestrial bacterium Photorhabdus luminescens. The strain, denoted as Anabaena CPB4337, showed a high constitutive luminescence with no need to add exogenous aldehyde. The tested factors were pH, EDTA (as organic ligand), and anions PO(4)(3-), CO(3)(2-), and Cl(-). Chemical modeling and correlation analyses were used to predict metal speciation and link it with toxicity. In general, metal toxicity significantly correlated to the predicted metal free-ion concentration, although Zn-EDTA complexes and certain Hg chloro-complexes could also exhibit some toxicity to cyanobacteria. An interesting feature of metal toxicity to strain Anabaena CPB4337 was that low amounts of PO(4)(3-) and CO(3)(2-) increased metal toxicity; this effect could not be related to significant changes in metal speciation and could be attributed to a modulating effect of these anions on metal/uptake toxicity. The combination of toxicity studies that take into account a range of factors that might modulate metal toxicity with chemical modeling to predict changes in metal speciation might be useful for interpreting complex toxicity data. Finally, this cyanobacterial bioreporter, due to its ecological relevance as a primary producer, could be used as a tool for toxicity assessment in freshwater environments.

In situ measurement of trace metals in estuarine waters of Patos Lagoon using diffusive gradients in thin films (DGT)

The diffusive gradients in thin-films (DGT) technique was used to determine labile metals in situ during different hydrological conditions in the Patos Lagoon estuary. Water samples were also analyzed for Chelex-labile fractions of Cd, Co, Cu, Mn, Ni and Zn using Chelex-100 resin. DGT-labile concentrations of Cd, Cu, Ni and Zn were lower than Chelex-labile concentrations, possibly because colloids were trapped in the Chelex resin column. There was a decrease with increasing deployment time in the concentrations of all elements measured by DGT, reflecting changes in metal speciation in solution caused by the decrease in the salinity and associated with change in pH in the estuary. The results demonstrated the sensitivity of DGT to metal speciation and the feasibility of using the DGT technique in highly dynamic estuarine waters to obtain a time-integrated record of labile trace metals.

Employing Chlorella protothecoides for metal bioavailability studies under acidic conditions

We report the challenges and resolutions facing the use of Chlorella protothecoides for metal bioavailability and toxicity research under acidic conditions. In our study, we found that a simplified growth medium recommended for metal bioavailability research did not support the optimum growth of C. protothecoides at pH 5.5, possibly due to nutrient deficiencies, rendering it unsuitable for bioavailability studies under acidic conditions. On the other hand, a modified Woods Hole MBL growth medium supplying all macro and micro nutrients, with chelators Tris and EDTA removed, and (NH4)2Fe(SO4)2 supplemented as the source of iron, produced excellent growth of the algae under identical conditions. This medium is therefore recommended as the alternative growth medium. While a pH increase of up to 2 units a day was observed in unbuffered media during algal growth, incorporation of CO2 into the aeration stream at a fixed partial pressure stabilized the medium pH. By initiating the metal (e.g. Cu) treatment at a culture optical density (750 nm) of 0.04, where the algal population was just entering the rapid growth phase, the Chlorella assay was completed within 48 h. This minimized metal speciation changes and nutrient limitation that may occur over longer test durations. As demonstrated with the case of Cu, a cell density of 7.5 x 105 cells mL–1 at the time of metal addition, caused only 5% initial loss of solution Cu, addressing the concern that such an initial cell density might deplete the metal from solution as a result of metal binding to algal cells. Overall, this study provides a valid means of employing Chlorella for metal bioavailability and toxicity research under acidic conditions, which ensures that algal growth is not impeded by nutrient deficiency, experimental duration is short, and more importantly, solution pH and metal speciation do not change significantly over the experimental period.

Changes in metal speciation and pH in olive processing waste and sulphur-treated contaminated soil

Degradation of organic matter from olive mill waste and changes in the heavy metal fractionation of a metal-contaminated calcareous soil were studied in a laboratory experiment, in which the olive mill waste was mixed with the soil and then incubated under aerobic conditions. The soil was calcareous (15% CaCO 3) with high Zn and Pb concentrations (2058 and 2947 mg kg −1, respectively). The organic amendment was applied at a rate equivalent to 20 g kg −1 soil, and unamended soil was run as a control. To discern if changes in metal solubility were due to the acidic character of the waste, elemental sulphur was applied to soil as a non-organic acidifying material. The S 0 rates used were 3.14, 4.71 and 6.28 g kg −1. The mineralisation of total organic-C (TOC) from the waste reached 14.8% of the original TOC concentration after 56 days of incubation. The CO 2–C produced from S 0-treated soils showed the carbonate destruction by the H 2SO 4 formed through S 0 oxidation. The organic waste increased EDTA-extractable Zn and Pb concentrations and CaCl 2-extractable Mn levels in soil after two days of incubation. The changes in metal availability with time indicated that the oxidation of phenols from the waste reduced Mn (IV) oxides, releasing Zn and Pb associated with this mineral phase. Organic waste addition did not decrease soil pH; the acidifying effect of S 0 did not change metal fractionation in the soil.