Importance of arsenic bioaccessibility in health risk assessment based on iron "Minette" rocks and related soils.

Total element concentrations by themselves are not always good predictors of toxicity and are therefore not suitable for eco- and/or human toxicological risk determination. In addition, despite the growing call for harmonization, countries show significant variation in risk assessment tools, screening/background values, protocols and legal management of soils. By incorporating mobility and bioaccessibility/availability into soil risk assessments, location-specific physico-chemical and geological conditions can be considered in routinely applied general risk assessment methodologies. Minette soils and rocks are a great case in point since they often are associated with high geogenic As concentrations and consequently potential risks. Minette iron ores form the world largest Fe ore deposits since the "great oxidation". For the first time, oral bioaccessibility during direct ingestion was assessed on Minettes from Luxembourg by applying the in vitro Solubility/Bioavailability Research Consortium (SBRC) method. Out of > 180 samples, 25 representative samples were selected providing a unique dataset which showed an average gastric bioaccessibility of ∼10% (7.8 ± 4.0 mg/kg) of the total As-concentration, with a maximum of 45% (17.9 mg/kg). Of importance is that bioaccessibility of As in Minette rocks and soils are controlled by, and can be estimated from, lithology, mineralogy and total Ca content. Soils and ooid grainstones with an iron oxide or clayey matrix, are characterized by average gastric bioaccessible As concentrations < 6 mg/kg. Gastric As bioaccessibility is highest in Fe-bearing calcite-cemented bioclastic grainstones (∼12 mg/kg). Importantly, for all samples the maximal bioaccessible As concentrations remain below the threshold from which significant adverse non-carcinogenic and/or carcinogenic health effects are expected. These new results are in strong contrast with what total As concentrations might suggest. Considering bioaccessibilities, consequently, can help to avoid disproportionate, costly and environmentally impacting risk management strategies. Furthermore, this study illustrates the importance of cross-disciplinary collaboration between geo- and health scientists.

Community capitals and (social) sustainability: Use and misuse of asset-based approaches in environmental management.

Sustainability has increasingly gained momentum as an underlying framework to orient decisions and actions in environmental management. However, while acting in view of sustainability goals is a noble intention, both the conceptualization and the implementation of sustainability remain a subject of debate. This is partly due to the widespread lack of consideration for its social dimension and the interactions this has with the environmental and economic dimensions. To this end, the Community Capitals Framework and other asset-based approaches are often used to deal with these problematic aspects of sustainability in environmental management. Through a systematic review of scientific peer-reviewed articles, this paper investigates the conceptual and practical application of such approaches. Results from our analysis show that different declinations of community capitals exist within environmental management. In all the forms they assume in the 42 frameworks identified, their employment seems effective in promoting the inclusion of social, economic and environmental dimensions when conducting sustainability assessments. However, we identified two main difficulties that challenge the application of asset-based approaches in practice. First, in most cases, capital assessment is not carried out in the planning phase of an environmental intervention in order to identify community resources; capitals are employed instead to measure the impact of an ecological change ex-post, thus being discordant with their theoretical foundations. Second, the existence of a vast array of terms to refer to community assets creates disorientation among exponents of different stakeholder groups and hinders a practical and effective application of this concept. On the basis of our results, we claim the importance of conducting community resources assessment and stakeholder consultation at different times and through practice oriented approaches and cross-silos communication efforts in order to develop a shared understanding of the problem and facilitate sustainable, adaptive and participatory approaches to environmental management.

Valorizing (cleaned) sulfidic mine waste as a resource for construction materials.

Proper management and storage of mine waste, e.g., tailings and waste rock, is one of the main issues that mining industries face. Additionally, there is already an uncountable amount of existent historical mine waste, which may, even centuries after the closure of the mine, still be leaching contaminants into the environment. One solution to minimize the risks associated with the mine waste, with also potential economic benefits, is through the valorization of the waste. This can be done by first recovering valuable metals and removing hazardous contaminants. Then, the remaining residue can be valorized into green construction materials, such as geopolymers, ceramics or cement. For some mine waste materials, such as those with only trace levels of metals that are not economically viable to extract, the "waste" can be reused directly without this additional cleaning step. In the present study, mine waste originating from three different sites was characterized and compared with the cleaned mine waste (i.e., cleaned by bioleaching or flotation methods) and with different types of green construction materials containing 13-80 wt% (cleaned and uncleaned) mine waste. Particular emphasis was given to the mobilization of metal(loid)s from the mine waste and construction materials (i.e., ceramics, alkali-activated materials and cement) under different conditions, through a series of leaching tests (i.e., EN 12457-2, US EPA's Toxicity Characteristic Leaching Procedure, and a pH-dependent leaching test). The leaching tests were applied to either mimic current 'natural' conditions at the mining site, conditions in a landfill (end of life) or extreme conditions (i.e., extremely acidic or alkaline pH). Most of the original mine waste samples contain high levels of Pb (18-3160 mg/kg), Zn (66-10500 mg/kg), and As (10-4620 mg/kg). . The cleaning methods were not always efficient in removing the metal(loid)s and sulfur. In some cases, the cleaned mine waste samples even contained higher total metal(loid) and sulfur concentrations than the original mine waste samples. Based on the leaching studies, some alkali-activated materials, ceramics, and cement effectively immobilized certain metals (e.g., <0.5 mg/kg of Pb and <4 mg/kg of Zn). Also, longer curing times of the alkali-activated materials, in most cases, improved the immobilization of metal(loid)s. Additionally, for ceramics, the temperature at which the test pieces were fired (up to 1060 °C), also played a major role in decreasing the mobility of some metal(loid)s, while increasing others (e.g., As, potentially via the structural rearrangement of As and Fe). Overall, through this detailed characterization, the environmental impact from the mine waste to the downstream products was evaluated, determining which valorization methods are the most viable to close the circular economy loop.

Critical review of decision support tools for sustainability assessment of site remediation options.

In Europe alone, there are more than 2,5 million potentially contaminated sites of which 14% are expected to require remediation. Contaminated soil and groundwater can cause damage to human health as well as to valuable ecosystems. Globally more attention has been paid to this problem of soil contamination in the past decades. For example, more than 58 000 sites have been remediated in Europe between 2006 and 2011. Together with this increase in remediation projects there has been a surge in the development of new remediation technologies and decision support tools to be able to match every site and its specific characteristics to the best possible remediation alternative. In the past years the development of decision support tools (DST) has evolved in a more sustainable direction. Several DSTs added the claim not only to denote effective or technologically and economically feasible remediation alternatives but also to point out the more or most sustainable remediation alternatives. These trends in the evaluation of site remediation options left users with a confusing clew of possibly applicable tools to assist them in decision making for contaminated site remediation. This review provides a structured overview on the extent decision support tools for contaminated site remediation, that claim to assist in choosing the most sustainable remediation alternative, actually include the different elements of sustainability proposed in our assessment framework. The review contains an in-depth analysis of thirteen tools specifically developed to assess the sustainability of site remediation alternatives. This analysis is based on six criteria derived from the definition of sustainable development of the Brundtland report. The six criteria were concretized by using the three pillars of sustainability, applied to site remediation according to the SuRF-UK framework, two criteria derived from Life Cycle Assessment and Cost-Benefit Analysis, and an 'User friendly' criterion. These elements come together in a framework, drafted for this study, containing six criteria covering the environmental, economic, social, time, uncertainty aspects and user friendliness of a sustainable site remediation. The main remarks uncovered by this review are the imbalance of used indicators still expressing a strong preference for the environmental aspect at the expense of the economic and social aspects of sustainability, the lack of consistency in the terminology used within the field and the failure in adapting released tools to recent legislation or scientific advancements.

Inclusion of social indicators in decision support tools for the selection of sustainable site remediation options.

Sustainable remediation requires a balanced decision-making process in which environmental, economic and social aspects of different remediation options are all considered together and the optimum remediation solution is selected. More attention has been paid to the evaluation of environmental and economic aspects, in particular to reduce the human and environmental risks and the remediation costs, to the exclusion of social aspects of remediation. This paper investigates how social aspects are currently considered in sustainability assessments of remediation projects. A selection of decision support tools (DSTs), used for the sustainability assessment of a remediation project, is analyzed to define how social aspects are considered in those tools. The social indicator categories of the Sustainable Remediation Forum - United Kingdom (SuRF-UK), are used as a basis for this evaluation. The consideration of social aspects in the investigated decision support tools is limited, but a clear increase is noticed in more recently developed tools. Among the five social indicator categories defined by SuRF-UK to facilitate a holistic consideration of social aspects of a remediation project only "Human health and safety" is systematically taken into account. "Neighbourhood and locality" is also often addressed, mostly emphasizing the potential disturbance caused by the remediation activities. However, the evaluation of 'Ethics and Equality', Communities and community involvement', and 'Uncertainty and evidence' is often neglected. Nevertheless, concrete examples can be found in some of the investigated tools. Specific legislation, standard procedures, and guidelines that have to be followed in a region or country are mainly been set up in the context of protecting human and ecosystem health, safety and prevention of nuisance. However, they sometimes already include some of the aspects addressed by the social indicators. In this perspective the use of DST to evaluate the sustainability of a site remediation project, should be tuned to the legislation, guidelines and procedures that are in force in a specific country or region.

Carbon footprint calculations in the soil remediation sector: A comparative analysis.

The CO2 Performance Ladder (CO2PL) is a CO2 management tool that helps companies in improving the environmental performance of projects and business operations. Since the summer of 2020, it can be applied to tenders for soil remediation projects commissioned by the Public Waste Agency (OVAM) of Flanders (Belgium). The CO2PL supports organizations in setting up a CO2 management system, calculating their carbon footprint and achieving CO2 reductions. However, at present, little information is available about the application of this instrument to the soil remediation sector. Carbon footprint calculators are already commonly applied to evaluate soil remediation projects, but have a narrower scope and system boundaries, as they are only meant to calculate the carbon footprint of soil remediation projects, and not of all business operations. Keeping these differences in mind, the CO2PL was compared with other evaluation tools (the CO2 calculator, the Sustainable Remediation Tool (SRT) and the Spreadsheets for Environmental Footprint Analysis (SEFA)), which are used to calculate the carbon footprint of soil remediation projects. The comparative analysis consists of a qualitative analysis and a quantitative carbon footprint calculation based on data from two case studies in Flanders (Belgium). The results show that besides differences in objectives, scope and required input data, the calculated carbon footprint of the remediation project differs between the instruments. Use of different conversion factors can result in significantly different results. Only some of these differences in the conversion factors are inherently related to regional differences. Especially for more complex remediation projects, in which less conventional techniques/materials are used, CO2 conversion factors are sometimes not consistent, or simply lacking. A systematic inventory of relevant emission factors, specific for the soil remediation sector, would improve the application of carbon footprint calculations and support the implementation of these kinds of evaluation instruments in the soil remediation sector.

Evaluation of the environmental impact of Brownfield remediation options: comparison of two life cycle assessment-based evaluation tools.

The choice between different options for the remediation of a contaminated site traditionally relies on economical, technical and regulatory criteria without consideration of the environmental impact of the soil remediation process itself. In the present study, the environmental impact assessment of two potential soil remediation techniques (excavation and off-site cleaning and in situ steam extraction) was performed using two life cycle assessment (LCA)-based evaluation tools, namely the REC (risk reduction, environmental merit and cost) method and the ReCiPe method. The comparison and evaluation of the different tools used to estimate the environmental impact of Brownfield remediation was based on a case study which consisted of the remediation of a former oil and fat processing plant. For the environmental impact assessment, both the REC and ReCiPe methods result in a single score for the environmental impact of the soil remediation process and allow the same conclusion to be drawn: excavation and off-site cleaning has a more pronounced environmental impact than in situ soil remediation by means of steam extraction. The ReCiPe method takes into account more impact categories, but is also more complex to work with and needs more input data. Within the routine evaluation of soil remediation alternatives, a detailed LCA evaluation will often be too time consuming and costly and the estimation of the environmental impact with the REC method will in most cases be sufficient. The case study worked out in this paper wants to provide a basis for a more sounded selection of soil remediation technologies based on a more detailed assessment of the secondary impact of soil remediation.

Environmental and human health risk assessment of sulfidic mine waste: Bioaccessibility, leaching and mineralogy.

Sulfidic mine waste can pose environmental and human health risks, especially when it contains high levels of mobile metal(loid)s. To assess the environmental and health risks of mine waste originating from three historic and active sulfidic Pb-, Zn- and/or Cu-mines in Europe, mineralogical and chemical characterizations were conducted in combination with in vitro bioaccessibility tests, sequential extractions and leaching tests. Results indicated that most samples contained highly elevated levels of metal(loid)s and key minerals consisting of pyrite, sphalerite and cerussite. The orally bioaccessible fraction varied amongst samples: Cd (13-100%), Zn (9-69%), Pb (4-67%), Cu (8-41%) and As (1-11%). Given these bioaccessible levels, the human health risk assessment indicated carcinogenic and non-carcinogenic risks for most investigated samples in a worst-case exposure scenario. The leaching tests revealed a high mobility of metal(loid)s, especially Pb, posing potential environmental risks. The sequential extractions coupled with mineralogical analyses highlighted the highly mobile levels of Cd, Pb and Zn, posing environmental and health risks. Cerussite dissolved in the easily exchangeable fraction, releasing elevated levels of Pb, while pyrite never completely dissolved. In conclusion, the studied wastes pose environmental and health risks, but the high mobility of some elements also provides opportunities for the valorization of the waste.

Arsenic anomalies in soils and rocks occurring in the southwestern part of the Grand Duchy of Luxembourg.

Developing legislation on soil protection, including soil quality standards, is not straightforward for areas with high geogenic metal(loid) concentrations in rocks and soils. Several rock types in southern Luxembourg (laterally continuous into Northern France and Southern Belgium) contain elevated potentially toxic element concentrations. Toarcian and Aalenian Minette ironstones, and soils on top, possess high As concentrations (average of ~100 mg/kg, maximum up to 278 mg/kg). Liassic shales show high Mo concentrations (up to 60 mg/kg). Preliminary health risk assessments suggest increased potential non-carcinogenic and carcinogenic risks. Trace metal and As anomalies, however, do not necessarily pose human and ecotoxicological risks. Petrographic, mineralogical and chemical analyses show a strong association of As to iron oxides present as ooids and rock matrix. Single extractions with CaCl2 (0.01 mol/l) indicated the low As mobility in the Minettes. The Minette rocks with 10-40 wt% iron oxides, and a clay content of typically 10-30 wt% strongly bind As. As long as Eh and pH do not drastically change in soils, As mobility will remain low. For soils that developed on Minettes, it is advised to consider Fe-content as well as As mobility for risk assessment and development of legislation on soil protection.

High geogenic arsenic concentrations in travertines and their spring waters: Assessment of the leachability and estimation of ecological and health risks.

Travertines and their springs are rarely investigated as a source of toxicity. Remarkably high contents of As (up to 10 g/kg) have been found in travertine deposits and associated spring waters, nearby Ghorveh city (western Iran). Two types of travertines were distinguished: (i) Fissure ridge travertines, in areas with a carbonate-dominated basement, are characterized by a relatively low content and leaching of As. Their spring waters contain > 150 µg/L of As; (ii) Mound travertines, rich in non-carbonate impurities, occur in areas with volcanic substrates and contain high As concentrations (on average ~1,500 mg/kg) with high leachability. Their spring waters have lower As concentrations than equivalent fissure ridge waters. Principal Component Analyses of the elemental and mineralogical composition show the unstable association of As over a wide range of pH values to non-carbonate related elements, in particular iron, related to clay minerals. The high potential release of As may result in adverse ecotoxicological effects in surrounding agricultural soils and crops. An ecological risk assessment confirms the enrichment and very high potential ecological risk of As around mound carbonates. The human health risk assessment based on calculation via exposure factors suggests adverse non-carcinogenic and high carcinogenic risk with regard to As, both for adults and children.

Sediment characterization during oxidation and ripening and evaluation of its potential reuse.

The environmental impact and possibilities for remediation and reuse of contaminated sediments was investigated. Water-soluble and (NH4)2-EDTA-soluble metal concentrations in sediments from three different rivers were monitored for five months after dredging. Furthermore, the pH-dependent leaching behaviour of heavy metals and the influence of elevated temperatures (900-1100 degrees C) on the release of metals were investigated in order to evaluate possibilities for remediation, through thermal treatment, and reuse of the sediments, such as for the production of bricks and lightweight aggregates. In general, the sediments investigated in this study present a relatively low risk to the environment when exposed to upland conditions. If the sediments were to be used for the production of bricks or lightweight aggregates, the increased mobility of As, Cr and V following thermal treatment of the sediments should be taken into account.

Contamination status and potential release of trace metals in a mangrove forest sediment in Ho Chi Minh City, Vietnam.

Can Gio district is located in the coastal area of Ho Chi Minh City, southern Vietnam. Discharge of wastewater from Ho Chi Minh City and neighboring provinces to the rivers of Can Gio has led to concerns about the accumulation of trace metals (As, Cu, Cr, Ni, Pb, and Zn) in the coastal sediments. The main objective of this study was to assess the distribution of As, Cu, Cr, Ni, Pb, and Zn in surface and core sediments and to evaluate the contamination status in relation to local background values, as well as the potential release of these selected trace metals from sediments to the water environment. Sediment characteristization, including determination of fine fraction, pH, organic matter, and major elements (Al, Fe, Ca, K, Mg, and S), was carried out to investigate which parameters affect the trace metal enrichment. Fine fraction and Al contents were found to be the controlling proxies affecting the distribution of trace metals while other sediment characteristics did not show any clear influence on trace metals' distribution. Although As concentrations in the sediments were much higher compared to its reference value in other areas, the enrichment factor based on local background values suggests minor contamination of this element as well as for Cr, Cu, and Pb. Risk assessment suggested a medium to very high risk of Mn, Zn, and Ni under acidification. Of importance is also that trace metals in sediments were not easily mobilized by organic complexation based on their low extractabilities by ammonium-EDTA extraction.

The application of pH(stat) leaching tests to assess the pH-dependent release of trace metals from soils, sediments and waste materials.

pH is one of the key parameters that determines heavy metal mobility in soils, sediments and waste materials. In many respects leaching behaviour as reflected by the pH(stat) leaching tests provide a better means of assessing environmental impact than analysis of total elemental composition. This paper discusses the use of pH(stat) leaching tests as a tool to assess the potential mobilisation of trace metals from soils, sediments and waste materials. The possibilities of pH(stat) leaching tests are illustrated by means of different examples. The mathematical fitting of metal leaching behaviour from soils and sediments enabled a distinction between 5 groups of elements with a different leaching behaviour, which could be related to 'pools' with different reactivity. Contrary to single and sequential extractions, where pH is difficult to control, the reactivity and mobility of metals at a user-defined pH can be investigated. Moreover, the potential buffering capacity of the sample and its sensitivity to pH changes as a result of external stresses (e.g. soil acidification, liming) can be estimated. A multidisciplinary approach combining mineralogical analysis (X-ray diffraction) with chemical analysis, pH(stat) leaching tests and geochemical modelling (MINTEQA2) can provide information on the solid-phase speciation and reactivity of heavy metals in soils, sediments and waste materials. Besides the influence of pH on heavy metal leaching behaviour, additional information on heavy metal leachability and retention by the solid matrix was obtained from the kinetics of metal release during a pH(stat) test.

Friends or foes? Monetized Life Cycle Assessment and Cost-Benefit Analysis of the site remediation of a former gas plant.

Site contamination is a global concern because of the potential risks for human health and ecosystem quality. Every contaminated site has its own specific characteristics and the increased availability and efficiency of remediation techniques makes the choice of remediation alternative increasingly complicated. In this paper an attributional Life Cycle Assessment (LCA) of the secondary environmental impacts of a site remediation is performed and its results are monetized using two different monetization techniques, namely Stepwise 2006 and Ecovalue 08. Secondly, we perform a social Cost-Benefit Analysis (CBA) on the same case study using the same data sources. The case study used in this paper entails the soil and groundwater remediation of a tar, poly-aromatic hydrocarbons (PAH) and cyanide contamination of a school ground by a former gas plant. The remediation alternative chosen in this case study is excavation with off-site thermal treatment of the contaminated soil. The outcome of the social CBA, stating that the remediation project is socially beneficial in the long term, is critically compared to the outcome of the different LCA monetization methods. This comparison indicates that monetized LCA is a good complement to social CBA when it comes to the assessment of secondary environmental impacts. Combining the two methods provides decision makers with a more extensive and detailed assessment of the soil remediation project.

Leachability of heavy metals and arsenic from slags of metal extraction industry at Angleur (eastern Belgium).

At Angleur (eastern Belgium), a 53,000 m3 dump site, related to former Zn extraction, contains high concentrations of heavy metals and arsenic associated with minerals such as arsenopyrite (FeAsS), franklinite (ZnFe2O4) and willemite (Zn2SiO4). Eight representative samples were investigated by means of a modified availability test, which pointed towards a considerable availability of Cd, Pb and Zn. In addition a detailed analysis of leaching behaviour as a function of pH was performed by means of a pH(stat) leaching test. The results of this test were supported by modelling predictions with MINTEQA2. pH(stat) titration results also allowed determination of the acid neutralising capacity, making it possible to predict heavy metal release upon acidification, assuming a worst-case scenario. On a short- to medium-long term (+/-100 years) a release of 900 mg/kg Zn has to be expected upon assumed natural acidification. However, a leaching test performed at the natural pH (i.e. pH 8 for the sample studied) indicates that heavy metal release is very limited and far below the European limit values for slag material on dumps category 1. Therefore, despite the elevated total heavy metal and As concentrations on the site, leaching is relatively low under present environmental conditions. Moreover, the slag material has a rather elevated pH (6.5-8) and no acid mine drainage is produced. Glass phases seem very important in controlling heavy metal mobility since potential reactive minerals that are locked up in a silicate matrix are protected against leaching.

Dredged sediments as a resource for brick production: possibilities and barriers from a consumers' perspective.

A possible solution for the oversupply of dredged sediments is their use as a raw material in brick production. Despite the fact that several examples (e.g., Agostini et al., 2007; Hamer and Karius, 2002; Xu et al., 2014) show that this application is feasible, some economic, technical and social limitations interfere with the development of a market of dredged materials in brick production in Flanders. While we describe the main characteristics of the supply side, we focus on the limitations and barriers from the demand side in the present study. Based on a consumers survey we analyze consumers' risk perceptions and attitudes towards bricks produced from dredged sediments. Consumers in Flanders are rather suspicious with respect to bricks produced from dredged sediments and their risk perception is mainly determined by the possibility of a bad bargain (brick of inferior quality) and the connotation with chemical contamination. The willingness to pay for bricks made from dredged sediments is mainly influenced by the age of the respondents, as well environmental awareness, and the respondents' belief in their ability to influence environmental problems. Sensitization and information of customers seems to be of primary importance to make dredged-sediment-derived bricks a successful product.

Insights into solid phase characteristics and release of heavy metals and arsenic from industrial sludge via combined chemical, mineralogical, and microanalysis.

This study investigates the solid phase characteristics and release of heavy metals (i.e., Cd, Co, Cu, Cr, Mo, Ni, Pb, and Zn) and arsenic (As) from sludge samples derived from industrial wastewater treatment plants. The emphasis is determining the influence of acidification on element mobilization based on a multidisciplinary approach that combines cascade and pHstat leaching tests with solid phase characterization through X-ray diffraction (XRD), field emission gun electron probe micro analysis (FEG-EPMA), and thermodynamic modeling (Visual MinteQ 3.0). Solid phase characterization and thermodynamic modeling results allow prediction of Ni and Zn leachabilities. FEG-EPMA is useful for direct solid phase characterization because it provides information on additional phases including specific element associations that cannot be detected by XRD analysis. Cascade and pHstat leaching test results indicate that disposal of improperly treated sludges at landfills may lead to extreme environmental risks due to high leachable concentrations of Zn, Ni, Cu, Cr, and Pb. However, high leachabilities under acid conditions of Ni and Zn as observed from pHstat leaching test results may provide a potential opportunity for acid extraction recovery of Ni and Zn from such sludges.

Assessment of acid neutralizing capacity and potential mobilisation of trace metals from land-disposed dredged sediments.

In the past decades, large amounts of contaminated sediments have been dredged and spread out along rivers. The understanding of the fate and the behaviour of contaminants in dredged sediments is essential to deal with the management of contaminated sediments. Heavy metal leaching behaviour in dredged sediments of different ages since disposal, varying from 10 to 70 years, was assessed by pH(stat) leaching test and potentiometric titrations. Based on the pH(stat) titration results, two operationally defined pools of heavy metals, i.e., a labile and a slowly labile pool of heavy metals, were distinguished and quantified by mathematical description of leaching behaviour. The mathematical description of leaching behaviour during pH(stat) and potentiometric titrations allowed deduction of four groups of elements with a different type of leaching behaviour. Considering heavy metals, Zn, Cd and Ni displayed a leaching behaviour similar to acid neutralizing capacity (ANC), whereas the release of Cu, Pb and Cr was slower than ANC. However, no significant differences with regard to heavy metal leaching behaviour were found between sediments with different time since disposal on land. The elevated acid neutralizing capacity of the dredged sediments analysed in this study strongly decrease the risk of soil acidification with associated heavy metal leaching. The prediction of soil acidification over an extended period of time, together with the potential release of trace metals, was considered an important advantage of pH(stat) leaching tests compared to conventional leaching procedures.

Solid phase speciation of arsenic by sequential extraction in standard reference materials and industrially contaminated soil samples.

Availability, mobility, (phyto)toxicity and potential risk of contaminants is strongly affected by the manner of appearance of elements, the so-called speciation. Operational fractionation methods like sequential extractions have been applied for a long time to determine the solid phase speciation of heavy metals since direct determination of specific chemical compounds can not always be easily achieved. The three-step sequential extraction scheme recommended by the BCR and two extraction schemes based on the phosphorus-like protocol proposed by Manful (1992, Occurrence and Ecochemical Behaviours of Arsenic in a Goldsmelter Impacted Area in Ghana, PhD dissertation, at the RUG) were applied to four standard reference materials (SRM) and to a batch of samples from industrially contaminated sites, heavily contaminated with arsenic and heavy metals. The SRM 2710 (Montana soil) was found to be the most useful reference material for metal (Mn, Cu, Zn, As, Cd and Pb) fractionation using the BCR sequential extraction procedure. Two sequential extraction schemes were developed and compared for arsenic with the aim to establish a better fractionation and recovery rate than the BCR-scheme for this element in the SRM samples. The major part of arsenic was released from the heavily contaminated samples after NaOH-extraction. Inferior extraction variability and recovery in the heavily contaminated samples compared to SRMs could be mainly contributed to subsample heterogeneity.

Potential release of selected trace elements (As, Cd, Cu, Mn, Pb and Zn) from sediments in Cam River-mouth (Vietnam) under influence of pH and oxidation.

Since contaminated river-bed sediments in the Cam River-mouth (Vietnam) are regularly dredged and disposed on land, an understanding of the influence of time, pH and oxidation on the leaching behavior of heavy metals (Cd, Cu, Mn, Pb and Zn) and arsenic is necessary for the management of these dredged materials. A 96 h pH(stat)-leaching test to examine the leaching behavior of elements at pre-set pH values (2, 4, 6, 8 (natural), 9 and 11) and a BCR 3-step extraction to clarify the element fractionation, were performed on a freshly-collected wet suboxic sediment and a dry oxidized sediment. All heavy metals and arsenic display a V-shaped pH-dependent leaching pattern with important releases at pHs 2 and 11. At the investigated pH values, the release of As, Mn, Pb and Zn from the oxidized sediment is slower and lower if compared with the suboxic sediment while the opposite trend is found for Cd and Cu at pHs 2-8. The transfer from the acid-soluble (exchangeable and carbonate-bound) fraction to the reducible (Fe and Mn hydr/oxide-bound) fraction is consistent with the lower leachability of As, Mn and Zn at pHs 2-8 and Pb at pHs 4-8 after oxidation, while the transfer from the oxidizable (organic matter and sulfide-bound) fraction to the reducible fraction relates to the higher leachability of Cd and Cu at pHs 2-8. The lower leachability of all elements at alkaline pHs 9-11 is due to lower leached concentration of organic matter from the oxidized sediment. Sulfides only play a minor role in controlling the leachability of heavy metals and arsenic.