France, Spain and Belgium

Funding Information: Our thanks to FCT / MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020), through national funds. Funding Information: The authors received funding from the EU Horizon2020 Framework Project, HBM4EU, Grant number 733032 . Publisher Copyright: © 2021 The AuthorsCadmium (Cd) is a toxic heavy metal widespread in the environment leading to human exposure in particular through diet (when smoking is excluded), as documented by recent human biomonitoring (HBM) surveys. Exposure to Cd at environmental low-exposure levels has been associated with adverse effects such as renal toxicity and more recently bone effects. The implication, even if limited, of Cd in the etiology of osteoporosis can be of high importance at the population level given the significant prevalence of osteoporosis and the ubiquitous and life-long exposure to Cd. Therefore, the osteoporosis cases attributable to Cd exposure was estimated in three European countries (Belgium, France and Spain), based on measured urinary Cd levels from HBM studies conducted in these countries. The targeted population was women over 55 years old, for which risk levels associated with environmental Cd exposure were available. Around 23% of the cases were attributed to Cd exposure. Moreover, in a prospective simulation approach of lifelong urinary Cd concentrations assuming different intakes scenarios, future osteoporosis attributable cases were calculated, based on urinary Cd levels measured in women aged under 55. Between 6 and 34% of the considered populations under 55 years were at risk for osteoporosis. Finally, the costs associated to the burden of osteoporosis-related fractures attributable to Cd for each country targeted in this paper were assessed, standing for a major contributing role of Cd exposure in the overall social costs related to osteoporosis. Absolute costs ranged between 0.12 (low estimate in Belgium) and 2.6 billion Euros (high estimate in France) in women currently over 55 years old and at risk for fractures. Our results support the importance of reducing exposure of the general population to Cd.publishersversionpublishe

Human urinary arsenic species, associated exposure determinants and potential health risks assessed in the HBM4EU Aligned Studies

The European Joint Programme HBM4EU coordinated and advanced human biomonitoring (HBM) in Europe in order to provide science-based evidence for chemical policy development and improve chemical management. Arsenic (As) was selected as a priority substance under the HBM4EU initiative for which open, policy relevant questions like the status of exposure had to be answered. Internal exposure to inorganic arsenic (iAs), measured as Toxic Relevant Arsenic (TRA) (the sum of As(III), As(V), MMA, DMA) in urine samples of teenagers differed among the sampling sites (BEA (Spain) > Riksmaten adolescents (Sweden), ESTEBAN (France) > FLEHS IV (Belgium), SLO CRP (Slovenia)) with geometric means between 3.84 and 8.47 μg/L. The ratio TRA to TRA + arsenobetaine or the ratio TRA to total arsenic varied between 0.22 and 0.49. Main exposure determinants for TRA were the consumption of rice and seafood. When all studies were combined, Pearson correlation analysis showed significant associations between all considered As species. Higher concentrations of DMA, quantitatively a major constituent of TRA, were found with increasing arsenobetaine concentrations, a marker for organic As intake, e.g. through seafood, indicating that other sources of DMA than metabolism of inorganic As exist, e.g. direct intake of DMA or via the intake of arsenosugars or -lipids. Given the lower toxicity of DMA(V) versus iAs, estimating the amount of DMA not originating from iAs, or normalizing TRA for arsenobetaine intake could be useful for estimating iAs exposure and risk. Comparing urinary TRA concentrations with formerly derived biomonitoring equivalent (BE) for non-carcinogenic effects (6.4 μg/L) clearly shows that all 95th percentile exposure values in the different studies exceeded this BE. This together with the fact that cancer risk may not be excluded even at lower iAs levels, suggests a possible health concern for the general population of Europe.HBM4EU is co-financed under Horizon 2020 (grant agreement No 733032). The authors thank all investigators of the contributing studies for their participation and contribution to the joint HBM4EU survey and the national programme owners for their financial support. Also thanks to the participating teenagers and their families, the field workers that collected the samples. The FLEHS IV study was conducted within the framework of the Flemish Center of Expertise on Environment and Health (FLEHS 2016–2020) and funded by the Flemish Government, Department of Environment & Spatial Development. We thank the teenagers and their families that participated in the study, the field workers from the Pro vincial Institute of Hygiene and VITO for the sample and data collection. All collaborators of the scientific teams of the Flemish Center of Expertise on Environment and Health (https://www.milieu-en-gezondheid.be/en/about-the-center-0) and Karen Van Campenhout and Caroline Teughels from the Flemish Department of Environment & Spatial Development for their valuable input in the field work committee. The funding of the German Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection is gratefully acknowledged. BEA study was co-funded by the Spanish Ministry of Agriculture, Fisheries and Food and the Insituto de Salud Carlos III (SEG 1321/15). In Slovenia the work was cofounded by the Slovenian Research Funding Agency – ARRS through a research programme P-0143. ESTEBAN was Funded by Sant´e Publique France and the French ministries of Health and the Environment. The study of RIKSMATEN was conducted and mainly financed by the Swedish Food Agency. Financial support was provided from the Swedish Civil Contingencies Agency and from the Swedish Environmental Pro tection Agency (SEPA).S

Human biomonitoring in health risk assessment in Europe: Current practices and recommendations for the future.

Human biomonitoring (HBM) is an important tool to survey the internal exposure of humans which represents the real life chemical body burden to chemicals and/or their metabolites. It results from total exposure to chemical substances from different sources and via different routes. These substances may be regulated under different legislative frameworks on chemicals (e.g., environmental, occupational, food safety etc). In occupational health, HBM has long traditions to control the exposures at workplaces. By providing accurate data on internal exposure, HBM data can improve human health risk assessment (RA) for both the general population and workers. Although the past few years have shown good examples on the use of HBM in the RA of chemicals, there is still quite some work to be done to improve its use in a regulatory RA. Under the scope of the European Human Biomonitoring Initiative (project HBM4EU, 2017-2021), the current study reviews the state-of-the-art of HBM use in chemicals RA with a special focus in Europe, and attempts to identify hurdles and challenges faced by regulators. To gather information on the use of HBM, including the availability of guidance on how to use it in RA, the RA schemes applied by different European or international organizations were analysed. Examples of such use were identified for a few selected groups of chemicals of concern for human health. In addition, we present the results of a survey, aimed at collecting information from national regulatory risk assessors on their day-to-day RA practices, the use of HBM data, and the obstacles and challenges related to their use. The results evidenced and explained some of the current obstacles of using HBM data in RA. These included the lack of HBM guidance values or biomonitoring equivalents (BEs), limited toxicokinetic information to support the interpretation of HBM data and, in the occupational health and safety (OSH) field, the lack of legal enforcement. Therefore, to support the integration of HBM in regulatory RA, we recommend, on one hand, the elaboration of a EU level guidance on the use of HBM in RA and, on the other hand, the continuation of research efforts to integrate HBM with new RA approaches using in vitro/in silico data and Adverse Outcome Pathways (AOPs).This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 733032 HBM4EU, and received co-funding from the author's organizations. The authors thank to all other participants that contributed to this work.S

EU-wide exposure data of 11 chemical substance groups from the HBM4EU Aligned Studies (2014–2021)

Funding Information: The authors would like to thank everybody who contributed to the HBM4EU Aligned Studies: the participating children, teenagers, adults and their families, the fieldworkers that collected the samples and database managers that made the information available to HBM4EU, the HBM4EU project partners, especially those from WP7 for developing all materials supporting the fieldwork, WP9 for organizing the QA/QC scheme under HBM4EU and all laboratories who performed the analytical measurements. We would like to acknowledge Sun Kyoung Jung from the National Institute of Environmental Research of South-Korea for providing the KoNEHS Cycle III results (crt adjusted). HBM4EU is co-financed under Horizon 2020 (grant agreement No 733032). The authors thank all principal investigators of the contributing studies for their participation and contribution to the HBM4EU Aligned Studies and the national program owners for their financial support. Further details on funding for all the participating studies can be found in the Supplemental Material, Table S12.As one of the core elements of the European Human Biomonitoring Initiative (HBM4EU) a human biomonitoring (HBM) survey was conducted in 23 countries to generate EU-wide comparable HBM data. This survey has built on existing HBM capacity in Europe by aligning national or regional HBM studies, referred to as the HBM4EU Aligned Studies. The HBM4EU Aligned Studies included a total of 10,795 participants of three age groups: (i) 3,576 children aged 6–12 years, (ii) 3,117 teenagers aged 12–18 years and (iii) 4,102 young adults aged 20–39 years. The participants were recruited between 2014 and 2021 in 11–12 countries per age group, geographically distributed across Europe. Depending on the age group, internal exposure to phthalates and the substitute DINCH, halogenated and organophosphorus flame retardants, per- and polyfluoroalkyl substances (PFASs), cadmium, bisphenols, polycyclic aromatic hydrocarbons (PAHs), arsenic species, acrylamide, mycotoxins (deoxynivalenol (total DON)), benzophenones and selected pesticides was assessed by measuring substance specific biomarkers subjected to stringent quality control programs for chemical analysis. For substance groups analyzed in different age groups higher average exposure levels were observed in the youngest age group, i.e., phthalates/DINCH in children versus teenagers, acrylamide and pesticides in children versus adults, benzophenones in teenagers versus adults. Many biomarkers in teenagers and adults varied significantly according to educational attainment, with higher exposure levels of bisphenols, phthalates, benzophenones, PAHs and acrylamide in participants (from households) with lower educational attainment, while teenagers from households with higher educational attainment have higher exposure levels for PFASs and arsenic. In children, a social gradient was only observed for the non-specific pyrethroid metabolite 3-PBA and di-isodecyl phthalate (DiDP), with higher levels in children from households with higher educational attainment. Geographical variations were seen for all exposure biomarkers. For 15 biomarkers, the available health-based HBM guidance values were exceeded with highest exceedance rates for toxicologically relevant arsenic in teenagers (40%), 3-PBA in children (36%), and between 11 and 14% for total DON, Σ (PFOA + PFNA + PFHxS + PFOS), bisphenol S and cadmium. The infrastructure and harmonized approach succeeded in obtaining comparable European wide internal exposure data for a prioritized set of 11 chemical groups. These data serve as a reference for comparison at the global level, provide a baseline to compare the efficacy of the European Commission's chemical strategy for sustainability and will give leverage to national policy makers for the implementation of targeted measures.publishersversionpublishe

Harmonized human biomonitoring in European children, teenagers and adults: EU-wide exposure data of 11 chemical substance groups from the HBM4EU Aligned Studies (2014–2021)

HBM4EU is co-financed under Horizon 2020 (grant agreement No 733032).As one of the core elements of the European Human Biomonitoring Initiative (HBM4EU) a human biomonitoring (HBM) survey was conducted in 23 countries to generate EU-wide comparable HBM data. This survey has built on existing HBM capacity in Europe by aligning national or regional HBM studies, referred to as the HBM4EU Aligned Studies. The HBM4EU Aligned Studies included a total of 10,795 participants from three age groups: (i) 3,576 children aged 6-12 years, (ii) 3,117 teenagers aged 12-18 years, and (iii) 4,102 young adults aged 20-39 years. The participants were recruited between 2014 and 2021 in 11-12 countries per age group, geographically distributed across Europe. Depending on the age group, internal exposure to phthalates and the substitute DINCH, halogenated and organophosphorus flame retardants, per- and polyfluoroalkyl substances (PFASs), cadmium, bisphenols, polycyclic aromatic hydrocarbons (PAHs), arsenic species, acrylamide, mycotoxins (deoxynivalenol (total DON)), benzophenones and selected pesticides was assessed by measuring substance specific biomarkers subjected to stringent quality control programs for chemical analysis. For substance groups analyzed in different age groups higher average exposure levels were observed in the youngest age group, i.e., phthalates/DINCH in children versus teenagers, acrylamide and pesticides in children versus adults, and benzophenones in teenagers versus adults. Many biomarkers in teenagers and adults varied significantly according to educational attainment, with higher exposure levels of bisphenols, phthalates, benzophenones, PAHs, and acrylamide in participants (from households) with lower educational attainment, while teenagers from households with higher educational attainment have higher exposure levels for PFASs and arsenic. In children, a social gradient was only observed for the non-specific pyrethroid metabolite 3-PBA and di-isodecyl phthalate (DiDP), with higher levels in children from households with higher educational attainment. Geographical variations were seen for all exposure biomarkers. For 15 biomarkers, the available health-based HBM guidance values were exceeded with the highest exceedance rates for toxicologically relevant arsenic in teenagers (40%), 3-PBA in children (36%), and between 11 and 14% for total DON, Σ (PFOA + PFNA + PFHxS + PFOS), bisphenol S and cadmium. The infrastructure and harmonized approach succeeded in obtaining comparable European-wide internal exposure data for a prioritized set of 11 chemical groups. These data serve as a reference for comparison at the global level, provide a baseline to compare the efficacy of the European Commission's chemical strategy for sustainability, and will give leverage to national policymakers for the implementation of targeted measures.info:eu-repo/semantics/publishedVersio

Harmonized human biomonitoring in European children, teenagers and adults : EU-wide exposure data of 11 chemical substance groups from the HBM4EU Aligned Studies (2014–2021)

Funding Information: The authors would like to thank everybody who contributed to the HBM4EU Aligned Studies: the participating children, teenagers, adults and their families, the fieldworkers that collected the samples and database managers that made the information available to HBM4EU, the HBM4EU project partners, especially those from WP7 for developing all materials supporting the fieldwork, WP9 for organizing the QA/QC scheme under HBM4EU and all laboratories who performed the analytical measurements. We would like to acknowledge Sun Kyoung Jung from the National Institute of Environmental Research of South-Korea for providing the KoNEHS Cycle III results (crt adjusted). HBM4EU is co-financed under Horizon 2020 (grant agreement No 733032). The authors thank all principal investigators of the contributing studies for their participation and contribution to the HBM4EU Aligned Studies and the national program owners for their financial support. Further details on funding for all the participating studies can be found in the Supplemental Material, Table S12. Funding Information: The authors would like to thank everybody who contributed to the HBM4EU Aligned Studies: the participating children, teenagers, adults and their families, the fieldworkers that collected the samples and database managers that made the information available to HBM4EU, the HBM4EU project partners, especially those from WP7 for developing all materials supporting the fieldwork, WP9 for organizing the QA/QC scheme under HBM4EU and all laboratories who performed the analytical measurements. We would like to acknowledge Sun Kyoung Jung from the National Institute of Environmental Research of South-Korea for providing the KoNEHS Cycle III results (crt adjusted). HBM4EU is co-financed under Horizon 2020 (grant agreement No 733032). The authors thank all principal investigators of the contributing studies for their participation and contribution to the HBM4EU Aligned Studies and the national program owners for their financial support. Further details on funding for all the participating studies can be found in the Supplemental Material, Table S12 . Publisher Copyright: © 2023 The AuthorsAs one of the core elements of the European Human Biomonitoring Initiative (HBM4EU) a human biomonitoring (HBM) survey was conducted in 23 countries to generate EU-wide comparable HBM data. This survey has built on existing HBM capacity in Europe by aligning national or regional HBM studies, referred to as the HBM4EU Aligned Studies. The HBM4EU Aligned Studies included a total of 10,795 participants of three age groups: (i) 3,576 children aged 6–12 years, (ii) 3,117 teenagers aged 12–18 years and (iii) 4,102 young adults aged 20–39 years. The participants were recruited between 2014 and 2021 in 11–12 countries per age group, geographically distributed across Europe. Depending on the age group, internal exposure to phthalates and the substitute DINCH, halogenated and organophosphorus flame retardants, per- and polyfluoroalkyl substances (PFASs), cadmium, bisphenols, polycyclic aromatic hydrocarbons (PAHs), arsenic species, acrylamide, mycotoxins (deoxynivalenol (total DON)), benzophenones and selected pesticides was assessed by measuring substance specific biomarkers subjected to stringent quality control programs for chemical analysis. For substance groups analyzed in different age groups higher average exposure levels were observed in the youngest age group, i.e., phthalates/DINCH in children versus teenagers, acrylamide and pesticides in children versus adults, benzophenones in teenagers versus adults. Many biomarkers in teenagers and adults varied significantly according to educational attainment, with higher exposure levels of bisphenols, phthalates, benzophenones, PAHs and acrylamide in participants (from households) with lower educational attainment, while teenagers from households with higher educational attainment have higher exposure levels for PFASs and arsenic. In children, a social gradient was only observed for the non-specific pyrethroid metabolite 3-PBA and di-isodecyl phthalate (DiDP), with higher levels in children from households with higher educational attainment. Geographical variations were seen for all exposure biomarkers. For 15 biomarkers, the available health-based HBM guidance values were exceeded with highest exceedance rates for toxicologically relevant arsenic in teenagers (40%), 3-PBA in children (36%), and between 11 and 14% for total DON, Σ (PFOA + PFNA + PFHxS + PFOS), bisphenol S and cadmium. The infrastructure and harmonized approach succeeded in obtaining comparable European wide internal exposure data for a prioritized set of 11 chemical groups. These data serve as a reference for comparison at the global level, provide a baseline to compare the efficacy of the European Commission's chemical strategy for sustainability and will give leverage to national policy makers for the implementation of targeted measures.Peer reviewe

From science to policy: How European HBM indicators help to answer policy questions related to phthalates and DINCH exposure

Within the European Human Biomonitoring (HBM) Initiative HBM4EU we derived HBM indicators that were designed to help answering key policy questions and support chemical policies. The result indicators convey information on chemicals exposure of different age groups, sexes, geographical regions and time points by comparing median exposure values. If differences are observed for one group or the other, policy measures or risk management options can be implemented. Impact indicators support health risk assessment by comparing exposure values with health-based guidance values, such as human biomonitoring guidance values (HBM-GVs). In general, the indicators should be designed to translate complex scientific information into short and clear messages and make it accessible to policy makers but also to a broader audience such as stakeholders (e.g. NGO's), other scientists and the general public. Based on harmonized data from the HBM4EU Aligned Studies (2014-2021), the usefulness of our indicators was demonstrated for the age group children (6-11 years), using two case examples: one phthalate (Diisobutyl phthalate: DiBP) and one non-phthalate substitute (Di-isononyl cyclohexane-1,2- dicarboxylate: DINCH). For the comparison of age groups, these were compared to data for teenagers (12-18 years), and time periods were compared using data from the DEMOCOPHES project (2011-2012). Our result indicators proved to be suitable for demonstrating the effectiveness of policy measures for DiBP and the need of continuous monitoring for DINCH. They showed similar exposure for boys and girls, indicating that there is no need for gender focused interventions and/or no indication of sex-specific exposure patterns. They created a basis for a targeted approach by highlighting relevant geographical differences in internal exposure. An adequate data basis is essential for revealing differences for all indicators. This was particularly evident in our studies on the indicators on age differences. The impact indicator revealed that health risks based on exposure to DiBP cannot be excluded. This is an indication or flag for risk managers and policy makers that exposure to DiBP still is a relevant health issue. HBM indicators derived within HBM4EU are a valuable and important complement to existing indicator lists in the context of environment and health. Their applicability, current shortcomings and solution strategies are outlined

Fixation of cadmium, copper, nickel and zinc in soil : kinetics, mechanisms and its effect on metal bioavailability

The total concentrations of trace metals such as Cu, Zn Ni and Cd increase with time in the majority of soils due to diffuse contamination. These metals become toxic at elevated concentrations. The bioavailability of these metals can decrease over time by fixation reactions in soil and can partly offset the risk due to increasing total metal concentrations. The term fixation is used here with reference to the slow immobilization reactions that take place in the weeks and years after the short-term (hours) immobilisation reaction. The objectives of this work are to characterize the extent of fixation of metals (Ni, Zn, Cd and Cu) in various soils, to assess which soil constituents are involved in metal fixation and to identify the role of fixation on metal availability to plants. It is postulated that metal fixation takes place in micro-porous amorphous iron (Fe) oxyhydroxides and in carbonates. Twenty eight soils with varying properties (pH 3.4-7.7) were sampled, contaminated with an environmental relevant dose of Ni, Zn, Cd and Cu and incubated in open air with free drainage for 850 days. Soils included two toposequences (Spain, Vietnam) with varying weathering stage and concentrations of Fe oxyhydroxides, and 13 European soils ranging from acid podzols to calcic cambisols. Fixation was measured as the increase of the fraction of added metals that was not isotopic exchangeable and was, on average among all soils, 43% (Cu), 41% (Zn), 41% (Ni) and 28% (Cd) after 850 days. Fixation of Cd, Zn and Ni was mainly explained and positively correlated with pH. Metal fixation within samples from each toposequence was positively related to total Fe oxyhydroxide concentration for Zn, Ni and Cd. Fixation of Zn and Cd in soils with pH > 7.0 increased with increasing concentrations of carbonates at initial ageing times. Fixed fractions of Zn, Ni and Cd were significantly released when experimentally removing 50% of carbonates by acidification. Fixation of Cu was most poorly related to soil properties. These data suggest that fixation is related to a pH dependent diffusion into oxyhydroxides (Cd, Zn and Ni) and to a diffusion/coprecipitation in carbonates (Cd, Zn). Fixation of Ni at pH neutral conditions may also be related to stabilisation of precipitates which readily form in soil. The role of Fe-oxyhydroxide structure and crystallinity on metal fixation was studied using 4 synthetic Fe oxyhydroxides (Hydrous Ferric Oxide (HFO), Ferrihydrite (FH), Goethite (GT), Hematite (HT)). Metal adsorption kinetics was characterised in suspensions during 70 days at varying initial metal concentration and various pH values (3.8-7.0) maintained within 0.2 units. The slow reactions, defined as those occurring beyond day 1, were most pronounced in GT and least in HT. The extent of slow reaction was surprisingly unrelated to crystallinity or microporosity as determined by N2 adsorption. Amorphous hydroxides such as HFO probably unfold in suspension thereby increasing their specific surface but reducing their micro-porosity and capacity for metal diffusion. Metals fixed on GT after 70 days, determined by isotopic exchange were 90% (Ni), 90% (Zn) and 54%Cd. Freundlich adsorption isotherms fitted to the data show that ageing between 1 and 70 days decreases metal concentrations in solution by factors 2-30 (Ni), 1-20 (Zn) and 1-4 (Cd) depending on the type of oxyhydroxide. These factors become significantly larger at lower concentration for Ni and Zn in some oxyhydroxides. This concentration dependency suggests that slow reactions are not only related to diffusion but that substitution for Fe in the structure might be involved as confirmed by spectroscopic evidence elsewhere. The extent of slow reactions on metal immobilization on GT decreased with decreasing pH and was less than a factor 2 within 70 days at pH 3.7. The role of soil organic matter on metal fixation was studied in humic acids and peat samples. Metal fixation was measured as the increase of the fraction of added metals that was not isotopic exchangeable after 70 days incubating the organic matter fractions with metals in suspensions at pH=7. Metal fixation varied from insignificantly different from zero to maximally 31% and was, on average for 5 organic matter samples, 19% (Cu), 17% (Zn), 7% (Ni) and 8% (Cd). These results show that the majority of metal added to soil binds reversibly with organic matter although a statically significant fraction can be fixed. Soil organic matter and oxyhydroxides are the dominant reactive surfaces for metal binding in soil. Soil organic matter can, therefore, keep metal in a reversible pool and limit their fixation in Fe-oxyhydroxides. A model system consisting of Fe oxyhydroxides and amberlite (as a model for organic matter with fully reversible binding) was made and showed that the relative changes of soluble Ni during long-term equilibration with goethite were significantly smaller when a resin was added to the sorption system. The resin acts as a reversible pool that limits the slow reactions of Ni with oxyhydroxides. A data analysis by modeling suggested no interactions among both adsorbents. The solubility of metals in the 28 soils as a function of ageing was predicted with an assemblage model (WHAM VI) considering soil organic matter, Fe-oxyhydroxides and clay minerals as reactive surfaces. The predictions were only successful by adjusting the specific surface area of Fe-oxyhydroxides to a value of 600 m2/g. The effects of time on solubility was included by using the measured values of isotopic exchangeable metals as reactive metals and these predictions were better than using total metal concentrations. The fixation observed in the Fe-oxyhydroxide studies was used to predict metal fixation in soil with the 2-component additive model described above. The assemblage model predicted the fraction of total metal present on the iron oxyhydroxide surfaces at the start of soil spiking and this fraction increased with increasing pH. The observed versus predicted fixed fractions agreed reasonably well for Ni and Zn which show that slow adsorption reactions in iron oxyhydroxides are capable of explaining metal ageing in soils. Finally, it was checked if ageing also reduced metal availability to plants. Italian ryegrass was grown simultaneously on the 28 different soils spiked with a mixture of Ni, Zn, Cu and Cd salts and aged for > 2 years and on corresponding freshly spiked soils with the same total metal concentration. Ageing significantly reduced shoot Ni concentrations in 6 and Cd and Zn concentrations in 3 soils out of 19 on which growth was successful. Changes in shoot metal concentrations were significantly explained by corresponding changes of soluble soil metal concentrations for Ni or by isotopic exchangeable concentrations for Ni and Cd. Unfortunately, there was a significant effect of soil ageing on plant yield in several soils which confounded the effects on shoot metal concentrations. Multivariate analysis including yield showed that ageing effects on Cd, Ni and Zn uptake were significant when using total soil metal concentrations whereas the isotopic exchangeable fractions explained these ageing effects, thereby predicting that shoot Cd and Ni concentrations decreased proportionally with decreasing isotopic exchangeable fractions during ageing. It was concluded that changes in metal supply due to ageing were relatively small compared to other factors that affect metal bioavailability. Our data show that Zn, Ni, Cu and Cd can be gradually fixed and can have reduced availability by ageing reactions, however the extent of these reactions, expressed as reduction in the labile fraction, is less than a factor 5 with some exceptions such as Ni in high pH soil and Zn in soils with high concentrations of carbonates. Our data suggest that fixation takes place in iron oxyhydroxides and in carbonates and that binding to soil organic matter is mainly reversible. The microporosity of Fe-oxyhydroxides in soil is likely to play a role in slow reactions; however there is no tool to quantify that factor. Metal fixation reduces metal mobility but effects of ageing on bioavailability are obscured by other factors that also affect bioavailability and which may change by ageing.Samenvatting iii Summary vii Abbrevations, notations and symbols xi Chapter 1 Fixation of trace metals in soils: an overview of existing concepts and objectives for this work 1 Chapter 2 Role of soil constituents on fixation of soluble Zn, Cu, Ni and Cd added to soils 13 Chapter 3 Long-term reactions of Ni, Zn and Cd with iron oxyhydroxides depend on crystallinity and structure and on metal concentrations 33 Chapter 4 Labile and inert fractions of Cu, Zn, Ni and Cd in soil organic matter detected by an isotopic exchange/resin sorption technique 53 Chapter 5 Fixation of Ni in iron oxyhydroxide and amberlite mixtures: evidence for additive reactions 63 Chapter 6 Prediction of Cd, Zn, Ni and Cu solubility during >2 years ageing reactions with an assemblage model 71 Chapter 7 Ageing of Cd, Zn, Cu and Ni in soils does not consistently reduce metal uptake by Lolium perenne L 91 Chapter 8 Major conclusions and suggestions for further research 107status: publishe

Radiolabile cadmium and zinc in soil as affected by pH and source of contamination

The determination of radio-labile metals in soil has gained renewed interest for predicting metal availability. There is little information on to what extent the fraction of labile metal is affected by the soil properties and the source of metal contamination. The radio-labile content (E value) of Cd and Zn was measured in field-collected soils with Cd and Zn originating from different sources. The E values were erratic and sometimes even exceeded total metal content when the concentration in the soil extract was less than 8 μg Zn l-1 or less than 3 μg Cd l-1. Addition of EDTA (0.1 mM) to the radio-labelled soil suspension resulted in larger concentrations of Cd and Zn in solution and smaller E values for these soils. The E values were, however, unaffected by the presence of EDTA (0.1 mM) in soils with larger concentrations of Cd and Zn in solution. The %E values (E value relative to metal soluble in aqua regia) ranged from 9% to 92% (mean 61%) for Cd and from 3% to 72% (mean 33%) for Zn. No correlation between soil properties and %E was observed for Cd, and the %E of Zn was negatively correlated with soil pH (r = -0.65). There was a strong negative correlation between pH and %E in soils enriched with metals in soluble form (e.g. metal salts, corrosion of galvanized structures). In soils where Cd or Zn were added in a less soluble form, no such correlation was found, and %E values were generally less than in soils spiked with metal salts, suggesting that the source of the contamination controls mainly the labile fractions of Cd and Zn.status: publishe