Predictive modelling of metal mixture toxicity to Daphnia magna populations

Current practice of environmental risk assessment lacks ecological realism, because it depends mostly on toxicity of single substances to individual organisms. It is desirable to develop mechanistic, predictive models that take mixture toxicity on higher levels of organization into account. We conducted a population experiment with Daphnia magna exposed to Cu-Ni-Zn mixtures and the single metals, in order to calibrate a Dynamic Energy Budget Individual-Based Model (DEB-IBM) with single-metal population data and generate blind predictions on mixture toxicity. Metals with different physiological modes of action (PMoA) can be implemented independently in the DEB-IBM, without making further assumptions concerning mixture toxicity. For metals with the same PMoA, we assume no interactions between metals.We first explored approaches to calibrate a DEB-IBM with population-level data, which imposes constraints on parameter estimation as compared to conventional DEB-IBM calibration with individual-level data.We further evaluated the predictive capacity of the DEBbased approach in comparison with common reference models IA and Concentration Addition (CA). While the performance of CA and IA was concentration-dependent, the DEB-IBM has the capacity to capture such trends, because mixture toxicity is an emergent property and interactions between organisms can be taken into account. We conclude that an approach based on DEB-IBMs is a promising way forward to generate predictive models and enhance understanding of mixture toxicity at higher levels of biological organization

Characterization of hemodialysis membranes by inverse size exclusion chromatography

Inverse size exclusion chromatography (i-SEC) was used to characterize three different cellulosic hollow fiber hemodialysis membranes, i.e. low-flux cuprophan and hemophan and high-flux RC-HP400A. With the i-SEC technique the pore size distribution and porosity of a membrane can be determined and adsorption phenomena can be studied. The membranes showed clear differences in pore size and porosity, the high-flux RC-HP400A membrane has a larger pore size as well as a higher porosity. For all the membranes it was found that the elution curves were best described by a homoporous pore volume distribution. It appeared that the bound or non-freezing water in the membranes was at least partly accessible to solutes. The test molecules creatinine and vitamin B 12 both adsorbed to the cellulosic membranes. The adsorption behavior of creatinine was strongly dependent on the NaCl concentration present. The observations could be explained by assuming that cuprophan and RC-HP400A are negatively charged whereas hemophan is positively charged due to the modification with N,N-diethylaminoethyl ether. The net charge of the hemophan is smaller

Extrapolation of Zinc toxicity from individuals to communities in three Daphnia species

There is growing evidence that, in order to effectively assess the risk of chemicals, it is crucial to take the role of species interactions into account. Due to the large number of possible species assemblies, it is desirable to develop predictive, mechanistic models that can be calibrated with standard toxicity data. Therefore, we have conducted life-table experiments with Daphnia magna, D. pulex and D. longispina, exposed to Cu, Ni and Zn, in order to calibrate individual-based models based on Dynamic Energy Budget Theory (DEB-IBM). We derived DEB parameters from control data and calibrated modules for lethal and sublethal effects of Cu, Ni and Zn. Species were combined in silico into binary and tertiary communities and community dynamics under metal exposure were simulated. In the DEB-IBM, interspecific interactions emerge from physiological properties via competition for a shared resource. Each DEB parameter has direct or indirect consequences for resource utilization, and therefore for species interactions. Chemical stressors have the potential to alter these interactions, because effects are implemented as changes in DEB parameters. We modelled the effects of metals on two community-level endpoints, productivity and community structure. The two endpoints are inherently different because only productivity is subject to functional redundancy, leading to large differences in community-level sensitivity, based on which endpoint is chosen. While effects of metals on community-level endpoints can in principle be deduced from DEB theory, experiments to validate the predictions generated with the DEB-IBM are still lacking, and are crucial to evaluate the usefulness of our approach in application. We believe that the use of DEB-IBMs to investigate effects of chemical stressors on higher levels of biological organizations can be fruitful, because data for calibration can be generated relatively easily and models can be developed from established, biology-based frameworks

Combining a Standardized Batch Test with the Biotic Ligand Model to Predict Copper and Zinc Ecotoxicity in Soils

Extraction of soil samples with dilute CaCl2 solution in a routinely performed batch test has potential to be used in site-specific assessment of ecotoxicological risks at metal-contaminated sites. Soil extracts could potentially give a measure of the concentration of bioavailable metals in the soil solution, thereby including effects of soil properties and contaminant "aging." We explored the possibility of using a 0.001 M CaCl2 batch test combined with biotic ligand models (BLMs) for assessment of ecotoxicity in soils. Concentrations of Cu2+ and Zn2+ in soil extracts were linked to responses in ecotoxicity tests (microbial processes, plants, and invertebrates) previously performed on metal-spiked soils. The batch test data for soils were obtained by spiking archived soil materials using the same protocol as in the original studies. Effective concentration values based on free metal concentrations in soil extracts were related to pH by linear regressions. Finally, field-contaminated soils were used to validate model performance. Our results indicate a strong pH-dependent toxicity of the free metal ions in the soil extracts, with R-2 values ranging from 0.54 to 0.93 (median 0.84), among tests and metals. Using pH-adjusted Cu2+ and Zn2+ concentrations in soil extracts, the toxic responses in spiked soils and field-contaminated soils were similar, indicating a potential for the calibrated models to assess toxic effects in field-contaminated soils, accounting for differences in soil properties and effects of contaminant "aging." Consequently, evaluation of a standardized 0.001 M CaCl2 batch test with a simplified BLM can provide the basis for an easy-to-use tool for site-specific risk assessment of metal toxicity to soil organisms. Environ Toxicol Chem 2022;00:1-14. (c) 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC

Remediation of acid mine drainage and immobilization of rare earth elements: Comparison between natural and residual alkaline materials

Acid mine drainage (AMD) is a well-known source of toxic trace metals in freshwaters. Traditional passive treatment systems rely on AMD neutralization with limestone and removal of most common toxic transition metals such as Cu and Zn with little attention to rare earth elements (REE). Alkaline waste materials now receive increasing attention as low cost AMD treatment alternatives in the circular economy. This study was set up to identify the efficiency of alkaline waste materials remediating AMD and scavenging REE in addition to other toxic trace elements. An AMD sample was collected from a lixiviate coming from pyrite heaps in the Iberian Pyrite Belt (pH =1.8, 30 μM ∑REY). The sample was treated with either blast furnace slag (BFS) generated during smelting of iron ore in a blast furnace or biomass ashes (BA) derived from combustion of biomass, thereby using analytical grade CaCO3, and NaOH as reference products. The batch alkalinization experiments were conducted by adding each alkaline material at an amount to obtain an equal pH to ≈6.5. The required amounts of the products were NaOH 99%) and the remaining REE concentrations in the solutions were clearly lower than values for Cu and Zn. The Zn and Cu removals were not consistently high enough (except with NaOH) to meet environmental limits in the discharge waters. The largest efficiency for REE removals was obtained with CaCO3. Indirect evidence here suggests that gypsum is a better host for the trivalent REE than Fe(III) minerals in the precipitates. The ionic radii of trivalent REE are more similar to Ca2+than to Fe3+, explaining the better potential of gypsum as REE host. This study showed also the potential of BFS as alkaline agent for the remediation of AMD in terms of its higher alkalinity generation potential as compared to BA, thus making BA less promising than BFSThis research has received funding from European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska- Curie Grant Agreement No 857989. C.R C´anovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I. The authors gratefully acknowledge the valuable assistance of the following people as well: Dr. Raul Moreno Gonzalez from the Department of Earth Sciences, University of Huelva in Spain for assistance in collecting acid mine water samples; Dr. Quoc Tri Phung from SCK CEN in Belgium for assistance in obtaining BFS samples; Dr. Lander Frederickx from SCK CEN in Belgium for supporting in XRD analysis; Dr. Claudia Moens, Mr. Benoit Bergen and Ms. Kristin Coorevits, ICP-MS Team, Division of Soil and Water management, KU Leuven for their enormous assistance in measuring ICP-MS samples; All the technicians of the Waste and Disposal Group, SCKCEN for their assistance in various ways. Authors also thank ENCE Energía y Celulosa Company for providing the B

Nickel speciation and ecotoxicity in European natural surface waters: development, refinement and validation of bioavailability models

The accurate prediction of Ni ecotoxicity in natural surface water with bioavailability models such as the biotic ligand model (BLM) depends on how well these models can predict both the speciation of Ni (i.e. Ni2+ concentration), the toxicity of Ni2+ ions to an organism, and the effects of water chemistry parameters thereupon, such as dissolved organic carbon (DOC), pH, and water hardness. The overall aim of the study was to calibrate existing speciation models to Ni speciation in natural surface waters and to use these data to validate and/or refine bioavailability models for aquatic organisms from three trophic levels, i.e. algae, invertebrates (daphnids), and fish. The developed chronic Ni toxicity models for daphnids, fish and algae exhibit sufficiently high predictive capacities to yield a marked reduction of uncertainty associated with differences in chronic Ni bioavailability among different test waters. This is due to the fact that they can predict both Ni2+ concentrations as a function of dissolved Ni and water chemistry (mainly DOC, pH, Ca, Mg), as well as the toxicity of the Ni2+ ion as a function of water chemistry (mainly pH, Ca, Mg). The use of the models presented in the present study for normalizing Ni toxicity data will therefore decrease the overall uncertainty of the risk assessment, provided that the variability of bioavailability modifying parameters across different EU regions and water bodies is acknowledged

Reductive dechlorination of trichloroethylene (TCE) in competition with Fe and Mn oxides – observed dynamics in H2-dependent terminal electron accepting processes

<p>The determination of hydrogen (H₂) concentration together with the products of microbial reduction reactions in a trichloroethylene dechlorinating system is conducted to delineate the ongoing predominant terminal electron accepting processes (TEAP). Formate was used as electron donor and synthetic Fe minerals or environmental samples were used as the substrate. Iron(III) and Mn(IV) reduction limited microbial dechlorination by the mixed anaerobic culture by decreasing the level of H₂ in the system. The H₂ measurements indicated that the H₂ concentration at which different TEAPs occur can overlap and thus these TEAPs can therefore occur concurrently rather than exclusively. Difference in Fe(III) bioavailability and hence, Fe(III) reduction partially explain this wide range. The distinction between dechlorination and other microbial reduction processes based on H₂ threshold values is not feasible under such conditions, though there appears to be a relation between the rates of H₂ consuming process and the observed H₂ level.</p

Field-scale demonstration of in situ immobilization of heavy metals by injecting iron oxide nanoparticle adsorption barriers in groundwater

Remediation of heavy metal-contaminated aquifers is a challenging process because they cannot be degraded by microorganisms. Together with the usually limited effectiveness of technologies applied today for treatment of heavy metal contaminated groundwater, this creates a need for new remediation technologies. We therefore developed a new treatment, in which permeable adsorption barriers are established in situ in aquifers by the injection of colloidal iron oxides. These adsorption barriers aim at the immobilization of heavy metals in aquifers groundwater, which was assessed in a large-scale field study in a brownfield site. Colloidal iron oxide (goethite) nanoparticles were used to install an in situ adsorption barrier in a very het-erogeneous, contaminated aquifer of a brownfield in Asturias, Spain. The groundwater contained high concen-trations of heavy metals with up to 25 mg/L zinc, 1.3 mg/L lead, 40 mg/L copper, 0.1 mg/L nickel and other minor heavy metal pollutants below 1 mg/L. High amounts of zinc (>900 mg/kg), lead (>2000 mg/kg), nickel (>190 mg/kg) were also present in the sediment. Ca. 1500 kg of goethite nanoparticles of 461 ±266 nm diameter were injected at low pressure (<0.6 bar) into the aquifer through nine screened injection wells. For each injection well, a radius of influence of at least 2.5 m was achieved within 8 h, creating an in situ barrier of 22 ×3 ×9 m. Despite the extremely high heavy metal contamination and the strong heterogeneity of the aquifer, successful immobilization of contaminants was observed in the tested area. The contaminant concentrations were strongly reduced immediately after the injection and the abatement of the heavy metals continued for a total post- injection monitoring period of 189 days. The iron oxide particles were found to adsorb heavy metals even at pH-values between 4 and 6, where low adsorption would have been expected. The study demonstrated the applicability of iron oxide nanoparticles for installing adsorption barriers for containment of heavy metals in contaminated groundwater under real conditions