Bioavailability Of Contaminants Research Articles

Probing atomic-scale processes at the ferrihydrite-water interface with reactive molecular dynamics

Interfacial processes involving metal (oxyhydr)oxide phases are important for the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. Consequently, these processes influence ecosystem health and functioning, and have shaped the biological and environmental co-evolution of Earth over geologic time. Here we employ reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy to study the molecular-scale interfacial processes that influence surface complexation in ferrihydrite-water systems containing aqueous MoO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext {MoO}_4}^{2-}$$\\end{document}. We validate the utility of this approach by calculating surface complexation models directly from simulations. The reactive force-field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. We find that upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. We observed how this restructuring leads to a different interfacial hydrogen bond network compared to bulk water by monitoring water dynamics. Using umbrella sampling, we constructed the free energy landscape of aqueous MoO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext {MoO}_4}^{2-}$$\\end{document} adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with the values reported by experimental surface complexation models. These findings are important as reactive molecular dynamics opens new avenues to study mineral-water interfaces, enriching and refining surface complexation models beyond their foundational assumptions.Graphic

Unraveling the impact of high arsenic, fluoride and microbial population in community tubewell water around coal mines in a semiarid region: Insight from health hazards, and geographic information systems

High arsenic (As), fluoride (F-), and microbial pathogens coexist in semiarid conditions afflicting > 240 million people worldwide including Pakistan. Groundwater quality has declined due to geogenic and manmade activities providing suitable ground for ubiquity, bioavailability, and toxicity of contaminants. We tested the health hazard, distribution, and apportionment of As, F-, and microbes in groundwater around coal mines in Quetta, Pakistan. The range of As, and F- concentrations in groundwater were 0.2–16.6 µg/L, 0.4–18.5 mg/L. Both, As and F- correlate with high HCO3-, pH, Na+, SO42-, Fe, and Mn, and negatively with Ca2+ water. The coalfield showed many folds higher As 15.8–28.5 µg/L, and F- 10.8–34.5 mg/L compared to groundwater-wells. Geochemical phases revealed saturation of groundwater with calcite, dolomite, fluorite, gypsum, and undersaturation with halite-mirabilite, and arsenopyrite minerals. The positive matrix factorization (PMF) model assessed five-factor solutions: geogenic, industrial, coal mining, sulfide & fluoride-bearing mineral-dissolution, and agriculture pollution delivered As, F-, and microbial contamination. About 24.6 % and 64.4 % of groundwater samples exceeded the WHO guidelines of As 10 µg/L, F- 1.5 mg/L. The carcinogenicity, and non-carcinogenicity of As, and F- were higher in children than adults. Therefore, health hazards in children are of great concern in achieving sustainable management goals.

Impact of four surfactants on the uptake of per- and polyfluoroalkyl substances (PFAS) by red fescue grass

Per- and polyfluoroalkyl substances (PFAS) pose great risks to human health and the ecosystem, necessitating effective remediation strategies such as phytoremediation. Surfactants, due to their ability to increase the bioavailability of hydrophobic contaminants, are considered as potential agents to improve phytoremediation for PFAS. In this research, we explored the impact of four surfactants (sodium dodecyl sulfate (SDS), rhamnolipid, Triton X-100, and Glucopone 600 CS UP) on plant growth and the uptake of PFAS by red fescue over 110 days. The results showed that while surfactants at lower concentrations did not negatively affect plant growth, the highest dose (2,500 mg/kg) significantly reduced the dry weight of plant shoots. Although none of the four surfactants led to an increased overall removal efficiency of ∑PFAS by red fescue over 110 days, SDS did enhance the uptake of PFAS compounds with long carbon chain lengths. With SDS addition at 2,500 mg/kg, the average fold increases of long chain PFAS removal were 1.99 for perfluorooctanoic acid (PFOA), 2.44 for perfluorononanoic acid (PFNA), 2.11 for perfluorodecanoic acid (PFDA), 1.52 for perfluoroundecanoic acid (PFUnA), 1.88 for perfluorohexanesulphonic acid (PFHxS), and 2.97 for perfluorooctanesulfonic acid (PFOS). The research indicated that using surfactants, such as SDS at appropriate doses could improve phytoremediation effectiveness in mitigating long-chain PFAS, which is a known challenge in soil remediation.

Fortifying casein phosphopeptides and Ca in wheat reduces the As, Cd, and Pb bioavailability based on a mouse model: Calcium and phosphate transporters and gut microbiota

Reducing the oral bioavailability of metal contaminants including As, Cd, , and Pb in foods can protect human health. Studies showed reduced metal bioavailability with elevated Ca and Fe intake; however, the effectiveness of enhancing food Ca and Fe bioavailability remains unknown. Based on a mouse bioassay and using metal accumulation in mouse tissues (kidneys and liver) as the bioavailability endpoint, this study investigated the roles of casein phosphopeptides (CPP, food nutrition fortifier) in lowering the As, Cd, and Pb bioavailability from consuming a metal-contaminated wheat. The CPP amendment at 0.10–0.50% in wheat promoted its Ca bioavailability, causing 33–62% and 59–80% decreases in the gene expression encoding for duodenal Ca and phosphate transporters in mice. This limited transcellular transport of Cd2+ and inorganic arsenate via Ca and phosphate transporters respectively, thus leading to 27% and 34% decreases in Cd and As contents in mouse kidneys fed with wheat at 0.50% CPP amendment. In addition, CPP promoted the colonization of Feacalibaculum and Bifidobacterium in mouse gut, likely promoting As excretion in feces by 81–112%. In contrast to As, and Cd, CPP failed to reduce Pb contents in mouse tissue after consuming CPP-amended wheat, probably by elevating wheat-Pb solubility in the intestinal fluid by 48–136%. However, co-amendment of 0.30% CPP and 500 ​μg ​g−1 Ca as Ca gluconate lowered the As, Cd, and Pb contents in mouse kidneys by 38–71%. The data indicate that fortifying Ca together with CPP in wheat can reduce human exposure to multi-metals via dietary intake.

Chronic metal contamination shapes the size structure of Gammarus fossarum populations in French headwater rivers.

Assessing the effects of multigenerational exposure of aquatic animal populations to chemical contamination is essential for ecological risk assessment. However, beyond rare examples reporting the sporadic emergence of a toxicological tolerance within populations that persist in contaminated environments, conclusive results are even more limited from field studies when it comes to the alteration of life-history traits. Here, we investigated whether long-term exposure to cadmium (Cd) influences size-related life-history traits (i.e., size at puberty, median adult size, maximum size) in Gammarus fossarum, a keystone species of European stream ecosystems. We studied 13 field populations of G. fossarum (cryptic lineage B) living in headwater rivers located in natural areas scattered at a large geographical scale and exposed to contrasted bioavailable Cd contamination levels due to different local geochemical backgrounds. We achieved a detailed description of the physical and physicochemical conditions of the river reaches investigated. Land-use parameters, hydrological characteristics (flow, slope, river width, flow structure, mosaic of substrates), and physicochemical conditions (temperature, conductivity, dissolved oxygen) were measured. Metallic bioavailable contamination was assessed using a standardized active biomonitoring procedure (Gammarus caging). Based on the field demographic census of the 13 populations, our results demonstrated that chronic Cd contamination significantly influences life-history in the G. fossarum species, with a significant reduction in all size traits of populations (size at puberty, median adult size, maximum size). In addition, we confirmed Cd-tolerance in contaminated populations during exposure tests in the laboratory. Various hypotheses can be then put forward to explain the modification of size-related life-history traits: a direct toxic effect of Cd, a cost of Cd-tolerance, or an adaptive evolution of life-history exposed to toxic pressure.

Sequential Fractionation of Heavy Metals from Flooded and Non-Flooded Soils in Obunagha Community, Bayelsa State, Nigeria

Soil samples from flooded and non-flooded areas of different farmlands in Obunagha community, Bayelsa State were collected for this study. The aim of the study was to investigate the chemical fractionation and bioavailability of Cr, Cd, Zn, Ni, & Fe in flooded and non-flooded farmlands. The soil samples were fractionated into six chemical fractions, each containing different heavy metal concentrations and analyzed using flame atomic absorption spectrophotometer. The highest average concentration for Cadmium (Cd) is 1.50g/kg, Zinc (Zn) is 7.53g/kg, Nickel (Ni) is 10.54g/kg, Iron (Fe) is 9.52g/kg, and Chromium (Cr) is 12.62g/kg all from the flooded areas of the farmlands. Sequential extraction showed heavy metals distributed throughout all extraction steps, with the water-soluble fraction prevailing, potentially increasing the mobility and bioavailability of these metals. The %bioavailability ranged from 37.98% – 90.00%. The results indicated also that the average concentration of the metals in flood affected farmland were more than the non-flooded areas. The results indicated that floods affect farmland metal content by altering contaminant bioavailability, causing adverse environmental effects. Also, the results of the heavy metals analyses revealed that the levels of nickel, zinc, chromium, cadmium and iron in all the farmland soil samples are above the maximum allowable concentration for heavy metals in soil set by WHO Guidelines provided. Hence, the farmland soils are not safe for agricultural activities. We therefore, recommend regular monitoring of the soils to prevent excessive build-up of these toxic heavy metals.

Measurement of total amine site concentrations on bacterial cell surfaces using selective site-blocking and potentiometric titrations

Bacterial cell surface amine binding sites can form strong complexes with both toxic metal cations and anionic contaminants, thereby affecting the behavior of these contaminants in both natural and engineered systems. In this study, a novel approach was developed to measure the concentration of total amine sites on bacterial cell surfaces by combining selective site-blocking, potentiometric titrations and surface complexation modeling. Our controls show that the amine blocker sulfo-N-hydroxysulfosuccinimide acetate (SNHS) selectively reacts with primary and secondary amine sites but does not react with other binding sites on the bacterial cell surface. Amine site concentrations on bacterial cell surfaces, therefore, can be measured as the difference between the total site concentrations of un-blocked and SNHS-blocked bacterial samples. We measured amine site concentrations on Bacillus subtilis and Pseudomonas putida of 52 ± 5 and 78 ± 6 μmol/g, respectively, which account for 24% and 32% of the total binding sites on each bacterial surface. Our results suggest that amine sites can be present in relatively high concentrations on bacterial surfaces, and further studies that are focused on the role of cell surface amine sites on the transport and bioavailability of toxic metal cations and anionic contaminants are crucial.

Biosurfactant production potentials of microorganisms isolated from atmosphere of five petroleum stations at Tanke, Ilorin, Kwara State, Nigeria

Biosurfactants aid in bioremediation by improving the bioavailability of hydrocarbon contaminants. The objective of this work was to isolate, enumerate and identify bacteria and fungi for their biosurfactant production potential in the atmosphere of five petroleum stations at Tanke, Ilorin, Kwara State, Nigeria using appropriate, standard microbiological methods (haemolysis test, emulsification index test, drop collapse test and oil displacement test). Fourteen bacteria and ten fungi were isolated in this study. The bacterial isolates belong to the genus Bacillus, Corynebacterium, Micrococcus, Staphylococcus, Listeria, Clostridium. The fungal isolates are of the genus Neurospora, Curvularia, Aspergillus, Fusarium, Rhizopus, Cladosporium, Colletotrichum, Sclerotinia. The mean number of bacteria counted during the sampling ranged from 3.48±1.15*102 CFU to 4.82 ±1.69*102 CFU, with petrol station 4 having the highest bacteria count (2.41*102 CFU) and petrol station 3 having the lowest bacteria count (1.74*102 CFU). The mean fungal count ranged from 7±3.7 CFU to 8.6±4.7 *102 CFU, with petrol station 4 having the highest fungal count (4.3 *10 CFU) and petrol station 3 having the lowest fungal count (3.4*10 CFU). Bacillus species showed promise of biosurfactant production after screening. Aspergillus fumigatus was the most prevalent fungus isolated (24%) while Staphylococcus epidermidis was the most prevalent bacterium isolated (11%). Some of these organisms are known opportunistic pathogens therefore, improved ventilation and sanitation of the petrol stations should be carried out to reduce the microbial load in the air. Also, bacteria that produce biosurfactant can be isolated from air of gas stations.

The dissipation of organophosphate esters mediated by ryegrass root exudate oxalic acid in soil: Analysis of enzymes activities, microorganism

Complex rhizoremediation is the main mechanism of phytoremediation in organic-contaminated soil. Low molecular weight organic acids (LMWOAs) in root exudates have been shown to increase the bioavailability of contaminants and are essential for promoting the dissipation of contaminants. The effects of root exudates on the dissipation of organophosphate esters (OPEs) in soil are unclear. Consequently, we studied the combined effects of root exudates, soil enzymes and microorganisms on OPEs (tri (1-chloro-2-propyl) phosphate (TCPP) and triphenyl phosphate (TPP)) dissipation through pot experiments. Oxalic acid (OA) was confirmed to be the main component of LMWOAs in root exudates of ryegrass. The existence of OA increased the dissipation rate of OPEs by 6.04%–25.50%. Catalase and dehydrogenase activities were firstly activated and then inhibited in soil. While, urease activity was activated and alkaline phosphatase activity was inhibited during the exposure period. More bacteria enrichment (e.g., Sphingomonas, Pseudomonas, Flavisolibacter, Pontibacter, Methylophilus and Massilia) improved the biodegradation of OPEs. In addition, the transformation paths of OPEs hydrolysis and methylation under the action of root exudates were observed. This study provided theoretical insights into reducing the pollution risk of OPEs in the soil.

Influences of dissolved organic matters on the adsorption and bioavailability of sulfadiazine: Molecular weight- and type-dependent heterogeneities

The bioavailability of contaminants in aquatic environments was highly related with the existing forms (soluble or adsorbed) and properties of dissolved organic matters (DOMs). In this study, the molecular weight (MWs)-dependent effects of DOMs on the adsorption and bioavailability of sulfadiazine were explored. Colloid ZnO and Al2O3 were employed as the representative colloidal particles, and algae-derived organic matter (AOM) and humic acid (HA) were selected as typical autochthonous and allochthonous DOMs. The ultrafiltration procedure was applied to divide the bulk DOMs into high MW (HMW-, 1 kDã0.45 μm) and low MW (LMW-, <1 kDa) fractions. Results showed that HMW-DOM contained more aromatic and protein-like substances as compared to the LMW counterparts. In addition, presence of AOM promoted sulfadiazine adsorption capabilities by 1.19–4.54 folds and mitigated the inhibition ratio by 0.56–0.78 folds, whereas those of HA inhibited sulfadiazine adsorption by 0.27–0.84 folds and enhanced the biotoxicity by 1.21–1.45 folds. Regardless of different DOM types, HMW-fraction exhibited highest effects on sulfadiazine adsorption and bioavailability, followed by the bulk- and LMW-fractions. Two-dimensional correlation spectroscopy showed that sulfadiazine was adsorbed on colloidal surfaces prior to AOM, and the subsequent adsorption of AOM can provide additional sites for sulfadiazine adsorption, which decreased the concentrations of aqueous sulfadiazine as well as the biotoxicity to Microcystis aeruginosa (M. aeruginosa). The HA, however, was preferentially adsorbed on colloidal surfaces, which hindered the subsequent sulfadiazine adsorption and resulted in a high sulfadiazine abundance in aqueous solution as well as the enhanced biotoxicity to M. aeruginosa. This study highlighted the importance of the types and MWs of DOMs in influencing the behaviors and ecological effects of aquatic contaminants.

Bioavailability enhancement of petroleum-contaminated soil by electrokinetic remediation

The Electro kinetic Remediation Technology (EKR) is recognized as the most potential remediation technology for soils with low permeability, like clay soil characteristics. Electrokinetic treatment could increase the bioavailability of contaminants in bioremediation petroleum-contaminated soil. The study, “Bioavailability enhancement of petroleum contaminated soil by electrokinetic remediation,” is experimental research in a laboratory to improve the bioavailability of petroleum hydrocarbons on clay during bioremediation with initial treatment using electrokinetic remediation techniques, finding optimum electrokinetic operating conditions of remediations, and analyzing the mechanism of remediation process in contaminated soil. Bioavailability enhancement was studied for 35 days. Polluted soil was treated with an electrokinetic box test (17cm×12cm×10cm), and DC power was used for 48 hours. Total Petroleum Hydrocarbon (TPH) concentration was determined by gravimetric methods. The results showed that the characteristics of the soil samples were dominated by 49.31% clay. The initial concentration of TPH in polluted soil is 3.7%. The electrokinetic applications during 48 hours and followed by bioremediation for 35 days those processes removed TPH up to 80.74 % (from 33780.66 mg HC (kg dry w)-1 to 6506.155176 mg HC (kg dry w)-1. There is an increase in bioavailability indicated by the rise in bacterial populations and an increase in biodegradation after electrokinetic remediation. With this approach, bioavailability has been increased by 70.18%. Bio-electrokinetic remediation is the recommended method for polluted clay soils with low bioavailability.

A Near-Real-Time Achromopeptidase-Based Enzyme Assay for Biomonitoring of Zinc Pollution in Kuah's Jetty in Langkawi

Enzyme-based assay in near-real-time biomonitoring provides high sensitivity to bioavailable contaminants, leading to quick results that support prompt action. It is essential to use this method to reduce pollution in drinking, agriculture and marine waters and protect the health of both humans and animals. This work applies a previously discovered enzyme test in biomonitoring to identify contaminants, particularly zinc, in marine water samples from the Langkawi Island, an island that harbors the UNESCO's Geoforest Park status. We used the achromopeptidase dye binding assay, specifically designed for detecting mercury zinc at levels below one part per million, to identify trace amounts of these metal successfully. The test demonstrated a sensitive, quick, and cost-efficient monitoring method with little inhibition (&lt;10%) during a 6-hour field trial for three consecutive days, suggesting low pollution levels and confirmed by instrumental analysis. This method allows for the prompt identification of environmental pollutants, which helps take appropriate actions and safeguard ecotourism locations by offering data-driven information for policy development. Enzyme tests are simple and visually appealing, making them effective instructional tools that help raise environmental awareness and support conservation initiatives. Our research highlights the need to use enzyme tests for broad environmental evaluation, harmonizing local monitoring methods with global standards, and promoting international cooperation in environmental conservation. This work enhances our comprehension of ecological well-being in marine and brackish waterways and underscores the significance of ongoing monitoring to protect natural environments.

Anaerobic reduction of graphene oxide induces the release of sorbed organic contaminants and enhances environmental risk

Graphene oxide (GO) is an oxidized form of graphene-based materials with abundant hydrophilic oxygen-containing functional groups, forming well-dispersed suspensions and serving as pollution carriers. The natural anaerobic environment might alter the sorption behavior of GO, which in turn affects the fate and bioavailability of GO-sorbed organic contaminants. In this study, GO can be reduced by diverse environmental reductants, including sodium sulfide, DL-1,4-dithiothretiol, and L-cysteine, forming aggregates. Meanwhile, the GO-sorbed organic contaminants were released during the reduction process owing to the decreasing oxygen content and sorption sites. The effect of solution chemistry conditions (dissolved humic acid/HA and ionic strength) on the reduction release process was also investigated. HA reduced the release rate of organic contaminants due to its stabilization effect. Adding NaCl did not alter the release rate, while CaCl2 markedly enhanced the release rate. Toxicity tests with Bacillus subtilis indicated that releasing the pre-sorbed organic compound on GO led to a lower survival ratio and enhanced the superoxide dismutase activity. The findings of this study imply that the anaerobic environment could alter the dispersion/aggregation status of GO, affecting the sorption interaction between GO and the organic compounds and consequently influencing the toxicity and risk of pollution in the environment.

In the presence of the other: How glyphosate and peptide molecules alter the dynamics of sorption on goethite

The interactions with soil mineral surfaces are among the factors that determine the mobility and bioavailability of organic contaminants and of nutrients present in dissolved organic matter (DOM) in soil and aquatic environments. While most studies focus on high molar mass organic matter fractions (e.g., humic and fulvic acids), very few studies investigate the impact of DOM constituents in competitive sorption. Here we assess the sorption behavior of a heavily used herbicide (i.e., glyphosate) and a component of DOM (i.e., a peptide) at the water/goethite interface, inclusive of potential glyphosate-peptide interactions. We used in-situ ATR-FTIR (attenuated total reflectance Fourier-transform infrared) spectroscopy to study sorption kinetics and mechanisms of interaction as well as conformational changes to the secondary structure of the peptide. NMR (nuclear magnetic resonance) spectroscopy was used to assess the level of interaction between glyphosate and the peptide and changes to the peptide' secondary structure in solution. For the first time, we illustrate competition for sorption sites results in co-sorption of glyphosate and peptide molecules that affects the extent, kinetics, and mechanism of interaction of each with the surface. In the presence of the peptide, the formation of outer-sphere glyphosate-goethite complexes is favored albeit inner-sphere glyphosate-goethite bonds (i.e., POFe) are still formed. The presence of glyphosate induces secondary structural shifts of the sorbed peptide that maximizes the formation of H-bonds with the goethite surface. However, glyphosate and the peptide do not seem to interact with one another in solution nor at the goethite surface upon sorption. The results of this work highlight potential consequences of competition for sorption sites, for example the transport of organic contaminants and nutrient-rich (i.e., nitrogen) DOM components in relevant environmental systems. Predicting the rate and extent with which organic pollutants are removed from solution by a given solid is also one of the most critical factors for the design of effective sorption systems in engineering applications.

Phytoextraction and Stabilization of Lead in Contaminated Soils using Plants

Lead is a toxic heavy metal contaminant that poses a serious threat to human health. It is present everywhere in the environment including agricultural, industrial and residential areas. To remediate lead from the contaminated soil, phytoremediation approaches are used. Phytoextraction and Phytostabilization are methods of phytoremediation which has been successfully used to remediate lead contaminant from the soil. Phytoextraction involves the use of hyperaccumulators; to accumulate lead contaminant within the shoots by using the uptake mechanism. Whereas, Phytostabilization involves the stabilization or maintenance of lead in the rhizosphere of the soil to reduce its harmful impact on the environment. Lead phytoextraction could be enhanced by adding chelating agents, such as EDTA, to increase the bioavailability of lead contaminant in the plants. Lead phytostabilization is an effective method to remediate lead contaminant. This method tolerates lead exposure and prevents it in or around the root zone which can restrict the movement of lead into other plants, avoiding resuspended dust and mitigating lead exposure. These approaches are cost effective, simple; ecofriendly and do not require a huge amount of labour.

Improving our Understanding of Environmental Stress Impacts and Responses of the Microbiome

Over the course of this century, it will be important to identify cost effective/low maintenance solutions for treating contaminants in receiving watersheds. Adopting these strategies will involve a better understanding of what defines a “natural” environment compared to these contaminated sites. Traditional geochemical testing and standard microbial community analyses (e.g., DNA profiling) or using isolates can be limited with respect to their ability to infer real-time, active processes of bacterial communities. In recent years the application of genomics to identify the microbial microbiome in anthropogenic stressed conditions has advanced considerably. In many cases, the activity of microorganisms will directly impact the chemical conditions in both surface and subsurface water column and contaminated sediment environments controlling the fate of nutrients and contaminants alike. Questions arise such as: What are the baselines or reference systems that can be used? What indices can be used to study the long-term and short-term controls on the mobility, cycling, and bioavailability of toxic metals and organic contaminants? What are the baselines or reference systems that can be used? What indices can be used to study the long-term and short-term controls on the mobility, cycling, and bioavailability of toxic metals and organic contaminants? In many cases the balance of chemical oxidizing and reducing components in water will control the development of chemical and nutrient gradients observed in either natural and/or applied systems (e.g., constructed wetlands or bioreactors). In these cases, biogeochemical systems will determine the direction and onset of specific metabolic pathways as defined by their favorable thermodynamic outcome, an issue for most bioremediators (i.e., microorganisms). Also, the degree of chemical alteration (toxicity or degradation products) can be directly linked to the proportion of their biological activity. In this presentation, contrasting case studies highlighting natural (baseline) and anthropogenically impacted landscapes will be discussed. The focus will be on identifying and linking physicochemical processes to microbial community function using emerging omics for geochemical applications and ascertaining novel contaminant bioindicators.

Improving toxicity prediction of metal-contaminated sediments by incorporating sediment properties

For the purpose of sediment quality assessment, the prediction of toxicity risk-levels for aquatic organisms based on simple environmental measurements is desirable. One commonly used approach is the comparison of total contaminant concentrations with corresponding water and sediment quality guideline values, serving as a Line of Evidence (LoE) based on chemistry-toxicity effects relationships. However, the accuracy of toxicity predictions can be improved by considering the factors that modify contaminant bioavailability. In this study we used paired chemistry-ecotoxicity data sets for sediments to evaluate the improvement in toxicity risk predictions using bioavailability-modified guidelines. The sediments were predominantly contaminated with metals, and measurements of sediment particle size, total organic carbon (TOC) and acid volatile sulfide (AVS) were used to modify hazard quotients (HQ). To further assess the predictive efficacy of the bioavailability-modified guideline models, sediments with differing contamination levels were tested for toxicity to a benthic amphipod's reproduction. To account for differences between laboratory exposure and field exposure scenarios, where the latter creates greater dilution, both static-renewal and flow-through test procedures were employed, and flow-through resulted in lower dissolved metal concentrations in the overlying waters. We also investigated how lower AVS concentration by oxidation modified the toxicity. This study reaffirmed that consideration of factors that influence contaminant bioavailability improves toxicity risk predictions, however the improvements may be modest. The sediment particle size data had the greatest influence on the modified HQ, indicating that higher percentage of fine particle size (<63 μm) contributed most to a lower predicted toxicity. The comparison of the static-renewal and flow-through test results continue to raise important questions about the relevance of static or static-renewal toxicity test results for risk assessment decisions, as both these test designs may cause unrealistically high contributions of dissolved metals in overlying waters to toxicity. Overall, this study underscores the value of incorporating outcomes from simple and routine sediment analysis (e.g., particle size, TOC, and consideration of AVS) to enhance the predictive efficacy of toxicity risk assessments in the context of sediment quality risk assessment.

Arsenic toxicity to earthworms in soils of historical As mining sites: an assessment based on various endpoints and chemical extractions

Eisenia fetida is an earthworm species often used to assess the toxicity of contaminants in soils. Several studies indicated that its response can be unpredictable because it depends both on total concentrations of contaminants and also on their forms that differ in susceptibility to be released from soil solid phase. The issue is complex because two various uptake routes are concurrently involved, dermal and ingestion in guts, where the bioavailability of contaminants can considerably change. The aim of this study was to analyze the toxicity of arsenic (As) in various strongly contaminated meadow and forest soils, representative for former As mining and processing area, to earthworms E. fetida and its accumulation in their bodies. An attempt was made to find relationships between the response of earthworms and chemical extractability of As. In the bioassay, carried out according to the standard ISO protocol, different endpoints were applied: earthworm survival, fecundity measured by the numbers of juveniles and cocoons, earthworm weight and As accumulation in the bodies. The results proved that E. fetida can tolerate extremely high total As concentrations in soils, such as 8000 mg/kg, however, the individual endpoints were not correlated and showed different patterns. The most sensitive one was the number of juveniles. No particular soil factor was identified that would indicate an exceptionally high As susceptibility to the release from one of soils, however, we have demonstrated that the sum of non-specifically and specifically bound As (i.e. fractions F1 + F2 in sequential extraction according to Wenzel) could be a good chemical indicator of arsenic toxicity to soil invertebrates.

Risk Assessment of a Coastal Ecosystem from SW Spain Exposed to CO2 Enrichment Conditions

The Weight-of-Evidence (WOE) approach uses multiple lines of evidence to analyze the adverse effects associated with CO2 enrichment in two stations from the Gulf of Cádiz (Spain) with different contamination degrees. Sediment contamination and metal (loid) mobility, toxicity, ecological integrity, and bioaccumulation from the samples exposed to different acidification scenarios (pH gradient from 8.0 to 6.0) were used in the WOE. The experiments were conducted under laboratory conditions using a CO2-bubbling system. Different integration approaches such as multivariate analyses were used to evaluate the results. The results indicated that the adverse biological effects under pH 6.5 were related to the mobility of dissolved elements (As, Fe, Cu, Ni, and Zn). Furthermore, the pH reduction was correlated to the increase of bioaccumulation of As, Cr, Cu, Fe, and Ni in the tissues of mussels at pH 7.0. The noncontaminated sediment showed environmental degradation related to the acidification at pH values of 7.0; whereas the sediment moderately contaminated showed both environmental risks, caused by acidification and the presence and the increase of the bioavailability of contaminants. The WOE approach supposes an effective tool to identify and distinguish the causes of adverse effects related to the enrichment of CO2 in marine environments.

Does Activated Carbon Used for Soil Remediation Impact Eisenia fetida?

Because granular activated carbon can sequester organic pollutants, a potential strategy for reducing the bioavailability of organic contaminants in soil is through its application to the soil's surface. It is well understood that activated carbon is effective in the remediation of air, water, sediment, and soil, but less information is available on the potential toxicity of activated carbon to native wildlife following in situ remedial applications. Several studies have evaluated the effects of activated carbon on aquatic species; however, less is known about its toxicity to terrestrial species. The present study aimed to evaluate the potential lethal and sublethal effects of activated carbon on adult and juvenile Eisenia fetida, which are earthworms in the family Lumbricidae. The percentage of mortality, initial weight, and pre- and postdepuration weights of the worms were observed following exposure to a range of activated carbon concentrations, from 0.5% to 10% based on the soil's wet weight. These concentrations exceeded the 2%-4% activated carbon typically applied in the field. Activated carbon had no statistically significant effects on E. fetida survival; however, significant although inconsistent effects were observed on earthworm biomass. Although some statistical significance in biomass was observed, the biological significance of these effects is unclear. Overall, the concentrations of activated carbon applied in the field for soil remediation are unlikely to impact earthworm survival, although further testing, specifically on potential sublethal toxic effects, is required. Environ Toxicol Chem 2023;42:1420-1430. © 2023 SETAC.