Dearomatization drives complexity generation in freshwater organic matter.

Dissolved organic matter (DOM) is one of the most complex, dynamic and abundant sources of organic carbon, but its chemical reactivity remains uncertain1-3. Greater insights into DOM structural features could facilitate understanding its synthesis, turnover and processing in the global carbon cycle4,5. Here we use complementary multiplicity-edited 13C nuclear magnetic resonance (NMR) spectra to quantify key substructures assembling the carbon skeletons of DOM from four main Amazon rivers and two mid-size Swedish boreal lakes. We find that one type of reaction mechanism, oxidative dearomatization (ODA), widely used in organic synthetic chemistry to create natural product scaffolds6-10, is probably a key driver for generating structural diversity during processing of DOM that are rich in suitable polyphenolic precursor molecules. Our data suggest a high abundance of tetrahedral quaternary carbons bound to one oxygen and three carbon atoms (OCqC3 units). These units are rare in common biomolecules but could be readily produced by ODA of lignin-derived and tannin-derived polyphenols. Tautomerization of (poly)phenols by ODA creates non-planar cyclohexadienones, which are subject to immediate and parallel cycloadditions. This combination leads to a proliferation of structural diversity of DOM compounds from early stages of DOM processing, with an increase in oxygenated aliphatic structures. Overall, we propose that ODA is a key reaction mechanism for complexity acceleration in the processing of DOM molecules, creation of new oxygenated aliphatic molecules and that it could be prevalent in nature.

The cerium oxide nanoparticles toxicity induced physiological, histological and biochemical alterations in freshwater mussels, Unio crassus.

INTRODUCTION: Releasing of cerium oxide nanoparticles (nano-CeO2) to the nature has increased due to the widespread use in many fields ranging from cosmetics to the food industry. Therefore, nano-CeO2 has been included in the Organization for Economic Co-operation and Development's (OECD) priority list for engineering nanomaterials. In this study, the effects of nano-CeO2 on the freshwater mussels were investigated to reveal the impact on the freshwater systems on model organism. METHODS: First, the chemical and structural properties of nano-CeO2 were characterized in details. Second, the freshwater mussels were exposed to environmentally relevant concentrations of nano-CeO2 as 10 mg, 25 mg and 50 mg/L during 48-h and 7-d. Third, after the exposure periods, hemolymph and tissue samples were taken to analyse the Total Hemocyte Counts (THCs) histology and oxidative stress parameters (total antioxidant status, glutathione, glutathione-S-transferase, and advanced oxidative protein products). RESULTS: Significant decrease of the THCs was observed in the nano-CeO2 exposed mussels compared to the control group (P < 0.05). The histological results showed a positive association between nano-CeO2 exposure concentration in the water and level of tissue damage and histopathological alterations were detected in the gill and the digestive gland tissues. Oxidative stress parameters were slightly affected after exposure to nano-CeO2 (P > 0.05). In conclusion, this study showed that acute exposure of freshwater mussels to nano-CeO2 did not pose significant biological risk. However, it has been proven that mussels are able to accumulate nano-CeO2 significantly in their bodies. CONCLUSION: This suggests that nano-CeO2 may be a potential risk to other organisms in the ecosystem through trophic transfer in the food-web based on their habitat and niche in the ecosystem.

Assessing diatom distribution in Cambay Basin, Western Arabian Sea: impacts of oil spillage and chemical variables.

Freshwater and marine diatoms produce the majority of the oxygen in aquatic systems. Estimates range from 12,000 to 30,000 species, and spatial distribution varies globally. There is significant variation in diatom diversity based on geographical and environmental conditions as well as the physicochemical characteristics of the habitat. Therefore, understanding the underlying factors that contribute to changes in diatom community structures requires a comprehensive understanding of taxons. A study of diatom assemblages from the Cambay Basin, Western Arabian Sea, was conducted, particularly on oil fields. A total of 37 samples were collected; nine were from oil fields. We evaluated micro-oil spills using Fourier transform infrared (FTIR) analysis and microscopic techniques. Correlations were established through the ordination analysis of pernicious physical and chemical water variables (BOD, COD, TDS, pH, temperature, and DO), including principal component analysis (PCA). The oil field sites showed more total dissolved solids (TDS) and chemical oxygen demand (COD) than the respective marine control sites. The study does not display a cause-and-effect relationship, but we observed a positive correlation between increasing silica concentrations and diatom growth in oil fields. In contrast, high aluminium concentrations in oil fields negatively impacted the growth of diatom assemblage and abundance. When surveyed in nine oil fields, we found that Gomphonella pseudosphaerophorum and Nitzschia palea are well adapted to oil concentrations up to 40 ppm.

Biomineralization biomarkers to assess microplastics toxic effects in the freshwater snail Pomacea canaliculata.

Microplastics (MPs) pollution has increased the number of reports on the toxic effects on biota, especially aquatic organisms. Recently, studies highlighted changes in ion transport and concentration, especially Ca2+, in organisms exposed to MPs. For calcifying organisms, such as mollusks, Ca2+ homeostasis is critical for their shells construction. We investigated the effects of polyethylene (PE) MPs at 20 µg/L on biomineralization biomarkers (Ca2+ATPase, carbonic anhydrase, hemolymph [Ca2+], and shell regeneration) of the freshwater gastropod Pomacea canaliculata. Two experimental sets were performed: (1) animals in physiological condition and (2) animals with their shells excised. The results of the first set showed that within 24 h, the hemolymph [Ca2+] decreased, and the Ca2+ATPase activity increased in the mantle edge. For carbonic anhydrase (CA), the activity decreased in the gland and increased in the mantle. By 72 h, the hemolymph [Ca2+] had not changed, whereas both enzymes had increased in both tissues. In the second set, the hemolymph [Ca2+] increased after 72 h, whereas Ca2+ATPase activity decreased in both tissues. For AC, the opposite results were observed. At 120 h, calcium pumping was still reduced and CA values increased in the digestive gland. Additionally, MPs exposure increased the capacity of the gastropods to recover their shells. Based on this, our work provides novel data associating PE microplastic exposures (at 20 µg/L) and their potential to stimulate biomineralization enzymes of P. canaliculata, as well as increase shell regeneration in excised animal; a good prerogative for further investigations on both subjects that still lacks of more robust evidence.

Development of Multiple Linear Regression Models for Predicting Chronic Iron Toxicity to Aquatic Organisms.

We developed multiple linear regression (MLR) models for predicting iron (Fe) toxicity to aquatic organisms for use in deriving site-specific water quality guidelines (WQGs). The effects of dissolved organic carbon (DOC), hardness, and pH on Fe toxicity to three representative taxa (Ceriodaphnia dubia, Pimephales promelas, and Raphidocelis subcapitata) were evaluated. Both DOC and pH were identified as toxicity-modifying factors (TMFs) for P. promelas and R. subcapitata, whereas only DOC was a TMF for C. dubia. The MLR models based on effective concentration 10% and 20% values were developed and performed reasonably well, with adjusted R2 of 0.68-0.89 across all species and statistical endpoints. Differences among species in the MLR models precluded development of a pooled model. Instead, the species-specific models were assumed to be representative of invertebrates, fish, and algae and were applied accordingly to normalize toxicity data. The species sensitivity distribution (SSD) included standard laboratory toxicity data and effects data from mesocosm experiments on aquatic insects, with aquatic insects being the predominant taxa in the lowest quartile of the SSD. Using the European Union approach for deriving WQGs, application of MLR models to this SSD resulted in WQGs ranging from 114 to 765 µg l-1 Fe across the TMF conditions evaluated (DOC: 0.5-10 mg l-1 ; pH: 6.0-8.4), with slightly higher WQGs (199-910 µg l-1 ) derived using the US Environmental Protection Agency (USEPA) methodology. An important uncertainty in these derivations is the applicability of the C. dubia MLR model (no pH parameter) to aquatic insects, and understanding the pH sensitivity of aquatic insects to Fe toxicity is a research priority. An Excel-based tool for calculating Fe WQGs using both European Union and USEPA approaches across a range of TMF conditions is provided. Environ Toxicol Chem 2023;42:1386-1400. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Validation of Nickel Bioavailability Models for Algae, Invertebrates, and Fish in Chinese Surface Waters.

Nickel (Ni) is used primarily in the production of alloys like stainless steel and is increasingly being used in the production of batteries for the electric vehicle market. Exposure of Ni to ecosystems is of concern because Ni can be toxic to aquatic organisms. The influence of water chemistry constituents (e.g., hardness, pH, dissolved organic carbon) on the toxicity of Ni has prompted the development and use of bioavailability models, such as biotic ligand models (BLMs), which have been demonstrated to accurately predict Ni toxicity in broadly different ecosystems, including Europe, North America, and Australia. China, a leading producer of Ni, is considering bioavailability-based approaches for regulating Ni emissions. Adoption of bioavailability-based approaches in China requires information to demonstrate the validity of bioavailability models for the local water chemistry conditions. The present study investigates the toxicity of Ni to three standard test species (Daphnia magna, Pseudokirchneriella subcapitata, and Danio rerio) in field-collected natural waters that are broadly representative of the range of water chemistries and bioavailabilities encountered in Chinese lakes and rivers. All experimental data are within a factor of 3 of the BLM predicted values for all tests with all species. For D. magna, six of seven waters were predicted within a factor of 2 of the experimental result. Comparison of experimental data against BLM predictions shows that the existing Ni bioavailability models are able to explain the differences in toxicity that result from water chemistry conditions in China. Validation of bioavailability models to water chemistries and bioavailability ranges within China provides technical support for the derivation of site-specific Ni water quality criteria in China. Environ Toxicol Chem 2023;42:1257-1265. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Updating the Chronic Freshwater Ecotoxicity Database and Biotic Ligand Model for Nickel for Regulatory Applications in Europe.

Bioavailability has been taken into account in the regulation of nickel in freshwater ecosystems in Europe for over a decade; during that time a significant amount of new information has become available covering both the sensitivity of aquatic organisms to nickel toxicity and bioavailability normalization. The ecotoxicity database for chronic nickel toxicity to freshwater organisms has been updated and now includes 358 individual data points covering a total of 53 different species, all of which are suitable for bioavailability normalization to different water chemistry conditions. The bioavailability normalization procedure has also been updated to include updates to the bioavailability models that enable more sensitive water chemistry conditions to be covered by the model predictions. The updated database and bioavailability normalization procedure are applicable to more than 95% of regulated European surface water conditions and have been used to calculate site-specific criteria for a variety of different water chemistry scenarios, to provide an indication of how the sensitivity to nickel varies between different water types. The hazardous concentration for 5% of a species (HC5) values for this diverse selection of water types range from 1.6 to 36 µg L-1 , clearly demonstrating the importance of accounting for nickel bioavailability in freshwaters. This updated database and bioavailability normalization procedure provide a robust basis for the derivation of regulatory thresholds for chronic nickel toxicity in freshwaters such as predicted no-effect concentrations and Environmental Quality Standards and are protective of the results of several mesocosm studies. Environ Toxicol Chem 2023;42:566-580. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sublethal cadmium exposure in the freshwater snail Lymnaea stagnalis meets a deficient, poorly responsive metallothionein system while evoking oxidative and cellular stress.

The Great Pond snail Lymnaea stagnalis (Gastropoda, Hygrophila) is a wide-spread freshwater gastropod, being considered as a model organism for research in many fields of biology, including ecotoxicology. The aim of the present study was to explore the Cd sensitivity of L. stagnalis through the measurement of a biomarker battery for oxidative, toxic and cellular stress. The interpretation of biomarker parameters occurred against the background of a truncated metallothionein protein with a limited Cd-binding capacity. Individuals of L. stagnalis were exposed through 14 days to uncontaminated water (controls) or to low (30 µg · L-1) or high (50 µg · L-1) Cd concentrations. The digestive gland of control and low-Cd exposed snails was processed for transcriptional analysis of the Metallothionein (MT) gene expression, and for determination of biomarkers for oxidative stress, toxicity and cellular stress. Digestive gland supernatants of high-Cd exposed snails were subjected to chromatography and subsequent analysis by spectrophotometry. It was shown that the MT system of L. stagnalis is functionally deficient, with a poor Cd responsiveness at both, the transcriptional and the protein expression levels. Instead, L. stagnalis appears to rely on alternative detoxification mechanisms such as Cd binding by phytochelatins and metal inactivation by compartmentalization within the lysosomal system. In spite of this, however, traces of Cd apparently leak out of the pre-determined detoxification pathways, leading to adverse effects, which is clearly indicated by biomarkers of oxidative and cellular stress.

Chemodynamic features of nickel(II) and its complexes: Implications for bioavailability in freshwaters.

A robust description of the bioavailability of Ni(II) in freshwaters is fundamental for the setting of environmental quality standards. Current approaches assume that bioavailability is governed by the equilibrium concentration of the free metal ion in the bulk aqueous medium. Such strategies generally have limited predictive value: a suite of empirical fitting parameters is required to deal with variations in water chemistry. Herein we compile data on Ni(II) speciation under typical freshwater conditions and compute the lability of Ni(II) complexes with typical molecular and nanoparticulate components of dissolved organic carbon. In combination with an analysis of the kinetic setting of Ni(II) biouptake by freshwater organisms, we assess the potential contribution from dissociation of Ni(II) complexes to the diffusive supply flux of free Ni2+. The strategy takes into account the absolute and relative magnitudes of the Michaelis-Menten bioaffinity and bioconversion parameters for a range of freshwater organisms, together with dynamic chemical speciation descriptors under environmentally relevant conditions. The results show that the dissociation kinetics of Ni(II) complexes play a crucial role in buffering the free metal ion concentration at the biointerface. Our results highlight the need to couple the timescales of chemical reactivity with those of biouptake to properly identify the bioavailable fraction of Ni(II) in freshwaters.

Assessing the Extent of Environmental Risks From Nickel in European Freshwaters: A Critical Reflection of the European Commission's Current Approach.

Nickel (Ni) has a been a Priority Substance under the European Water Framework Directive since 2008. As such it is deemed to present an European Union-wide risk to surface waters. Since 2013, the Ni Environmental Quality Standard (EQS) has been bioavailability-based, and new European Guidance supports accounting for bioavailability in assessing Ni compliance with the EQS. The European Commission has developed an approach to determine whether Priority Substances present a sufficient European Union-wide risk to justify an ongoing statutory monitoring programme, effectively to deselect a substance. This is a key step to ensure that finite monitoring resources are targeted at delivering environmental benefit, when there is an ever-growing burden of determinands to measure for all regulators. When the European Commission performed this exercise for Ni without accounting for bioavailability, they concluded that Ni should not be deselected, and Ni is an European Union-wide risk. Performing this same exercise with the same methodology, using regulatory monitoring data for over 300 000 samples, from more than 19 000 sites across Europe, and accounting for bioavailability, as detailed in the Directive, >99% of sites comply with the Ni EQS. Nickel shows very low risks for all of the criteria identified by the European Commission that need to be met for deselection. Accounting for bioavailability is key in the assessment of Ni risks in surface waters to deliver ecologically relevant outcomes. Environ Toxicol Chem 2022;41:1604-1612. © 2022 NiPERA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Impact of a large dam on reproduction of a non-migratory teleost species, Acestrorhynchus lacustris (Characiformes: Acestrorhynchidae) / Impacto de uma grande barragem na reprodução de uma espécie de teleósteo não migradora, Acestrorhynchus lacustris (Characiformes: Acestrorhynchidae)

The release of water from the reservoir hypolimnion, lower concentration of oxygen and the anthropogenic regulation of the river flow, could affect the reproduction of fish, especially migratory species. However, little is known about the effects of these changes in water on non-migratory species. In this sense, the reproduction of Acestrohynchus lacustris was evaluated in two sections of São Francisco River, Minas Gerais, Brazil. Section 1, located immediately downstream from Três Marias Dam (18°09'31.65"S and 45°13'36.00"W) and section 2, located at the confluence of the São Francisco and the Abaeté Rivers (18°02'47.78"S and 45°1057.95"W). For this, we obtained the physico-chemical parameters of water of each study section. Additionally, biometric data and biological indices ofall specimens were measured. Fecundity and follicles diameters were measured in females. Temperature, dissolvedoxygen and flow showed lower values in section 1. Fish captured in this section, had lower values of GSI in bothsexes, and females presented decreased values of fecundity and follicles diameter. This species showed reproductiveactivity in the two sections analyzed, however, in section 1 where the temperature and dissolved oxygen presentedsignificant lower values, the reproductive capacity of A. lacustris, was negatively affected.

A liberação de água do hipolímnio do reservatório, baixa concentração de oxigênio e a regulação antropogênica do fluxo do rio podem afetar a reprodução de peixes, principalmente espécies migradoras. No entanto, pouco se sabe sobre os efeitos dessas mudanças nas condições da água em espécies não migradoras. A reprodução de Acestrohynchus lacustris foi avaliada em duas seções do rio São Francisco. Seção 1, localizada imediatamente a jusante da barragem de Três Marias e seção 2, localizada na confluência dos rios São Francisco e Abaeté. Para isso, foram obtidos os parâmetros físico-químicos da água de cada seção do estudo. Além disso, dados biométricos e índices biológicos de todos os peixes capturados foram obtidos. Adicionalmente, nas fêmeas foram medidos os diâmetros dos folículos vitelogênicos e a fecundidade. Temperatura, oxigênio dissolvido e fluxo apresentaram valores mais baixos na seção 1. Os peixes capturados nesta seção apresentaram menores valores de IGS em ambos os sexos, e as fêmeas apresentaram menores valores de fecundidade e diâmetro dos folículos. Essa espécie apresentou atividade reprodutiva nas duas seções analisadas, porém, na seção 1, onde os parâmetros da água apresentam piores condições para o processo reprodutivo de peixes, a capacidade reprodutiva de A. lacustris foi afetada negativamente.

Cationic Photothermal Hydrogels with Bacteria-Inhibiting Capability for Freshwater Production via Solar-Driven Steam Generation.

Solar-driven steam generation has been recognized as a sustainable and low-cost solution to freshwater scarcity using abundant solar energy. To harvest freshwater, various interfacial evaporators with rational designs of photothermal materials and structures have been developed concentrating on increasing the evaporation rate in the past few years. However, pathogenic microorganism accumulation on the evaporators by long-duration contact with natural water resources may lead to the deterioration of water transportation and the reduction of the evaporation rate. Here, we develop cationic photothermal hydrogels (CPHs) based on [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) and photothermal polypyrrole (PPy) with bacteria-inhibiting capability for freshwater production via solar-driven steam generation. A rapid water evaporation rate of 1.592 kg m-2 h-1 under simulated solar irradiation is achieved with CPHs floating on the water surface. Furthermore, we find that CPHs possess nearly 100% antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The significant bacteria-inhibiting capability is mainly attributed to the large number of ammonium groups on the CPH network. Moreover, we show that CPHs exhibit good applicability with stable evaporation in natural lake water over 2 weeks, and the number of bacteria in purified lake water is significantly reduced. The device based on CPHs can achieve ∼0.49 kg m-2 h-1 freshwater production from lake water under natural sunlight. This study provides an attractive strategy for the evaporator to inhibit biological contamination and a potential way for long-term stable freshwater production from natural water resources in practical application.

Using Design of Experiments to Optimize a Screening Analytical Methodology Based on Solid-Phase Microextraction/Gas Chromatography for the Determination of Volatile Methylsiloxanes in Water.

Volatile methylsiloxanes (VMSs) constitute a group of compounds used in a great variety of products, particularly personal care products. Due to their massive use, they are continually discharged into wastewater treatment plants and are increasingly being detected in wastewater and in the environment at low concentrations. The aim of this work was to develop and validate a fast and reliable methodology to screen seven VMSs in water samples, by headspace solid-phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The influence of several factors affecting the extraction efficiency was investigated using a design of experiments approach. The main factors were selected (fiber type, sample volume, ionic strength, extraction and desorption time, extraction and desorption temperature) and optimized, employing a central composite design. The optimal conditions were: 65 µm PDMS/Divinylbenzene fiber, 10 mL sample, 19.5% NaCl, 39 min extraction time, 10 min desorption time, and 33 °C and 240 °C as extraction and desorption temperature, respectively. The methodology was successfully validated, showing low detection limits (up to 24 ng/L), good precision (relative standard deviations below 15%), and accuracy ranging from 62% to 104% in wastewater, tap, and river water samples.

Coping strategies in response to different levels of elevated water hardness in channel catfish (Ictalurus punctatus): Insight into ion-regulatory and histopathological modulations.

Water hardness above the optimal level can incite toxic effects in fish, which are often species specific. Hence, we aimed at obtaining insights on the potential effects of elevated water hardness as well as coping strategies in channel catfish (Ictalurus punctatus). First, a toxicity assay was performed where the 96 h-LC50 was calculated as 4939 mg/L CaCO3. Thereafter, to gain knowledge on the underlying adaptive strategies to high water hardness, fish were exposed to seven hardness levels (150, 600, 1000, 1500, 2000, 3000 and 4000 mg/L CaCO3 at pH 8.15) for 15 days. Results showed that branchial activities of Ca2+-ATPase and Na+/K+-ATPase, which facilitate Ca2+ uptake, reduced starting respectively from 1000 mg/L and 1500 mg/L CaCO3. Nevertheless, Ca2+ burden in plasma and tissue (gills, liver and intestine) remained elevated. Hardness exposure also disturbed cations (Na+, K+, Mg2+) and minerals (iron and phosphorus) homeostasis in a tissue-specific and dose-dependent manner. Both hemoglobin content and hematocrit dropped significantly at 3000-4000 mg/L CaCO3, with a parallel decline in iron content in plasma and gills. Muscle water content rose dramatically at 4000 mg/L CaCO3, indicating an osmo-regulation disruption. Higher hardness of 3000-4000 mg/L CaCO3 also incited a series of histopathological modifications in gills, liver and intestine; most likely due to excess Ca2+ accumulation. Overall, these data suggest that channel catfish can adapt to a wide range of elevated hardness by modulating Ca2+ regulatory pathways and histomorphological alterations, however, 1500 mg/L CaCO3 and above can impair the performance of this species.

New tyrosinases with putative action against contaminants of emerging concern.

Tyrosinases (EC 1.14.18.1) are type-3 copper metalloenzymes with strong oxidative capacities and low allosteric selectivity to phenolic and non-phenolic aromatic compounds, which have been used as biosensors and biocatalysts to mitigate the impacts of environmental contaminants over aquatic ecosystems. However, the widespread use of these polyphenol oxidases is limited by elevated production costs and restricted knowledge on their spectrum of action. Here, six tyrosinase homologs were identified and characterized from the genomes of four widespread freshwater ciliates using bioinformatics. Next, we performed a virtual screening to calculate binding energies between 3D models of these homologs and ~ 1000 contaminants of emerging concern (CECs), as an indirect approach to identify likely and unlikely targets for tyrosinases. Many fine chemicals, pharmaceuticals, personal care products, illicit drugs, natural toxins, and pesticides exhibited strong binding energies to these new tyrosinases, suggesting the spectrum of targets of these enzymes might be considerably broader than previously thought. Many ciliates, including those carrying tyrosinase genes, are fast-growing unicellular microeukaryotes that can be efficiently cultured, at large scales, under in vitro conditions, suggesting these organisms should be regarded as potential low-cost sources of new environmental biotechnological molecules.

A Review of Water Quality Factors that Affect Nickel Bioavailability to Aquatic Organisms: Refinement of the Biotic Ligand Model for Nickel in Acute and Chronic Exposures.

A review of nickel (Ni) toxicity to aquatic organisms was conducted to determine the primary water quality factors that affect Ni toxicity and to provide information for the development and testing of a biotic ligand model (BLM) for Ni. Acute and chronic data for 66 aquatic species were compiled for the present review. The present review found that dissolved organic carbon (DOC) and hardness act as toxicity-modifying factors (TMFs) because they reduced Ni toxicity to fish and aquatic invertebrates, and these effects were consistent in acute and chronic exposures. The effects of pH on Ni toxicity were inconsistent, and for most organisms there was either no effect of pH or, in some cases, a reduction in toxicity at low pH. There appears to be a unique pH effect on Ceriodaphnia dubia that results in increased toxicity at pHs above 8, but otherwise the effects of TMFs were consistent enough across all organisms and endpoints that a single set of parameters in the Ni BLM worked well with all acute and chronic toxicity data for fish, amphibians, aquatic invertebrates, and aquatic plants and algae. The unique effects of pH on C. dubia may be due to mixture toxicity involving both Ni and bicarbonate. The implications of this mixture effect on BLM modeling and a proposed set of BLM parameters for C. dubia are addressed in the review. Other than this exception, the Ni BLM with a single set of parameters could successfully predict toxicity to all acute and chronic data compiled in the present review. Environ Toxicol Chem 2021;40:2121-2134. © 2021 SETAC.

Comparison of Multiple Linear Regression and Biotic Ligand Models to Predict the Toxicity of Nickel to Aquatic Freshwater Organisms.

Toxicity-modifying factors can be modeled either empirically with linear regression models or mechanistically, such as with the biotic ligand model (BLM). The primary factors affecting the toxicity of nickel to aquatic organisms are hardness, dissolved organic carbon (DOC), and pH. Interactions between these terms were also considered. The present study develops multiple linear regressions (MLRs) with stepwise regression for 5 organisms in acute exposures, 4 organisms in chronic exposures, and pooled models for acute, chronic, and all data and compares the performance of the Pooled All MLR model to the performance of the BLM. Independent validation data were used for evaluating model performance, which for pooled models included data for organisms and endpoints not present in the calibration data set. Hardness and DOC were most often selected as the explanatory variables in the MLR models. An attempt was also made at evaluating the uncertainty of the predictions for each model; predictions that showed the most error tended to show the highest levels of uncertainty as well. The performances of the 2 models were largely equal, with differences becoming more apparent when looking at the performance within subsets of the data. Environ Toxicol Chem 2021;40:2189-2205. © 2021 SETAC.

Comparative Exposure Assessment of Potential Health Risks through the Consumption of Vegetables Irrigated by Freshwater/Wastewater: Gujranwala, Pakistan.

The motive of this study is the rapid increase of industrial and domestic wastewater application for the growth of agricultural crops, which is closely associated with human health. In this study, the accumulation of eight heavy metals (Zn, Cu, Fe, Mn, Pb, Cr, Ni, and Cd) in the edible parts of five different species of common vegetables-cauliflower, bitter gourd, radish, pumpkin, and apple gourd-irrigated by two different water irrigation sources (wastewater/freshwater) grown in Pakistan's industrial and agricultural city Gujranwala and human health risks associated with the consumption of vegetables were evaluated. The mean concentration of each metal (Zn, Cu, Fe, Mn, Pb, Cr, Ni, and Cd) in five selected freshwater irrigated vegetables was observed as 48.91, 38.47, 133, 87.5, 4.62, 0.92, 1.46, and 0.36 mg/kg, respectively, while the mean concentration of each corresponding metal in wastewater irrigated vegetables was found to be 59.2, 49.5, 188, 90.9, 6.08, 2.66, 3.98, and 1.76 mg/kg, respectively. The estimated daily intake of metals (EDI), target health quotient (THQ), hazard index (HI), and target cancer risk (TCR) were computed to assess the impact of a raised level of metals in vegetables on human health. The grand THQ (G-THQ) values of individual freshwater irrigated vegetables were lower than the G-THQ values of individual wastewater irrigated vegetables and the G-THQ values of Cu, Cr, Pb, and Cd were found to be greater than the safety limit in wastewater irrigated vegetables. The HI values were found to be 7.94 and 4.01 for the vegetables irrigated with wastewater and freshwater, respectively. The TCR data reveal adverse carcinogenic risks induced by Ni, Cr, and Cd through the consumption of wastewater irrigated vegetables and Ni and Cd from the consumption of freshwater fed vegetables. The principal component analysis (PCA) to predict the sources of metals and Monte Carlo simulation were conducted to reduce the uncertainty in the data. The results indicate that higher significant health risks (carcinogenic and non-carcinogenic) would be posed to the adult population through the consumption of wastewater irrigated vegetables comparatively.

Occurrence of Heavy Metals in Groundwater Along the Lithological Interface of K/T Boundary, Peninsular India: A Special Focus on Source, Geochemical Mobility and Health Risk.

Evaluation of the hydrogeochemical processes governing the heavy metal distribution and the associated health risk is important in managing and protecting the health of freshwater resources. This study mainly focused on the health impacts due to the heavy metals pollution in a known Cretaceous-Tertiary (K/T) contact region (Tiruchinopoly, Tamilnadu) of peninsular India, using various pollution indices, statistical, and geochemical analyses. A total of 63 samples were collected from the hard rock aquifers and sedimentary formations during southwest monsoon and analysed for heavy metals, such as Li, Be, Al, Rb, Sr, Cs, Ba, pb, Mn, Fe, Cr, Zn, Ga, Cu, As, Ni, and Co. Ba was the dominant element that ranged from 441 to 42,638 µg/l in hard rock aquifers, whereas Zn was the major element in sedimentary formations, with concentrations that ranged from 44 to 118,281 µg/l. The concentrations of Fe, Ni, Cr, Al, Cr, and Ni fell above the permissible limit in both of the formations. However, the calculated heavy metal evaluation index (HEI), heavy metal pollution index (HPI), and the degree of contamination (Cd) parameters were higher in the sedimentary formation along the contact zone of the K/T boundary. Excessive health risks from consumption of contaminated groundwater were mostly confined to populations in the northern and southwestern regions of the study area. Carcinogenic risk assessment suggests that there are elevated risks of cancer due to prolonged consumption of untreated groundwater. Ba, Sr, and Zn were found to be geochemically highly mobile due to the partitioning between the rock matrix and groundwater, aided by the formation of soluble carbonato-complexes. Factor analysis indicates that the metals are mainly derived from the host rocks and anthropogenic inputs are relatively insignificant. Overall, this study indicated that groundwater in K/T contact zones is vulnerable to contamination because of the favorable geochemical factors. Long-term monitoring of such contact zones is required to avert the potential health hazards associated with consumption of the contaminated groundwater.