Acute toxicity of binary-metal mixtures of copper, zinc, and nickel to Pimephales promelas: Evidence of more-than-additive effect

Metals in sediment of the upper Great Lakes: Spatial distribution, temporal trends, anthropogenic enrichment, and risk assessments

Thirteen elements including Al, Ag, As, Co, Cu, Cd, Cr, Fe, Mn, Ni, Se, Zn, and Pb were measured in 107 surface grab sediment samples and 175 segments of eight cores from Lakes Superior, Michigan, and Huron, using inductively coupled plasma mass spectrometry (ICP-MS). Concentrations in Ponar grabs vary considerably among metals and among locations, ranging from the highest median for Fe in Lake Superior (42,000 mg/kg) to the lowest median for Ag in the main Lake Huron (0.05 mg/kg). The inventory at coring sites ranged from 7 × 106 mg/m2 of Fe to 3 mg/m2 of Ag. The background concentrations were estimated from deeper core segments, and enrichment factors (EFs) were calculated with Fe or Al as the reference element. The results show that Al, Fe, Co, Cr, and Mn did not enrich, Ag, Cu, and Ni were present higher than expected from natural sources alone, while Pb, Cd, Se, Zn, and As have been enriched at most sites after European settlement in the region. EFs of most metals are higher for Lake Michigan than the other lakes. However, EF comparison among sampling sites revealed intrinsic problems of this approach for the assessment of human interference. Preliminary risk assessment, conducted by calculating risk quotients, revealed environmental risks of some metals in each lake; however, the results should be interpreted with caution because the approach used is considered to be conservative.

Nonlinear Regression Modelling: A Primer with Applications and Caveats

Use of nonlinear statistical methods and models are ubiquitous in scientific research. However, these methods may not be fully understood, and as demonstrated here, commonly-reported parameter p-values and confidence intervals may be inaccurate. The gentle introduction to nonlinear regression modelling and comprehensive illustrations given here provides applied researchers with the needed overview and tools to appreciate the nuances and breadth of these important methods. Since these methods build upon topics covered in first and second courses in applied statistics and predictive modelling, the target audience includes practitioners and students alike. To guide practitioners, we summarize, illustrate, develop, and extend nonlinear modelling methods, and underscore caveats of Wald statistics using basic illustrations and give key reasons for preferring likelihood methods. Parameter profiling in multiparameter models and exact or near-exact versus approximate likelihood methods are discussed and curvature measures are connected with the failure of the Wald approximations regularly used in statistical software. The discussion in the main paper has been kept at an introductory level and it can be covered on a first reading; additional details given in the Appendices can be worked through upon further study. The associated online Supplementary Information also provides the data and R computer code which can be easily adapted to aid researchers to fit nonlinear models to their data.

Selenium and zinc alleviate hepatotoxicity induced by heavy metal mixture (cadmium, mercury, lead and arsenic) via attenuation of inflammo-oxidant pathways

Heavy metals (HM) are believed to be injurious to humans. Man is exposed to them on daily basis unknowingly, with no acceptable protocol to manage its deleterious effects. These metals occur as mixture of chemicals with varying concentrations in our atmosphere. There are growing calls for the use of essential metals in mitigating the injurious effects induced by heavy metals exposure to man; therefore, the aim of this study was to evaluate the protective effects of essential metals (Zinc and Selenium) in a mixture of heavy metal toxicity. In this study, except for negative controls, all other groups were treated with lead (PbCl2 , 20 mg kg-1 ); cadmium (CdCl2 , 1.61 mg kg-1 ); mercury (HgCl2 , 0.40 mg kg-1 ), and arsenic (NaAsO3, 10 mg kg-1 ) that were formed in distilled water. Pb, Cd, As, and Hg were administered as mixtures to 35, 6 weeks old rats weighing between 80 to 100 g for 60 days. Group I served as normal control without treatment, group II positive control received HM mixture, while groups III to V received HMM with Zn, Se, and Zn + Se respectively. Animal and liver weights, HM accumulation in the liver, food intake (FI), water intake (WI), liver function test, malondialdehyde (MDA), and inflammatory/transcription factor/apoptosis markers were checked. Also, antioxidant enzymes, and histological studies were carried out. Metal mixture accumulated in the liver and caused toxicities which were ameliorated by Zn and Se administration. HM caused significant decrease in FI, WI and distorted the level of liver enzymes, lipid peroxidation, inflammatory markers, antioxidants and architecture of the liver. Co administration with Zn or Se or both reversed the distortions. This study lays credence to the evolving research on the public health implications of low dose metal mixtures and the possible ameliorative properties of Zn and Se.

Assessing the ecological risk and ecotoxicity of the microbially mediated restoration of heavy metal-contaminated river sediment

Anthropogenic activities such as mining, smelting industries, and the application of pesticides in agriculture might result in contamination of multiple heavy metals in the environment. Heavy metal contamination of sediment is a serious environmental problem, and thus the remediation of contaminated sediment is a worldwide challenge. Several strategies have been developed for the remediation of contaminated sediment, however the ecological risk and ecotoxicity of the restored sediment have rarely been evaluated. We assessed whether river sediment highly contaminated with heavy metals could be restored using microbial bioleaching followed by evaluating the residual toxicity and ecological risk of the microbially remediated sediment. Sequential extraction revealed that the bioavailable levels of Cu, Ni, and Zn in the contaminated sediment exceeded sediment quality guideline (SQG) thresholds. It was consequently found that acidophilic sulfur-oxidizing Acidicaldus sp. SV5 effectively bioleached Cu, Ni, and Zn from the contaminated sediment, reducing the bioavailable fraction of these elements below SQG thresholds. The ecological risk assessment indicated that SV5-driven remediation significantly reduced the potential ecological risk of the contaminated sediment. The residual ecotoxicity of the microbially remediated sediment was also tested with the soil nematode Caenorhabditis elegans. There was a significant decrease in the body burden of Cu, Ni, and Zn in C. elegans and a reduction in the toxicological effect on survival, growth, and reproduction in the microbially remediated sediment. Our study suggests that a combination of chemical analysis, chemical-based ecological risk assessment, and ecotoxicity tests would be helpful for the development of efficient and eco-friendly strategies for the restoration of contaminated sediment, which could be incorporated into sediment quality management practices.

The impact of co-treatment with graphene oxide and metal mixture on Salmo trutta at early development stages: The sorption capacity and potential toxicity

Graphene oxide (GO) are novel nanomaterials with a wide range of applications due to their high absorption capacity. This study was undertaken with a view to assess the bioaccumulation and acute toxicity of GO used in combination with the heavy metal mixture (Cr, Cu, Ni and Zn) to fish embryos and larvae. For this purpose, Salmo trutta embryos and larvae were subjected to the 4-day long treatment with three different concentrations of GO, the metal mixture, which was prepared of four metals at the concentrations corresponding to the maximum-permissible-concentrations for EU inland waters (Cr-0.01, Cu-0.01, Ni-0.034, and Zn-0.1 mg/L), and with GO in combination with MIX (GO+MIX). When used in combination with the metal mixture, GO exhibited a high metal sorption capacity. The obtained confocal fluorescence microscopy results showed that GO located in the embryo chorion causing its damage; in larvae, however, GO were found only in the gill region. Results of these experiments confirmed the hypothesis that GO affects the accumulation of metals and mitigates their toxic effects on organism. In embryos, the acute toxicity of exposure to GO and co-exposure to MIX+GO was found to manifest itself through the decreased heart rate (HR) and malondialdehyde (MDA) level and through the increased metallothionein (MT) concentration. Meanwhile, in larvae, GO and MIX+GO were found to induce genotoxicity effects. However, changes in HR, MDA, MT, gill ventilation frequency, yolk sack absorption and cytotoxicity compared with those of the control group were not recorded in larvae. The obtained results confirmed our hypothesis: the combined effect of MIX and GO was less toxic to larvae (especially survival) than individual effects of MIX components. However, our results emphasize that fish exposure to GO alone and in combination with heavy metal contaminants (MIX+GO) even at environmentally relevant concentrations causes health risks that cannot be ignored.

Synergistic effect of chloroquine and copper to the euryhaline rotifer Proales similis

Chloroquine (CQ) has been widely used for many years against malaria and various viral diseases. Its important use and high potential to being persistent make it of particular concern for ecotoxicological studies. Here, we evaluated the toxicity of CQ alone and in combination with copper (Cu) to the euryhaline rotifer Proales similis. All experiments were carried out using chronic toxicity reproductive five-day tests and an application factor (AF) of 0.05, 0.1, 0.3, and 0.5 by multiplying the 24-h LC₅₀ values of CQ (4250 µg/L) and Cu (68 µg/L), which were administered in solution. The rate of population increase (r, d^-1) ranged from 0.50 to 52 (controls); 0.20 to 0.40 (CQ); 0.09 to 0.43 (Cu); and -0.03 to 0.30 (CQ-Cu) and showed significant decrease as the concentration of both chemicals in the medium increased. Almost all tested mixtures induced synergistic effects, mainly as the AF increased. We found that the presence of Cu intensifies the vulnerability of organisms to CQ and vice versa. These results stress the potential hazard that these combined chemicals may have on the aquatic systems. This research suggests that P. similis is sensitive to CQ as other standardized zooplankton species and may serve as a potential test species in the risk assessment of emerging pollutants in marine environments.

Removal of nickel and copper ions in strongly acidic conditions by in-situ formed amyloid fibrils

The research investigated a novel strategy that can synchronously remove Ni²⁺ and Cu²⁺ by synthesizing amyloid fibrils under harsh conditions. The adsorption capacity of Ni²⁺ and Cu²⁺ increased by 18.5% and 34.1% respectively in the in-situ scenario as compared to that Ni²⁺ and Cu²⁺ were introduced after amyloid fibrils preparation, meantime, it avoids the generation of acidic waste liquid in the process of preparing amyloid fibrils. The adsorption behaviors of Ni²⁺ and Cu²⁺ can be well described by the pseudo-second-order kinetic model and Langmuir isotherm. The functional groups of amide, hydroxyl, and carboxyl played determining roles in the adsorption process. Moreover, when the amyloid fibrils were prepared in the presence of Ni²⁺ and Cu²⁺, i.e., the in-situ adsorption scenario, metal ions tended to occupy the functional sites, inhibit protein aggregation, and affect long amyloid fibrils synthesis accordingly. Metal ion-binding site prediction server was used to predict the binding sites of metal ions towards the protein sequence within amyloid fibrils, and the metal ion was observed to preferentially bind to a particular residue such as glutamic acid, cysteine, and serine. The amyloid fibrils be potentially valuable for the removal of heavy metals in strongly acidic wastewater such as acidic mining drainage.

Adsorption kinetics and isotherms of binary metal ion aqueous solution using untreated venus shell

Among available technologies to remove heavy metals from wastewater, biosorption has gained more attention due to its high removal efficiency, friendly operation, and inexpensive cost. Despite many studies on metal adsorption from single ion solutions, kinetics and isotherms of binary metal ions simultaneously adsorbed onto biosorbents have not been thoroughly investigated to provide insight on involving mechanisms. This study explored the adsorption potential of untreated venus shells (UVS) that can be utilized in economical and environmentally-friendly ways. In this work, UVS of different sizes were prepared without chemical treatment as a biosorbent. Characterization of UVS was accomplished using nitrogen adsorption isotherm, FTIR, and SEM-EDX. Batch adsorption was carried out to study the effect of initial metal ion concentration, adsorbent dosage, and size on removing Cu(II) and Zn(II) from a binary solution of both metal ions using UVS. The experimental values of maximum adsorption capacities of Cu(II) and Zn(II) were 0.446 and 0.465 mg/g, respectively. The adsorption data were analyzed using the pseudo-first order, pseudo-second order, Elovich, and intraparticle diffusion rate equations. The pseudo-second order and the intraparticle diffusion model yielded the best fit to the experimental data for Cu(II) and Zn(II) ions, respectively. The equilibrium isotherm was examined using the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (D–R), and Elovich models. The Freundlich model best fits the Cu(II) and Zn(II) equilibrium adsorption data. The results indicated that the adsorption of Cu(II) and Zn(II) onto UVS-600 adsorbent could undergo a chemisorption mechanism. Both metal ions in an aqueous solution were competitively adsorbed onto the heterogeneous active sites available on the shell surfaces. Cu(II) and Zn(II) ions in the binary system could result in ionic interference between the adsorbed ions and the active sites.

Effects of Zinc in an Outdoor Freshwater Microcosm System

A long-term exposure outdoor microcosm study was conducted to evaluate the effects of zinc (Zn) on zooplankton, phytoplankton, and periphyton in a freshwater system. Five Zn treatment concentrations (nominal: 8, 20, 40, 80, and 160 μg/L Zn) and an untreated control with 3 replicates each were used. Various physical and chemical characteristics of the microcosms and biological assessment endpoints (e.g., total abundance, group abundance, species richness, chlorophyll a, etc.) were measured to determine the effects of Zn over time. In general, physical and chemical characteristics (e.g., total dissolved solids, total suspended solids, dissolved oxygen, pH, dissolved organic carbon) of water fluctuated over time, but they were not significantly different within treatments and controls during the study. Zinc significantly affected the population dynamics and community structure of plankton. The effects occurred 7 d after initial treatment exposures began and continued to the end of the treatment phase, especially at the high treatment concentrations. Total and group abundance, species richness, the Shannon index, and chlorophyll a concentrations for high Zn treatment concentrations were significantly lower than the controls during the treatment phase. The no-observed-effect, lowest-observed-effect, and median effect concentrations were generally lower than the literature-reported results from single-species toxicity tests for fish and invertebrates, suggesting that plankton are more sensitive to Zn than planktivores. Although primary producers play an important role in the ecosystem, they have not been consistently incorporated into numerical environmental quality criteria for freshwater organisms, at least in the United States. The results of the present study are useful for development of environmental quality guidelines for freshwater ecosystems and ecological risk assessment. Environ Toxicol Chem 2021;40:2053-2072. © 2021 SETAC.

Effect of Dissolved Organic Matter Concentration and Source on the Chronic Toxicity of Copper and Nickel Mixtures to Chlorella sp

There have been limited studies on the effects of toxicity-modifying factors, such as dissolved organic matter (DOM), on the toxicity of metal mixtures to aquatic biota. The present study investigated the effects of DOM concentration (low, 2.8 ± 0.1 mg C/L; high, 11 ± 1.0 mg C/L) and DOM source (predominantly terrestrial or microbial) on the chronic toxicity of copper (Cu) and nickel (Ni) binary mixtures to the green freshwater microalga Chlorella sp. This was assessed by using a full factorial design of 72-h growth inhibition bioassays. Measured algal growth rate was compared with growth predicted by the concentration addition and independent action reference models. Model predictions were based on concentrations of dissolved metals, labile metals (measured by diffusive gradients in thin films [DGT]), and calculated free metal ions (determined by the Windermere Humic Aqueous Model). Copper/Ni mixture toxicity was synergistic to Chlorella sp. in the absence of added DOM, with evidence of metal concentration-dependent toxicity at low effect concentrations. As DOM concentration increased, the mixture interaction changed from synergism to noninteraction or antagonism depending on the metal speciation method used. The DOM source had no significant effect on mixture interaction when based on dissolved and free metal ion concentrations but was significantly different when based on DGT-labile metal concentrations. Ratio-dependent mixture interaction was observed in all treatments, with increased deviation from the reference model predictions as the mixture changed from Ni- to Cu-dominated. The present study demonstrated that both DOM concentration and source can significantly change metal mixture toxicity interactions and that these interactions can be interpreted differently depending on the metal speciation method used. Environ Toxicol Chem 2021;40:1908-1918. © 2021 SETAC.

Comparison of Joint Effect of Acute and Chronic Toxicity for Combined Assessment of Heavy Metals on Photobacterium sp.NAA-MIE

Predicting the crucial effect of single metal pollutants against the aquatic ecosystem has been highly debatable for decades. However, dealing with complex metal mixtures management in toxicological studies creates a challenge, as heavy metals may evoke greater toxicity on interactions with other constituents rather than individually low acting concentrations. Moreover, the toxicity mechanisms are different between short term and long term exposure of the metal toxicant. In this study, acute and chronic toxicity based on luminescence inhibition assay using newly isolated Photobacterium sp.NAA-MIE as the indicator are presented. Photobacterium sp.NAA-MIE was exposed to the mixture at a predetermined ratio of 1:1. TU (Toxicity Unit) and MTI (Mixture Toxic Index) approach presented the mixture toxicity of Hg²⁺ + Ag⁺, Hg²⁺ + Cu²⁺, Ag⁺ + Cu²⁺, Hg²⁺ + Ag⁺ + Cu²⁺, and Cd²⁺ + Cu²⁺ showed antagonistic effect over acute and chronic test. Binary mixture of Cu²⁺ + Zn²⁺ was observed to show additive effect at acute test and antagonistic effect at chronic test while mixture of Ni²⁺ + Zn²⁺ showing antagonistic effect during acute test and synergistic effect during chronic test. Thus, the strain is suitable and their use as bioassay to predict the risk assessment of heavy metal under acute toxicity without abandoning the advantage of chronic toxicity extrapolation.

Cultivation substrata differentiate the properties of river biofilm EPS and their binding of heavy metals: A spectroscopic insight

River biofilms inevitably serve as recipients of heavy metals including copper (Cu) and cadmium (Cd) following their introduction in fluvial systems. Nevertheless, the effects of cultivation substrata on the characteristics of river biofilm extracellular polymeric substances (EPS) and the binding behaviors of heavy metals on biofilms remain unclear. Integrating spectroscopic methods with chemometric analyses, we explored the binding behaviors of Cu(II) and Cd(II) onto biofilm EPS cultivated from two representative substrata at the molecular level. Chemical analysis revealed that biofilm cultivated on polyethylene (PE) pieces contained more non-fluorescent protein fractions, whereas EPS from periphyton grown on mineral, i.e., cobblestones was richer in aromatic fractions and polysaccharides. Excitation-emmision matrix combined with parallel factor analysis suggested a stronger interaction between fluorophores in periphytic EPS with Cu(II) compared to fluorophores in plastic biofilm EPS. Integrated use of infrared spectroscopy and two-dimensional correlation analyses revealed that, during the heavy metal binding processes, the amines and phenolics in plastic biofilm EPS gave the fastest responses to metal binding. While the amides and the aliphatic fractions in periphytic EPS showed a preferential binding to heavy metals. This study differentiates the effects of cultivation substrata on structuring the biofilm EPS characteristics and offers new insights into the environmental behaviors of heavy metal discharge into fluvial systems in river biofilm matrix.

Antifouling paint particles cause toxicity to benthic organisms: Effects on two species with different feeding modes

Antifouling paint particles (APPs) are residues generated primarily during maintenance of vessels and marine structures, and usually occur in boat maintenance areas that are adjacent to aquatic environments, such as estuaries. APPs end up in sediment layers after their release into aquatic systems and represent a threat to benthic invertebrates, which have different habitat and feeding modes. Thus, the aim of the present study was to evaluate the toxicity of APPs-spiked sediment to the benthic microcrustaceans Monokalliapseudes schubarti (a tanaid) and Hyalella azteca (an amphipod), testing whole sediment and elutriate solutions under estuarine conditions. Whole sediment spiked with APPs was more toxic to these organisms than the elutriate solution. This toxicity was attributed to the high concentrations of Cu and Zn metals quantified in the APPs. During the whole sediment test, M. schubarti was more sensitive than H. azteca. M. schubarti is an infauna organism, and its interaction with sediments (e.g. by ingestion of sediment particles) makes it more susceptible to compounds released from APPs than H. azteca, which tends to interact with these compounds at the sediment-water interface. In addition, in tests with sediment elutriate and without sediment, M. schubarti was not affected, while elutriate with 1.50% APPs showed to be significantly toxic to H. azteca. Moreover, these results indicate that APPs act as continuous and localized sources of metals to benthic organisms, highlighting the importance of better APP management and disposal practices in boat maintenance areas to avoid local aquatic contamination.

Context-Dependent Responses of Aquatic Insects to Metals and Metal Mixtures: A Quantitative Analysis Summarizing 24 Yr of Stream Mesocosm Experiments

Modernizing water quality criteria to predict how contaminants affect natural aquatic communities requires that we utilize data obtained across multiple lines of evidence, including laboratory, mesocosm, and field studies. We report the results of 29 mesocosm experiments conducted from 1994 to 2017 at the Colorado State University Stream Research Laboratory (Fort Collins, CO, USA). The primary goal of the present study was to quantify responses of aquatic insect communities collected from 8 different locations to different combinations of cadmium (Cd), copper (Cu), iron (Fe), and zinc (Zn). Treatments that included Cu or Fe, either alone or in combination with other metals, were especially toxic to aquatic insects. The results showed that effects of metals were context dependent and varied significantly among the 8 sites where communities were collected. In particular, effects on communities from smaller streams were significantly greater than those from larger streams. Our analyses also showed that several morphological (body size, shape, gills, degree of sclerotization) and life history (voltinism) traits were significantly correlated with sensitivity to metals. Across all taxa and experiments, aquatic insects broadly classified as small (maximum body length <8 mm) were significantly more sensitive to metals than medium or large individuals. These findings demonstrate the advantages of integrating results of mesocosm experiments with species traits to develop a mechanistic understanding of biotic and abiotic factors that influence community responses to contaminants. Environ Toxicol Chem 2019;38:2486-2496. © 2019 SETAC.

Concise Review of Nickel Human Health Toxicology and Ecotoxicology

Nickel (Ni) metal and Ni compounds are widely used in applications like stainless steel, alloys, and batteries. Nickel is a naturally occurring element in water, soil, air, and living organisms, and is essential to microorganisms and plants. Thus, human and environmental nickel exposures are ubiquitous. Production and use of nickel and its compounds can, however, result in additional exposures to humans and the environment. Notable human health toxicity effects identified from human and/or animal studies include respiratory cancer, non-cancer toxicity effects following inhalation, dermatitis, and reproductive effects. These effects have thresholds, with indirect genotoxic and epigenetic events underlying the threshold mode of action for nickel carcinogenicity. Differences in human toxicity potencies/potentials of different nickel chemical forms are correlated with the bioavailability of the Ni2+ ion at target sites. Likewise, Ni2+ has been demonstrated to be the toxic chemical species in the environment, and models have been developed that account for the influence of abiotic factors on the bioavailability and toxicity of Ni2+ in different habitats. Emerging issues regarding the toxicity of nickel nanoforms and metal mixtures are briefly discussed. This review is unique in its covering of both human and environmental nickel toxicity data.

Ecotoxicological characterization of possible degradation products of the polymeric flame retardant "Polymeric FR" using algae and Daphnia OECD tests

History has shown that brominated flame retardants often pose risks to the environment. However, the new group of polymeric brominated flame retardants might be a safer alternative compared to previously used monomers due to their high molecular weight. An example for this new group is "Polymeric FR", which is persistent by design. Within this publication, we study the acute and chronic toxicity of possible degradation products that were previously described for this polymer following UV irradiation and heat exposure at 60 °C. We have applied the OECD tests No. 201 (Algae growth inhibition), 202 (Daphnia acute immobilisation), and 211 (Daphnia reproduction) to four individual substances, indicated to originate as degradation products of "Polymeric FR" as well as a combination of these. In addition, we have used trend analysis to predict effects on fish as an additional trophic level. The results suggest that acute toxicity to the aquatic organisms chosen is rather limited or even not occurring. Chronic exposure, however, does exert effects that might be relevant from an environmental perspective.

Exposure to mixtures of mercury, cadmium, lead, and arsenic alters the disposition of single metals in tissues of Wistar rats

Humans throughout the world are exposed regularly to mixtures of environmental toxicants. Four of the most common heavy metal toxicants in the environment are mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Numerous studies have assessed the effects and disposition of individual metals in organ systems; however, humans are usually exposed to mixtures of toxicants or metals rather than to a single toxicant. Therefore, the purpose of the current study was to test the hypothesis that exposure to a mixture of toxic heavy metals alters the disposition of single metals in target organs. Wistar rats (Rattus norvegicus) were exposed to Hg, Cd, Pb, or As as a single metal or as a mixture of metals. Rats were injected intravenously for three days, following which kidneys, liver, brain, and blood were harvested. Samples were analyzed for content of Hg, Cd, Pb, and As via inductively coupled plasma mass spectrometry. In general, exposure to a mixture of metals reduced accumulation of single metals in target organs. Interestingly, exposure to mixtures of metals with Pb and/or As increased the concentration of these metals specifically in the liver. The findings from this study indicate that exposure to mixtures of toxic heavy metals may alter significantly the distribution and accumulation of these metals in target organs and tissues.

Subchronic, chronic, lethal and sublethal toxicity of insensitive munitions mixture formulations relative to individual constituents in Hyalella azteca

Insensitive munitions (IMs) are replacing conventional munitions, improving safety from unintended detonation. IMs are deployed in mixture formulations but little is known about their mixture toxicology. We characterized mixture effects of the IM formulations IMX-101 (mixture of 2,4-dinitroanisole [DNAN], 3-nitro-1,2,4-triazol-5-one [NTO], and nitroguanidine [NQ]) and IMX-104 (DNAN, NTO, and hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX]) in subchronic (10 d) and chronic (35 d) water-only tests in Hyalella azteca assessing impacts on survival, growth and reproduction. In 10-d single chemical exposures, DNAN was the most potent constituent, eliciting an LC50 of 16.0 mg/L; the LC50s for NTO and NQ were 891 and 565 mg/L, respectively. RDX did not elicit significant mortality up to 29.5 mg/L, a concentration near its solubility limit. Based on toxic-units (TUs), the toxicity of IMX-101 was driven by the effective concentration of DNAN; however, the presence of NTO, RDX, or both elicited interactive effects causing an approximately 2-fold decrease in lethality for IMX-104. Growth reduction was observed in 10-d exposures to DNAN, IMX-101 and IMX-104, but not for NQ, NTO, or RDX. Longer exposure duration (35 d) to IMX-101, IMX-104, and DNAN resulted in 3-6 times higher sensitivity for lethality and resulted in the most sensitive endpoint for DNAN, RDX, and IMX-101 exposures, decreased reproduction. Slight, but statistically significant, antagonistic responses among IMX-101 constituents were observed for survival and reproduction at 35d. Overall, the results support response-additive summation as a sufficient method to provide conservative hazard assessments of subchronic, chronic, and sublethal IMX-101 and IMX-104 mixture impacts in H. azteca.

Toxicity of Diclofenac: Cadmium Binary Mixtures to Algae Desmodesmus subspicatus Using Normalization Method

Algal test using chlorococcal algae Desmodesmus subspicatus was used to determine single acute toxicity of either diclofenac or cadmium and to assess acute toxicity of their binary mixtures. The test confirmed significant acute toxicity of both diclofenac and cadmium; diclofenac with acute toxicity E_rC50 60.44 ± 0.20 mg/L and cadmium with acute toxicity E_rC50 2.14 ± 0.02 mg/L. This study of acute toxicity of binary cadmium-diclofenac mixtures confirmed their negative effects on aquatic producers and it also proved influence of the above substances on acute toxicity of their mixtures. Normalization method was applied to predict acute toxicity of binary mixtures composed of chemicals with significantly different acute toxicities. Normalization method used molar ratio (R) of chemicals in binary mixtures as their composition descriptor.

Transcriptomics provides mechanistic indicators of mixture toxicology for IMX-101 and IMX-104 formulations in fathead minnows (Pimephales promelas)

Within the US military, new insensitive munitions (IMs) are rapidly replacing conventional munitions improving safety from unintended detonation. Toxicity data for IM chemicals are expanding rapidly, however IM constituents are typically deployed in mixture formulations, and very little is known about their mixture toxicology. In the present study we sought to characterize the mixture effects and toxicology of the two predominant IM formulations IMX-101 and IMX-104 in acute (48 h) larval fathead minnow (Pimephales promelas) exposures. IMX-101 consists of a mixture of 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ) while IMX-104 is composed of DNAN, NTO, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). DNAN was the most potent constituent in IMX-101 eliciting an LC50 of 36.1 mg/L, whereas NTO and NQ did not elicit significant mortality in exposures up to 1040 and 2640 mg/L, respectively. Toxic unit calculations indicated that IMX-101 elicited toxicity representative of the component concentration of DNAN within the mixture. Toxicogenomic responses for the individual constituents of IMX-101 indicated unique transcriptional expression and functional responses characteristic of: oxidative stress, impaired energy metabolism, tissue damage and inflammatory responses in DNAN exposures; impaired steroid biosynthesis and developmental cell-signaling in NQ exposures; and altered mitogen-activated protein kinase signaling in NTO exposures. Transcriptional responses to the IMX-101 mixture were driven by the effects of DNAN where expression and functional responses were nearly identical comparing DNAN alone versus the fractional equivalent of DNAN within IMX-101. Given that each individual constituent of the IMX-101 mixture elicited unique functional responses, and NTO and NQ did not interact with DNAN within the IMX-101 mixture exposure, the overall toxicity and toxicogenomic responses within acute exposures to the IMX-101 formulation are indicative of "independent" mixture toxicology. Alternatively, in the IMX-104 exposure both DNAN and RDX were each present at concentrations sufficient to elicit lethality (RDX LC50 = 28.9 mg/L). Toxic-unit calculations for IMX-104 mixture formulation exposures indicated slight synergistic toxicity (ΣTU LC50 = 0.82, 95% confidence interval = 0.73-0.90). Unique functional responses relative to DNAN were observed in the IMX-104 exposure including responses characteristic of RDX exposure. Based on previous transcriptomics responses to acute RDX exposures in fathead minnow larvae, we hypothesize that the potentially synergistic responses within the IMX-104 mixture are related to interactive effects of each DNAN and RDX on oxidative stress mitigation pathways.

Competitive sorption of Ni and Zn at the aluminum oxide/water interface: an XAFS study

Trace metals (e.g. Ni, Zn) leached from industrial and agricultural processes are often simultaneously present in contaminated soils and sediments. Their mobility, bioavailability, and ecotoxicity are affected by sorption and cosorption at mineral/solution interfaces. Cosorption of trace metals has been investigated at the macroscopic level, but there is not a clear understanding of the molecular-scale cosorption processes due to lack of spectroscopic information. In this study, Ni and Zn cosorption to aluminum oxides (γ-Al₂O₃) in binary-sorbate systems were compared to their sorption in single-sorbate systems as a function of pH using both macroscopic batch experiments and synchrotron-based X-ray absorption fine structure spectroscopy. At pH 6.0, Ni and Zn were sorbed as inner-sphere surface complexes and competed for the limited number of reactive sites on γ-Al₂O₃. In binary-sorbate systems, Ni had no effect on Zn sorption, owning to its lower affinity for the metal oxide surface. In contrast, Zn had a higher affinity for the metal oxide surface and reduced Ni sorption. At pH 7.5, Ni and Zn were sorbed as mixed-metal surface precipitates, including Ni-Al layered double hydroxides (LDHs), Zn-Al LDHs, and likely Ni-Zn-Al layered triple/ternary hydroxides. Additionally, at pH 7.5, Ni and Zn do not exhibit competitive sorption effects in the binary system. Taken together, these results indicated that pH critically influenced the reaction products, and provides a crucial scientific basis to understand the potential mobility, bioavailability, and ecotoxicity of Ni and Zn in natural and contaminated geochemical environments.

Mixtures of Cu, Ni, and Zn act mostly noninteractively on Pseudokirchneriella subcapitata growth in natural waters

Freshwater biota are usually exposed to mixtures of different metals in the environment, which raises concern because risk-assessment procedures for metals are still mainly based on single-metal toxicity. Because microalgae are primary producers and therefore at the base of the food web, it is of utmost importance to understand the effects of metal mixtures on these organisms. Most studies that have investigated the combined interactive effects of mixtures on microalgae performed tests in only one specific water. The objective of the present study was to test if combined effects of mixtures to Pseudokirchneriella subcapitata were the same or different across natural waters showing diverse water-chemistry characteristics. This was done by performing experiments with ternary Cu-Ni-Zn mixtures in 3 natural waters and with binary Cu-Ni mixtures in 5 natural waters. We showed that the ternary mixture acted noninteractively on algal growth, except in one water in which the mixture acted antagonistically. We suggest that a low-cationic competition situation in the latter water could be the reason for the antagonistic interaction between the metals. On the other hand, the binary mixture acted noninteractively on algal growth in all tested waters. We showed that both the concentration addition and independent action models can serve as accurate models for toxicity of ternary Cu-Ni-Zn and binary Cu-Ni mixtures to P. subcapitata in most cases and as protective models in all cases. In addition, we developed a metal mixture bioavailability model, by combining the independent action model and the single-metal bioavailability models, that can be used to predict Cu-Ni-Zn and Cu-Ni toxicity to P. subcapitata as a function of metal concentration and water characteristics. Environ Toxicol Chem 2018;37:587-598. © 2017 SETAC.

Potential ecotoxicity of metals leached from antifouling paint particles under different salinities

Antifouling paint particles (APPs) are residues generated during maintenance of vessels. In boat maintenance areas of South America, waste generation and disposal are not completely regulated. Therefore, APPs can enter into the aquatic environment and act as a source of contamination by metals and other biocides. Thus, the aim of the present study was to evaluate the potential ecotoxicity of the metal mixture present in APPs leached under different salinities. Therefore, the copepod Acartia tonsa was exposed to different concentrations of a leachate solution prepared by the addition of APPs (1.25g/L) in artificial saline water (salinities 5, 15 and 30). Thereafter, complexing agents (EDTA and sodium thiosulfate) were added to the experimental media in order to evaluate metal influence in APPs toxicity. APPs leachate solutions were very toxic to A. tonsa, reaching an estimated LC₅₀ of 1% at salinities 5% and 15%, and 2% at salinity 30. The addition of the chelators in leachate solutions showed that metals are the major responsible compounds for the observed toxicity. Moreover, results from the calculated toxic units suggested a slightly synergic effect between Cu and Zn in the paint formulation. A metal speciation modelling showed that Zn was predominant as a free ion at all salinities, therefore, explaining the high leachate toxicity. Furthermore, the release of Zn was observed more at lower salinities, whereas Cu was observed at higher salinities. APPs are frequently released in estuarine systems, under conditions of salinity gradients. Therefore, navigated estuaries might be under the threat of this neglected residue.

Toxicity of platinum, palladium and rhodium to Daphnia magna in single and binary metal exposure experiments

Mainly due to automobile traffic, but also due to other sources, the platinum group elements (PGE) platinum (Pt), palladium (Pd) and rhodium (Rh) are introduced into aquatic biotopes where they accumulate in sediments of lakes and rivers. However, the toxicity of these noble metals to aquatic organisms is not well understood and especially toxicity studies under standardized condition are lacking. Thus, the toxicity of Pt, Pd and Rh to Daphnia magna was tested in single metal exposure experiments according to OECD guideline 202. Immobility and lethality was recorded after 24 h and 48 h of exposure and EC₅₀ and LC₅₀, respectively, were determined. As the nominal exposure concentration of Pd differed significantly from the quantified concentration, the control of the real exposure concentration by chemical analysis is mandatory, especially for Pd. The toxicity decreased in the order Pd > Pt ≫ Rh with e.g. LC₅₀(48 h) values of 14 μg/L for Pd, 157 μg/L for Pt and 56,800 μg/L for Rh. The exposure period had a clear effect on the toxicity of Pt, Pd and Rh. For Pt and Rh the endpoint immobility was more sensitive than the endpoint lethality whereas Pd toxicity was similar for both endpoints. The Hill slopes, which are a measure for the steepness of the concentration-response curves, showed no significant discrepancies between the different metals. The binary metal exposure to Pt and Pd revealed a more-than-additive, i.e. a synergistic toxicity using the toxic unit approach. The present study is a start to understand the toxicity of interacting PGE. The modes of action behind the synergistic effect are unclear.

Acute Toxicity of Ternary Cd-Cu-Ni and Cd-Ni-Zn Mixtures to Daphnia magna: Dominant Metal Pairs Change along a Concentration Gradient

Multiple metals are usually present in surface waters, sometimes leading to toxicity that currently is difficult to predict due to potentially non-additive mixture toxicity. Previous toxicity tests with Daphnia magna exposed to binary mixtures of Ni combined with Cd, Cu, or Zn demonstrated that Ni and Zn strongly protect against Cd toxicity, but Cu-Ni toxicity is more than additive, and Ni-Zn toxicity is slightly less than additive. To consider multiple metal-metal interactions, we exposed D. magna neonates to Cd, Cu, Ni, or Zn alone and in ternary Cd-Cu-Ni and Cd-Ni-Zn combinations in standard 48 h lethality tests. In these ternary mixtures, two metals were held constant, while the third metal was varied through a series that ranged from nonlethal to lethal concentrations. In Cd-Cu-Ni mixtures, the toxicity was less than additive, additive, or more than additive, depending on the concentration (or ion activity) of the varied metal and the additivity model (concentration-addition or independent-action) used to predict toxicity. In Cd-Ni-Zn mixtures, the toxicity was less than additive or approximately additive, depending on the concentration (or ion activity) of the varied metal but independent of the additivity model. These results demonstrate that complex interactions of potentially competing toxicity-controlling mechanisms can occur in ternary-metal mixtures but might be predicted by mechanistic bioavailability-based toxicity models.

A multi-metal risk assessment strategy for natural freshwater ecosystems based on the additive inhibitory free metal ion concentration index

Scientifically sound risk assessment strategies and derivations of environmental quality standards for metals present in freshwater environments are currently hampered by insufficient chronic toxicity data collected from natural ecosystems, as well as inadequate information on metal speciation. Thus, the aim of the present study was to evaluate the impact of freshwater containing multiple metals (Cd, Cr, Cu, Ni, Pb and Zn) on the chronic toxicity (72h) to the alga Pseudokirchneriella subcapitata and compare the observed toxicity results to the total and free metal concentration of the samples. Based on the information obtained herein, an additive inhibitory free multi-metal ion concentration index, calculated as the sum of the equivalent toxicities to the free metal ion concentration of each sample, was developed. The proposed index was well correlated to the observed chronic toxicity results, indicating that the concentration addition, when expressed as the free-ion activity, can be considered a reliable indicator for the evaluation of ecological risk assessments for natural waters containing multiple metals.

Joint toxic action of binary metal mixtures of copper, manganese and nickel to Paronychiurus kimi (Collembola)

The joint toxic effects of binary metal mixtures of copper (Cu), manganese (Mn) and nickel (Ni) on reproduction of Paronhchiurus kimi (Lee) was evaluated using a toxic unit (TU) approach by judging additivity across a range of effect levels (10-90%). For all metal mixtures, the joint toxic effects of metal mixtures on reproduction of P. kimi decreased in a TU-dependent manner. The joint toxic effects of metal mixtures also changed from less than additive to more than additive at an effect level lower than or equal to 50%, while a more than additive toxic effects were apparent at higher effect levels. These results indicate that the joint toxicity of metal mixtures is substantially different from that of individual metals based on additivity. Moreover, the close relationship of toxicity to effect level suggests that it is necessary to encompass a whole range of effect levels rather than a specific effect level when judging mixture toxicity. In conclusion, the less than additive toxicity at low effect levels suggests that the additivity assumption is sufficiently conservative to warrant predicting joint toxicity of metal mixtures, which may give an additional margin of safety when setting soil quality standards for ecological risk assessment.

Evaluation of time-dependent toxicity and combined effects for a series of mono-halogenated acetonitrile-containing binary mixtures

Mixture and time-dependent toxicity (TDT) was assessed for a series of mono-halogenated acetonitrile-containing combinations. Inhibition of bioluminescence in Aliivibrio fischeri was measured after 15, 30 and 45-min of exposure. Concentration-response (x/y) curves were determined for each chemical alone at each timepoint, and used to develop predicted x/y curves for the dose-addition and independence models of combined effect. The x/y data for each binary mixture was then evaluated against the predicted mixture curves. Two metrics of mixture toxicity were calculated per combined effect model: (1) an EC₅₀-based dose-addition (AQ) or independence (IQ) quotient and (2) the mixture/dose-addition (MX/DA) and mixture/independence (MX/I) metrics. For each single chemical and mixture tested, TDT was also calculated. After 45-min of exposure, 25 of 67 mixtures produced curves that were consistent with dose-addition using the MX/DA metric, with the other 42 being less toxic than predicted by MX/DA. Some mixtures had toxicity that was consistent with both dose-addition and independence. In general, those that were less toxic than predicted for dose-addition were also less toxic than predicted for independence. Of the 25 combinations that were consistent with dose-addition, 22 (88%) mixtures contained chemicals for which the individual TDT values were both >80%. In contrast, of the 42 non-dose-additive combinations, only 2 (4.8%) of the mixtures had both chemicals with individual TDT values >80%. The results support previous findings that TDT determinations can be useful for predicting chemical mixture toxicity.

A test of the additivity of acute toxicity of binary-metal mixtures of ni with Cd, Cu, and Zn to Daphnia magna, using the inflection point of the concentration-response curves

Mixtures of metals are often present in surface waters, leading to toxicity that is difficult to predict. To provide data for development of multimetal toxicity models, Daphnia magna neonates were exposed to individual metals (Cd, Cu, Ni, Zn) and to binary combinations of those metals in standard 48-h lethality tests conducted in US Environmental Protection Agency moderately hard reconstituted water with 3 mg dissolved organic carbon (DOC)/L added as Suwannee River fulvic acid. Toxicity tests were performed with mixtures of Ni and 1) Cd, which is considerably more toxic than Ni; 2) Cu, which is less toxic than Cd but more toxic than Ni; and 3) Zn, which has a toxicity threshold similar to Ni. For each combination of metals in the binary mixtures, the concentration of 1 metal was held constant while the second metal was varied through a series that ranged from nonlethal to lethal concentrations; then the roles of the metals were reversed. Inflection points of the concentration-response curves were compared to test for additivity of toxicity. Sublethal concentrations of Ni caused less-than-additive toxicity with Cd, slightly less-than-additive toxicity with Zn, and greater-than-additive toxicity with Cu. One explanation of these results might be competition among the metals for binding to biological ligands and/or dissolved organic matter. Therefore, models might have to incorporate sometimes competing chemical interactions to accurately predict metal-mixture toxicity. Environ Toxicol Chem 2016;35:1843-1851. © 2015 SETAC.