Chronic Toxicity of Iron to Aquatic Organisms under Variable pH, Hardness, and Dissolved Organic Carbon Conditions.

A series of chronic toxicity tests was conducted exposing three aquatic species to iron (Fe) in laboratory freshwaters. The test organisms included the green algae Raphidocelis subcapitata, the cladoceran Ceriodaphnia dubia, and the fathead minnow Pimephales promelas. They were exposed to Fe (as Fe (III) sulfate) in waters under varying pH (5.9-8.5), hardness (10.3-255 mg/L CaCO3 ), and dissolved organic carbon (DOC; 0.3-10.9 mg/L) conditions. Measured total Fe was used for calculations of biological effect concentrations because dissolved Fe was only a fraction of nominal and did not consistently increase as total Fe increased. This was indicative of the high concentrations of Fe required to elicit a biological response and that Fe species that did not pass through a 0.20- or 0.45-µm filter (dissolved fraction) contributed to Fe toxicity. The concentrations frequently exceeded the solubility limits of Fe(III) under circumneutral pH conditions relevant to most natural surface waters. Chronic toxicity endpoints (10% effect concentrations [EC10s]) ranged from 442 to 9607 µg total Fe/L for R. subcapitata growth, from 383 to 15 947 µg total Fe/L for C. dubia reproduction, and from 192 to 58,308 µg total Fe/L for P. promelas growth. Toxicity to R. subcapitata was variably influenced by all three water quality parameters, but especially DOC. Toxicity to C. dubia was influenced by DOC, less so by hardness, but not by pH. Toxicity to P. promelas was variable, but greatest under low hardness, low pH, and low DOC conditions. These data were used to develop an Fe-specific, bioavailability-based multiple linear regression model as part of a companion publication. Environ Toxicol Chem 2023;42:1371-1385. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Chronic Toxicity of Cobalt to Marine Organisms: Application of a Species Sensitivity Distribution Approach to Develop International Water Quality Standards.

Water quality standards for cobalt (Co) have yet to be developed for the European Union or the United States. The primary objective of the present study was to produce a data set comprising marine Co toxicity data that could be used by both the European Union and the United States to determine a predicted-no-effect concentration and ambient water quality criteria, respectively. Ten marine species, ranging from algae to fish, were subjected to chronic Co toxicity tests that were designed to meet international water quality testing standards. Chronic 10% effect concentration values ranged from a low of 1.23 µg dissolved Co/L for red algae (Champia parvula) to a high of 31 800 µg dissolved Co/L for sheepshead minnow (Cyprinodon variegatus). The species sensitivity ranking for chronic marine Co exposure was as follows (from most to least sensitive): C. parvula > Neanthes arenaceodentata (polychaete) > Americamysis bahia (mysid shrimp) > Skeletonema costatum (marine diatom) > Dendraster excentricus (sand dollar) > Mytilus galloprovincialis (mussel) > Strongylocentrotus purpuratus (purple sea urchin) > Crassostrea gigas (oyster) > Dunaliella tertiolecta (marine flagellate) > C. variegatus. Chronic test results indicated that invertebrate and plant species were substantially more sensitive to Co exposure than fish. The chronic toxicity data were used to calculate a species sensitivity distribution, from which a hazardous concentration 5th percentile of 7.09 µg dissolved Co/L (95% CI 0.025-47.3 µg Co/L) was derived. Environ Toxicol Chem 2021;40:1405-1418. © 2021 SETAC.

Updated Multiple Linear Regression Models for Predicting Chronic Aluminum Toxicity to Freshwater Aquatic Organisms and Developing Water Quality Guidelines.

Multiple linear regression (MLR) models for predicting chronic aluminum toxicity to a cladoceran (Ceriodaphnia dubia) and a fish (Pimephales promelas) as a function of 3 toxicity-modifying factors (TMFs)-dissolved organic carbon (DOC), pH, and hardness-have been published previously. However, the range over which data for these TMFs were available was somewhat limited. To address this limitation, additional chronic toxicity tests with these species were subsequently conducted to expand the DOC range up to 12 mg/L, the pH range up to 8.7, and the hardness range up to 428 mg/L. The additional toxicity data were used to update the chronic MLR models. The adjusted R2 for the C. dubia 20% effect concentration (EC20) model increased from 0.71 to 0.92 with the additional toxicity data, and the predicted R2 increased from 0.57 to 0.89. For P. promelas, the adjusted R2 increased from 0.87 to 0.92 and the predicted R2 increased from 0.72 to 0.87. The high predicted R2 relative to the adjusted R2 indicates that the models for both species are not overly parameterized. When data for C. dubia and P. promelas were pooled, the adjusted R2 values were comparable to the species-specific models (0.90 and 0.88 for C. dubia and P. promelas, respectively). This indicates that chronic aluminum EC20s for C. dubia and P. promelas respond similarly to variation in DOC, pH, and hardness. Overall, the pooled model predicted EC20s that were within a factor of 2 of observed in 100% of the C. dubia tests and 94% of the P. promelas tests. Environ Toxicol Chem 2020;39:1724-1736. © 2020 SETAC.

Acute and Chronic Toxicity of Cobalt to Freshwater Organisms: Using a Species Sensitivity Distribution Approach to Establish International Water Quality Standards.

Water quality standards for cobalt (Co) have not been developed for the European Union or United States. The objective of the present study was to produce freshwater Co toxicity data that could be used by both the European Union and the United States to develop appropriate regulatory standards (i.e., environmental quality standards or predicted-no-effect concentrations in Europe and ambient water quality criteria or state water quality standards in the United States). Eleven species, including algae, an aquatic plant, and several invertebrate and fish species, were used in the performance of acute and chronic Co toxicity tests. Acute median lethal or median effective concentration (LC50 or EC50) values ranged from 90.1 µg Co/L for duckweed (Lemna minor) to 157 000 µg Co/L for midges (Chironomus tentans). Chronic 10% effect concentration (EC10) values ranged from 4.9 µg Co/L for duckweed to 2170 µg Co/L for rainbow trout (Oncorhynchus mykiss). Chronic 20% effect concentration (EC20) values ranged from 11.1 µg Co/L for water flea (Ceriodaphnia dubia) to 2495 µg Co/L for O. mykiss. Results indicated that invertebrate and algae/plant species are more sensitive to chronic Co exposures than fish. Acute-to-chronic ratios (derived as acute LC50s divided by chronic EC20s) were lowest for juvenile O. mykiss (0.6) and highest for the snail Lymnaea stagnalis (2670). Following the European-based approach and using EC10 values, species sensitivity distributions (SSDs) were developed and a median hazardous concentration for 5% of the organisms of 1.80 µg Co/L was derived. Chronic EC20 values were used, also in an SSD approach, to derive a US Environmental Protection Agency-style final chronic value of 7.13 µg Co/L. Environ Toxicol Chem 2020;39:799-811. © 2020 SETAC.

Determination of Bioavailable Aluminum in Natural Waters in the Presence of Suspended Solids.

Analyses of natural waters frequently show elevated levels of total aluminum (Al) attributable to acid extraction of Al from the total suspended solids (TSS) minerals. Hence, there is a need for an analytical method that measures only bioavailable Al. Natural waters high in TSS were collected to study the chronic effects of Al on Ceriodaphnia dubia. In the collected waters TSS ranged from 30 to 411 mg/L; total Al concentrations ranged from 2.0 to 44.8 mg/L. The TSS in natural waters inhibited reproduction of C. dubia up to 40% in comparison to the same filtered waters. This inhibition did not correlate with the concentration of TSS or total Al; it was attributed to nutritional deficiency and was prevented by increasing the food supply. To demonstrate that toxicity can be measured in natural waters, samples with elevated TSS were spiked with soluble Al, and survival and reproduction were measured in chronic studies performed at pH 6.3 and 8.0. To properly characterize the Al concentrations in the toxicity studies, a method was needed that could discriminate bioavailable Al from mineral forms of Al. An extraction method at pH 4 for bioavailable Al was developed and evaluated using C. dubia chronic toxicity studies in the presence of TSS. It is concluded that the proposed method is better able to discriminate chronic toxicity effects attributable to bioavailable Al from mineralized nontoxic forms of Al compared with existing methods using total or total recoverable Al (i.e., extraction at pH ≤ 1.5). We propose that this new method be used when assessing the potential for Al in natural surface waters to cause toxicity. Environ Toxicol Chem 2019;38:1668-1681. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Acute and chronic toxicity of aluminum to a unionid mussel (Lampsilis siliquoidea) and an amphipod (Hyalella azteca) in water-only exposures.

The US Environmental Protection Agency (USEPA) is reviewing the protectiveness of the national ambient water quality criteria (WQC) for aluminum (Al) and compiling a toxicity data set to update the WQC. Freshwater mussels are one of the most imperiled groups of animals in the world, but little is known about their sensitivity to Al. The objective of the present study was to evaluate acute 96-h and chronic 28-d toxicity of Al to a unionid mussel (Lampsilis siliquoidea) and a commonly tested amphipod (Hyalella azteca) at a pH of 6 and water hardness of 100 mg/L as CaCO3 . The acute 50% effect concentration (EC50) for survival of both species was >6200 µg total Al/L. The EC50 was greater than all acute values in the USEPA acute Al data set for freshwater species at a pH range of 5.0 to <6.5 and hardness normalized to 100 mg/L, indicating that the mussel and amphipod were insensitive to Al in acute exposures. The chronic 20% effect concentration (EC20) based on dry weight was 163 µg total Al/L for the mussel and 409 µg total Al/L for the amphipod. Addition of the EC20s to the USEPA chronic Al data set for pH 5.0 to <6.5 would rank the mussel (L. siliquoidea) as the fourth most sensitive species and the amphipod (H. azteca) as the fifth most sensitive species, indicating the 2 species were sensitive to Al in chronic exposures. The USEPA-proposed acute and chronic WQC for Al would adequately protect the mussel and amphipod tested; however, inclusion of the chronic data from the present study and recalculation of the chronic criterion would likely lower the proposed chronic criterion. Environ Toxicol Chem 2018;37:61-69. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Evaluating the effects of pH, hardness, and dissolved organic carbon on the toxicity of aluminum to freshwater aquatic organisms under circumneutral conditions.

Although it is well known that increasing water hardness and dissolved organic carbon (DOC) concentrations mitigate the toxicity of aluminum (Al) to freshwater organisms in acidic water (i.e., pH < 6), these effects are less well characterized in natural waters at circumneutral pHs for which most aquatic life regulatory protection criteria apply (i.e., pH 6-8). The evaluation of Al toxicity under varying pH conditions may also be confounded by the presence of Al hydroxides and freshly precipitated Al in newly prepared test solutions. Aging and filtration of test solutions were found to greatly reduce toxicity, suggesting that toxicity from transient forms of Al could be minimized and that precipitated Al hydroxides contribute significantly to Al toxicity under circumneutral conditions, rather than dissolved or monomeric forms. Increasing pH, hardness, and DOC were found to have a protective effect against Al toxicity for fish (Pimephales promelas) and invertebrates (Ceriodaphnia dubia, Daphnia magna). For algae (Pseudokirchneriella subcapitata), the protective effects of increased hardness were only apparent at pH 6, less so at pH 7, and at pH 8, increased hardness appeared to increase the sensitivity of algae to Al. The results support the need for water quality-based aquatic life protection criteria for Al, rather than fixed value criteria, as being a more accurate predictor of Al toxicity in natural waters. Environ Toxicol Chem 2018;37:49-60. © 2017 SETAC.

Development and application of a biotic ligand model for predicting the chronic toxicity of dissolved and precipitated aluminum to aquatic organisms.

Aluminum (Al) toxicity to aquatic organisms is strongly affected by water chemistry. Toxicity-modifying factors such as pH, dissolved organic carbon (DOC), hardness, and temperature have a large impact on the bioavailability and toxicity of Al to aquatic organisms. The importance of water chemistry on the bioavailability and toxicity of Al suggests that interactions between Al and chemical constituents in exposures to aquatic organisms can affect the form and reactivity of Al, thereby altering the extent to which it interacts with biological membranes. These types of interactions have previously been observed in the toxicity data for other metals, which have been well described by the biotic ligand model (BLM) framework. In BLM applications to other metals (including cadmium, cobalt, copper, lead, nickel, silver, and zinc), these interactions have focused on dissolved metal. A review of Al toxicity data shows that concentrations of Al that cause toxicity are frequently in excess of solubility limitations. Aluminum solubility is strongly pH dependent, with a solubility minimum near pH 6 and increasing at both lower and higher pH values. For the Al BLM, the mechanistic framework has been extended to consider toxicity resulting from a combination of dissolved and precipitated Al to recognize the solubility limitation. The resulting model can effectively predict toxicity to fish, invertebrates, and algae over a wide range of conditions. Environ Toxicol Chem 2018;37:70-79. © 2017 SETAC.

Chronic toxicity of aluminum, at a pH of 6, to freshwater organisms: Empirical data for the development of international regulatory standards/criteria.

The chemistry, bioavailability, and toxicity of aluminum (Al) in the aquatic environment are complex and affected by a wide range of water quality characteristics (including pH, hardness, and dissolved organic carbon). Data gaps in Al ecotoxicology exist for pH ranges representative of natural surface waters (pH 6-8). To address these gaps, a series of chronic toxicity tests were performed at pH 6 with 8 freshwater species, including 2 fish (Pimephales promelas and Danio rerio), an oligochaete (Aeolosoma sp.), a rotifer (Brachionus calyciflorus), a snail (Lymnaea stagnalis), an amphipod (Hyalella azteca), a midge (Chironomus riparius), and an aquatic plant (Lemna minor). The 10% effect concentrations (EC10s) ranged from 98 µg total Al/L for D. rerio to 2175 µg total Al/L for L. minor. From these data and additional published data, species-sensitivity distributions (SSDs) were developed to derive concentrations protective of 95% of tested species (i.e., 50% lower confidence limit of a 5th percentile hazard concentration [HC5-50]). A generic HC5-50 (not adjusted for bioavailability) of 74.4 µg total Al/L was estimated using the SSD. An Al-specific biotic ligand model (BLM) was used to develop SSDs normalized for bioavailability based on site-specific water quality characteristics. Normalized HC5-50s ranged from 93.7 to 534 µg total Al/L for waters representing a range of European ecoregions, whereas a chronic HC5 calculated using US Environmental Protection Agency aquatic life criteria methods (i.e., a continuous criterion concentration [CCC]) was 125 µg total Al/L when normalized to Lake Superior water in the United States. The HC5-50 and CCC values for site-specific waters other than those in the present study can be obtained using the Al BLM. Environ Toxicol Chem 2018;37:36-48. © 2017 SETAC.