Development Of Water Quality Criteria Research Articles

Temperature and winter duration requirements for reproductive success in johnny darter Etheostoma nigrum in the South Platte River basin, Colorado

Abstract Changes in water temperature and its seasonal timing influences the physiological processes of many aquatic ectotherms. Wastewater treatment plants (WWTP) contribute to warmer and more consistent water temperatures in streams draining the North American Great Plains, particularly during winter months. Reduced variation in seasonal water temperature may adversely affect fishes that rely on temperature fluctuation or specific overwintering temperatures for reproductive cues. We used johnny darter Etheostoma nigrum (Family Percidae), a thermally sensitive species native to the South Platte River Basin, as a focal species to assess the effects of winter water temperature regulations in Colorado. Our objective was to evaluate the effects of winter stream temperature and winter duration on reproductive success of johnny darter in the laboratory to inform development of water quality criteria for the South Platte River Basin. Winter duration (60, 90 or 120 days) and temperature (4 or 12°C) were crossed in a factorial design of six treatments that simulated warmed effluent‐impacted streams as well as streams with a more natural thermal regime. We defined reproductive success in johnny darter by examining four reproductive endpoints: (1) spawning timing, (2) egg and larvae production, (3) egg success, and (4) egg development. Across the four endpoints, seven main response variables were measured: spawning initiation date, eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, egg‐to‐larva survival and days to hatch. Winter temperature and duration influenced spawning timing and egg development. Earlier spawning initiation dates were observed in fish exposed to 12°C winters and was associated with a higher number of days to hatch. Eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, and egg‐to‐larva survival were similar among winter treatments. Although the State of Colorado chronic winter water temperature standard of 12°C appears to be adequate for egg and larvae production in johnny darter, our results showed that fish exposed to the standard began spawning significantly earlier than fish exposed to 4°C winters. Evaluating reproductive output in the context of seasonal timing is valid because spawning timing has the potential to affect overall production and egg development, and consequently recruitment and population sustainability. Therefore, spawning timing should be considered when making management decisions and revising water temperature standards. The warming of streams and rivers from WWTP effluent is a global issue, especially in areas that are undergoing rapid urbanisation. Fishes are particularly sensitive to water temperature and many fishes worldwide are likely to be experiencing changes in important physiological processes, affecting both reproduction and survival. Our study indicates that reproductive timing could be influenced by stream warming and stresses the need for further studies on the influence of anthropogenic effects on stream warming.

Salinity-dependent aquatic life criteria of inorganic mercury in coastal water and its ecological risk assessment

Mercury (Hg) is one of the most toxic pollutants to aquatic organisms. The influence of salinity on Hg toxicity, an important factor restricting the development of global marine aquatic life criteria (ALC), is unclear. Therefore, mercury toxicity data were corrected based on salinity using the aggregate slope method, and the ALC values were derived. Short-term aquatic life criteria (SALC) and long-term aquatic life criteria (LALC) were derived using the species sensitivity distribution method based on Log-logistic, Log-normal, Burr III, Gumbel, and Weibull models. The hazard quotient (HQ) and joint probability curve (JPC) methods were used to evaluate the ecological risk of Hg in the coastal waters of China. The results showed that the SALC and LALC of Hg in the coastal waters of China were 2.21 and 0.54 μg/L. The toxicity data and salinity were positively correlated for Chordate and Arthropoda and negatively correlated for Mollusca. The SALC values increased by approximately 75%, with salinities ranging from 10 to 20 ppt. A slight peak in the SALC at mid-salinities was also observed. The ecological risk assessment of Hg in China's coastal waters showed that attention should be paid to Hg pollution in the Bohai Sea and East China Sea, especially the ecological risk of Hg to crustacean organisms. This study could promote the development of water quality criteria for coastal waters and provide a technical reference for mercury management in the coastal waters of China.

Data and Diversity in the Development of Acute Water Quality Criteria in the United States.

The US Environmental Protection Agency (USEPA) is responsible for the development of water quality criteria, regulatory standards that protect aquatic organisms from harmful chemical exposure. Although these criteria are intended to be broadly protective of aquatic life, the data used to derive criteria do not necessarily reflect the actual diversity of natural communities nor are they available for most chemicals. In addition, although the USEPA's current procedures emphasize using toxicity data with a certain minimum amount of biological diversity, the quantitative impact of such diversity on criteria is unclear. In the present study we assessed the changes to acute toxicity data over time, determined the prevalence of significant taxonomic differences in sensitivity, and investigated the effect of biological diversity on criteria. We found major gaps in existing toxicity data that we hypothesize have contributed to the absence of acute criteria for the majority of chemical pollutants. Taxonomic patterns of sensitivity in these data are abundant, although the resolution of the patterns is relatively poor. In addition, we found that the amount of biological diversity in a toxicity data set and the data set's taxonomic composition does not quantitatively affect criteria in most cases. Because the USEPA has published acute criteria for fewer than 20% of priority pollutants and the persistence of major gaps in toxicity data over the last 37 years, we recommend that the USEPA consider revisions to their water quality criteria guidelines that will expedite the criteria development process and advance the responsible management of pollutants in the aquatic environment. Environ Toxicol Chem 2022;41:1333-1343. © 2022 SETAC.

Acute and Chronic Effects of Clothianidin, Thiamethoxam and Methomyl on Chironomus dilutus

Organism tolerance thresholds for emerging contaminants are vital to the development of water quality criteria. Acute (96-h) and chronic (10-day) effects thresholds for neonicotinoid pesticides clothianidin and thiamethoxam, and the carbamate pesticide methomyl were developed for the midge Chironomus dilutus to support criteria development using the UC Davis Method. Median lethal concentrations (LC50s) were calculated for acute and chronic exposures, and the 25% inhibition concentrations (IC25) were calculated for the chronic exposures based on confirmed chemical concentrations. Clothianidin effect concentrations were 4.89 µg/L, 2.11 µg/L and 1.15 µg/L for 96-h LC50, 10-day LC50 and 10-day IC25, respectively. Similarly, thiamethoxam concentrations were 56.4 µg/L, 32.3 µg/L and 19.6 µg/L, and methomyl concentrations were 244 µg/L, 266 µg/L and 92.1 µg/L. Neonicotinoid effect concentrations compared favorably to previously published 96-h and 14-day LC50 concentrations, and methomyl effect concentrations were within the acute survival range reported for Chironomus species and other organisms.

Chironomidae (Midge) Sensitivities to Ammonia Using Multiple Endpoints in China and Australia for the Development of Water Quality Criteria for Freshwater River Systems in China.

Deriving water quality criteria (WQC) for aquatic risk assessment requires sufficient toxicity data, which can determine the accuracy of WQC. Given that toxicity data vary between test species and endpoints, there is a great need to compare such data to generate the most suitable data set for WQC derivation. In the present study, a series of 11 ammonia exposure bioassays were conducted on Chironomidae species in either China or Australia, with test species and test endpoints varied (2 Chironomus sp., enzymatic up to lethal endpoints, and no-observed-effect concentration up to median lethal concentration [LC50] as endpoint metrics). There were no statistically significant differences between toxicity results generated from China compared to Australia using Chironomus sp., indicating that published data on native species generated in different countries could be appropriate for inclusion in the development of local Chinese WQC. In addition, the Chironomidae larvae laboratory-based toxicity value (LC50 = 384.6 mg/L) was lower than that of the in situ field-based toxicity value (LC50 ≥ 451.2 mg/L) where sensitive life stages are used, and, specifically for C. riparius, endpoints linked to biochemical and gene expression effects could be as sensitive as or more sensitive than chronic endpoints, both of which were more sensitive than acute endpoints. These findings help in the development of WQC by demonstrating the suitability of inclusion of toxicity data from a range of sources, as well as adding to the overall pool of knowledge regarding sensitivity to ammonia which can be used in aquatic risk assessment. Environ Toxicol Chem 2021;40:2899-2911. © 2021 SETAC.

Freshwater quality criteria of four strobilurin fungicides: Interspecies correlation and toxic mechanism

Strobilurin fungicides are widely used pesticides in the world. They can have toxic effects not only to target organisms, but also to nontarget organisms. To assess their ecological risk, species sensitivity distributions (SSDs) are required for the development of water quality criteria (WQC). In this paper, the acute toxicity of four methoxyacrylate fungicides were experimentally determined and evaluated at 24, 48, 72 and 96 h for the species of Rana chensinensis and Limnodrilus hoffmeisteri, respectively. Acute and chronic HC5 (5% hazard concentration) values and WQC values were calculated from SSDs based on the toxicity values determined in this paper and compiled from literature. SSDs revealed that aquatic animals were relatively sensitive species and aquatic plants are insensitive species for the four fungicides. However, different orders of species sensitivity in the acute and chronic toxicity indicated that these four fungicides had different toxic mechanisms or mode of action (MOA) to different species. According to toxicity correlation and principal component analysis (PCA), the kresoxim-methyl toxicity was very close to trifloxystrobin as compared with others due to that they are neutral compounds with very similar physicochemical properties. Quantitative structure-activity relationship (QSAR) revealed that toxicity of strobilurin fungicides were dependent both on chemical hydrophobicity and hydrogen bond basicity. These two molecular descriptors reflect the bio-uptake process and interaction of compounds with target receptors in an organism. WQC values and interspecies correlation are valuable for assessing water quality and understanding toxic mechanisms to different species.

Application of the health risk assessment of acetochlor in the development of water quality criteria

Acetochlor is a widely used herbicide in agricultural production. Studies have shown that acetochlor has obvious environmental hormone effects, and long-term exposure may pose a threat to human health. To quantify the hazards of acetochlor in drinking water, a health risk assessment of acetochlor was conducted in major cities of China based on the data of acetochlor residue concentrations in drinking water. The approach of the Species Sensitivity Distributions (SSD) method is used to extrapolate from animal testing data to reflect worst case human toxicity. Results show that hazard quotients related to acetochlor residues in drinking water for different age groups range from 1.94 × 10−4 to 6.13 × 10−4, so, there are no indication of human risk. Compared to the total estimated hazard quotient from oral intake of acetochlor, the chronic exposure imputed to acetochlor residues in drinking water in China accounts for 0.4%. This paper recommends 0.02 mg/L to be the maximum acetochlor residue concentration level in drinking water and source water criteria.

Water quality criteria for the protection of human health of 15 toxic metals and their human risk in surface water, China.

In the absence of water quality criteria (WQC) support for the current water quality standard (WQS), systematic WQC studies have been carried out in recent years in China. WQC for the protection of human health is established to reflect long-term consumption safety of aquatic products and water. Human health WQC for 15 toxic metals and metalloids based on exposure factors of the Chinese population and 40 field bioaccumulation factors (BAFs) were developed and analyzed in this study. Moreover, age-specific (age 2-5, 6-8, 9-11, 12-14, 15-17, and adult) and region-specific (east, central and west China) WQC were analyzed to better understanding of the impact of specific parameter values on WQC. Human health WQC with consumption of fishes and water, consumption of fishes only, and consumption of water only were derived separately. WQC with consumption of water and organism for Hg, Cd, As, Sb, Se, Zn, Co, Cu, Ni, Pb, Mn, Sn, Ba, and Sr were 0.0264, 0.710, 0.827, 3.48, 22.1, 25.7, 32.2, 32.9, 35.5, 41.8, 72.1, 97.1, 206 and 2.20×103μg/L, and were 13.3 and 6.67×103μg/L for Cr(VI) and Cr(III) with consumption of water only. Comparison of age-specific and region-specific WQC showed that the protection for a specific population should be considered in the development of WQC and WQS, as well as cancer effect for carcinogenic metals. Health risk analysis showed that Cd, Cu, Zn, As, Hg and Mn average concentrations in 7, 5, 9, 22, 11 and 5 provinces exceeded the WQC values with consumption of water and aquatic product, showing potential long-term health risk (HQ≥1) to the local population. Therefore, health risks posed by these metals from dietary intake related to surface water should be paying more attention.

Making the Biotic Ligand Model kinetic, easier to develop, and more flexible for deriving water quality criteria

In aquatic environments, the ecological risks posed by metals are greatly affected by water chemistry, thereby creating challenges for water quality management. Biotic ligand models (BLMs) have become the most widely used tools to interpret and predict water chemistry effects. Traditional BLM development methods require a large number of toxicity tests and organisms, and model predictions are limited to certain toxicity statistics (e.g., 48-h median effective concentration, 48-h EC50), to which the models were calibrated. To address these limitations, we propose a new method to develop BLMs by integrating them into the toxicokinetic-toxicodynamic (TK-TD) framework. Metal bioaccumulation was predicted from metal exposure and water chemistry using the BLM-type toxicokinetics, whilst metal toxicity was predicted from metal bioaccumulation using the toxicodynamics. Using the new method, we developed a kinetic BLM of cadmium for Daphnia magna with only six toxicity tests and 1540 daphnids; this represents a 60−80% reduction compared to the traditional methods. The model was validated in the presence of commercial dissolved organic matter (DOM) and in natural waters sampled from 12 lakes. The kinetic BLM was able to accurately simulate the protective effects of the commercial DOM by employing the Stockholm humic model, whilst the complexation capabilities of some natural DOM were overestimated. We further used the model to predict Cd EC50 and no-effect concentrations for different waters, generating predictions close to the effect concentrations reported in the literature. Overall, our method requires fewer resources and presents an easier approach to develop BLMs; the kinetic BLM is more flexible and can serve as a useful tool for developing water quality criteria.

Development of water quality criteria for arsenic to protect aquatic life based on species sensitivity distribution.

Arsenic is a hazardous environmental pollutant widely distributed globally. Arsenic toxicity is well known and it is regulated by many countries in terms of managing water quality and protecting aquatic organisms. Unfortunately, water quality criterion (WQC) to protect aquatic organisms has not been introduced in Korea yet. Thus, it is of great importance and necessity to introduce WQC to protect aquatic organisms from arsenic, as WQC play a significant role in protecting aquatic ecosystems from pollutants. Therefore, the purpose of this study is to derive arsenic water quality criterion for aquatic life in Korea. Arsenic acute toxicity tests were performed with 10 Korean native aquatic species, which belong to 7 different taxonomic groups. Based on the results of acute toxicity test and additional toxicity data from literature, the species sensitivity distribution (SSD) method was used in ecological risk assessment. The arsenic concentration of 95% protection level for aquatic life was 0.229 mg L-1 in this study. An assessment factor 3 and a background concentration 0.0004 mg L-1 were applied to the concentration value in consideration of the uncertainty of the data and the amount of arsenic natural generation. Consequently, the WQC value derived for arsenic was found to be 0.077 mg L-1. These results will serve as reference values to establish water quality criterion for the protection of aquatic life in Korea.

Screening and prioritization of chemical hazards for deriving human health ambient water quality criteria in China

A two-step screening and prioritization approach of the chemical hazard to derive water quality criteria for the protection of human health in China was developed. Seventy-five potential candidate chemicals were identified in Step 1, and then were screened and scored in Step 2, based on three characteristics: detection frequency, toxicity, and human exposure. Substances with a score above 900 were considered the proposed candidates. Using this approach, 18 chemicals were successfully identified, and ranked in the following order: zinc, di(2-ethylhexyl) phthalate, dibutyl phthalate, trichloromethane, arsenic, cadmium, gamma-hexachlorocyclohexane (HCH), copper, benzo[a]pyrene, lead, benzene, fluoranthene, mercury, beta-HCH, anthracene, p,p'-DDT, and alpha-HCH. Additional chemical contaminants, including thallium, antimony, chromium (VI), and nitrobenzene, suggested by the Ministry of Environmental Protection for consideration during the development of the water quality criteria, brought the final number of proposed candidates to 22. These candidates belong to different groups: nine metals, four polycyclic aromatic hydrocarbons (PAHs), four pesticides, two phthalic acid esters, one halogenated hydrocarbon, and two monocyclic aromatic hydrocarbons. This list of pollutants will provide guidance when selecting the substances to be considered during the development of water quality criteria for the protection of human health in China.

Development of Water Quality Criteria for Fenneropenaeus indicus Against Arsenic by Flow-through System in the Central West Coast of India at Goa

Development of Water Quality Criteria for <i>Fenneropenaeus indicus</i> Against Arsenic by Flow-through System in the Central West Coast of India at Goa

Development of water quality criteria of ammonia for protecting aquatic life in freshwater using species sensitivity distribution method

Ammonia is deemed one of the most important pollutants in the freshwater environment because of its highly toxic nature and ubiquity in surface water. This study thus aims to derive the criteria for ammonia in freshwater to protect aquatic life because there are no water quality criteria for ammonia in Korea. Short-term lethal tests were conducted to perform the species sensitivity distribution (SSD) method. This method is widely used in ecological risk assessment to determine the chemical concentrations to protect aquatic species. Based on the species sensitivity distribution method using Korean indigenous aquatic biota, the hazardous concentration for 5% of biological species (HC5) value calculated in this study was 44mg/L as total ammonia nitrogen (TAN). The value of the assessment factor was set at 2. Consequently, the criteria for ammonia were derived as 22mg/L at pH7 and 20°C. When the derived value was applied to the monitoring data nationwide, 0.51%, 0.09%, 0.18%, 0.20%, and 0.35% of the monitoring sites in Han River, Nakdong River, Geum River, Youngsan River, and lakes throughout the nation, respectively, exceeded this criteria. The Ministry of Environment in Korea has been considering introducing water quality standard of ammonia for protecting aquatic life. Therefore, our results can provide the basis for introducing the ammonia standard in Korea.

Evaluation of joint effects of cyprodinil and kresoxim-methyl on zebrafish, Danio rerio

Aquatic organisms are usually exposed to a mixture of pesticides instead of individual chemicals. However, risk assessment of pesticides is traditionally based on toxicity data of individual compounds. In this study, we aimed to examine the joint toxicity of two fungicides cyprodinil (CYP) and kresoxim-methyl (KRM) to zebrafish (Danio rerio) using a systematic experimental approach. Results from 96-h semi-static test indicated that the LC50 values of KRM to D. rerio at multiple life stages (embryonic, larval, juvenile and adult stages) ranged from 0.034 (0.015–0.073) to 0.61 (0.39–0.83) mg a.i. L−1, which were higher than those of CYP ranging from 1.05 (0.88–1.52) to 4.42 (3.24–6.02) mg a.i. L−1. Pesticide mixtures of CYP and KRM exhibited synergistic effect on embryonic zebrafish. The activities of carboxylesterase (CarE) and cytochrome P450 (Cyp450) were significantly altered in most of the individual and combined exposures compared with the control group. The expressions of seven genes (Mnsod, cyp17, crhr 2, crh, gnrhr 4, gnrhr 1 and hmgrb) were significantly altered upon exposure to combined pesticides compared with their individual pesticides. Collectively, these findings suggested joint effects should be considered in the risk assessment of pesticides and development of water quality criteria for the protection of aquatic environment.

An Integrative Methodological Framework for Setting Environmental Criteria: Evaluation of Public Preferences

The main objective of the present study is to introduce public preferences into the development of water-quality criteria that effectively balance environmental concerns and socioeconomic values. A novel feature of our research is the analysis of subjective public judgments with Bayesian inference techniques, which are ultimately connected with environmental conditions through mathematical modeling. Our case study is the Bay of Quinte, Ontario, Canada; an embayment at the northeastern end of Lake Ontario with a long history of eutrophication, characterized by frequent and spatially extensive algal blooms and predominance of toxic cyanobacteria. In this study, we present a major survey to determine public opinions on water quality in the area. Our survey was conducted among a random sample of 1527 local residents and tourists during the summers of 2013 and 2014. The key findings of the survey were: (i) fishing (29%) and beauty of the area (20%) were the main reasons for public use of the Bay of Quinte; (ii) among different water-quality problems, the public chose the algal scums (26%) and the integrity of fish populations (22%) as the main issues; (iii) only 30% of the returning visitors noticed that the clarity of water is better now relative to the prevailing conditions five years ago; (iv) there is a dramatic change in public sentiment between the beginning and end of the summer season; and (v) a substantial portion of local residents were willing to contribute financially towards the restoration of the bay. Our modeling analysis suggests that the likelihood of public satisfaction increases significantly when the total phosphorus concentrations fall below the critical levels of 20–25 μg L−1, which however is a difficult target to achieve even under significantly reduced nutrient-loading conditions. Other biological variables such as chlorophyll a concentrations, harmful algal blooms, and toxin levels in locations frequently used by the public appear to more closely influence their satisfaction level.

A flow-chart for developing water quality criteria from two field-based methods

Field-based methods increase relevance and realism when setting water quality criteria. They also pose challenges. To enable a consistent process, a flow chart was developed for choosing between two field-based methods and then selecting among candidate results. The two field-based methods estimated specific conductivity (SC) levels likely to extirpate 5% of benthic invertebrate genera: an extirpation concentration distribution (XCD) method and a background-to-criterion (B-C) model developed by the U.S. Environmental Protection Agency. The B-C model is a least squares regression of the 5th centile of XCD (XCD05) values against estimates of background SC. Selection of an XCD05 from the flowchart is determined by characteristics of the paired chemical and biological data sets and method for estimating the XCD05 values. Confidence in these example SC XCD05 values is based on the size of the data sets and ecoregional SC disturbance. The level of ecoregional SC disturbance was judged by comparing the background SC (the 25th centile of the data set used to calculate a XCD05) and an estimate of natural base-flow SC modeled from geophysical attributes in the region. The B-C approach appears to be a viable option for estimating a SC benchmark with inexpensive estimates of SC background while the XCD method is used when the data are abundant. To illustrate the use of the flow chart, example SC XCD05 values were calculated for 63 of 86 Level III ecoregions in the conterminous United States of America.

Validation of a biotic ligand model on site-specific copper toxicity to Daphnia magna in the Yeongsan River, Korea

The objective of this study was to determine whether the water effect ratio (WER) or biotic ligand model (BLM) could be applied to efficiently develop water quality criteria (WQC) in Korea. Samples were collected from 12 specific sites along the Yeongsan River (YSR), Korea, including two sewage treatment plants and one estuary lake. A copper toxicity test using Daphnia magna was performed to determine the WER and to compare to the BLM prediction. The results of the WER from YSR samples also indicated significantly different copper toxicities in all sites. The model-based predictions showed that effluent and estuary waters had significantly different properties in regard to their ability to be used to investigate water characteristics and copper toxicity. It was supposed that the slight water characteristics changes, such as pH, DOC, hardness, conductivity, among others, influence copper toxicity, and these variable effects on copper toxicity interacted with the water composition. The 38% prediction was outside of the validation range by a factor of two in all sites, showing a poor predictive ability, especially in STPs and streams adjacent to the estuary, while the measured toxicity was more stable. The samples that ranged from pH 7.3–7.7 generated stable predictions, while other samples, including those with lower and the higher pH values, led to more unstable predictions. The results also showed that the toxicity of Cu in sample waters to D. magna was closely proportional to the amounts of acidity, including the carboxylic and phenolic groups, as well as the DOC concentrations. Consequently, the acceptable prediction of metal toxicity in various water samples needs the site-specific results considering the water characteristics such as pH and DOC properties particularly in STPs and estuary regions.

Modernizing Water Quality Criteria in the United States: A Need to Expand the Definition of Acceptable Data.

The development of water quality criteria (WQC) for the protection of aquatic life is a fundamental component of the Clean Water Act-the primary US legislation responsible for protecting aquatic ecosystems from pollution. Water quality criteria define acceptable levels of contamination in the environment and thus play an important role in society. Rules for how science is used to develop WQC were created in 1985. Most rely on only data and knowledge obtained through a single methodology, the single-species laboratory toxicity test. Since 1985, understanding of the fate and effects of environmental contaminants has advanced markedly from multiple perspectives and disciplines. However, many of these advances are routinely discarded in WQC development because they do not adhere to data limits imposed by the 1985 guidelines. The present Focus article outlines how multiple lines of inquiry have played important roles in improving understanding of the ecological implications of environmental contaminants. The authors focus on gains in understanding that would not have been possible through traditional toxicity bioassays alone and argue that more robust scientific understanding can be used to modernize WQC development. In particular, the present article highlights ways to increase the relevance of toxicity testing (at different spatiotemporal scales) and incorporate all relevant lines of evidence into WQC modernization. Environ Toxicol Chem 2017;36:285-291. © 2017 SETAC.

Combined toxicity of arsenite and dimethylarsenic acid on the freshwater diatom Nitzschia palea.

The toxicity and bioavailability of single arsenic species have been widely investigated, however, the biological effects of mixed arsenic species co-existing in natural waters still remain unknown. The objective of this work was to discern the adverse effects of combined arsenite (As(III)) and dimethylarsenic acid (DMA) on diatom Nitzschia palea. The combined ecotoxicity of As(III) and DMA on N. palea was observed to be time-dependent and showed dose-effect relation. The toxicity of DMA and As(III) mixture was higher than individual DMA or As(III) when the As(III) concentration was in the range of 0.085-0.316 mg L-1. As the As(III) concentration increased from 0.487 to 0.858 mg L-1, the antagonistic effect was found, which could be due to the higher thiols contents in the thiol-containing proteins (e.g., frustulins, silaffins and other glycoproteins). The content of malondialdehyde (MDA) in the treatment of mixed arsenic species was found to be at the same level compared to the As-free control after 72 h of exposure, indicating that the co-toxicity of As(III) and DMA on diatom frustules was not significant. Furthermore, the increase of frustule formation rate in the mixture of EC50 As(III)-EC10 DMA at 72 h exposure time indicated that the damaged diatom cell walls was likely repaired gradually. The results from this study suggested that the effects of co-existed arsenic species were concentration-specific and should be considered in the risk assessment of arsenic and development of water quality criteria for the protection of aquatic ecosystems.

Acute sensitivity of a broad range of freshwater mussels to chemicals with different modes of toxic action.

Freshwater mussels, one of the most imperiled groups of animals in the world, are generally underrepresented in toxicity databases used for the development of ambient water quality criteria and other environmental guidance values. Acute 96-h toxicity tests were conducted to evaluate the sensitivity of 5 species of juvenile mussels from 2 families and 4 tribes to 10 chemicals (ammonia, metals, major ions, and organic compounds) and to screen 10 additional chemicals (mainly organic compounds) with a commonly tested mussel species, fatmucket (Lampsilis siliquoidea). In the multi-species study, median effect concentrations (EC50s) among the 5 species differed by a factor of ≤2 for chloride, potassium, sulfate, and zinc; a factor of ≤5 for ammonia, chromium, copper, and nickel; and factors of 6 and 12 for metolachlor and alachlor, respectively, indicating that mussels representing different families or tribes had similar sensitivity to most of the tested chemicals, regardless of modes of action. There was a strong linear relationship between EC50s for fatmucket and the other 4 mussel species across the 10 chemicals (r2 = 0.97, slope close to 1.0), indicating that fatmucket was similar to other mussel species; thus, this commonly tested species can be a good surrogate for protecting other mussels in acute exposures. The sensitivity of juvenile fatmucket among different populations or cultured from larvae of wild adults and captive-cultured adults was also similar in acute exposures to copper or chloride, indicating captive-cultured adult mussels can reliably be used to reproduce juveniles for toxicity testing. In compiled databases for all freshwater species, 1 or more mussel species were among the 4 most sensitive species for alachlor, ammonia, chloride, potassium, sulfate, copper, nickel, and zinc; therefore, the development of water quality criteria and other environmental guidance values for these chemicals should reflect the sensitivity of mussels. In contrast, the EC50s of fatmucket tested in the single-species study were in the high percentiles (>75th) of species sensitivity distributions for 6 of 7 organic chemicals, indicating mussels might be relatively insensitive to organic chemicals in acute exposures. Environ Toxicol Chem 2017;36:786-796. Published 2016 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.