Water Effect Ratio Research Articles

Bioavailability and Toxicity Models of Copper to Freshwater Life: The State of Regulatory Science.

Efforts to incorporate bioavailability adjustments into regulatory water quality criteria in the United States have included four major procedures: hardness-based single-linear regression equations, water-effect ratios (WERs), biotic ligand models (BLMs), and multiple-linear regression models (MLRs) that use dissolved organic carbon, hardness, and pH. The performance of each with copper (Cu) is evaluated, emphasizing the relative performance of hardness-based versus MLR-based criteria equations. The WER approach was shown to be inherently highly biased. The hardness-based model is in widest use, and the MLR approach is the US Environmental Protection Agency's (USEPA's) present recommended approach for developing aquatic life criteria for metals. The performance of criteria versions was evaluated with numerous toxicity datasets that were independent of those used to develop the MLR models, including olfactory and behavioral toxicity, and field and ecosystem studies. Within the range of water conditions used to develop the Cu MLR criteria equations, the MLR performed well in terms of predicting toxicity and protecting sensitive species and ecosystems. In soft waters, the MLR outperformed both the BLM and hardness models. In atypical waters with pH <5.5 or >9, neither the MLR nor BLM predictions were reliable, suggesting that site-specific testing would be needed to determine reliable Cu criteria for such settings. The hardness-based criteria performed poorly with all toxicity datasets, showing no or weak ability to predict observed toxicity. In natural waters, MLR and BLM criteria versions were strongly correlated. In contrast, the hardness-criteria version was often out of phase with the MLR and, depending on waterbody and season, could be either strongly overprotective or underprotective. The MLR-based USEPA-style chronic criterion appears to be more generally protective of ecosystems than other models. Environ Toxicol Chem 2023;42:2529-2563. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

Water-effect ratio of copper and its application on setting site-specific water quality criteria for protecting marine ecosystems of Hong Kong.

Generic water quality criteria (WQC) of a chemical are usually set based on results generated from toxicity tests which were conducted using standard laboratory water with well-controlled physiochemical properties. However, in natural aquatic environments, physiochemical characteristics, such as salinity, total suspended solid, total organic carbon and the co-existence of chemical contaminants, often vary spatially and temporally. These parameters can, in turn, alter the bioavailability of target chemicals and, thus, influence their toxicity to marine organisms. To account for site specificity, the US Environmental Protection Agency's water-effect ratio (WER=site water-LC50/laboratory water-LC50) procedure can be applied to derive site-specific WQC. Most past studies, however, were conducted for freshwater systems. Here, for the first time, the WER of copper (Cu) was determined for three marine water control zones (WCZs) in Hong Kong: Victoria Harbour, Deep Bay and Southern WCZs. Samples of water were collected from three locations within each WCZ, while acute toxicities to the marine diatom Skeletonema costatum, intertidal copepod Tigriopus japonicus and larvae of marine medaka Oryzias melastigma were determined in site or laboratory (artificial seawater) waters. Results of this study showed that conservative final WER relative coefficients for Cu ranged from 0.57 to 0.73 for the three WCZs, and water from some locations caused >30% mortality in the fish larvae in the controls (without Cu addition). These results suggested that current generic WQC for Cu are likely under-protective for marine organisms in the three areas, and it should be tightened by multiplying it with site-specific WER to offer better protection to marine biodiversity and integrity of the ecosystem.

Site-specific water quality criteria for aquatic ecosystems: A case study of pentachlorophenol for Tai Lake, China

Given the widely varying types of aquatic ecosystems and bioavailability of chemicals, it is important to develop site-specific water quality criteria (WQC) to ensure criteria are neither over- nor under-protective. In the study, using pentachlorophenol (PCP) as an example, several approaches to derive site-specific WQC were investigated, including the conventional species sensitivity distribution (SSD), weighted SSD based on the proportion of each trophic level, and water effect ratio (WER) method. When corrected to a pH of 7.8, the conventional SSD approach resulted in criteria maximum concentration (CMC) and criteria continuous concentration (CCC) of 18.11 and 1.74 μg/L, respectively. If SSD was weighted according to the current species composition in Tai Lake, the CMC and CCC were 32.81 and 4.48 μg/L, respectively. However, available data suggest that many sensitive species inhabiting Tai Lake during 1980s were disappeared. Considering the species composition of the healthier ecosystem in 1980s, the CMC and CCC were 10.99 and 0.38 μg/L, respectively, which provide more protective water quality standards. Water effect ratio (WER) was further used to correct for co-occurrence of other toxicants and factors affecting bioavailability of PCP. A final WER of 4.72 was applied to adjust the criteria derived by using the weighted SSD for the 1980s aquatic community, and the final CMC and CCC obtained were 51.87 and 1.79 μg/L, respectively, at a pH of 7.8. Water quality criteria derived using the 1980s species composition and adjusted with WER were deemed the most appropriate WQC for water management and aquatic life protection. Merits of the various approaches for developing WQC for protection of aquatic species were discussed.

Development of a regression model to predict copper toxicity to Daphnia magna and site-specific copper criteria across multiple surface-water drainages in an arid landscape.

The water effect ratio (WER) procedure developed by the US Environmental Protection Agency is commonly used to derive site-specific criteria for point-source metal discharges into perennial waters. However, experience is limited with this method in the ephemeral and intermittent systems typical of arid climates. The present study presents a regression model to develop WER-based site-specific criteria for a network of ephemeral and intermittent streams influenced by nonpoint sources of Cu in the southwestern United States. Acute (48-h) Cu toxicity tests were performed concurrently with Daphnia magna in site water samples and hardness-matched laboratory waters. Median effect concentrations (EC50s) for Cu in site water samples (n=17) varied by more than 12-fold, and the range of calculated WER values was similar. Statistically significant (α=0.05) univariate predictors of site-specific Cu toxicity included (in sequence of decreasing significance) dissolved organic carbon (DOC), hardness/alkalinity ratio, alkalinity, K, and total dissolved solids. A multiple-regression model developed from a combination of DOC and alkalinity explained 85% of the toxicity variability in site water samples, providing a strong predictive tool that can be used in the WER framework when site-specific criteria values are derived. The biotic ligand model (BLM) underpredicted toxicity in site waters by more than 2-fold. Adjustments to the default BLM parameters improved the model's performance but did not provide a better predictive tool compared with the regression model developed from DOC and alkalinity.

Acute toxicity of copper, lead, cadmium, and zinc to early life stages of white sturgeon (Acipenser transmontanus) in laboratory and Columbia River water.

Populations of white sturgeon (Acipenser transmontanus) are in decline in North America. This is attributed, primarily, to poor recruitment, and white sturgeon are listed as threatened or endangered in several parts of British Columbia, Canada, and the United States. In the Columbia River, effects of metals have been hypothesized as possible contributing factors. Previous work has demonstrated that early life stage white sturgeon are particularly sensitive to certain metals, and concerns over the level of protectiveness of water quality standards are justified. Here we report results from acute (96-h) toxicity tests for copper (Cu), cadmium (Cd), zinc (Zn), and lead (Pb) from parallel studies that were conducted in laboratory water and in the field with Columbia River water. Water effect ratios (WERs) and sensitivity parameters (i.e., median lethal accumulations, or LA50s) were calculated to assess relative bioavailability of these metals in Columbia River water compared to laboratory water, and to elucidate possible differences in sensitivity of early life stage white sturgeon to the same concentrations of metals when tested in the different water sources. For Cu and Pb, white sturgeon toxicity tests were initiated at two life stages, 8 and 40 days post-hatch (dph), and median lethal concentrations (LC50s) ranged between 9-25 μg Cu/L and 177-1,556 μg Pb/L. LC50s for 8 dph white sturgeon exposed to Cd in laboratory water and river water were 14.5 and 72 μg/L, respectively. Exposure of 8 dph white sturgeon to Zn in laboratory and river water resulted in LC50s of 150 and 625 μg/L, respectively. Threshold concentrations were consistently less in laboratory water compared with river water, and as a result, WERs were greater than 1 in all cases. In addition, LA50s were consistently greater in river water exposures compared with laboratory exposures in all paired tests. These results, in combination with results from the biotic ligand model, suggest that the observed differences in toxicity between river water exposures and laboratory water exposures were not entirely due to differences in water quality and metal bioavailability but rather in combination with differences in fish sensitivity. It is hypothesized that differences in concentrations of calcium in the different water sources might have resulted in differences in acquired sensitivity of sturgeon to metals. Canadian water quality guidelines, US national criteria for the protection of aquatic life, and water quality criteria for the state of Washington were less than LC50 values for all metals and life stages tested in laboratory and Columbia River water. With the exception, however, that 40 dph white sturgeon exposed to Cu in laboratory water resulted in threshold values that bordered US national criteria and criteria for the state of Washington.

Predict Metal Toxicity and Water Quality Criteria of Different Types of Water Into Taihu Lake, China Using Biotic Ligand Model

The Biotic Ligand Model (BLM) is an important tool in predicting acute toxicity of metal to aquatic organisms. This study used the BLM to predict acute toxicity (LC50, the lethal concentration for 50% of test organisms) of Cu and Zn to Daphnia magna, and to predict water quality criteria (WQC) for different types of water (river water, treated and untreated sewage, and rainwater) into Taihu Lake, an important drinking water source for millions of population. Their effects of metal toxicity on Taihu Lake were also explored. The results showed that Taihu Lake water had a relatively higher LC50 (Cu) value (1.38 ± 0.60 mg/L) than other types of water except for untreated sewage (2.25 ± 2.13 mg/L). Of these types of water, predicted LC50 value of Cu followed the order of untreated sewage > rainwater > Taihu Lake > river water > sewage effluent. In addition, acute toxicity of Zn followed the order of river water > rainwater > Taihu Lake > sewage effluent > untreated sewage. Comparison of the predicted WQC values with the Chinese National Water Quality Standard of Surface waters indicated that the existing standard for copper might over-protect the aquatic organisms in Taihu Lake. The correlation analysis showed that increased DOC (dissolved organic carbon) concentration resulted in a higher LC50 value due to complexation between metal and organic matters, which reduced Cu toxicity. A significant positive relationship existed between cation concentration and predicted LC50 value, also indicating that cation concentration may reduce metaltoxicity. The work provided basic data for the study of water effect ratio (WER) and for the establishment of China’s own water quality critieria based on Chinese water environmental conditions.

Using the Biotic Ligand Model, Water Effect Ratio, and Translator for Site-Specific Copper Criteria to Update Effluent Limits at a Wastewater Treatment Plant

Using the Biotic Ligand Model, Water Effect Ratio, and Translator for Site-Specific Copper Criteria to Update Effluent Limits at a Wastewater Treatment PlantUsing EPA guidance, a study of copper in the Weber River showed that effluent limits for copper at a municipal wastewater treatment plant could be revised upward. A copper translator of 0.53 was derived, and site specific acute and chronic criteria for copper were derived based on the biotic ligand model (BLM) and the water effect ratios (WER). However, the WERs would result in adjusted criteria...Author(s)Scott TobiasonPhil HeckSharonne ParkKaren TobiasonSourceProceedings of the Water Environment FederationSubjectSession 93 - NPDES Permit Compliance Options for Metals: Striving for EconomyDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2009ISSN1938-6478SICI1938-6478(20090101)2009:9L.6325;1-DOI10.2175/193864709793956914Volume / Issue2009 / 9Content sourceWEFTECFirst / last page(s)6325 - 6344Copyright2009Word count161Subject keywordsWastewaterCopperBiotic Ligand ModelWater Effect RatioTranslatorCriteria

A biotic ligand model-based toxicodynamic approach to predict arsenic toxicity to tilapia gills in cultural ponds

Farming of tilapia Oreochromis mossambicus is an important aquacultural activity in Taiwan. Due to the elevated arsenic (As) concentration in pond water, it is important to assess the bioavailability and toxicity of As to tilapia for protection of aquatic life and human health. In the present study, we developed a biotic ligand model (BLM)-based toxicodynamic approach to dynamically predict both acute and chronic effective concentrations of As to tilapia in two tilapia farms located at Pudai and Chiangchun counties in southwestern Taiwan. Parameters revealed in the mechanistic model were obtained by fitting this model to the toxicokinetic and toxicodynamic data from our previous laboratory experiments. Based on our extended BLM concepts, the site-specific water effect ratios and ambient water quality criteria can be determined with known water chemistry. The proposed methodology was capable of bridging the gap between laboratory toxicity bioassays and field investigations. With respect to risk assessments, our research may also provide an useful means of generating and adjusting the site-specific ambient water quality criteria.

Effects of Water Quality Parameters on Boron Toxicity to Ceriodaphnia dubia

The potential modifying effects of certain water quality parameters (e.g., hardness, alkalinity, pH) on the acute toxicity of boron were tested using a freshwater cladoceran, Ceriodaphnia dubia. By comparison, boron acute toxicity was less affected by water quality characteristics than some metals (e.g., copper and silver). Increases in alkalinity over the range tested did not alter toxicity. Increases in water hardness appeared to have an effect with very hard waters (>500 mg/L as CaCO(3)). Decreased pH had a limited influence on boron acute toxicity in laboratory waters. Increasing chloride concentration did not provide a protective effect. Boron acute toxicity was unaffected by sodium concentrations. Median acute lethal concentrations (LC(50)) in natural water samples collected from three field sites were all greater than in reconstituted laboratory waters that matched natural waters in all respects except for dissolved organic carbon. Water effect ratios in these waters ranged from 1.4 to 1.8. In subsequent studies using a commercially available source of natural organic matter, acute toxicity decreased with increased dissolved organic carbon, suggesting, along with the natural water studies, that dissolved organic carbon should be considered further as a modifier of boron toxicity in natural waters where it exceeds 2 mg/L.

Biotic Ligand Model estimation of copper bioavailability and toxicity in the Yacyretá Reservoir on the Paraná River

AbstractThe Biotic Ligand Model (BLM) was used to assess copper bioavailability, toxicity and water‐effect ratios (WER) for the Yacyretá Reservoir on the Paraná River. Copper in the Yacyretá Reservoir watershed is ubiquitous (median dissolved concentration = 4.4 µg L−1), being contributed mainly by non‐point surface run‐off from citrus fields and urban sewage point sources. BLM simulations indicated that copper bioavailability is negligible, as almost 100% of the dissolved copper is complexed by dissolved organic carbon (DOC). Copper bioavailability in the Paraná River, which has a mean hardness concentration of 16.5 mg CaCO3 L−1, is controlled by the presence of humic substances (≈60% of humic acids) in DOC. BLM estimates of acute toxicity for a cyprinid fish species were of the same order of magnitude as those corresponding to daphnids (EC50 = 63.54 µg L−1). However, zooplankton species were chosen to represent the aquatic biota for water quality regulatory purposes because of their slightly higher sensitivity to copper toxicity. Based on the corresponding minimum WER (14.6) for copper in Yacyretá Reservoir on the Paraná River, a site‐specific copper criterion for the protection of the aquatic biota of 24 µg L−1 was derived. All measured dissolved copper concentrations for Yacyretá Reservoir during the 2001–2002 period were in compliance with this criterion. Development and application of the BLM provides a useful tool for managing metal loads in reservoir environments.

Speciation, behavior, and bioavailability of copper downstream of a mine‐impacted lake

A combination of Cu speciation analysis and toxicity testwork was conducted to assess the behavior, speciation, and bioavailability of Cu in a stream system rich in dissolved organic carbon (DOC) downstream of a mine-impacted lake (East Lake, ON, Canada). Elevated levels (approximately 50 microg/L) of Cu exist in the lake due to the release of dissolved Cu to the water column from underlying sediments. Most of the Cu present in East Lake and downstream is present as filterable species that represent 74 to 100% of the total. Measurements of labile Cu as measured by diffusive gradients in thin films (DGT) suggest that most of the Cu is unavailable to aquatic biota. The DGT results indicate that 9 to 24% of Cu within the receiving environment is biologically available. Decreases in the labile Cu fraction with distance downstream of East Lake correlate well with increases in the concentration of DOC (r(2) = 0.79-0.95), presumably due to the progressive importance of Cu-organic complexes. The relationship between filterable Cu and SO(4)(2-) downstream of East Lake was linear (r(2) = 0.99) for all sampling periods, suggesting that decreases in filterable Cu concentration downstream of East Lake could be attributed solely to dilution (i.e., conservative behavior). Variations in the filterable Cu concentration resulting in 50% mortality (LC50 = 96-203 microg/L) and the concentration resulting in an inhibition of reproduction by 25% (IC25 = 75-156 microg/L) with respect to Ceriodaphnia dubia (7-d incubation) in Cu-spiked solutions could be explained by differences in labile-Cu concentrations as determined by DGT. The considerable complexation capacity afforded by lake and stream waters can be attributed to complexation of Cu with abundant DOC (7-17 mg/L). The relevance of the toxicity data to water-effect ratio testwork, and the associated development of site-specific water quality objectives, are discussed.

Application of the biotic ligand model for regulatory purposes to selected rivers in Argentina with extreme water‐quality characteristics

The biotic ligand model (BLM) was used to assess copper (Cu) bioavailability, toxicity, water-effect ratios (WER), and Cu site-specific water-quality criteria (SSWQC) in the Matanza River and Pilcomayo River, Argentina, where anthropogenic inputs and natural phenomena have led to high concentrations of chemical species capable of reducing metal toxicity: Sodium, total hardness, alkalinity, dissolved organic carbon, and suspended particulate matter (SPM), as well as other metals. The purpose of this study was to evaluate the feasibility of developing Cu-SSWQC from a modified scenario of the BLM-Monte-Carlo method model. The response of the BLM model in these rivers, with water quality near its application boundary conditions, was evaluated during the 2003 to 2004 hydrological cycle. Cu toxicity tests were conducted with Daphnia magna as the test organism. The BLM (Version ap08) toxicity estimates for D. magna were within a factor of 2 of the line of perfect agreement with toxicity test results, although highly variable relevant water-quality parameters showed that mean estimates were more than 2 times the mean 50% effective concentration (EC50) derived from the corresponding toxicity tests. Suspended particulate matter was an important sink for Cu added to unfiltered water of the Pilcomayo River, but it also exerted some toxic effect. Minimums WER, estimated with a modified scenario of the BLM-MONTE, ranged from 1.5 (Pilcomayo River, at Misión La Paz) up to 11 (Matanza River, at Route 3). The corresponding Cu-SSWQC values were 30 and 105 microg/L, respectively.

Science, policy, and trends of metals risk assessment at EPA: How understanding metals bioavailability has changed metals risk assessment at US EPA

The US Environmental Protection Agency (EPA) and the Office of Water have made significant changes in the approaches taken to assessing metals in the aquatic environment. Over the last 20 years, the Office of Water has progressed through a variety of metals assessment tools from total recoverable metal to the biotic ligand model. These changes were initially driven by the recognition that the total metals criteria were out of date and that emerging science would make it possible to address bioavailability more thoroughly. More recent drivers are expectations that the agency ensure the criteria are protective of endangered species and that the agency can bring the best available science to conducting total maximum daily loads (TMDLs) for waters not meeting uses because of metal contamination. Changes have included: moving from total recoverable metals concentration to dissolved metals and the development of dissolved metal to total metal translator guidance, the development of water effect ratios (WERs) guidance, and most recently incorporation of the biotic ligand model (BLM) into criteria derivation for aquatic life protection (USEPA, 2007a. Aquatic Life Ambient Freshwater Quality Criteria-Copper 2007 Revision. EPA-822-R-07-001. http://www.epa.gov/waterscience/criteria/copper/index.htm.). On March 8, 2007, the agency published its Framework for Metals Risk Assessment (USEPA, 2007b. Framework for Metals Risk Assessment. EPA 120/R-07/001. http://www.epa.gov/osa/metalsframework.) discussing the state of the science for the persistent bioaccumulative, and toxic nature of metals and the considerations of this science that will impact many programs. This paper provides a brief insight to these agency activities.

Evaluation of the Biotic Ligand Model relative to other site-specific criteria derivation methods for copper in surface waters with elevated hardness

The goal of this study was to evaluate the reliability of the Biotic Ligand Model to predict Cu toxicity in very hard surface water (>200 mg/L as CaCO 3), relative to current copper criteria methodologies (hardness-based equation and the water-effect ratio; WER). To test these methods, we conducted acute Cu toxicity tests with three aquatic test species ( Ceriodaphnia dubia, Daphnia pulex and Pimephales promelas) in seven surface waters. The sites were representative of effluent-dependent or effluent-dominated streams common to the arid western United States of America (arid West) and a wide range of water quality variables were tested. In addition, concurrent Cu toxicity tests were conducted in laboratory waters that were matched to hardness and alkalinity of the sites to facilitate calculation of WER values. Results were used to characterize empirical relationships between water quality characteristics and Cu toxicity, and to compare measured Cu toxicity with Biotic Ligand Model (BLM) predictions. Acute toxicity tests were also conducted with C. dubia and P. promelas in a range of Ca or Mg-dominated hardness concentrations to determine the independent effects of Ca or Mg on Cu toxicity at high hardness levels. Conclusions from this study suggest that the BLM generates appropriate criteria for the waters tested in this study when compared to the hardness-based equation or WER approach. Although the historical site-specific methods are useful for surface waters with hardness ≤250 mg/L as CaCO 3, the unique conditions of arid West streams require site-specific methods that account for the influences of critical water quality variables (i.e., pH, dissolved organic carbon, alkalinity, Ca, Mg and Na). Therefore, the BLM offers an improved alternative to the hardness-based and WER approaches, particularly for situations where the current methods would be under-protective of sensitive aquatic life.

Assessment of aquatic ecological risk and site‐specific criteria of copper in San Francisco Bay, California, USA

A new regression-based copper toxicity model was applied in a case study of San Francisco Bay, California, USA, to demonstrate its utility in estimating risk and site-specific water quality criteria. This was accomplished using probabilistic techniques and a simple model relating dissolved organic carbon (DOC) concentrations with the toxicity of dissolved copper to embryos of the most copper sensitive taxon (Mytilus) in the US Environmental Protection Agency's (USEPA) water quality criteria database. Similar probabilistic techniques were applied to data developed for San Francisco Bay using the USEPA's water-effect ratio (WER) methods for comparison with the DOC-based method. Based on 595 site- and date-specific DOC model observations at 26 sites in San Francisco Bay, none suggested risk of chronic toxicity. Safety factors (1/risk quotient) on average across all sites ranged from 2.4 to 9.1. Comparisons were made between 1) estimates of site-specific criteria made using the DOC method, 2) estimates of site-specific criteria made using the WER method, 3) USEPA national and California Toxics Rule criteria, and 4) region-specific criteria recommended for regulatory implementation by the Clean Estuary Partnership. The DOC- and WER-based methods indicated that copper criteria for San Francisco Bay could be increased above USEPA and California Toxics Rule criteria and will retain the level of protection (> or =97%) embodied in the USEPA copper saltwater water quality criteria. The DOC method overall was more conservative (i.e., implies the need for lower criteria in the Bay) than the WER method. The DOC method suggests that the region-specific criteria being recommended for regulatory implementation would be underprotective in some areas and yet could be increased and remain protective in other areas of San Francisco Bay.

Probability‐based estimates of site‐specific copper water quality criteria for the Chesapeake Bay, USA

The object of this study was to estimate site- and region-specific dissolved copper criteria for a large embayment, the Chesapeake Bay, USA. The intent is to show the utility of 2 copper saltwater quality site-specific criteria estimation models and associated region-specific criteria selection methods. The criteria estimation models and selection methods are simple, efficient, and cost-effective tools for resource managers. The methods are proposed as potential substitutes for the US Environmental Protection Agency's water effect ratio methods. Dissolved organic carbon data and the copper criteria models were used to produce probability-based estimates of site-specific copper saltwater quality criteria. Site- and date-specific criteria estimations were made for 88 sites (n = 5,296) in the Chesapeake Bay. The average and range of estimated site-specific chronic dissolved copper criteria for the Chesapeake Bay were 7.5 and 5.3 to 16.9 microg Cu/L. The average and range of estimated site-specific acute dissolved copper criteria for the Chesapeake Bay were 11.7 and 8.3 to 26.4 microg Cu/L. The results suggest that applicable national and state copper criteria can increase in much of the Chesapeake Bay and remain protective. Virginia Department of Environmental Quality copper criteria near the mouth of the Chesapeake Bay, however, need to decrease to protect species of equal or greater sensitivity to that of the marine mussel, Mytilus sp.

Predicting the Toxicity of Substituted Phenols to Aquatic Species and Its Changes in the Stream and Effluent Waters

The changes in the acute toxicity of 16 phenols toward Selenastrum capricornutum and Daphnia magna were examined as a function of their physical/chemical properties. The results demonstrated that phenols with a higher octanol-water partition coefficient (K(ow)) had a higher toxicity toward aquatic organisms. The toxicity of phenols was closely related to the log K(ow) values, with correlation coefficients of 0.93 (except for the nitrophenols) and 0.89 for S. capricornutum and D. magna, respectively. The changes in the phenols toxicities in the site waters (i.e., stream and effluent waters) were investigated by calculating the water effect ratios (WER) from the results of the toxicity tests in the site waters using D. magna. The results showed that the degree of ionization for each phenolic compound was altered by the differences in the dissociation constant (pK(a)), and the change in the toxicity could be predicted. Therefore, the WER should be considered when the toxicity of phenolic compounds is estimated in site waters. The quantitative structure-activity relationships (QSAR) study showed that the toxicity of the phenols to D. magna could be predicted by the hydrophobicity (log K(ow)) alone and by combining the log K(ow) with pK(a), while the toxicity to S. capricornutum was predicted by a combination of hydrophobicity (log K(ow)) and E(LUMO) (or pK(a)).

Effect of Varying Physicochemistry of European Surface Waters on the Copper Toxicity to the Green Alga Pseudokirchneriella subcapitata

Most standard toxicity test results, used in present environmental risk assessment and water quality criteria (WQC) setting procedures are obtained with standard test media that are not representative for natural surface waters when metal toxicity modifying factors like pH, water hardness and dissolved organic carbon (DOC) are considered. The aim of this study was, using the green alga Pseudokirchneriella subcapitata, (1) to investigate the individual effects of Ca, Mg (the hardness cations) and pH on the toxicity of copper in reconstituted artificial test waters and (2) to study the copper toxicity in 13 spiked surface waters originating from different European eco-regions. Surface waters were selected such that a broad range of DOC (1.55-20.4 mg/l), pH (5.52-8.30) and water hardness (7-238 mg CaCO(3)/l) was covered. Tests in reconstituted artificial waters demonstrated that the 72 h-E(b)C50 (expressed as dissolved Cu) increased by about a factor of 3 when the Ca and Mg concentrations increased from 0.25 to 2.5 mM. When pH was increased from 5.8 to 8.0, dissolved 72 h-E(b)C50 decreased by a factor of 3. It is suggested that competition between Cu2+, Ca2+, Mg2+ and H+ ions at the cell surface are the most likely explanation for these observations. Dissolved 72 h-E(b)C50s in the natural surface waters varied between 32.0 and 245 mug Cu/l and were up to a factor 15 higher than the 72 h-E(b)C50 in standard artificial medium (16.5+/-4.8 mug Cu/l). Consequently, Water Effect Ratio's (WER, the ratio between the EC50 in natural water to the EC50 in standard test water) ranged from 1.9 to 14.8. Linear regression analysis revealed that higher E(b)C50 were significantly related to higher DOC-concentration of the natural waters (R2 = 0.69), but that water hardness and pH did not show a significant relation with copper toxicity in these surface waters. In European surface waters, a positive correlation is observed between water hardness and pH. As a result, hardness and pH effects on copper toxicity are counteractive in European surface waters, resulting in the highly significant relation between the 72 h-E(b)C50 and DOC-concentration. Normalisation of the obtained effect concentrations using a Biotic Ligand based predictive Cu-toxicity model revealed that variation in DOC and pH are mainly responsible for the observed differences of Cu-toxicity in natural waters.

Evaluation of acute copper toxicity to larval fathead minnows (Pimephales promelas) in soft surface waters

The hardness-based regulatory approach for Cu prescribes an extrapolation of the toxicity-versus-hardness relationship to low hardness (< or =50 mg/L as CaCO3). Hence, the objective of the present research was to evaluate the influences of water quality on acute Cu toxicity to larval fathead minnow (Pimephales promelas) in low-hardness surface waters. Seasonal water sampling was conducted at 24 sites throughout South Carolina, USA, to determine the site-specific influences of soft surface-water conditions on acute Cu toxicity. Concurrent toxicity tests in laboratory water, matched for hardness and alkalinity (modified method), also were conducted to allow calculation of water-effect ratios (WERs). In addition, tests were conducted at recommended hardness levels (recommended method) for comparison of WER methodology in soft water. Surface-water conditions (average+/-standard deviation, n = 53) were hardness of 16+/-8 mg/L as CaCO3, alkalinity of 18+/-11 mg/L as CaCO3, and dissolved organic carbon of 6+/-4 mg/L. Dissolved Cu 48-h median lethal concentration (LC50) values varied nearly 45-fold across the dataset and greater than four-fold at individual sites. Spatial (p < 0.0001) and seasonal (p = 0.026) differences among LC50 values were determined for eight sites that had multiple toxicity results for one year. All modified WERs were greater than 1.0, suggesting that the site waters were more protective of Cu toxicity than the matched laboratory water. Some WERs generated using recommended methods were less than 1.0, suggesting limited site-specific protection. Based on these observations, extrapolation of the hardness-based equation for Cu at 50 mg/L or less as CaCO3 would adequately protect fathead minnow populations in soft surface waters. The WER results presented here demonstrate the inconsistency between hardness-based criteria and the methodology for deriving site-specific water-quality criteria in low-hardness waters.