Final Chronic Value Research Articles

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.

Chronic Toxicity of Ferric Iron for North American Aquatic Organisms: Derivation of a Chronic Water Quality Criterion Using Single Species and Mesocosm Data

Iron is a common pollutant in waters near coal and hard rock mine disturbances. The current 1000 µg/L total recoverable chronic criterion for iron (Fe) for protection of aquatic life in the United States was developed using very limited data in 1976 and has not been revised since. To develop a more scientifically based criterion, several chronic laboratory toxicity experiments (> 30 days) were conducted with ferric Fe at circumneutral pH on a taxonomically diverse group of organisms including brown trout (Salmo trutta), mountain whitefish (Prosopium williamsoni), boreal toad tadpoles (Bufo boreas), the oligochaete worm Lumbriculus variegatus, the mayfly Hexagenia limbata, and the planarian Dugesia dorotocephala. Results of these tests and those of previously published toxicity data were used to derive a Final Chronic Value (FCV) of 499 µg/L by using the US Environmental Protection Agency’s recommended methods based on single species toxicity tests. In addition to single species toxicity tests, ferric Fe toxicity experiments (10 days) were performed on mesocosms containing naturally colonized communities of benthic macroinvertebrates. Fourteen genera in the mesocosms occurred at sufficient densities to estimate an iron concentration resulting in 20% reduction in abundance (EC20). Three of these taxa had EC20s less than the FCV of 499 µg/L derived from single species tests: the mayfly Epeorus sp. (335 µg/L), the caddisfly Micrasema sp. (356 µg/L), and midge Tanytarsini (234 µg/L). When mesocosm results were included, the FCV was lowered to 251 µg/L. These findings support the suggestion that modernization of water quality criteria should include data generated from mesocosm experiments and other lines of evidence.

Distributions, fluxes, and toxicities of heavy metals in sediment pore water from tributaries of the Ziya River system, northern China.

The distributions and mobilities of metals in pore water strongly influence the biogeochemical processes and bioavailabilities of metals at sediment-water interfaces. Heavy metal concentrations were measured in pore water samples from the Shaocun River (SR), the Wangyang River (WR), and the Xiao River (XR), tributaries of the Ziya River system, northern China. The aim was to assess heavy metal contamination in the system and the associated environmental risks. The mean Cd, Cr, Cu, Ni, Pb, and Zn concentrations in all three tributaries were 0.373, 57.1, 37.7, 20.4, 14.0, and 90.6 μg/L, respectively. The calculated Cd, Cr, Cu, Ni, Pb, and Zn diffusion fluxes in the rivers were -0.427 to 0.469, -71.8 to 42.5, 3.16 to 86.6, 5.29 to 14.0, 7.24 to 19.0, and -204 to 21.9 μg/(m(2) day), respectively, showing that the pore water was a source of most of the metals to the water column. Only Cu and Pb in the XR and Cu in the WR exceeded the final chronic value recommended by the US Environmental Protection Agency, but the metals in the WR sediment could have caused toxic effects. These results are likely to be useful to the authorities responsible for sustainable river management.

Deriving freshwater quality criteria for copper, cadmium, aluminum and manganese for protection of aquatic life in Malaysia

Freshwater quality criteria for copper (Cu), cadmium (Cd), aluminum (Al), and manganese (Mn) were developed with particular reference to aquatic biota in Malaysia, and based on USEPA’s guidelines. Acute toxicity tests were performed on eight different freshwater domestic species in Malaysia, which were Macrobrachiumlanchesteri (prawn), two fish –Poeciliareticulata and Rasborasumatrana, Melanoidestuberculata (snail), Stenocyprismajor (ostracod), Chironomusjavanus (midge larvae), Naiselinguis (annelid), and Duttaphrynusmelanostictus (tadpole), to determine 96-h LC50 values for Cu, Cd, Al, and Mn. The final acute values (FAVs) for Cu, Cd, Al, and Mn were 2.5, 3.0, 977.8, and 78.3μgL−1, respectively. Using an estimated acute-to-chronic ratio (ACR) of 8.3, the value for final chronic value (FCV) was derived. Based on FAV and FCV, a Criterion Maximum Concentration (CMC) and a criterion Continuous Concentration (CCC) for Cu, Cd, Al, and Mn of 1.3, 1.5, 488.9, and 39.1μgL−1 and 0.3, 0.36, 117.8, and 9.4μgL−1, respectively, were derived. The results of this study provide useful data for deriving national or local water quality criteria for Cu, Cd, Al, and Mn based on aquatic biota in Malaysia. Based on LC50 values, this study indicated that R.sumatrana, M.lanchesteri, C.javanus, and N.elinguis were the most sensitive to Cu, Cd, Al, and Mn, respectively.

Deriving freshwater quality criteria for iron, lead, nickel, and zinc for protection of aquatic life in Malaysia.

Freshwater quality criteria for iron (Fe), lead (Pb), nickel (Ni), and zinc (Zn) were developed with particular reference to aquatic biota in Malaysia, and based on USEPA's guidelines. Acute toxicity tests were performed on eight different freshwater domestic species in Malaysia which were Macrobrachium lanchesteri (prawn), two fish: Poecilia reticulata and Rasbora sumatrana, Melanoides tuberculata (snail), Stenocypris major (ostracod), Chironomus javanus (midge larvae), Nais elinguis (annelid), and Duttaphrynus melanostictus (tadpole) to determine 96 h LC50 values for Fe, Pb, Ni, and Zn. The final acute value (FAV) for Fe, Pb, Ni, and Zn were 74.5, 17.0, 165, and 304.9 μg L−1, respectively. Using an estimated acute-to-chronic ratio (ACR) of 8.3, the value for final chronic value (FCV) was derived. Based on FAV and FCV, a criterion maximum concentration (CMC) and a criterion continuous concentration (CCC) for Fe, Pb, Ni, and Zn that are 37.2, 8.5, 82.5, and 152.4 μg L−1 and 9.0, 2.0, 19.9, and 36.7 μg L−1, respectively, were derived. The results of this study provide useful data for deriving national or local water quality criteria for Fe, Pb, Ni, and Zn based on aquatic biota in Malaysia. Based on LC50 values, this study indicated that N. elinguis, M. lanchesteri, N. elinguis, and R. sumatrana were the most sensitive to Fe, Pb, Ni, and Zn, respectively.

Derivation of predicted no effect concentrations (PNEC) for 2,4,6-trichlorophenol based on Chinese resident species

2,4,6-Trichlorophenol (2,4,6-TCP) is a common chemical intermediate and a by-product of water chlorination and combustion processes, and is a priority pollutant of the aquatic environment in many countries. Although information on the toxicity of 2,4,6-TCP is available, there is a lack of information on the predicted no-effect concentration (PNEC) of 2,4,6-TCP, mainly due to the shortage of chronic and site-specific toxicity data. In the present study, acute and sub-chronic toxicity of 2,4,6-TCP on six different resident Chinese aquatic species were determined. PNEC values were calculated and compared by use of two approaches: assessment factor (AF) and species sensitivity distribution (SSD). Values for acute toxicity ranged from 1.1mgL−1 (Plagiognathops microlepis) to 42mgL−1 (Corbicula fluminea) and the sub-chronic no observed effect concentrations (NOECs) ranged from 0.05mgL−1 (Mylopharyngodon piceus) to 2.0mgL−1 (C. fluminea). PNECs obtained by the assessment factor approach with acute (AF=1000, 0.001mgL−1) or chronic (AF=10, 0.005mgL−1) toxicity data were one order of magnitude less than those from SSD methods (0.057mgL−1). PNEC values calculated using SSD methods with a 50% certainty for 2,4,6-TCP was less than those obtained by use of the USEPA recommend final chronic value (FCV) method (0.097mgL−1) and the one obtained by use of the USEPA recommend acute-to-chronic (ACR) methods (0.073mgL−1). PNECs derived using AF methods were more protective and conservative than that derived using SSD methods.

Influence of dissolved organic carbon on toxicity of copper to a unionid mussel (Villosa iris) and a cladoceran (Ceriodaphnia dubia) in acute and chronic water exposures

Acute and chronic toxicity of copper (Cu) to a unionid mussel (Villosa iris) and a cladoceran (Ceriodaphnia dubia) were determined in water exposures at four concentrations of dissolved organic carbon (DOC; nominally 0.5, 2.5, 5, and 10 mg/L as carbon [C]). Test waters with DOC concentrations of 2.5 to 10 mg C/L were prepared by mixing a concentrate of natural organic matter (Suwannee River, GA, USA) in diluted well water (hardness 100 mg/L as CaCO(3) , pH 8.3, DOC 0.5 mg C/L). Acute median effect concentrations (EC50s) for dissolved Cu increased approximately fivefold (15-72 µg Cu/L) for mussel survival in 4-d exposures and increased about 11-fold (25-267 µg Cu/L) for cladoceran survival in 2-d exposures across DOC concentrations from 0.5 to 10 mg C/L. Similarly, chronic 20% effect concentrations (EC20s) for the mussel in 28-d exposures increased about fivefold (13-61 µg Cu/L for survival; 8.8-38 µg Cu/L for biomass), and the EC20s for the cladoceran in 7-d exposures increased approximately 17-fold (13-215 µg Cu/L) for survival or approximately fourfold (12-42 µg Cu/L) for reproduction across DOC concentrations from 0.5 to 10 mg C/L. The acute and chronic values for the mussel were less than or approximately equal to the values for the cladoceran. Predictions from the biotic ligand model (BLM) used to derive the U.S. Environmental Protection Agency's ambient water quality criteria (AWQC) for Cu explained more than 90% of the variation in the acute and chronic endpoints for the two species, with the exception of the EC20 for cladoceran reproduction (only 46% of variation explained). The BLM-normalized acute EC50s and chronic EC20s for the mussel and BLM-normalized chronic EC20s for the cladoceran in waters with DOC concentrations of 2.5 to 10 mg C/L were equal to or less than the final acute value and final chronic value in the BLM-based AWQC for Cu, respectively, indicating that the Cu AWQC might not adequately protect the mussel from acute and chronic exposure, and the cladoceran from chronic exposure.

Deriving freshwater quality criteria for 2,4,6-trichlorophenol for protection of aquatic life in China

Freshwater quality criteria of 2,4,6-trichlorophenol (2,4,6-TCP) were developed with particular reference to the aquatic biota in China, and based on USEPA’s guidelines. Acute toxicity tests were performed on nine different domestic species indigenous to China to determine 48 h LC50 and 96 h LC50 values for 2,4,6-TCP. In addition, 21 d survival–reproduction test with Daphnia magna, 30 d embryo-larval test with Carassius auratus, 60 d fry-juvenile test with Ctenopharyngodon idellus, 30 d early life stage test with Bufo bufo gargarizans and 96 h growth inhibition test with Scenedesmus obliqaus were also conducted to estimate lower chronic limit and upper chronic limit values. The final acute value (FAV) was 2.01 mg/l 2,4,6-TCP. Acute-to-chronic ratios ranged from 5.01 to 12.2. The final chronic value (FCV) and the final plant value (FPV) of 2,4,6-TCP were 0.226 and 2.24 mg/l respectively. Based on FAV, FCV and FPV for 2,4,6-TCP, a criteria maximum concentration of 1.01 mg/l and a criterion continuous concentration of 0.226 mg/l were derived. The results of this study provide useful data for deriving national or local water quality criteria for 2,4,6-TCP based on aquatic biota in China.

Deriving freshwater quality criteria for 2,4-dichlorophenol for protection of aquatic life in China

Freshwater quality criteria for 2,4-dichlorophenol (2,4-DCP) were developed with particular reference to the aquatic biota in China, and based on USEPA's guidelines. Acute toxicity tests were performed on nine different domestic species indigenous to China to determine 48-h LC 50 and 96-h LC 50 values for 2,4-DCP. In addition, 21 day survival-reproduction tests with Daphnia magna, 30-day embryo-larval tests with Carassius auratus, 60 day fry-juvenile test with Ctenopharyngodon idellus, 30 d early life stage tests with Bufo bufo gargarizans and 96 h growth inhibition tests with Scenedesms obliqaus were conducted, to estimate lower chronic limit (LCL) and upper chronic limit (UCL) values. The final acute value (FAV) was 2.49 mg/l 2,4-DCP. Acute-to-chronic ratios (ACR) ranged from 3.74 to 22.5. The final chronic value (FCV) and the final plant value (FPV) of 2.4-DCP were 0.212 mg/l and 7.07 mg/l respectively. Based on FAV, FCV, and FPV, a criteria maximum concentration (CMC) of 1.25 mg/l and a criterion continuous concentration (CCC) of 0.212 mg/l were derived. The results of this study provide useful data for deriving national or local water quality criteria for 2,4-DCP based on aquatic biota in China.

Chronic toxicity of arsenic to the Great Salt Lake brine shrimp, Artemia franciscana

We determined the chronic toxicity of arsenic (sodium arsenate) to the Great Salt Lake brine shrimp, Artemia franciscana. Chronic toxicity was determined by measuring the adverse effects of arsenic on brine shrimp growth, survival, and reproduction under intermittent flow-through conditions. The study commenced with <24-h-old nauplii, continued through reproduction of the parental generation, and ended after 28 days of exposure. The concentrations tested were 4, 8, 15, 31, and 56 mg/L dissolved arsenic. The test was conducted using water from the Great Salt Lake, Utah as the dilution water. Adult survival was the most sensitive biological endpoint, with growth and reproduction somewhat less sensitive than survival. The no observed effect concentration (NOEC) for survival was 8 mg/L, and the lowest observed effect concentration (LOEC) was 15 mg/L dissolved arsenic. The LOEC for growth and reproduction was greater than the highest concentration tested, 56 mg/L. Based on survival, the final chronic value (geometric mean of the NOEC and LOEC) was 11 mg/L dissolved arsenic. The F 1 generation appeared to acclimate to the prior arsenic exposure of the parental generation and was significantly less sensitive than the parental generation. For example, survival for the F 1 generation through day 12 was 100% in 56 mg/L dissolved arsenic, compared to 26% for the parental generation. Growth of the F 1 generation was significantly less than that of the parental generation across all concentrations including the control, indicating a generational difference in brine shrimp growth rather than an arsenic effect. This study represents one of the few full life cycle toxicity tests conducted with brine shrimp.

Aquatic toxicity of acetonitrile and its water quality criteria for the protection of aquatic life in China

The freshwater quality criteria of acetonitrile were studied on the basis of the features of the aquatic biota in China, and with reference to US EPA's guidelines. Acute tests were performed on 13 different species to determine 48h-EC50/96h-EC50 (or 96h-LC50) values for acetonitrile. 2ld survival-reproduction tests with Daphnia magna and growth inhibition tests with Lemna minor were also conducted to estimate lower chronic limit and upper chronic limit values. In the acute tests, Radix plicatula was the most sensitive species to acetonitrile followed by Chironomus sp., Cyprinus carpio and D. magna in turn. The final acute value of acetonitrile was 2290 mg/l. In the chronic tests, reproduction of daphnids was significantly reduced by acetonitrile at 320 mg/l. Acute-to-chronic ratios ranged from 2 to 15.8. A final chronic value of 413.9 mg/l was obtained and a final plant value was 1342 mg/I. A criterion maximum concentration (1145 mg/l) and a criterion continuous concentration (413.9 mg/l) were derived.

Technical basis for narcotic chemicals and polycyclic aromatic hydrocarbon criteria. I. Water and tissue

AbstractA method is presented for developing water quality criteria (WQC) for type I narcotic chemicals in general and PAHs in particular. The criteria can be applied to any individual or mixture of narcotic chemicals using only the chemical's octanol‐water partition coefficientKOW. It is derived from a database of LC50s comprising 156 chemicals and 33 species, including fish, amphibians, arthropods, mollusks, polychaetes, coelenterates, and protozoans. A target lipid model is proposed that accounts for variations in toxicity due to differing species sensitivities and chemical differences. The model is based on the idea that a target lipid is the site of action in the organism. Further, it is assumed that target lipid has the same lipid‐octanol linear free energy relationship for all species. This implies that the slope of the log(LC50)–log(KOW) relationship is the same for all species. However, individual species may have varying target lipid body burdens that cause toxicity. The target lipid LC50 body burdens derived from concentration data in the water only are compared to measured total lipid LC50 body burdens for five species. They are essentially equal, indicating that the target lipid concentration is equal to the total extracted lipid concentration. The precise relationship between partitioning in target lipid and octanol is established. The species‐specific body burdens are used to determine the WQC final acute value, i.e., the 95‐percentile level of protection. An acute‐to‐chronic ratio is used to compute the body burden corresponding to the WQC final chronic value, which is the procedure used to derive the U.S. Environmental Protection Agency water quality criteria. The criteria are expressed either as dissolved concentrations in the water column or as tissue concentrations.

Effects of Waterborne Exposure to 4-Nonylphenol and Nonylphenol Ethoxylate on Secondary Sex Characteristics and Gonads of Fathead Minnows (Pimephales promelas)

Fathead minnows were exposed to 4-nonylphenol (NP) or nonylphenol ethoxylate (NPEO) to determine the effects of these weak estrogen agonists on secondary sex characteristics and gonads of sexually mature males and females during 42-day continuous-flow exposures. Neither NP nor NPEO caused statistically significant effects on tubercles or fatpad size at the concentrations tested. Exposure to 1.1 or 3.4 μg NP/L caused changes in the number and size of Sertoli cells and germ cell syncytia. Necrotic aggregates of various stages of germ cells in the spermatogenic sequence were observed in the testes of males exposed to NP. Electron microscopy of the testes of NP-exposed males revealed the presence of phagocytic cells in the lumina of seminiferous tubules. The cytoplasm of some Sertoli cells was distended with myelin figures and necrotic spermatozoa. No significant effects on the stages of follicular development were observed in females exposed to NP. There were no differences in the gonads or secondary sex characteristics of males or females exposed to 5.5 μg NPEO/L, the greatest concentration studied. The histologic responses observed are sensitive indicators of waterborne exposure to NP at environmentally relevant concentrations, but not as sensitive as induction of plasma vitellogenin. The secondary sex characteristics were not affected by concentrations of NP or NPEO as great as 3.4 or 5.5 μg/L, respectively. Histologic responses occurred at concentrations that were less than the final chronic value based on survival and approximately the same as those required to cause effects on egg production. The histologic effects caused by NP were similar to, but not exactly the same as those caused by exposure of fathead minnows to 17β-estradiol.

Nitroaromatic munition compounds: environmental effects and screening values.

Available data on the occurrence, transport, transformation, and toxicity of eight nitroaromatic munition compounds and their degradation products, TNT, TNB, DNB, DNA, 2-ADNT, RDX, HMX, and tetryl were used to identify potential fate in the environment and to calculate screening benchmarks or safe environmental levels for aquatic and terrestrial organisms. Results of monitoring studies revealed that some of these compounds persist at sites where they were produced or processed. Most of the compounds are present in soil, sediment, and surface water or groundwater at military sites. Soil adsorption coefficients indicate that these chemicals are only moderately adsorbed to soil and may leach to groundwater. Most of these compounds are transformed by abiotic or biotic mechanisms in environmental media. Primary transformation mechanisms involve photolysis (TNT, RDX, HMX, tetryl), hydrolysis (tetryl), and microbial degradation (TNT, TNB, DNB, DNA, 2-ADNT, and HMX). Microbial degradation for both nitro and nitramine aromatic compounds involves rapid reduction of nitro groups to amino groups, but further metabolism is slow. With the exception of DNB, complete mineralization did not usually occur under the conditions of the studies. RDX was resistant to microbial degradation. Available ecotoxicological data on acute and chronic studies with freshwater fish and invertebrates were summarized, and water quality criteria or ecotoxicological screening benchmarks were developed. Depending on the available data, criteria/benchmarks were calculated according to USEPA Tier I or Tier II guidelines. The munitions chemicals are moderately to highly toxic to freshwater organisms, with chronic screening values < 1 mg/L. For some chemicals, these low values are caused by inherent toxicity; in other cases, they result from the conservative methods used in the absence of data. For nonionic organic munitions chemicals, sediment quality benchmarks were calculated (based on Kow values and the final chronic value) according to USEPA guidelines. Available data indicate that none of the compounds is expected to bioconcentrate. In the same manner in which reference doses for humans are based on studies with laboratory animals, reference doses or screening benchmarks for wildlife may also be calculated by extrapolation among mammalian species. Chronic NOAELs for the compounds of interest were determined from available laboratory studies. Endpoints selected for wildlife species were those that diminish population growth or survival. Equivalent NOAELs for wildlife were calculated by scaling the test data on the basis of differences in body weight. Data on food and water intake for seven selected wildlife species--short-tailed shrew, white-footed mouse, meadow vole, cottontail rabbit, mink, red fox, and whitetail deer--were used to calculate NOAELs for oral intake. In the case of TNB, a comparison of toxicity data from studies conducted with both the white-footed mouse and the laboratory rat indicates that the white-footed mouse may be more resistant to the toxic effects of chemicals than the laboratory rat and may further indicate the lesser sensitivity of wildlife species to chemical insult. Chronic NOAEL values for the test species based on the laboratory studies indicate that, by the oral route of exposure, TNB and RDX are not highly toxic to mammalian species. However, as seen with TNB, values are less conservative when chronic studies are available or when studies were conducted with wildlife species. Insufficient data were located to calculate NOAELs for avian species. In the absence of criteria or guidelines for terrestrial plants, invertebrates, and soil heterotrophic processes, LOECs were used as screening benchmarks for effect levels in the environment. In most cases, too few data were available to derive a screening benchmark or to have a high degree of confidence in the benchmarks that were derived. (ABSTRACT TRUNCATED)

Quality criteria of acrylonitrile for the protection of aquatic life in China

Freshwater quality criteria of acrylonitrile were developed on the basis of the features of the aquatic biota in China, and with reference to U.S.EPA's guidelines. Acute tests were performed on each of eight different domestic species to determine 48h-EC 50/96h-EC 50 (or 96h-LC 50) values for acrylonitrile. 21d survival-reproduction test with Daphnia magna, 28d early life stage test with Bufo bufo gargarizans and 96h growth inhibition test with Lemna minor were also conducted to estimate lower chronic limit / upper chronic limit values. The final acute value, the final chronic value and the final plant value of acrylonitrile was 3.842 mg/L, 0.4827 mg/L and 8.803 mg/L respectively. A criterion maximum concentration (1.921 mg/L) and a criterion continuous concentration (0.4827 mg/L) were derived. The results of this study may provide useful data to derive national WQC for acrylonitrile as well as the procedures of deriving WQC for other chemicals based on aquatic biota in China.

Technical basis for establishing sediment quality criteria for nonionic organic chemicals using equilibrium partitioning

AbstractThe purpose of this review paper is to present the technical basis for establishing sediment quality criteria using equilibrium partitioning (EqP). Equilibrium partitioning is chosen because it addresses the two principal technical issues that must be resolved: the varying bioavailability of chemicals in sediments and the choice of the appropriate biological effects concentration.The data that are used to examine the question of varying bioavailability across sediments are from toxicity and bioaccumulation experiments utilizing the same chemical and test organism but different sediments. It has been found that if the different sediments in each experiment are compared, there is essentially no relationship between sediment chemical concentrations on a dry weight basis and biological effects. However, if the chemical concentrations in the pore water of the sediment are used (for chemicals that are not highly hydrophobic) or if the sediment chemical concentrations on an organic carbon basis are used, then the biological effects occur at similar concentrations (within a factor of two) for the different sediments. In addition, the effects concentrations are the same as, or they can be predicted from, the effects concentration determined in water‐ only exposures.The EqP methodology rationalizes these results by assuming that the partitioning of the chemical between sediment organic carbon and pore water is at equilibrium. In each of these phases, the fugacity or activity of the chemical is the same at equilibrium. As a consequence, it is assumed that the organism receives an equivalent exposure from a water‐only exposure or from any equilibrated phase, either from pore water via respiration, from sediment carbon via ingestion; or from a mixture of the routes. Thus, the pathway of exposure is not significant. The biological effect is produced by the chemical activity of the single phase or the equilibrated system.Sediment quality criteria for nonionic organic chemicals are based on the chemical concentration in sediment organic carbon. For highly hydrophobic chemicals this is necessary because the pore water concentration is, for those chemicals, no longer a good estimate of the chemical activity. The pore water concentration is the sum of the free chemical concentration, which is bioavailable and represents the chemical activity, and the concentration of chemical complexed to dissolved organic carbon, which, as the data presented below illustrate, is not bioavailable. Using the chemical concentration in sediment organic carbon eliminates this ambiguity.Sediment quality criteria also require that a chemical concentration be chosen that is sufficiently protective of benthic organisms. The final chronic value (FCV) from the U.S. Environmental Protection Agency (EPA) water quality criteria is proposed. An analysis of the data compiled in the water quality criteria documents demonstrates that benthic species, defined as either epibenthic or infaunal species, have a similar sensitivity to water column species. This is the case if the most sensitive species are compared and if all species are compared. The results of benthic colonization experiments also support the use of the FCV.Equilibrium partitioning cannot remove all the variation in the experimentally observed sediment‐ effects concentration and the concentration predicted from water‐only exposures. A variation of approximately a factor of two to three remains. Hence, it is recognized that a quantification of this uncertainty should accompany the sediment quality criteria.The derivation of sediment quality criteria requires the octanol/water partition coefficient of the chemical. It should be measured with modern experimental techniques, which appear to remove the large variation in reported values. The derivation of the final chronic value should also be updated to include the most recent toxicological information.

Derivation of a freshwater silver criteria for the New River, Virginia, using representative species

AbstractThe U.S. Environmental Protection Agency (EPA) has not published a 30‐d average or continuous criterion for silver due to the apparent toxicity of this element and the lack of available chronic exposure data. The present study examined acute effects on nine species representative or indigenous to the New River, Virginia, and sublethal effects on three of those species using the Resident Species Approach. Our results showed that invertebrates were much more sensitive to silver than fish, including juvenile rainbow trout (Oncorhynchus mykiss). Hyalella azteca (amphipod) was the most sensitive species followed by the mayflies Stenonema sp. and Isonychia bicolor and the stonefly Leuctra sp. The Final Acute Value in this study was 1.32 μg/L total recoverable silver. In sublethal tests, Isonychia growth, as measured by the number of molts over time, was the most sensitive effect observed. Estimated acute:“chronic” ratios ranged from two to 34 with Corbicula fluminea having the largest ratio. Our study results, along with available published data, suggested a Final Chronic Value of 0.13 μg/L total silver which is approximately one‐half the level obtained using the EPA acute formula and ambient water hardness. Our results suggest that a continuous criterion for silver may be predictable using the hardness‐dependent formula and a safety factor of 0.5.