Comparison of acute and chronic toxicity of silver nanoparticles and silver nitrate to Daphnia magna

Silver nanoparticles (AgNP) are now widely used as antibacterial products, and their potential toxicities in aquatic organisms are a matter of increasing concern. In the present study, we conducted experiments to reveal the acute and chronic toxicities of AgNP and its bioaccumulation from both aqueous and dietary sources in a model freshwater cladoceran, Daphnia magna. No mortality was observed in 48-h acute toxicity testing when the daphnids were exposed up to 500?μg Ag/L as AgNP. The AgNP accumulation reached as high as 22.9?mg Ag/g dry weight at the highest AgNP concentration tested (500?μg/L). In contrast, D. magna was extremely sensitive to free Ag ion (Ag(+) , added as AgNO(3) ), with a measured 48-h 50% lethal concentration of 2.51?μg/L. Thus, any AgNP potential acute toxicity may be caused by the release of Ag(+) into the solution. During the 21-d chronic exposure, dietborne AgNO(3) had the most significant influence on reproduction, whereas waterborne AgNP had the most significant inhibition on growth. Significant delay and decrease of reproduction in daphnids exposed to dietborne AgNO(3) occurred at a dissolved Ag concentration of 0.1?μg/L added to the algae. Significant inhibitions of growth and reproduction were also found for the AgNP exposure, with the lowest observed effective concentration of 5?μg/L and 50?μg/L, respectively. Chronic effects of AgNP were probably caused by the low food quality of algae associated with AgNP and the low depuration of ingested AgNP. Environmental risk assessments of AgNP should therefore include tests on the chronic toxicity to aquatic organisms as well as the direct and indirect effects of AgNP resulting from the release of Ag(+) into the environment.     

Nicosulfuron Plus Atrazine Herbicides and Trichogrammatidae (Hymenoptera) in No-Choice Test: Selectivity and Hormesis

Methods are needed to prepare stable suspensions of engineered nanoparticles in aqueous matrixes for ecotoxicity testing and ecological risk assessments. We developed a novel method of preparing large volumes of silver nanoparticles (AgNP) in suspension using a commercially available rotor–stator dispersion mill. AgNP in powder form (PVP capped, 30–50 nm) was suspended in deionized water and natural lake water at 1 g/L and the addition of 0.025% (w/v) gum arabic (GA) increased stability over 2 weeks after preparation. The concentrations of total and dissolved Ag in the suspensions did not change significantly over this period. Analysis of hydrodynamic diameters of the major peaks in suspension using dynamic light scattering showed that suspensions prepared with GA were stable, and this was confirmed by single-particle ICP-MS analysis. This method for dispersing AgNPs provides an inexpensive, yet reliable method for preparing suspensions for toxicity testing and ecosystem level studies of the fate and biological effects of AgNPs in aquatic ecosystems.     

Effects of silver nanoparticles on bacterial activity in natural waters

Silver nanoparticles (AgNPs) may be introduced into aquatic ecosystems because of their widespread use as antimicrobial agents. However, few studies have investigated the impacts of AgNPs on natural aquatic microbial activity in an environmentally relevant context. In this study, bacterioplankton were collected from nine aquatic habitats and exposed to six concentrations of carboxy-functionalized AgNP (ViveNano, 10-nm particle size, 20% Ag w/w) over 48?h. After 1?h of exposure, bacterial production and extracellular alkaline phosphatase affinity were significantly reduced in all AgNP-exposed samples. However, across a 48-h exposure, extracellular aminopeptidase affinity was not consistently impacted by AgNPs. After 48?h, bacterial production recovered by 40 to 250% at low AgNP nominal concentrations (0.05 and 0.1?mg/L) but remained inhibited at the two highest AgNP nominal concentrations (1 and 10?mg/L). In contrast, AgNO(3) additions between 0.01 to 2?mg Ag/L fully inhibited bacterial production over the 48-h exposure. At 48-h exposure, the lowest observed effective concentrations and average median effective concentration for bacterial production ranged from 8 to 66 and 15 to 276?μg Ag/L, respectively. Thus, in natural aquatic systems, AgNP concentrations in the nanogram per liter range are unlikely to negatively impact aquatic biogeochemical cycles. Instead, exposures in the low microgram per liter range would likely be required to negatively impact natural aquatic bacterioplankton processes.     

Toxicity of metals to roots of cowpea in relation to their binding strength

Metal phytotoxicity is important in both environmental and agricultural systems. A solution culture study examined the toxicity of 26 metals to roots of cowpea (Vigna unguiculata (L.) Walp.); new data were collected for 15 metals and published data for 11 metals. Metal toxicity, calculated as causing a 50% reduction in root elongation rate, was determined based on either the measured concentration in the bulk solution (EC50(b)) or the calculated activity at the outer surface of the plasma membrane (EA50(0)°). The EC50(b) values ranged from 0.007?μM for Tl to 98,000?μM for K, with the order of rhizotoxicity to cowpea, from most to least toxic, being Tl?=?Ag?>?Cu?>?Hg?=?Ni?=?Ga?=?Ru?=?In?>?Sc?=?Cd?=?Gd?=?La?=?Co?=?Cs?=?Pb?>?Zn?=?Al?=?H?>?Mn?>?Ba?=?Sr?>?Li?>?Mg?>?Ca?=?Na?>?K. The EA50(0)° values suggest that the binding of metals to hard ligands is an important, general, nonspecific mechanism of toxicity, a hypothesis supported by the similar toxicity symptoms to roots of cowpea by many metals. However, additional mechanisms, such as strong binding to soft ligands, substantially increase rhizotoxicity of some metals, especially Tl, Ag, and Cs. Besides direct toxic effects, osmotic effects or reduced activity of Ca(2+) at the outer surface of the root plasma membrane (and resultant Ca deficiency) may decrease short-term root growth.     

Toxicological evaluation of nitrofurazone and furaltadone on Selenastrum capricornutum, Daphnia magna, and Musca domestica

Short-term toxicity of nitrofurans, nitrofurazone, furaltadone tartrate, and furaltadone chlorohydrate, was tested in the laboratory on two freshwater organisms, Selenastrum capricornutum (algae) and Daphnia magna (crustaceans). Toxicity studies with nitrofurazone were also carried out on larval development of the house fly Musca domestica L. Nitrofurazone was invariably the most toxic compound (the 96-hr EC50 of algal species was 1.45 mg/liters; the EC50 values for D. magna were 40.04 and 28.67 mg/liter after 24 and 48 hr, respectively) followed by furaltadone tartrate and furaltadone chlorohydrate. This study provides some evidence of the potential ecotoxicity of nitrofurans, indicating the need for further investigations.     

Effects from filtration, capping agents, and presence/absence of food on the toxicity of silver nanoparticles to Daphnia magna

Relatively little is known about the behavior and toxicity of nanoparticles in the environment. Objectives of work presented here include establishing the toxicity of a variety of silver nanoparticles (AgNPs) to Daphnia magna neonates, assessing the applicability of a commonly used bioassay for testing AgNPs, and determining the advantages and disadvantages of multiple characterization techniques for AgNPs in simple aquatic systems. Daphnia magna were exposed to a silver nitrate solution and AgNPs suspensions including commercially available AgNPs (uncoated and coated), and laboratory-synthesized AgNPs (coated with coffee or citrate). The nanoparticle suspensions were analyzed for silver concentration (microwave acid digestions), size (dynamic light scattering and electron microscopy), shape (electron microscopy), surface charge (zeta potentiometer), and chemical speciation (X-ray absorption spectroscopy, X-ray diffraction). Toxicities of filtered (100 nm) versus unfiltered suspensions were compared. Additionally, effects from addition of food were examined. Stock suspensions were prepared by adding AgNPs to moderately hard reconstituted water, which were then diluted and used straight or after filtration with 100-nm filters. All nanoparticle exposure suspensions, at every time interval, were digested via microwave digester and analyzed by inductively coupled argon plasma-optical emission spectroscopy or graphite furnace-atomic absorption spectroscopy. Dose-response curves were generated and median lethal concentration (LC50) values calculated. The LC50 values for the unfiltered particles were (in μg/L): 1.1 ± 0.1-AgNO(3) ; 1.0 ± 0.1-coffee coated; 1.1 ± 0.2-citrate coated; 16.7 ± 2.4 Sigma Aldrich Ag-nanoparticles (SA) uncoated; 31.5 ± 8.1 SA coated. LC50 values for the filtered particles were (in μg/L): 0.7 ± 0.1-AgNO(3) ; 1.4 ± 0.1-SA uncoated; 4.4 ± 1.4-SA coated. The LC50 resulting from the addition of food was 176.4 ± 25.5-SA coated. Recommendations presented in this study include AgNP handling methods, effects from sample preparation, and advantages/disadvantages of different nanoparticle characterization techniques.     

Physiological analysis of silver nanoparticles and AgNO3 toxicity to Spirodela polyrhiza

Silver nanoparticles (AgNPs) are commonly used in consumer products for their antibacterial activity. Silver nanoparticles may adversely influence organisms when released into the environment. The present study investigated the effect of AgNPs on the growth, morphology, and physiology of the aquatic plant duckweed (Spirodela polyrhiza). The toxicity of AgNPs and AgNO(3) was also compared. The results showed that silver content in plant tissue increased significantly with higher concentrations of AgNPs and AgNO(3) . Silver nanoparticles and AgNO(3) significantly decreased plant biomass, caused colonies of S. polyrhiza to disintegrate, and also resulted in root abscission. Physiological analysis showed that AgNPs and AgNO(3) significantly decreased plant tissue nitrate-nitrogen content, chlorophyll a (Chl a) content, chlorophyll a/b (Chl a/b), and chlorophyll fluorescence (Fv/Fm). Changes in soluble carbohydrate and proline content were also detected after both AgNO(3) and AgNPs treatment. However, after 192 h of recovery, total chlorophyll content increased, and Fv/Fm returned to control level. Median effective concentration (EC50) values for Chl a and phosphate content showed that AgNO(3) was more toxic than AgNPs (EC50 values: 16.10 ± 0.75 vs 7.96 ± 0.81 and 17.33 ± 4.47 vs 9.14 ± 2.89 mg?Ag?L(-1) , respectively), whereas dry-weight EC50 values showed that AgNPs were more toxic than AgNO(3) (13.39 ± 1.06 vs 17.67 ± 1.16 mg?Ag?L(-1) ).     

A study of the leachate toxicity of metal-containing solid wastes using Daphnia magna

This paper examines the ecotoxicity of different actual inorganic wastes containing some potentially toxic metals commonly found in many industrial residues and the reduction in ecotoxicity obtained when the wastes are submitted to a solidification/stabilization process. The ecotoxicity was assessed as defined in the Spanish regulations on hazardous wastes, by means of the Daphnia magna Straus acute toxicity test applied to the toxicity characteristic leaching procedure (TCLP) waste leachate. On the basis of the EC50 values of the individual metals and the effect of the pH of the aqueous medium on D. magna, we have explored a method for estimating the toxicity of the TCLP waste leachate by calculating its EC50 value in the D. magna test. Although the method is only valid in cases in which a clear cause for the toxicity exists, the procedure described allows us to more completely explain the observed effects on the daphnids. The ecotoxicity of the residues after stabilization is less than that of the untreated waste, generally as a consequence of the reduction in metal leachability achieved by the immobilization treatment. The stabilization process was analyzed in terms of both the chemical and the ecotoxicological parameters, and the influence of leachate pH on the objectives of waste treatment is discussed.     

Effects of dissolved organic carbon concentration and source, pH, and water hardness on chronic toxicity of copper to Daphnia magna

The effects of pH (5.3-8.7), water hardness (CaCO3 at 25-500 mg/L), dissolved organic carbon (DOC) concentration (1.6-18.4 mg/L), and DOC source on the chronic toxicity of copper to Daphnia magna were investigated by using a multifactorial, central composite test design. Natural dissolved organic matter (DOM) was collected at three sites in Belgium and The Netherlands by using reverse osmosis. For a total number of 35 toxicity tests performed, 21-d no-observed-effect concentrations (NOECs) of copper based on reproduction ranged from 29.4 to 228 microg/L and 21-d concentrations of copper causing 50% reduction of reproduction (EC50s) ranged from 41.5 to 316 microg/L. Statistical analysis revealed that DOC concentration and pH had a significant effect on copper toxicity but hardness (at the levels tested) did not. In general, an increase in pH or DOC resulted in a linear increase of 21-d NOEC and EC50 values. All DOMs (originating from three different sources) reduced copper toxicity to the same extent. Multiple linear regression analysis on the results of all 35 toxicity tests revealed that DOC concentration is the most important factor for chronic toxicity of copper to D. magna, explaining about 60% of the observed variability, whereas pH only explained about 15% of the observed variability. Regression models were developed (with DOC and pH as parameters) that were capable of predicting NOECs and EC50s within a factor of 1.9 from observed NOEC and EC50 values obtained with eight natural surface waters spiked with copper. Until future research further elucidates the mechanisms underpinning the observed bioavailability relations, these empirical regression models can become a first simple tool for regulatory applications.     

Application of an acute biotic ligand model to predict chronic copper toxicity to Daphnia magna in natural waters of Chile and reconstituted synthetic waters

The objective of the present study was to assess the predictive capacity of the acute Cu biotic ligand model (BLM) as applied to chronic Cu toxicity to Daphnia magna in freshwaters from Chile and synthetic laboratory-prepared waters. Samples from 20 freshwater bodies were taken, chemically characterized, and used in the acute Cu BLM to predict the 21-d chronic Cu toxicity for D. magna. The half-maximal effective concentration (EC50) values, determined using the Organisation for Economic Co-operation and Development (OECD) 21-d reproduction test (OECD Method 211), were compared with the BLM simulated EC50 values. The same EC50 comparison was performed with the results of 19 chronic tests in synthetic media, with a wide range of hardness and alkalinity and a fixed 2 mg/L dissolved organic carbon (DOC) concentration. The acute BLM was modified only by adjustment of the accumulation associated with 50% of an effect value (EA50). The modified BLM model was able to predict, within a factor of two, 95% of the 21-d EC50 and 89% of the 21-d half-maximal lethal concentrations (LC50) in natural waters, and 100% of the 21-d EC50 and 21-d LC50 in synthetic waters. The regulatory implications of using a slightly modified version of an acute BLM to predict chronic effects are discussed.     

强效杀生剂水生毒理学毒性评价研究

目的研究中央空调循环冷却水中杀生剂的生态安全性,探讨其毒性评价方法。方法采用大型水蚤急性毒性试验、卤虫无节幼体急性毒性试验和斜生栅藻生长抑制试验对强效杀生剂的生态毒性进行评价,用直线内插法计算EC50值及LC50值。结果强效杀生剂对大型水蚤的半数致死浓度24、48、96 h LC50分别为0.004 4、0.001 2及0.000 8 mg/L,半数影响浓度24、48、96 h EC50分别为0.002 7、0.001 3、0.000 8 mg/L。强效杀生剂对卤虫无节幼体的半数致死浓度24、48、96 h LC50分别为0.096、0.048、0.032 mg/L。强效杀生剂对斜生栅藻的半数影响浓度24、48和96 h EC50分别为57、28及1.62 mg/L。结论强效杀生剂对大型水蚤和斜生栅藻有较强的毒性,因此对水环境中的生物具有较强的生态毒性,应该加强对其使用的管理。     

三种农药对挠足动物Nitocra的毒性研究

采用国外新推出的实验生物Nitocra spinipes(挠足动物,美丽猛水蚤属Nitocra的一种)对两种拟菊酯类杀虫剂新农药溴氰菊酯及速灭杀丁以及我国现用的农药杀虫脒进行了毒性测定。获得了24、48及96h的半数活动受抑制浓度EC_50值及半数致死浓度LC_50值。其毒性大小顺序:溴氰菊酯>速灭杀丁>杀虫脒。     

A critical body residue approach for predicting persistent bioaccumulative toxicant effects on reproduction and population dynamics of meiobenthic copepods

Critical body residues (CBRs) are the measured tissue toxicant concentrations yielding a median dose-response on a dry-weight or lipid-normalized basis. They facilitate management decisions for species protection using tissue analysis. Population CBR is the mean dose yielding 50% population suppression and was predicted here in Amphiascus tenuiremis for fipronil sulfide (FS) using lifetables and the Leslie matrix. Microplate bioassays (ASTM E-2317-14) produced biomass sufficient for dry mass and lipid-normalized CBR estimates of reproduction (fertility) and population growth suppression. Significant FS toxic effects were delayed naupliar development (at ≥0.10?μg?L(-1)), delayed copepodite development (at 0.85?μg?L(-1)), decreased reproductive success (at ≥ 0.39?μg?L(-1)), and decreased offspring production (at 0.85?μg?L(-1)). A reproductive median effective concentration (EC50) of 0.16?μg?L(-1) (95% CI: 0.12-0.21?μg?L(-1)) corresponded to an adult all-sex CBR and lipid-normalized CBR of 0.38?pg FS?·?μg(-1) dry weight (95% CI: 0.27-0.52?pg FS?·?μg(-1)) or 2.8?pg FS?·?μg(-1) lipid (95% CI: 2.2-3.6?pg FS?·?μg(-1)), respectively. Copepod log bioconcentration factor (BCF)?=?4.11?±?0.2. Leslie matrix projections regressed against internal dose predicted fewer than five gravid females in a population by the third generation at 0.39 and 0.85?μg FS?·?L(-1) (i.e., 9.6-10.2?μg FS?·?μg(-1) lipid), and 50% population suppression at a CBR of 1.6?pg FS?·?μg(-1) lipid. This more integrative population CBR as a management tool would fall 1.75 times below the CBR for the single most sensitive endpoint-fertility rate.     

Effects of dissolved organic carbon on the toxicity of copper to the developing embryos of the Pacific oyster (Crassostrea gigas)

The effects of humic acid (HA) on copper speciation and its subsequent toxicity to the sensitive early life stages of the Pacific oyster (Crassostrea gigas) are presented. Differential pulse anodic stripping voltammetry with a hanging mercury drop electrode was used to measure the copper species as labile copper (LCu; free ion and inorganic copper complexes) and total copper (TCu) with respect to increasing HA concentration. The TCu and LCu 50% effect concentrations (EC50s) in the absence of HA were 20.77 microg/L (95% confidence interval [CI], 24.02-19.97 microg/L) and 8.05 microg/L (95% CI, 9.6-5.92 microg/L) respectively. A corrected dissolved organic carbon (DOC) concentration (HA only) of 1.02 mg/L was required to significantly increase the TCu EC50 to approximately 41.09 microg/L (95% CI, 44.27-37.52 microg/L; p < 0.05), almost doubling that recorded when DOC (as HA) was absent from the test media. In contrast, the LCu EC50 was unaffected by changes in DOC concentration and was stable throughout the corrected DOC concentration range. The absence of change in the LCu EC50, despite increased HA concentration, suggests that the LCu fraction, not TCu, was responsible for the observed toxicity to the oyster embryo. This corresponds with the current understanding of copper toxicity and supports the free-ion activity model for copper toxicity.     

Ecotoxicity and genotoxicity assessment of cytostatic pharmaceuticals

The fate and effects of cytostatic (anticancer or antineoplastic) pharmaceuticals in the environment are largely unknown, but they can contaminate wastewater treatment effluents and consequently aquatic ecosystems. In this paper, we have focused on five cytostatic compounds used in high amounts (cyclophosphamide, cisplatin, 5-fluorouracil, doxorubicin, and etoposide), and we have investigated their ecotoxicity in bacterial Pseudomonas putida growth-inhibition test, algal Pseudokirchneriella subcapitata growth-inhibition test, and Dapnia magna acute immobilization test. Genotoxicity also was assessed with Escherichia coli SOS-chromotest (with and without metabolic activation) and the GreenScreen Assay using yeast S. cerevisiae. All tested compounds showed significant effects in most of the assays with lowest-observed-effect concentrations and concentrations causing 50% effects (EC50s) values ranging within microg/L to mg/L. The most toxic compound was 5-fluorouracil in the assays with P. putida (EC50 = 0.027 mg/L) and P. subcapitata (EC50 = 0.11 mg/L), although cisplatin and doxorubicin were the most toxic to D. magna (EC50 = 0.64 and 2.0 mg/L, respectively). These two chemicals were also the most genotoxic in the SOS-chromotest (minimum genotoxic concentrations [MGC] = 0.07-0.2 mg/L), and 5-fluorouracil was the most genotoxic in the eukaryotic yeast assay (MGC = 0.02 mg/L). Our investigation seems to indicate generally lower risks of acute effects at concentrations expected in the environment. However, some effective concentrations were relatively low and chronic toxicity of cytostatics (and/or their transformation products), as well as specific sources of human pharmaceuticals such as hospital effluents, require research attention.     

Detecting nanoparticulate silver using single-particle inductively coupled plasma-mass spectrometry

The environmental prevalence of engineered nanomaterials, particularly nanoparticulate silver (AgNP), is expected to increase substantially. The ubiquitous use of commercial products containing AgNP may result in their release to the environment, and the potential for ecological effects is unknown. Detecting engineered nanomaterials is one of the greatest challenges in quantifying their risks. Thus, it is imperative to develop techniques capable of measuring and characterizing exposures, while dealing with the innate difficulties of nanomaterial detection in environmental samples, such as low-engineered nanomaterial concentrations, aggregation, and complex matrices. Here the authors demonstrate the use of inductively coupled plasma-mass spectrometry, operated in a single-particle counting mode (SP-ICP-MS), to detect and quantify AgNP. In the present study, two AgNP products were measured by SP-ICP-MS, including one of precisely manufactured size and shape, as well as a commercial AgNP-containing health food product. Serial dilutions, filtration, and acidification were applied to confirm that the method detected particles. Differentiation of dissolved and particulate silver (Ag) is a feature of the technique. Analysis of two wastewater samples demonstrated the applicability of SP-ICP-MS at nanograms per liter Ag concentrations. In this pilot study, AgNP was found at 100 to 200?ng/L in the presence of 50 to 500?ng/L dissolved Ag. The method provides the analytical capability to monitor Ag and other metal and metal oxide nanoparticles in fate, transport, stability, and toxicity studies using a commonly available laboratory instrument. Rapid throughput and element specificity are additional benefits of SP-ICP-MS as a measurement tool for metal and metal oxide engineered nanoparticles.     

Acute toxicity of locust insecticides to two indigenous invertebrates from Sahelian temporary ponds

During desert locust plagues large amounts of insecticides are used for control operations. Drift from these treatments and accidental overspraying may contaminate small surface waters such as temporary ponds. The present study describes methods for static acute toxicity tests with two abundant organisms that occur in temporary ponds in the African Sahel region: the fairy shrimp Streptocephalus sudanicus Daday (Branchiopoda, Anostraca, Streptocephalidae) and the backswimmer Anisops sardeus Herrich-Sch?ffer (Hemiptera, Notonectidae). The organisms were captured in the field and 48-h static toxicity tests were conducted in the laboratory. The assays were used to screen the toxicity of 11 formulated synthetic insecticides used in desert locust control and of spores of the mycopesticide Metarhizium anisopliae var. acridum. Most of the synthetic insecticides tested were highly toxic to both organisms (LC50 or EC50<1 mg/L). Exceptions were the toxicity of diflubenzuron to A. sardeus (moderately toxic: 1相似文献   

产毒节菱孢培养物对大型溞的毒性研究

本文以国际标准实验生物大型溞做为实验动物研究了节菱孢毒性培养物的毒性。结果表明节菱孢毒性培养物对大型溞的EC_(50)值分别为29.07mg/L(24h);20.57mg/L(48h);7.53mg/L(96h)。LC_(50)值分别为38.07mg/ (24h);24.37mg/L(48h);10.67mg/L(96h)。     

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.     

A relationship between gill silver accumulation and acute silver toxicity in the freshwater rainbow trout: support for the acute silver biotic ligand model

Rainbow trout were exposed to a range of silver concentrations (as AgNO3) in flowing synthetic soft water (0.05 mM Na+, 0.05 mM Cl-, 0.05 mM Ca2+, 0.02 mM Mg2+, 0.02 mM K+, pH 7.0, approximately 0.7 mg C/L dissolved organic carbon, 10 mg CaCO3/L, 10 +/- 2 degrees C) to investigate a possible relationship between short-term gill silver accumulation (3 h or 24 h) and acute silver toxicity (96-h mortality). We also investigated potential relationships between gill silver accumulation and inhibition of Na+ uptake plus inhibition of gill Na+K(+)-adenosine triphosphatase (ATPase) activity. The 96-h median lethal concentration (LC50) values were 13.3 microg total Ag L(-1) and 3.3 microg dissolved Ag L(-1). A relationship was demonstrated between 3-h and 24-h gill silver accumulation and 96-h mortality. A relationship also was demonstrated between gill silver accumulation and inhibition of Na+ uptake at 24 h of exposure. No relationship between gill silver accumulation and inhibition of gill Na+K(+)-ATPase activity was found. The 96-h median lethal gill accumulation (LA50) values of 129 (at 3 h) and 191 ng g(-1) (at 24 h) and a conditional equilibrium binding constant of 8.0 for Ag+ binding to the gills were calculated. These observations support use of the silver biotic ligand model (BLM) as a regulatory tool to predict acute silver toxicity.