96-h LC50s Research Articles

Developmental stage-specific life-cycle bioassay for assessment of sediment-associated toxicant effects on benthic copepod production.

In chronic bioassays of sediment organic compounds, toxicant exposures often decline through time, such that the beginning of a test yields disproportionately higher exposures than the end. Thus, those life stages initiating a test often are exposed to the highest concentrations, and for rapidly maturing test fauna, this may lead to varying conclusions regarding compound toxicities depending on the initial life stage chosen. This problem can be addressed by comparative full life-cycle tests initiated with different test-organism life stages. Thus, a full life stage-to-life stage toxicity test was developed for the rapidly maturing meiobenthic copepod Amphiascus tenuiremis to assess the importance of developmental stage at the onset of sediment toxicant exposure relative to reproduction, net population growth, and sex and age structure. Tests were conducted with a model spiked-sediment insecticide, chlorpyrifos, for each of the major life stages (P1) of A. tenuiremis (nauplius, copepodite, and adult). Each P1 stage was allowed to mature and reproduce in low chlorpyrifos concentrations (6-33% of stage-specific 96-h LC50s; 4-22 ng chlorpyrifos/g dry sediment) for 26 d. Test endpoints were numbers of surviving adult females, males, eggs per female (clutch), first generation (F1) nauplii, F1 copepodites, F1 total production, and realized F1 production per surviving female. Only the copepodite P1 test showed a significant decline in survival of an adult age class: females declined by 28% at 22 ng/g. Reductions in total production ranged from 33-96% of controls from nauplius to adult. The P1 naupliar stage was most sensitive, with F1 production being 33-47% of that in controls. However, on a realized production per female basis, both the copepodite and naupliar P1 yielded significantly reduced F1s of 23 and 40% of controls at 11 and 22 ng/g.

Toxicity of copper sulfate for survival, growth, molting and feeding of juveniles of the tiger shrimp, Penaeus monodon

The aim of this study was to determine the acute and chronic toxicity of copper sulfate for juveniles of Penaeus monodon. The 96-h LC50s (median lethal concentrations) of copper on juvenile P. monodon (0.63±0.13 g) were 3.13 and 7.73 mg/l in seawater of 15‰ and 25‰, respectively. The mortality rates of P. monodon juveniles (0.19±0.02 g) following exposure to 0 (control), 0.45, 0.90, 1.80 and 4.50 mg/l copper after 30 days was 0%, 0%, 5.6%, 22.2% and 55.6%, respectively. After 30 days of exposure, the body weight and total length of shrimps exposed to copper at 0.90 mg/l and higher was significantly lower ( P<0.05) than those in the control. The 30-day EC50 (concentration that reduced weight gain by 50% of that of the controls) and 60-day EC50 were 2.82 and 1.89 mg/l copper, respectively. The ratio of carapace length to total length of shrimps exposed to copper at 0.90 mg/l was significantly higher ( P<0.05) than the controls. Following exposure to copper as low as 0.90 mg/l, P. monodon shortened the time to the first molt, and decreased its growth and molting frequency. Following exposure to copper as low as 5.0 mg/l, P. monodon juveniles (6.25±0.09 g) decreased their feeding. The MATC (maximum acceptable toxicant concentration) was 0.45 mg/l copper based on the growth and molting of shrimps weighing 0.18–1.03 g, and was 1.0 mg/l copper based on the feeding of shrimps weighing 6.25 g.

Hazard/Risk Assessment of Pyridaben: II. Outdoor Aquatic Toxicity Studies and the Water-Effect Ratio

Outdoor acute aquatic toxicity studies with pyridaben and bluegill sunfish (Lepomis macrochirus) and mysid (Mysidopsis bahia) showed that the 96-h LC50s in site-specific water were significantly greater than in classical laboratory studies. In addition, outdoor acute studies showed that pyridaben degrades rapidly in water, in hours, which supports other laboratory and field studies on the fate of pyridaben in aquatic systems. Chronic toxicity to aquatic organisms is not an issue after application in the field because exposures will be brief. The water-effect ratio (WER) of site-specific to laboratory-water 96-h LC50s for L. macrochirus and M. bahia were 18.5 and 24.5, respectively. The lowest WER was used as an application factor with the laboratory LC50 values of several other aquatic organisms to develop “adjusted” site-specific LC50 values. Comparison of the distribution of “adjusted” LC50 values with a distribution of potential environmental exposure concentrations for pyridaben in water indicates minimal acute risk to aquatic organisms. When only acute laboratory data are available, the WER approach is a relevant and realistic means for determining an application factor and for estimating the aquatic hazard/risk assessment of non-persistent pesticides, because it considers a host of factors that affect bioavailability and subsequent toxicity.

Combining sediment quality criteria and sediment bioassays with photoactivation for assessing sediment quality along the Swedish West Coast

Sediments from 48 sites along the Swedish West Coast were sampled for determination of priority pollutants (metals, polycyclic aromatic hydrocarbons and chlorinated hydrocarbons). Toxicity to two crustaceans ( Daphnia magna and Nitocra spinipes) were also determined within 2 weeks and after 12 months of storage at 4°C. Since, according to earlier studies, polycyclic aromatic hydrocarbons may exhibit photoinduced toxicity, all test vessels (including exposed test organisms) were subjected to ultraviolet irradiation after immobility/lethality was recorded. Thereafter, the vessels were recorded again for immobility/lethality and the data were compared with phototoxicity data of analyzed substances, in order to estimate the bioavailability of phototoxic hydrocarbons in these sediments. Immobility of Daphnia exposed to 16% sediment (wet weight) ranged from 0 to 80% both before and after photo treatment. Nitocra 96-h LC 50s (% wet weight of sediment) ranged from 1.9 to >32% before, and from 1.0 to >32% after ultraviolet treatment. The sensitivity to the different sediments as well as the photo-activation was species dependent and differed between fresh and stored sediments. Photoactivation in Daphnia was generally low but significant in an analysis of variance test. Compared with two different sediment quality guidelines it was found that some sediments would be classified as moderately or strongly polluted. These values did not always coincide with toxicity to any of the two species. The guidelines were thus of no value in predicting sediment toxicity. Correlations between toxicity and chemicals measured in the sediments were also highly variable and inconsistent. Photo-induced toxicity in Nitocra did not correlate (p<0.01) to any of the analyzed substances, and a clear pattern between ultraviolet-induced toxicity to Daphnia and polycyclic aromatic hydrocarbon concentrations in the sediments was not obtained, possibly because most sediments contained relatively low amounts of bioavailable material. However, the sediment sample with the highest concentrations of photoactive PAHS such as pyrene did demonstrate the greatest increase in toxicity (39%) following ultraviolet irradiation.

Lethal levels of selected water quality variables to larval and juvenile Lost River and shortnose suckers

Resource managers hypothesize that occasional fish kills during summer–early fall in Upper Klamath Lake, Oregon, may be linked to unfavorable water quality conditions created by massive algal blooms. In a preliminary effort to address this concern, short-term (96-h-long) laboratory tests were conducted with larval and juvenile Lost River ( Deltistes luxatus) and shortnose ( Chasmistes brevirostris) suckers to determine the upper median lethal concentrations (LC 50s; also referred to as median tolerance limits) for pH, un-ionized ammonia, and water temperature, and the lower LC 50s for dissolved oxygen. The mean LC 50s varied among species and life stages as follows: for pH, 10.30–10.39; for un-ionized ammonia, 0.48–1.06 mg litre −1; for temperature, 30.35–31.82°C; and for dissolved oxygen, 1.34–2.10 mg litre −1. Comparisons of 95% confidence limits indicated that, on average, the 96-h LC 50s were not significantly different from those computed for shorter exposure times (i.e., 24 h, 48 h, and 72 h). According to two-way analysis of variance, LC 50s for the four water quality variables did not vary significantly ( p>0.05) between fish species. However, LC 50s for pH (exposure times of 24 h and 48 h) and dissolved oxygen (exposure times of 48 h, 72 h, and 96 h) differed significantly ( p≤0.05) between life stages, whereas LC 50s for un-ionized ammonia and water temperature did not exhibit significant differences. In general, larvae were more sensitive than juveniles to high pH and low dissolved oxygen concentrations. When compared to ambient water quality conditions in Upper Klamath Lake, our results strongly suggest that near-anoxic conditions associated with the senescence phase of algal blooms are most likely to cause high mortalities of larval and juvenile suckers.

Combining sediment quality criteria and sediment bioassays with photoactivation for assessing sediment quality along the Swedish West Coast

Abstract Sediments from 48 sites along the Swedish West Coast were sampled for determination of priority pollutants (metals, polycyclic aromatic hydrocarbons and chlorinated hydrocarbons). Toxicity to two crustaceans (Daphnia magna and Nitocra spinipes) were also determined within 2 weeks and after 12 months of storage at 4°C. Since, according to earlier studies, polycyclic aromatic hydrocarbons may exhibit photoinduced toxicity, all test vessels (including exposed test organisms) were subjected to ultraviolet irradiation after immobility/lethality was recorded. Thereafter, the vessels were recorded again for immobility/lethality and the data were compared with phototoxicity data of analyzed substances, in order to estimate the bioavailability of phototoxic hydrocarbons in these sediments. Immobility of Daphnia exposed to 16% sediment (wet weight) ranged from 0 to 80% both before and after photo treatment. Nitocra 96-h LC50s (% wet weight of sediment) ranged from 1.9 to &amp;gt; 32% before, and from 1.0 to &amp;gt; 32% after ultraviolet treatment. The sensitivity to the different sediments as well as the photoactivation was species dependent and differed between fresh and stored sediments. Photoactivation in Daphnia was generally low but significant in an analysis of variance test. Compared with two different sediment quality guidelines it was found that some sediments would be classified as moderately or strongly polluted. These values did not always coincide with toxicity to any of the two species. The guidelines were thus of no value in predicting sediment toxicity. Correlations between toxicity and chemicals measured in the sediments were also highly variable and inconsistent. Photo-induced toxicity in Nitocra did not correlate (p &amp;lt; 0.01) to any of the analyzed substances, and a clear pattern between ultraviolet-induced toxicity to Daphnia and polycyclic aromatic hydrocarbon concentrations in the sediments was not obtained, possibly because most sediments contained relatively low amounts of bioavailable material. However, the sediment sample with the highest concentrations of photoactive PAHS such as pyrene did demonstrate the greatest increase in toxicity (39%) following ultraviolet irradiation.

Toxicity of Scrap Tire Leachates in Estuarine Salinities: Are Tires Acceptable for Artificial Reefs?

Shredded scrap tires were leached in a modified toxicity characteristic leaching procedure (TCLP) extraction method in synthetic saltwater solutions for three sequential 7-d periods. Test salinities were 5, 15, and 25‰. Acute toxicity tests were conducted with larval sheepshead minnows Cyprinodon variegatus and daggerblade grass shrimp Palaemonetes pugio. Mortality decreased following multiple sequential leaching periods. Toxicity decreased with increasing salinity. The fish were more sensitive than the grass shrimp. Dilution series toxicity bioassays were performed with fish and grass shrimp at 5‰ salinity and at 15‰ with fish only. The 96-h LC50s (lethal concentration for half of the test animals) for fish were 10% leachate at 5‰ and 26% at 15‰. The 96-h LC50 for grass shrimp at 5‰ was 63%. The 96-h lowest observed effect concentrations (LOEC) for fish survival were 12.5% at 5‰ and 25% at 15‰. The 96-h LOEC for grass shrimp survival was 50% at 5‰. Growth LOEC values were 12.5% at both salinities for fish and 50% for grass shrimp at 5‰. Chemical analyses revealed no specific components as the cause of observed toxicity. Antagonism between sea salt and toxic chemicals is hypothesized to cause differential toxicity at varying salinities, as opposed to differential solubility of the toxicants. Extrapolation of laboratory results indicates that proposed tire reefs should not pose a serious threat to water quality in Chesapeake Bay. No observed effects concentrations (NOEC) were an order of magnitude or greater above field concentrations calculated from simplified methods. Toxic substances appear to leach from the surface of the tires not from the tire matrix. The use of tires in higher salinity environments appears to pose little direct toxicological risk to resident organisms. However, because unknown toxic chemicals were present in leachates at all test salinities, no assessment can be made regarding persistence, fate, transport, or possible bioaccumulative effects.

Acute and chronic toxicity of the herbicide Stam M-4 in field and laboratory exposures.

Propanil (3',4'-dichloropropionanilide), the active ingredient in the herbicide Stam M-4, is possibly the most extensively used herbicide for rice production in the world. Propanil and its metabolites are transported within characteristic ditch ecosystems in the production landscape of northeast Arkansas. Runoff from these ditch ecosystems is further transported to a river or other water body supplied by the Mississippi River Alluvial aquifer. Forty-eight-hour acute toxicity tests with Ceriodaphnia dubia (cladoceran) and Pimphales promelas (fathead minnow) were conducted on stormwater runoff, laboratory synthetic water, and irrigation (ground) water. No effects on survival were observed in this study following 48-h toxicity testing with the stormwater. Survival studies indicated assimilative capacity in irrigation (ground) water as opposed to laboratory synthetic water. Mean 48-h LC50s of C. dubia increased from 2.94 mg/L Stam M-4 in laboratory synthetic water to 8.01 mg/L Stam M-4 in irrigation water. Likewise, P. promelas mean 48-h LC50s increased from 23.76 (laboratory synthetic water) to 33.52 mg/L Stam(R)M-4 (ground water). In 7-d chronic tests, there was an increase in mean LC50s of C. dubia when comparing synthetic water to irrigation water (0.48 to 1.24 mg/L Stam M-4, respectively). P. promelas, however, had less tolerance for Stam M-4 in irrigation water (4.45 mg/L) than in synthetic water (5.93 mg/L) in 7-d chronic toxicity tests. Forty-eight-hour toxicity tests indicate that ground water affords organisms some assimilative capacity that laboratory synthetic water does not. Since herbicides and most other pesticides are manufactured to elicit rapid responses, 48-h toxicity results best describe potential nontarget organism effects in aquatic ecosystems.

Comparative acute ammonia toxicity in marine fish and plasma ammonia response

Using a continuous-flow method a total of 14 acute toxicity bioassays were conducted using seabass ( Dicentrarchus labrax), seabream ( Spams aurata) and turbot ( Scophthalmus maximus) juveniles weighing from 6 to 163 g (wet weight). Median LC50s of un-ionized ammonia-nitrogen (UIA-N) and median LT50s (plus their confidence intervals) were calculated for 6, 12, 24, 48 and 96-h exposures for each trial. Under optimal environmental conditions (17–18 °C, 34%. S, 8.15 pH and oxygen over 75% saturation), median 96-h LC50s averaged 1.7 mg 1 −1 UIA-N (40 mg 1 −1 TAN, total ammonia nitrogen) in seabass compared with 2.5–2.6 mg 1 −1 UIA-N (57–59 mg 1 −1 TAN) in seabream and turbot. Median LC50s did not change significantly from 24 to 96-h exposure and were not related to fish size. Significant variations in fish sensitivity were observed from one group to another and seabass juveniles appeared to be more susceptible to ammonia than seabream and turbot. In all species, mortality occurred over a relatively narrow range of ammonia concentrations. Lethal threshold concentrations (LTC) were estimated to be over 90% of 96-h LC50s. In starved fish, blood plasma levels of ammonia, which were positively correlated with ambient ammonia, can be used to estimate the extent of ammonia toxicity. The same increase in plasma TAN vs. ambient ammonia level was observed in seabass, seabream and turbot. A mortality of 50% was observed after a 4-day exposure when the increase in TAN was 4 times the initial level in seabass and more than 10 times the normal level in seabream and turbot. These results show, for the first time, that seabass unlike seabream and turbot have lower thresholds of physiological disturbances, which explains why they are more sensitive to ammonia.

Chronic effects of low insecticide concentrations on freshwater caddisfly larvae

The insecticide load in surface waters does not ordinarily reach concentrations acutely toxic to aquatic fauna. The effects of the low insecticide concentrations typical of natural habitats are still not clear, for they often appear only after relatively long exposure times. To test such a situation, the insecticides lindane and parathion were introduced into a static-with-renewal outdoor aquaria system at concentrations about four and five orders of magnitude lower than their respective 96-h LC50s, and their chronic (about 90 days) effects on the survival rate of freshwater caddisfly larvae were observed. The emergence and hence survival rate of Limnephilus lunatus Curtis was significantly reduced by lindane at 0.1 ng l−1, a value nearly five orders of magnitude lower than the 96-h LC50. Parathion, with acute and subacute toxicity similar to that of lindane, did not significantly alter the emergence rate of this species. In contrast, this substance did produce a significant reduction in emergence rate of the closely related species Limnephilus bipunctatus Curtis at 1 ng l−1, even though this species was significantly less susceptible than L. lunatus to parathion at high concentrations. We conclude that chronic insecticide exposure can be hazardous to freshwater macroinvertebrates even at unexpectedly low concentrations. The low-concentration effects may depend on both species and substance and therefore cannot be predicted from toxicity data at higher concentrations.

The Toxicity of Diquat, Endothall, and Fluridone to the Early Life Stages of Fish

ABSTRACT While most aquatic herbicides have undergone some toxicity testing for effects on non-target aquatic organisms, little of this testing has been conducted on early life stages of gamefish found in lakes undergoing treatment. Commercial formulations of diquat, endothall, and fluridone were selected for acute toxicity testing using very early life stages of walleye (Stizostedion vitreum), largemouth bass (Micropterus salmoides), and smallmouth bass (Micropterus dolomieu). In addition, the rates of diquat photodegradation and uptake by sediment were determined. These results were used to predict diquat concentrations in lakes of various depths. The results of the toxicity tests were compared to the predicted concentrations. Diquat, with 96-h LCSOs of 0.74–4.9 mg/L, was more toxic to these early life stages than endothall or fluridone, with 96-h LC50s of 16–130 mg/L and 1.8–13 mg/L respectively. The LC50s for endothall and fluridone were at least one order of magnitude greater than the labeled application concentrations. As the LC50s for diquat were very close to the predicted concentration, the safety margin for the use of diquat appears to be very small.

Effects of varying salinities on the toxicity of potassium permanganate to larval and juvenile striped bass, Morone saxatilis (Walbaum)

. Eight-day-old striped bass, Morone saxatilus (Walbaum) larvae, and one-month-old juveniles were held in varying salinities and exposed to a range of concentrations of potassium permanganate. Lethal concentrations of potassium permanganate for 50% of the larval fish exposed for96h (96h LC50) were 1middot;02, 2 middot;11, 1 middot;41 and 1 middot;73mg/1 for salinities of 0, 3, 6and 9 g/l, respectively; The 96h LC50S for juveniles were 0 middot;96, 3 middot;26, 1 middot;63 and 1 middot;48 mg/l for salinities of 0, 5, 10 and 15g/l, respectively. There were significant differences in 96h LC50 values at different salinities for both life stages. The 96 h LC50 values derived for both life stages revealed a decrease in toxicity as salinity increased from 0 to 3–5g/l. Results indicated potassium permanganate to be toxic in fresh water to striped bass larvae and fingerlings at recommended treatment levels (3 middot;0mg/l).

Influence of Salinity on Atrazine Toxicity to a Chesapeake Bay Copepod (Eurytemora affinis) and Fish (Cyprinodon variegatus)

The objective of this study was to determine the influence of a range of salinities (5%., 15%., and 25%.) on the acute toxicity of atrazine to nauplii of the copepodEurytemora affinis and larvae of the sheepshead minnow,Cyprinodon variegatus. Ninety-six-hour LC50 values for the copepod were 0.5 mg 1−1, 2.6 mg 1−1, and 13.2 mg 1−1 at salimities of 5%., 15%. and 25%. respectively. A comparison of LC50 values between adjacent salinities showed a statistical difference between 15%. and 25%. but not between 5%. and 15%.. Atrazine was more toxic toE. affinis at the lowest salinity. The 96-h LC50s for the sheepshead minnow were 16.2 mg 1−1, 2.3 mg 1−1, and 2.0 mg 1−1 at salinities of 5%., 15%., and 25%., respectively. There was a statistical difference between LC50 values at 5%. and 15%. but not between 15%. and 25%.. In contrast toE. affinis results, atrazine was more toxic toC. variegatus at the highest salinity. The toxicity data from these species suggest that development of estuarine water quality criteria is warranted.

Acute and chronic effects of four commercial herbicide formulations on Ceriodaphnia dubia

Toxicity tests with Ceriodaphnia dubia were conducted to determine acute (48 h) and chronic (7-day survival and reproduction) effects of four commonly used herbicide formulations. The 48-h LC50s in decreasing order of toxicity were 14.36 mg/L (Micro-Tech®), 15.93 mg/L (Bicep®), 32.99 mg/L (Extrazine®), and 35.36 mg/L (Lexone®). Reduced reproduction was detected at concentrations below 48-h LC50s for three of the formulations. The 7-day chronic values (ChV) based on reproduction were 17.68 mg/L (Micro-Tech®), 8.84 mg/L (Bicep®), 17.68 mg/L (Extrazine®), and 8.84 mg/L (Lexone®). The acute-to-chronic ratios (ACRs) for Micro-Tech® (0.81), Bicep® (1.80), Extrazine® (1.86), and Lexone® (4.00) indicate a relatively narrow range between acute and chronic sensitivity in daphnids. A comparison of these response data to environmental concentrations suggests these herbicides are not likely to directly impact invertebrates. Potential impacts on plants and human health should be of primary ecological and regulatory concern.

A review of the relationship between acute toxicity (LC 50) of γ-hexachlorocyclohexane (γ-HCH, Lindane) and total lipid content of different fish species

This paper provides an explanation for a 40-fold difference in the acute toxicity (LC 50) of γ-hexachlorocyclohexane (γ-HCH, Lindane) in 14 different fish species, based on well recognized principles of toxicokinetics and toxicodynamics in combination with a compilation of data from the literature and some original data. The 48-h median lethal concentration (48-h LC 50) of γ-HCH in 14 fish species, belonging to 6 families, range from 22 to 900 μg/l. A significant positive linear relationship was found between lipid content (% of wet weight) and the 48-h LC 50 of γ-HCH in these fish species, revealing that the toxicity of γ-HCH in various fish species in decreasing with increasing total lipid content. If median lethal concentrations are normalized for 1% lipid content, then the range of 48-h LC 50s is reduced to between 18 and 32 μg/l. It is concluded that lipids of aquatic organisms can serve (among other functions) as a protective storage site against the toxic effects of γ-HCH and, possibly, of other lipophilic, persistent organic chemicals which are bioconcentrated in body lipids. Therefore, in organisms with higher lipid content, a smaller fraction of a lipophilic chemical will reach target organs (liver, lung, central and peripheral nerves, etc.) to cause adverse effects. Results suggest that this correlation can be used to extrapolate the acute toxicity (48-h LC 50) of γ-HCH to other fish species if their lipid content is known. Furthermore, the data generated by extrapolation of this correlation could be useful in the environmental risk assessment of freshwater and marine organisms.

Toxicity of leachate from automobile tires to aquatic biota

A laboratory study was conducted to determine if automobile tires immersed in fresh water leach chemicals which are toxic to aquatic biota. Three tire types were examined - tires obtained from a floating tire breakwater; road-worn tires from the same vehicle; and new tires. Whole tires were immersed in 300 L of water (natural groundwater) and subsamples (40 L) of water were removed at 5, 10, 20 and 40 d for use in acute static lethality tests. Overlying water from both new and used tires was lethal to rainbow trout ( Oncorhynchus mykiss) but leachate from used tires was more toxic (96-h LC50s - 11.8 to 19.3 %v/v) than leachate from new tires (96-h LC50s - 52.1 to 80.4 %v/v). In addition, leachate remained relatively toxic to rainbow trout over time (8 d for new and 32 d for used) after tires were removed from the aquaria indicating that the chemicals responsible for toxicity degrade slowly and are non-volatile. No toxicity to cladocerans ( Daphnia magna; 48-h exposure) or fathead minnows ( Pimephales promelas; 96-h exposure to leachate from 20 and 40 d only) was observed with these same leachates. Tires from a floating tire breakwater which had been installed for several (10) years did not release chemicals which were toxic to any species tested. In separate experiments, concentrated (10X) leachate from tires immersed for 25 d in water inhibited bioluminescence in the marine bacterium, Photobacterium phosphoreum, (Microtox™ test), the enzyme, β-galactosidase, in mutant Escherichia coli (ToxiChromo™ Test) and the enzyme, NADH-coenzyme Q reductase, in the inner membrane of mitochondria (beef heart submitochrondria particle test). Several other screening tests (e.g., nematode lethality/mutagenicity test; bacterium ( Spirillum volutans) motility inhibition test and the SOS-Chromotest with and without S-9 activation) were not sensitive to tire leachates. Further studies to identify the toxic compounds and to determne the extent of toxicity under field conditions of dilution are necessary.

Effect of pH and Dissolved Organic Carbon on the Toxicity of Copper to Larval Fathead Minnow (Pimephales promelas) in Natural Lake Waters of Low Alkalinity

The impacts of pH and dissolved organic carbon (DOC) on the acute toxicity of Cu to larval fathead minnow (Pimephales promelas) were determined using natural soft water from two Precambrian Shield lakes in south-central Ontario. By artificially manipulating the pH and DOC levels of the water, we demonstrated that both acidification and the removal of DOC increased the toxicity of Cu. The 96-h Cu LC50s were determined over a pH range from 5.4 to 7.3 and a DOC concentration range from 0.2 to 16 mg∙L−1. The LC50s ranged from a low of 2 μg∙L−1(pH 5.6, DOC 0.2 mg∙L−1) to a high of 182 μg∙L−1(pH 6.9, DOC 15.6 mg∙L−1). A multiple regression model (log1096-h Cu LC50 = −0.308 + 0.192 pH + 0.136 (pH∙log10DOC)) was used to describe the relationship between Cu toxicity, pH, and DOC. The model was significant (p &lt; 0.00001) and explained 93% of the variability in the toxicity data. These results suggest that current water quality objectives for Cu, and possibly for other metals, may not be sufficiently protective of aquatic life in soft, moderately acidic water containing low levels of DOC.

The relationship of total copper 48-H LC50s toDaphnia magnadry weight

A study was conducted with Daphnia magna to determine the effect of neonate weight loss or lack of weight gain on experimentally derived copper 48-h LC50s. Standard unfed tests as well as algal-fed (Selenastrum capricornutum) tests were used to look at weight loss and gain. No significant relationship was found between amount of weight loss and copper LC50s. However, dry weight of unfed and algal-fed control organisms could be used to predict total copper LC50s.

Effect of hardness on bioavailability and toxicity of cadmium to rainbow trout

Water quality characteristics affecting toxicity of metals to aquatic life include pH, inorganic and organic ligands (negatively charged ions and molecules), and water hardness. Ligands control the ability of natural waters to bind metals which could adversely affect aquatic life. Bioavailability of metals in natural waters is primarily controlled by alkalinity. Hardness does not affect metal complexation but can reduce acute toxicity through antagonistic mechanisms. In most natural waters, concentrations of alkalinity and hardness are similar, but they may be very different in some waters.Most toxicity studies have not distinguished between reduced toxicity resulting from effects of hardness and that resulting from complexation of metals by ligands. A series of acute and long-term experiments were conducted to assess these relationships while exposing rainbow trout (Oncorhynchus mykiss) to cadmium (Cd) in waters of low alkalinity (30 mg L−1) and hardnesses of 400, 200, and 50 mg L−1 adjusted with magnesium sulfate (MgSO4). These tests did not show a strong antagonistic influence of Mg hardness on Cd toxicity. At Mg hardnesses of 50, 200, and 400 mg L−1, 96-h LC50s were 3.02, 6.12, and 5.70 μg Cd L−1, differing by a factor of only 1.8. Similarly, chronic values derived from 100-day experiments in waters with the same range of hardness were 1.47, 3.57, and 3.64 μg L−1, respectively. With an eight-fold difference in Mg hardness, chronic values differed by a factor of only 2.5. Antagonistic properties of hardness are primarily controlled by Ca with Mg playing a minor role. The long-term role of Ca in reducing metal toxicity will require further investigation.

Bicarbonate as a Potential Confounding Factor in Cladoceran Toxicity Assessments of Pore Water from Contaminated Sediments

Elevated alkalinity values measured in sediment pore water samples from the Grand Calumet River–Indiana Harbor Canal, an International joint Commission Area of Concern (AOC), caused concern over the potential effects of alkalinity on cladoceran test responses. Forty-eight-hour tests with NaHCO3and NaCl as reference toxicants indicated that NaHCO3toxicity to Daphnia magna and Ceriodaphnia dubia was due to both Na+and HCO3−, although greater HCO3−toxicity was observed to D. magna. Theoretical HCO3−concentrations in sediment pore waters from the AOC demonstrated sufficient HCO3−in several samples to produce acute toxicity, based on 48-h LC50s from the reference toxicant tests. X-ray microanalysis was conducted to qualitatively assess the effects on internal Cl−levels of D. magna after exposure to NaHCO3, to an AOC sediment pore water sample, and to NaSCN, a metabolic inhibitor of Cl−uptake. Based on these results the proposed mechanism of HCO3−toxicity to D. magna is the inhibition of the active uptake of Cl−from water. We suggest that pore water alkalinity should be considered when interpreting the results of sediment pore water and effluent toxicity tests with D. magna, other cladocerans, and, perhaps, other invertebrates and fish.