Toxicity of chlorinated benzenes to fathead minnows (Pimephales promelas)

The toxicities of several chlorinated benzene compounds to fathead minnows (Pimephales promelas) were determined. Chronic toxicities were estimated from 32–33 day embryo through early juvenile development exposures. The ranges between the highest no observable effect concentration (NOEC) and lowest observed effect concentration (LOEC) were 1,000–2,300, 570–1,000, and 240–410 g/L for 1,3-dichlorobenzene (1,3-DCB), 1,4-dichlorobenzene (1,4-DCB), and 1,2,3,4-tetrachlorobenzene (1,2,3,4-TCB), respectively. Pentachlorobenzene (Penta-CB) and hexachlorobenzene (HCB) were non-toxic at the highest concentrations of 55 and 4.8 g/L (near water saturation), respectively, that could be maintained in the test chambers. The tissue concentrations associated with the NOEC and LOEC for 1,3-DCB, 1,4-DCB and 1,2,3,4,-TCB were 120–160, 70–100, and 640–1,100 g of chemical per gram of fish tissue (wet weight), respectively. The mean Penta-CB and HCB tissue concentration obtained at the NOEC of 55 and 4.8 g/L were 390 and 97 g/g, respectively. Mean bioconcentration factors obtained in these tests were 97, 110, 2,400, 8,400 and 22,000 for 1,3-DCB, 1,4-DCB, 1,2,3,4-TCB, Penta-CB and HCB, respectively. At a Penta-CB concentration of 130 g/L (near water saturation) in a six day exposure conducted in the reservoir of the chemical saturating apparatus and control, juvenile fathead minnow behavior was affected and lipid content was reduced when compared to the control. Ninety-six hr LC50 values, obtained with juvenile fish, for 1,3-DCB, 1,4-DCB, and 1,2,3,4-TCB were 7,800, 4,200, and 1,100 (g/L, respectively.     

Acute and chronic toxicity of nickel to a cladoceran (Ceriodaphnia dubia) and an amphipod (Hyalella azteca)

This study evaluated acute and chronic nickel (Ni) toxicity to Ceriodaphnia dubia and Hyalella azteca with the objective of generating information for the development of a biotic ligand model for Ni. Testing with C. dubia was used to evaluate the effect of ambient hardness on Ni toxicity, whereas the larger H. azteca was used to derive lethal body burden information for Ni toxicity. As was expected, acute C. dubia median lethal concentrations (LC50s) for Ni increased with increasing water hardness. The 48-h LC50s were 81, 148, 261, and 400 microg/L at hardnesses of 50, 113, 161, and 253 mg/L (as CaCO3), respectively. Ceriodaphnia dubia was found to be significantly more sensitive in chronic exposures than other species tested (including other daphnids such as Daphnia magna); chronic toxicity was less dependent on hardness than was acute toxicity. Chronic 20% effective concentrations (EC20s) were estimated at <3.8, 4.7, 4.0, and 6.9 microg/L at hardnesses of 50, 113, 161, and 253 mg/L, respectively. Testing with H. azteca resulted in a 96-h LC50 of 3,045 microg/L and a 14-d EC20 of 61 microg/L at a hardness of 98 mg/L (as CaCO3). Survival was more sensitive than was growth in the chronic study with H. azteca. The 20% lethal accumulation effect level based on measured Ni body burdens was 247 nmol/g wet weight.     

Joint acute toxicity of esfenvalerate and diazinon to larval fathead minnows (Pimephales promelas)

California (USA) agriculture employs pyrethroid and organophosphate insecticides to control insects in orchards and other crops. Diazinon and esfenvalerate were selected for this study because of their application overlaps. Toxicological and biochemical responses of larval fathead minnows (Pimephales promelas) exposed singly and in combinations to esfenvalerate and diazinon were determined. Exposures were 96-h static renewal tests that used standard U.S. Environmental Protection Agency acute toxicity test methods. After pesticide exposures, larvae were evaluated for carboxylesterase and acetylcholinesterase activity, and histopathological effects. Carboxylesterase activity was examined because of its potential influence on the toxicity of both organophosphates and pyrethroids. In vivo studies demonstrated that diazinon significantly inhibited carboxylesterase activity at nominal water concentrations as low as 50 microg/L. However, esfenvalerate did not affect carboxylesterase activity at any concentration tested. Liver glycogen depletion was the only histopathological effect observed; this effect was demonstrated with the individual pesticides and pesticide combinations (i.e., mixtures). The combinations of diazinon and esfenvalerate causing acute toxicity to fathead minnow larvae appeared to be greater than additive (i.e., synergistic) in all three tests.     

Comparison of short-term chronic and chronic silver toxicity to fathead minnows in unamended and sodium chloride-amended waters

The chronic (early life stage [ELS]) and short-term chronic (STC) toxicity of silver (as silver nitrate) to fathead minnows (FHM) was determined concurrently in flow-through exposures (33 volume additions/d). Paired ELS (approximately 30 d) and STC (7 d) studies were conducted with and without the addition of 60 mg/L Cl (as NaCl). The paired studies in unamended water were later repeated using standard flow conditions (9 volume additions/d). The purpose of the paired studies was to determine if short-term chronic endpoints can be used to predict effects in ELS studies. For each experiment, a "split-chamber" design (organisms were held in a common exposure chamber) allowed the direct comparison between short-term and chronic exposures. It appeared that the chronic toxicity of silver was mitigated to some extent by NaCl addition. The maximum acceptable toxicant concentration for growth in the ELS study was 0.53 microg dissolved Ag/L under standard flow conditions. Early life stage and STC endpoints in all three studies typically agreed within a factor of two. Whole-body sodium and silver concentrations measured in individual fathead minnows during these studies showed an increase in silver body burdens and a decrease in sodium concentration. These results indicate that the STC study could be used as a surrogate test to estimate chronic toxicity and that the mechanism of chronic silver toxicity may be the same as for acute toxicity.     

Influence of water quality and age on nickel toxicity to fathead minnows (Pimephales promelas)

This research characterized the effects of water quality and organism age on the toxicity of nickel (Ni) to fathead minnows (Pimephales promelas) to facilitate the accurate development of site-specific water-quality criteria. Nickel sulfate hexahydrate (NiSO4 x 6H2O) was used as the Ni source for performing acute toxicity tests (median lethal concentration after 96-h exposure [96-h LC50]) with < 1-d-old and 28-d-old P. promelas under varying regimes of hardness, pH, alkalinity, and natural organic matter (NOM). The toxicity of Ni was inversely related to water hardness between hardness values of 20 and 150 mg/L (as CaCO3). Below 30 mg/L alkalinity, Ni toxicity was related to alkalinity. The effect of pH was confounded by hardness and the presence of NOM. In the absence of NOM, the toxicity of Ni increased as pH increased at high hardness and alkalinity. In general, 28-d-old fish were less sensitive than < 1-d-old fish to Ni. This lower sensitivity ranged from 12-fold at low hardness and alkalinity (20 and 4 mg/L, respectively) to 5-fold at high hardness and alkalinity (100 and 400 mg/L, respectively). The presence of NOM (10 mg/L as dissolved organic carbon [DOC]) reduced Ni toxicity by up to 50%, but this effect appeared to be saturated above DOC at 5 mg/L. Incubating Ni with the NOM solution from 1 to 17 days had no effect on Ni toxicity. When using multivariate analysis, the 96-h LC50 for Ni was a function of fish age, alkalinity, hardness, and NOM (96-h LC50 = -0.642 + 0.270(fish age) + 0.005(alkalinity) + 0.018(hardness) + 0.138(DOC)). When using this model, we found a strong relationship between measured and predicted 96-h LC50 values (r2 = 0.94) throughout the treatment water qualities. The biotic ligand model (BLM) did not accurately predict Ni toxicity at high or low levels of alkalinity. Results of our research suggest that the BLM could be improved by considering NiCO3 to be bioavailable.     

Toxicity to fathead minnows of endrin in food and water

Fathead minnows (Pimephales promelas) were exposed during a partial chronic toxicity study to endrin concentrations in the water or food, or both, for 300 days encompassing reproduction. Tissue residues were analyzed at preset intervals for first-generation fish, and were also determined for embryos, larvae at hatch, and 30-day progeny. Gas-chromatographic and liquid-scintillation techniques were used to monitor the contribution of endrin from each source. The food was clams that had accumulated 14C-endrin when exposed to an endrin water concentration similar to that to which the fish were exposed. Higher endrin tissue residues were accumulated from the water than from food. Maximum concentration factors were 0.8 from the food and 13,000 from the water. Residues contributed by endrin in the food were additive to those from the water at all life stages. Endrin in the food (0.63 ppm) significantly reduced survival of the fathead minnows, and fish exposed to both endrin sources had lower survival than those exposed to either source alone. Endrin residues in embryos and larvae were highest and larval survival lowest for progeny of adults exposed to endrin in both food and water. Survival of 30-day progeny was significantly reduced at all test exposures (0.63 ppm in the food, water exposures of 0.14 and 0.25 ppb, and all combinations of food and water exposure).     

Toxicity of oil sands to early life stages of fathead minnows (Pimephales promelas)

The present study examines the effects of exposure to oil sands on the early life stages (ELS) of fathead minnows (Pimephales promelas). Sediments within and outside natural oil sand deposits were collected from sites along the Athabasca River (AB, Canada). The ELS toxicity tests were conducted with control water, natural oil sands, reference sediments, and oil-refining wastewater pond sediments. Eggs and larvae were exposed to 0.05 to 25.0 g sediment/L and observed for mortality, hatching, malformations, growth, and cytochrome P4501A induction as measured by immunohistochemistry. Natural bitumen and wastewater pond sediments caused significant hatching alterations and exposure-related increases in ELS mortality, malformations, and reduced size. Larval deformities included edemas, hemorrhages, and spinal malformations. Exposure to reference sediments and controls showed negligible embryo mortality and malformations and excellent larval survival. Sediment analyses using gas chromatography-mass spectrometry revealed high concentrations of alkyl-substituted polyaromatic hydrocarbons (PAHs) compared to unsubstituted PAHs in natural oil sands (220-360 microg/g) and oil-mining wastewater pond sediments (1,300 microg/g). The ELS sediment toxicity tests are rapid and sensitive bioassays that are useful in the assessment of petroleum toxicity to aquatic organisms.     

Influence of multiple water-quality characteristics on copper toxicity to fathead minnows (Pimephales promelas)

Water quality influences the bioavailability and toxicity of copper to aquatic organisms. Understanding the relationships between water-quality parameters and copper toxicity may facilitate the development of site-specific criteria for water quality and result in better protection of aquatic biota. Many studies have examined the influence of a single water-quality parameter on copper toxicity, but the interactions of several characteristics have not been well studied in low-hardness water. The goal of the present research was to examine the interactions among water-quality characteristics and their effects on copper toxicity to larval fathead minnows (Pimephales promelas). The effects of dissolved organic carbon (DOC) concentration, DOC source, pH, and hardness on acute copper toxicity were determined using a complete factorially designed experiment. Hardness, pH, DOC, and interaction of pH and DOC all significantly affected copper toxicity. A predictive model based on these data described 88% of the variability in copper toxicity. This model also explained 58% of the variability in copper toxicity for an independent dataset of South Carolina (USA) waters. The biotic ligand model underpredicted the acute copper toxicity to fathead minnows when compared with observed values.     

Toxicity of uranium mine-receiving waters to caged fathead minnows, Pimephales promelas

Larval fathead minnows (Pimephales promelas) were placed at four exposure sites for 7 days in each of five lakes surrounding the Key Lake uranium mine in northern Saskatchewan, Canada. Fish placed in lakes receiving Mo-contaminated mill effluent demonstrated higher mortalities than those placed in lakes receiving Ni-contaminated mine-dewatering effluent, which was not significantly different from reference sites. No significant differences were detected in fish growth among the study lakes because of the high (90%) mortality in Fox and Unknown lakes. Principal components analysis characterized exposure sites by total and dissolved metal concentration. Stepwise multiple regression of fish mortality on principal components generated from total metal data revealed that principal component 1 could account for 84% of the variance associated with fish mortality. Careful examination of the metals that correlated strongly with principal component 1 and with fish mortality suggested that dietary Se toxicity probably resulted in the differential fathead minnow mortality observed among study lakes.     

Metal effects on fathead minnows (Pimephales promelas) under field and laboratory conditions

The consequences of low-level metal exposure to early life stages of fathead minnows (Pimephales promelas) were investigated along a contamination gradient near Sudbury, Canada. Field exposures resulted in elevated hatching time and increased mortality in metal-contaminated lakes, in contrast to laboratory exposures where no effects were observed. Dissolved and ionic Cd and Ni were associated with changes in hatching time and larval mortality under field conditions, though other potential contaminants were not examined and may also have had an influence. The increased biological response of field-exposed fish, relative to fish exposed to the same water in laboratory conditions, may be the result of higher stress in natural environments, which could sensitize fish to contaminants. Analysis also indicated that, as contamination increases, the discrepancies between laboratory and field estimates of effect also increase. A temperature versus hatching time relationship was also quantified for fathead minnows.     

Uptake,elimination, and metabolism of three phenols by fathead minnows

Uptake rates of total¹⁴C in fathead minnows (Pimephales promelas) exposed to sublethal concentrations of radiolabeled test compounds followed the order: phenol > 2,4,5-trichlorophenol >p-nitrophenol. Mean whole body¹⁴C concentration factors were 15,800, 1,850, and 180 for phenol, 2,4,5-trichlorophenol, andp-nitrophenol exposures, respectively. Only minor amounts of tissue¹⁴C was parent compound after 28 days of exposure in fish exposed to phenol andp-nitrophenol, while 78.6% of the¹⁴C was parent compound in 2,4,5-trichlorophenol exposed fish. Tissue¹⁴C in fish exposed to 2,4,5-trichlorophenol was eliminated at a faster rate than in fish exposed to phenol orp-nitrophenol. Observed mean¹⁴C depuration half-lives for lower and higher exposures combined were 387, 150, and 12 hours for phenol,p-nitrophenol, and 2,4,5-trichlorophenol, respectively. Parent compound comprised 1.5, 2.7, and 0.7% of total¹⁴C for phenol, 2,4,5-trichlorophenol, andp-nitrophenol, respectively, after 28 days of depuration.The percentage of acetone-unextractable¹⁴C increased from the end of uptake to the end of depuration for phenol and 2,4,5-trichlorophenol, and decreased slightly forp-nitrophenol.¹⁴C contribution from polar metabolites increased relative to total¹⁴C during the depuration phase for 2,4,5-trichlorophenol andp-nitrophenol.     

Joint toxicity of chlorpyrifos and esfenvalerate to fathead minnows and midge larvae

The joint toxicity of esfenvalerate and chlorpyrifos to the fathead minnow (Pimephales promelas) and the aquatic midge larvae (Chironomus tentans) was determined using comparisons to independent action (IA) and concentration addition (CA) models. Equipotent mixtures of the two insecticides were used for initial testing of both species. A secondary study evaluating the effects of low-level chlorpyrifos on esfenvalerate toxicity also was performed. For fathead minnows, the equipotent mixture and the low-level chlorpyrifos exposure resulted in toxicity greater than that predicted by either model. In both studies, however, the observed concentrations causing 50% effect (EC50) were within a factor of two of the values predicted by the CA model. For midges, the observed EC50s were similar to the values predicted by the CA model, whereas the IA model slightly underpredicted toxicity. The observance of toxicity that was not predicted by either of the conceptual models tested likely results from a toxicokinetic interaction occurring between the toxicants.     

Effects of dietary methylmercury on reproductive behavior of fathead minnows (Pimephales promelas)

We examined the effects of dietary methylmercury on the production of testosterone in and the reproductive behavior of male fish. Juvenile fathead minnows (Pimephales promelas) were fed one of three diets contaminated with methylmercury at concentrations of 0.06 (control), 0.87 (low), and 3.93 (medium) microg Hg/g dry weight. After attaining sexual maturity, fish were paired for mating, and male behaviors were recorded. Carcass mercury and plasma testosterone concentrations also were measured. No significant differences were found in the amount of time spent by male fish in nest preparation or courtship activities, but dietary methylmercury suppressed mating behavior. Fish that were fed control diets spent approximately 5% of their time spawning; fish that were fed methylmercury-contaminated diets spent approximately 0.5% of their time spawning. Total mercury concentration in the carcass was not correlated with any individual reproductive behavior but was correlated with hypoactivity. Fish that were fed the low- and medium-methylmercury diets and with mean carcass concentrations of 0.71 to 4.2 microg Hg/g dry weight spent an average of 19 to 26% of their time being inactive; control fish with an average of 0.07 microg Hg/g dry weight spent only 8% of their time being inactive. No significant difference was found in testosterone concentrations among dietary treatments; however, testosterone was positively correlated with individual nest preparatory, courtship, and spawning behaviors and negatively correlated with the total amount of time spent in all nonreproductive behaviors. The relation between testosterone, reproductive behavior, and spawning success suggests that altered behavior is, in part, responsible for suppression of reproduction in methylmercury-exposed fish. Moreover, reproductive behavior may be more sensitive than steroid hormones to alteration by dietary methylmercury.     

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

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