Effects of water hardness on toxicological responses to chronic waterborne silver exposure in early life stages of rainbow trout (Oncorhynchus mykiss)

Rainbow trout embryos and larvae were exposed to 0, 0.1, and 1 microg/L total silver (as AgNO3) in water of three different hardnesses (soft water [2 mg/L as CaCO3], moderately hard water [150 mg/L], and hard water [400 mg/L]) in a flow-through system from fertilization to swim-up (64 d). The objective of the study was to investigate the effects of water hardness on chronic silver toxicity. In the absence of silver, elevating hardness had a positive effect on early life stage survival and development, significantly decreasing mortality and accelerating time to 50% swim-up. Following hatch, exposure to 1 microg/L Ag significantly increased mortality relative to exposure to 0 microg/L Ag. No significant effects of silver on time to 50% hatch were observed; however, time to 50% swim-up was delayed, and 50% swim-up was not achieved over the course of the experiment during some exposures to 1 microg/L Ag. These results suggest that the current Canadian Water Quality Guideline (http://www.ccme.ca/assets/pdf/e1_062.pdf) of 0.1 microg/L Ag is sufficient in preventing mortality and altered development in early life stages of rainbow trout. Increasing water hardness from 2 to 150 or 400 mg/L was modestly protective against the mortality and delays in time to 50% swim-up associated with exposure to 1 microg/L Ag. The 150- and 400-mg/L hardnesses were equally protective against mortality, but 150-mg/L was more protective than 400-mg/L hardness against the delays in time to 50% swim-up. Overall, the protective effects of hardness on chronic silver toxicity in early life stages of rainbow trout are modest but similar to the protection afforded to acute silver toxicity in juvenile and adult rainbow trout.     

An Ecological Risk Assessment of the Exposure and Effects of 2,4-D Acid to Rainbow Trout (<Emphasis Type="Italic">Onchorhyncus mykiss</Emphasis>)

Numerous state and federal agencies are increasingly concerned with the rapid expansion of invasive, noxious weeds across the United States. Herbicides are frequently applied as weed control measures in forest and rangeland ecosystems that frequently overlap with critical habitats of threatened and endangered fish species. However, there is little published chronic toxicity data for herbicides and fish that can be used to assess ecological risk of herbicides in aquatic environments. We conducted 96-h flowthrough acute and 30-day chronic toxicity studies with swim-up larvae and juvenile rainbow trout (Onchorhyncus mykiss) exposed to the free acid form of 2,4-D. Juvenile rainbow trout were acutely sensitive to 2,4-D acid equivalent at 494 mg/L (95% confidence interval [CI] 334–668 mg/L; 96-h ALC₅₀). Accelerated life-testing procedures, used to estimate chronic mortality from acute data, predicted that a 30-day exposure of juvenile rainbow trout to 2,4-D would result in 1% and 10% mortality at 260 and 343 mg/L, respectively. Swim-up larvae were chronically more sensitive than juveniles using growth as the measurement end point. The 30-day lowest observable effect concentration (LOEC) of 2,4-D on growth of swim-up larvae was 108 mg/L, whereas the 30-day no observable effect concentration (NOEC) was 54 mg/L. The 30-day maximum acceptable toxicant concentration (MATC) of 2,4-D for rainbow trout, determined as the geometric mean of the NOEC and the LOEC, was 76 mg/L. The acute:chronic ratio was 6.5 (i.e., 494/76). We observed no chronic effects on growth of juvenile rainbow trout at the highest concentration tested (108 mg/L). Worst-case aquatic exposures to 2,4-D (4 mg/L) occur when the herbicide is directly applied to aquatic ecosystems for aquatic weed control and resulted in a 30-day safety factor of 19 based on the MATC for growth (i.e., 76/4). Highest nontarget aquatic exposures to 2,4-D applied following terrestrial use is calculated at 0.136 mg/L and resulted in a 30-day safety factor of 559 (e.g., 76/0.163). Assessment of the exposure and response data presented herein indicates that use of 2,4-D acid for invasive weed control in aquatic and terrestrial habitats poses no substantial risk to growth or survival of rainbow trout or other salmonids, including the threatened bull trout (Salvelinus confluentus).     

Sensitivity of mottled sculpins (Cottus bairdi) and rainbow trout (Onchorhynchus mykiss) to acute and chronic toxicity of cadmium, copper, and zinc

Studies of fish communities of streams draining mining areas suggest that sculpins (Cottus spp.) may be more sensitive than salmonids to adverse effects of metals. We compared the toxicity of zinc, copper, and cadmium to mottled sculpin (C. bairdi) and rainbow trout (Onchorhynchus mykiss) in laboratory toxicity tests. Acute (96-h) and early life-stage chronic (21- or 28-d) toxicity tests were conducted with rainbow trout and with mottled sculpins from populations in Minnesota and Missouri, USA, in diluted well water (hardness = 100 mg/L as CaCO3). Acute and chronic toxicity of metals to newly hatched and swim-up stages of mottled sculpins differed between the two source populations. Differences between populations were greatest for copper, with chronic toxicity values (ChV = geometric mean of lowest-observed-effect concentration and no-observed-effect concentration) of 4.4 microg/L for Missouri sculpins and 37 microg/L for Minnesota sculpins. Cadmium toxicity followed a similar trend, but differences between sculpin populations were less marked, with ChVs of 1.1 microg/L (Missouri) and 1.9 microg/L (Minnesota). Conversely, zinc was more toxic to Minnesota sculpins (ChV = 75 microg/L) than Missouri sculpins (chronic ChV = 219 microg/L). Species-average acute and chronic toxicity values for mottled sculpins were similar to or lower than those for rainbow trout and indicated that mottled sculpins were among the most sensitive aquatic species to toxicity of all three metals. Our results indicate that current acute and chronic water quality criteria for cadmium, copper, and zinc adequately protect rainbow trout but may not adequately protect some populations of mottled sculpins. Proposed water quality criteria for copper based on the biotic ligand model would be protective of both sculpin populations tested.     

Acute and chronic toxicity of nitrate to early life stages of lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis)

The acute and chronic toxicity of the nitrate ion (NO3-) to the embryos, alevins, and swim-up fry of lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis) were tested in laboratory aquaria. The acute (96-h) median lethal concentration (LC50) for swim-up fry was 1,121 mg NO3-N/L for lake trout and 1,903 mg NO3-N/L for lake whitefish. The chronic (approximately 130-150-d) LC50s for embryos to swim-up fry were 190 and 64 mg NO3-N/L, respectively. Sublethal effects on developmental timing and fry body size were observed at concentrations of 6.25 and 25 mg NO3-N/L, respectively, in the chronic tests. These results confirm that the Canadian nitrate water-quality guideline of 2.9 mg NO3-N/L, which was derived from chronic tests on a temperate-zone amphibian, is applicable to the early life stages of two species of Arctic fish. However, it does not support use of the guideline for acute exposures during early life stages of salmonid fish or for acute or chronic exposures to adult fish, which are relatively insensitive to nitrate.     

Effects of sodium chloride on chronic silver toxicity to early life stages of rainbow trout (Oncorhynchus mykiss)

The chronic (early life stage) toxicity of silver to rainbow trout (Oncorhynchus mykiss) was determined in flow-through exposures. Rainbow trout embryos were exposed to silver (as AgNO3) from 48 h or less postfertilization to 30 d postswimup in soft water in the presence and absence of 49 mg/L of NaCl (30 mg/L of Cl). The studies determined effect levels for rainbow trout exposed throughout an extended development period and assessed possible protective effects of sodium chloride. Lowest-observed-effect concentrations were greater than 1.25 microg/L of dissolved silver for survival, mean day to hatch, mean day to swimup, and whole-body sodium content in both studies. Whole-body silver concentrations increased significantly at 0.13 microg/L of dissolved silver in unmodified water and at 1.09 microg/L of dissolved silver in amended water. The maximum-acceptable toxicant concentration for growth was greater than 1.25 microg/L of dissolved silver in unmodified water and 0.32 microg/L of dissolved silver in amended water. Whole-body silver concentrations were more sensitive than survival and growth end points in unmodified water. Interpretation of sodium chloride effects on chronic silver toxicity to rainbow trout was complicated by differences in measured effect levels that were potentially the result of strain differences between test organisms in the two studies.     

An Ecological Risk Assessment of the Acute and Chronic Toxicity of the Herbicide Picloram to the Threatened Bull Trout (<Emphasis Type="Italic">Salvelinus confluentus</Emphasis>) and the Rainbow Trout (<Emphasis Type="Italic">Onchorhyncus mykiss</Emphasis>)

We conducted acute and chronic toxicity studies of the effects of picloram acid on the threatened bull trout (Salvelinus confluentus) and the standard coldwater surrogate rainbow trout (Oncorhynchus mykiss). Juvenile fish were chronically exposed for 30 days in a proportional flow-through diluter to measured concentrations of 0, 0.30, 0.60, 1.18, 2.37, and 4.75 mg/L picloram. No mortality of either species was observed at the highest concentration. Bull trout were twofold more sensitive to picloram (30-day maximum acceptable toxic concentration of 0.80 mg/L) compared to rainbow trout (30-day maximum acceptable toxic concentration of 1.67 mg/L) based on the endpoint of growth. Picloram was acutely toxic to rainbow trout at 36 mg/L (96-h ALC50). The acute:chronic ratio for rainbow trout exposed to picloram was 22. The chronic toxicity of picloram was compared to modeled and measured environmental exposure concentrations (EECs) using a four-tiered system. The Tier 1, worst-case exposure estimate, based on a direct application of the current maximum use rate (1.1 kg/ha picloram) to a standardized aquatic ecosystem (water body of 1-ha area and 1-m depth), resulted in an EEC of 0.73 mg/L picloram and chronic risk quotients of 0.91 and 0.44 for bull trout and rainbow trout, respectively. Higher-tiered exposure estimates reduced chronic risk quotients 10-fold. Results of this study indicate that picloram, if properly applied according to the manufacturer’s label, poses little risk to the threatened bull trout or rainbow trout in northwestern rangeland environments on either an acute or a chronic basis.     

Using accelerated life testing procedures to compare the relative sensitivity of rainbow trout and the federally listed threatened bull trout to three commonly used rangeland herbicides (picloram, 2,4-D, and clopyralid)

We conducted 96-h static acute toxicity studies to evaluate the relative sensitivity of juveniles of the threatened bull trout (Salvelinus confluentus) and the standard cold-water surrogate rainbow trout (Onchorhyncus mykiss) to three rangeland herbicides commonly used for controlling invasive weeds in the northwestern United States. Relative species sensitivity was compared using three procedures: standard acute toxicity testing, fractional estimates of lethal concentrations, and accelerated life testing chronic estimation procedures. The acutely lethal concentrations (ALC) resulting in 50% mortality at 96 h (96-h ALC50s) were determined using linear regression and indicated that the three herbicides were toxic in the order of picloram acid > 2,4-D acid > clopyralid acid. The 96-h ALC50 values for rainbow trout were as follows: picloram, 41 mg/L; 2.4-D, 707 mg/L; and clopyralid, 700 mg/L. The 96-h ALC50 values for bull trout were as follows: picloram, 24 mg/L; 2.4-D, 398 mg/L; and clopyralid, 802 mg/L. Fractional estimates of safe concentrations, based on 5% of the 96-h ALC50, were conservative (overestimated toxicity) of regression-derived 96-h ALC5 values by an order of magnitude. Accelerated life testing procedures were used to estimate chronic lethal concentrations (CLC) resulting in 1% mortality at 30 d (30-d CLC1) for the three herbicides: picloram (1 mg/L rainbow trout, 5 mg/L bull trout), 2,4-D (56 mg/L rainbow trout, 84 mg/L bull trout), and clopyralid (477 mg/L rainbow trout; 552 mg/L bull trout). Collectively, the results indicated that the standard surrogate rainbow trout is similar in sensitivity to bull trout. Accelerated life testing procedures provided cost-effective, statistically defensible methods for estimating safe chronic concentrations (30-d CLC1s) of herbicides from acute toxicity data because they use statistical models based on the entire mortality:concentration:time data matrix.     

An Ecological Risk Assessment of the Acute and Chronic Effects of the Herbicide Clopyralid to Rainbow Trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is a pyridine herbicide frequently used to control invasive, noxious weeds in the northwestern United States. Clopyralid exhibits low acute toxicity to fish, including the rainbow trout (Oncorhynchus mykiss) and the threatened bull trout (Salvelinus confluentus). However, there are no published chronic toxicity data for clopyralid and fish that can be used in ecological risk assessments. We conducted 30-day chronic toxicity studies with juvenile rainbow trout exposed to the acid form of clopyralid. The 30-day maximum acceptable toxicant concentration (MATC) for growth, calculated as the geometric mean of the no observable effect concentration (68 mg/L) and the lowest observable effect concentration (136 mg/L), was 96 mg/L. No mortality was measured at the highest chronic concentration tested (273 mg/L). The acute:chronic ratio, calculated by dividing the previously published 96-h acutely lethal concentration (96-h ALC₅₀; 700 mg/L) by the MATC was 7.3. Toxicity values were compared to a four-tiered exposure assessment profile assuming an application rate of 1.12 kg/ha. The Tier 1 exposure estimation, based on direct overspray of a 2-m deep pond, was 0.055 mg/L. The Tier 2 maximum exposure estimate, based on the Generic Exposure Estimate Concentration model (GEENEC), was 0.057 mg/L. The Tier 3 maximum exposure estimate, based on previously published results of the Groundwater Loading Effects of Agricultural Management Systems model (GLEAMS), was 0.073 mg/L. The Tier 4 exposure estimate, based on published edge-of-field monitoring data, was estimated at 0.008 mg/L. Comparison of toxicity data to estimated environmental concentrations of clopyralid indicates that the safety factor for rainbow trout exposed to clopyralid at labeled use rates exceeds 1000. Therefore, the herbicide presents little to no risk to rainbow trout or other salmonids such as the threatened bull trout.     

Acute toxicity of copper, ammonia, and chlorine to glochidia and juveniles of freshwater mussels (Unionidae)

The objective of the present study was to determine acute toxicity of copper, ammonia, or chlorine to larval (glochidia) and juvenile mussels using the recently published American Society for Testing and Materials (ASTM) Standard guide for conducting laboratory toxicity tests with freshwater mussels. Toxicity tests were conducted with glochidia (24- to 48-h exposures) and juveniles (96-h exposures) of up to 11 mussel species in reconstituted ASTM hard water using copper, ammonia, or chlorine as a toxicant. Copper and ammonia tests also were conducted with five commonly tested species, including cladocerans (Daphnia magna and Ceriodaphnia dubia; 48-h exposures), amphipod (Hyalella azteca; 48-h exposures), rainbow trout (Oncorhynchus mykiss; 96-h exposures), and fathead minnow (Pimephales promelas; 96-h exposures). Median effective concentrations (EC50s) for commonly tested species were >58 microg Cu/L (except 15 microg Cu/L for C. dubia) and >13 mg total ammonia N/L, whereas the EC50s for mussels in most cases were <45 microg Cu/L or <12 mg N/L and were often at or below the final acute values (FAVs) used to derive the U.S. Environmental Protection Agency 1996 acute water quality criterion (WQC) for copper and 1999 acute WQC for ammonia. However, the chlorine EC50s for mussels generally were >40 microg/L and above the FAV in the WQC for chlorine. The results indicate that the early life stages of mussels generally were more sensitive to copper and ammonia than other organisms and that, including mussel toxicity data in a revision to the WQC, would lower the WQC for copper or ammonia. Furthermore, including additional mussel data in 2007 WQC for copper based on biotic ligand model would further lower the WQC.     

Influence of exposure duration on the toxicity of triclopyr ester to fish and aquatic insects

Flow-through toxicity tests were conducted to determine the effects of exposure time on the toxicity of triclopyr butoxyethyl ester (Garlon^® 4) to fish (rainbow trout and chinook salmon) and stream insects (Hydropsyche sp. and Isonychia sp.). The toxicity of triclopyr ester to fish increased with exposure time, but the rate of increase in toxicity declined with increasing exposure duration. Median lethal concentrations for rainbow trout exposed for 1, 6, or 24 h were 22.5, 1.95, and 0.79 mg/L triclopyr ester (expressed as acid equivalent, nominal concentrations), respectively. Comparable values for chinook salmon were 34.6, 4.7, and 1.76 mg/L. The toxicity of triclopyr ester to aquatic insects also increased with increasing exposure time, but was considerably less than the toxicity to fish. There was no significant mortality (chi-square p>0.05) of insects following 3-h exposures to the maximum test concentration of approximately 110 mg/L. Median lethal concentrations following 9- and 24-h exposures were 14.9 and 4.0 ml/L for Hydropsyche sp., and 37.0 and 8.8 mg/L for Isonychia sp., respectively. At each exposure time in the toxicity tests, there was a sharp increase in mortality over relatively small increases in concentration, resulting in extremely steep slopes of the probit lines (6.3–33.8), and indicating an apparent response threshold. The herbicide exhibited delayed lethal effects, particularly in fish, but only at short term exposures to higher concentrations. The risk of adverse effects on fish and aquatic insects from triclopyr ester contamination, based on the results of these time-toxicity tests, is discussed.     

Effects of chronic waterborne nickel exposure on two successive generations of Daphnia magna

In a 21-d chronic toxicity test in which an F0 generation of Daphnia magna were exposed to waterborne Ni, the no-observable-effect concentration (for survival, reproduction, and growth) was 42 microg Ni L(-1), or 58% of the measured 21-d median lethal concentration (LC50) of 71.9 microg Ni L(-1) (95% confidence interval, 56.5-95.0). Chronic exposure to 85 microg Ni L(-1) caused marked decreases in survival, reproduction, and growth in F0 animals. In the F1 generation (daphnids born of mothers from the chronically exposed F0 generation), animals chronically exposed to 42 microg Ni L(-1) for 11 d weighed significantly less (20%) than controls, indicating increased sensitivity of F1 animals. Additionally, in this successive generation, significant decreases in whole-body levels of metabolites occurred following exposure to both 42 microg Ni L(-1) (decreased glycogen and adenosine triphosphate [ATP]) and 21 microg Ni L(-1) (decreased ATP). No significant changes were observed in whole-body total lipid, total protein, and lactate levels at any concentration. Whereas F1 neonates with mothers that were exposed to 21 microg Ni L(-1) showed increased resistance to acute Ni challenge, as measured by a significant (83%) increase in the acute (48-h) LC50, F1 neonates with mothers that were exposed to 42 microg Ni L(-1) were no more tolerant of acute Ni challenge than control animals were. Nickel accumulations in F1 animals chronically exposed to 21 and 42 microg Ni L(-1) were 11- and 18-fold, respectively, above control counterparts. The data presented suggest that chronic Ni exposure to two successive generations of D. magna lowered the overall energy state in the second generation. Whereas the quantity of neonates produced was not affected, the quality was; thus, environmentally meaningful criteria for regulating waterborne Ni concentrations in freshwater require consideration of possible multigenerational effects.     

Acute and chronic toxicity of lead in water and diet to the amphipod Hyalella azteca

We evaluated the influence of waterborne and dietary lead (Pb) exposure on the acute and chronic toxicity of Pb to the amphipod Hyalella azteca. Test solutions were generated by a modified diluter with an extended (24-h) equilibration period. Acute (96-h) toxicity of Pb varied with water hardness in the range of 71 to 275 mg/L as CaCO3, despite similar dissolved Pb concentrations. Acute toxicity was greatest in soft test water, with less than 50% survival at the lowest dissolved Pb concentration (151 microg/L). Survival also was significantly reduced in medium-hardness water but not in hard test water. In chronic (42-d) studies, amphipods were exposed to waterborne Pb and fed either a control diet or a diet equilibrated with waterborne Pb levels. For animals fed the control diet, the median lethal concentration (LC50) for Pb was 24 degrees g/L (as dissolved Pb), and significant reductions in survival occurred at 16 microg/L. Exposure to Pb-treated diets significantly increased toxicity across a wide range of dissolved Pb concentrations, with a LC50 of 16 microg/L and significant reductions in growth and reproduction at 3.5 microg/L. Significant effects on growth and reproduction occurred at dissolved Pb concentrations close to the current U.S. chronic water-quality criterion. Our results suggest that both aqueous- and dietary-exposure pathways contribute significantly to chronic Pb exposure and toxic effects in aquatic biota.     

Toxicity of atrazine to the juvenile hard clam, Mercenaria mercenaria

The herbicide atrazine is one of the most heavily used pesticides in the United States. The effects of atrazine on the clam Mercenaria mercenaria were evaluated in aqueous and sediment laboratory assays. Juvenile clams of approximately 1mm in size were used for all experiments. An acute aqueous bio-assay was used to determine the 96-h LC(50) for the juvenile clams. A chronic aqueous bioassay was conducted at lower atrazine concentrations over a 10-day exposure period to examine both lethal and sublethal (dry mass, shell size, and condition index) endpoints. A chronic sediment bioassay examined mortality and sublethal endpoints in a 10-day exposure. The acute 96-h LC(50) was 5608 microg/L with 95% confidence intervals ranging from 5003 to 6287 microg/L. Results of the chronic aqueous assay indicated both lethal and sublethal (reduced shell size) effects at high atrazine concentrations. In the 10-day chronic aqueous assay, the no observable effect concentration was 500 microg/L, the lowest observable effect concentration was 1000 microg/L, and the maximum allowable toxicant concentration (MATC) was 707 microg/L. There were no significant effects of atrazine in the chronic sediment exposure. Safe concentrations for the aqueous experiments were estimated by applying an uncertainty factor of 10 to the calculated MATC values. While there were adverse effects of atrazine at high concentrations, these results suggest that atrazine is not directly toxic to M. mercenaria at environmentally relevant concentrations.     

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.     

Effects of pulsed copper exposures on early life-stage Pimephales promelas

Effects of pulsed copper exposures were investigated using Pimephales promelas aged less than 24 h in short-term chronic testing (7 or 14 d) with moderately hard synthetic water. Concentrations tested were between the species mean chronic value (22 microg/L at a hardness of 100 mg/L as CaCO3) and the 7-d continuous exposure EC50 for survival (40 microg/L) to examine exposures that were not acutely toxic and representative of actual wastewater discharge permit exceedences. Factors tested included pulse duration, recovery time between pulses, and pulse frequency. Survival was the main endpoint affected in all treatments (analysis of variance, p < 0.05). Effects on fish biomass, independent of survival effects, were observed in only 2 of 86 treatments examined. Fish survival was negatively affected at average copper concentrations between 7 and 50% of the 7-d continuous exposure EC50. Exposures having a 48- to 96-h recovery time between pulses had less effect on fish survival than did treatments with shorter (12-24 h) or longer (>120 h) recovery times. Results suggest that the criteria averaging periods used in the United States, and the averaging periods typically used in wastewater discharge permit limits for copper, may not protect against effects of certain pulsed exposures.     

Toxicity of the herbicide glyphosate and several of its formulations to fish and aquatic invertebrates

Studies were initiated to determine the acute toxicity of technical grade glyphosate (MON0573), the isopropylamine salt of glyphosate (MON0139), the formulated herbicide Roundup^® (MON02139), and the Roundup^® surfactant (MON0818) to four aquatic invertebrates and four fishes: daphnids (Daphnia magna), scuds (Gammarus pseudolimnaeus), midge larvae (Chironomous plumosus), mayfly nymphs (Ephemerella walkeri), Rainbow trout (Salmo gairdneri), fathead minnows (Pimephales promelas), channel catfish (Ictalurus punctatus), and bluegills (Lepomis macrochirus). Acute toxicities for Roundup ranged from 2.3 mg/L (96-h LC50, fathead minnow) to 43 mg/L (48-h EC50, mature scuds). Toxicities of the surfactant were similar to those of the Roundup formulation. Technical glyphosate was considerably less toxic than Roundup or the surfactant; for midge larvae, the 48-h EC50 was 55 mg/L and for rainbow trout, the 96-h LC50 was 140 mg/L. Roundup was more toxic to rainbow trout and bluegills at the higher test temperatures, and at pH 7.5 than at pH 6.5. Toxicity did not increase at pH 8.5 or 9.5. Eyed eggs were the least sensitive life stage, but toxicity increased markedly as the fish entered the sac fry and early swim-up stages. No changes in fecundity or gonadosomatic index were observed in adult rainbow trout treated with the isopropylamine salt or Roundup up to 2.0 mg/L. The aging of Roundup test solutions for seven days did not reduce toxicity to midge larvae, rainbow trout or bluegills. In avoidance studies, rainbow trout did not avoid concentrations of the isopropylamine salt up to 10.0 mg/L; mayfly nymphs avoided 10.0 mg/L of Roundup, but not 1.0 mg/L. In a simulated field application, midge larvae avoided 2.0 mg/L of Roundup. Application of Roundup, at recommended rates, along ditchbank areas of irrigation canals should not adversely affect resident populations of fish or invertebrates. However, spring applications in lentic situations, where dissolved oxygen levels are low or temperatures are elevated, could be hazardous to young-of-the-year-fishes.     

Chronic effects of silver exposure on ion levels, survival, and silver distribution within developing rainbow trout (Oncorhynchus mykiss) embryos

Rainbow trout embryos were chronically exposed to silver (as AgNO3) in moderately hard water (120 mg CaCO3/L, 0.70 mM Cl-, 1.3 mg/L dissolved organic matter. 12.3+/-0.1 degrees C) at nominal concentrations of 0.1, 1, and 10 microg/L (measured = 0.117+/-0.008, 1.22+/-0.16, and 13.51+/-1.58 microg/L, respectively) to investigate the effects on mortality, ionoregulation, and silver uptake and distribution of the embryo. Mortalities in the low concentrations (0.1 and 1.2 microg/L) were not significantly different from controls throughout embryonic development (days 1-32 postfertilization). Mortalities of embryos in the 13.5-microg/L treatment reached 56% by day 32 postfertilization (33% when accounting for control mortality), by which time more than 50% of surviving embryos had hatched. Accumulation of silver in whole embryos of 1.2- and 13.5-microg/L treatments reached the highest concentrations of 0.13 and 0.24 microg/g total silver, respectively, by day 32, but whole embryo silver burden was not correlated with mortality. Silver concentrations in different compartments of the whole embryo (chorion, dissected embryo, and yolk) were greatest just before hatch and were higher in the chorion for all experimental treatments. Up to 85% of total whole embryo silver content was bound to the chorion, which acts as a protective barrier during silver exposure. Whole embryo Na+ concentration in the 13.5-microg/L treatment was significantly reduced relative to controls from days 23 to 32 postfertilization, and levels in the embryo were reduced by 40% at day 32 postfertilization, indicating that silver toxicity in the whole embryo is associated with an ion regulatory disturbance that is similar to the acute effect of AgNO3 in juvenile and adult trout.     

The effect of repeated exposure to azamethiphos on survival and spawning in the American lobster (Homarus americanus)

The azamethiphos formulation Salmosan has been used to control sea lice on Atlantic salmon. To determine the effect of this pesticide on spawning in the American lobster, pre-ovigerous females acclimated to 13 degrees C were given biweekly 1-h exposures to Salmosan at concentrations of 1.25-10 microg/L azamethiphos. In March and April, four exposures to 1.25, 2.5, or 5.0 microg/L had no significant effect on survival or spawning incidence, while three or four exposures to 10 microg/L caused high mortality (43-100%). Spawning incidence in the surviving lobsters in the 10 microg/L groups was significantly reduced in the group given four treatments, but not in the group given three treatments. In December and January, four exposures to 10 microg/L azamethiphos had no significant effect on either survival or spawning incidence. The results demonstrate that repeated 1-h biweekly exposures to azamethiphos can have a negative effect on survival and spawning in female American lobsters. The response to this pesticide appears to be influenced by time of year, as well as concentration and number of exposures.     

Acute toxicity of cadmium, lead, zinc, and their mixtures to stream-resident fish and invertebrates

The authors conducted 150 tests of the acute toxicity of resident fish and invertebrates to Cd, Pb, and Zn, separately and in mixtures, in waters from the South Fork Coeur d'Alene River watershed, Idaho, USA. Field-collected shorthead sculpin (Cottus confusus), westslope cutthroat trout (Oncorhynchus clarkii lewisi), two mayflies (Baetis tricaudatus and Rhithrogena sp.), a stonefly (Sweltsa sp.), a caddisfly (Arctopsyche sp.), a snail (Gyraulus sp.), and hatchery rainbow trout (Oncorhynchus mykiss), were tested with all three metals. With Pb, the mayflies (Drunella sp., Epeorus sp., and Leptophlebiidae), a Simuliidae black fly, a Chironomidae midge, a Tipula sp. crane fly, a Dytiscidae beetle, and another snail (Physa sp.), were also tested. Adult westslope cutthroat trout were captured to establish a broodstock to provide fry of known ages for testing. With Cd, the range of 96-h median effect concentrations (EC50s) was 0.4 to >5,329 μg/L, and the relative resistances of taxa were westslope cutthroat trout ≈ rainbow trout ≈ sculpin < other taxa; with Pb, EC50s ranged from 47 to 3,323 μg/L, with westslope cutthroat trout < rainbow trout < other taxa; and with Zn, EC50s ranged from 21 to 3,704 μg/L, with rainbow trout < westslope cutthroat trout ≈ sculpin < other taxa. With swim-up trout fry, a pattern of decreasing resistance with increasing fish size was observed. In metal mixtures, the toxicities of the three metals were less than additive on a concentration-addition basis.     

An evaluation of sodium loss and gill metal binding properties in rainbow trout and yellow perch to explain species differences in copper tolerance

The main objective of the study was to use a species comparison approach in order to understand sensitivity and tolerance differences to copper. We hypothesized that species differences in toxicity would be reflected by differences in copper binding to high-affinity sites on the gill. Specifically, the strength of copper binding (affinity, logK) and maximum number of binding sites (saturation, Bmax) for copper at the gill surface would vary among different species of fish. Two species that are different in their copper sensitivity are the rainbow trout (Oncorhynchus mykiss) and yellow perch (Perca flavescens). We explicitly compared acute toxicity (median lethal concentrations via 96-h LC50s) and whole-body Na+ loss in both organisms in two distinct water chemistries (i.e., hard and soft water). For both species, the copper binding sites at the gill surface were characterized for their affinity and saturability. The binding properties of the gill were quite similar between the two species in each water chemistry. Based on estimations of the free cupric ion concentration, the affinity, or logK, was 8.4 for both species in soft water, whereas in hard water, the affinity was higher (approximately 9.7). The Bmax value in soft water was 1.88 nmol/g for rainbow trout and yellow perch, while in hard water, saturation occurred at 3.63 nmol/g for rainbow trout and 9.01 nmol/g for yellow perch. More importantly, the amount of copper bound to the gills at 50% mortality (i.e., lethal accumulation; the LA50) was different between the two species (yellow perch LA50s were nine times higher than those of rainbow trout in soft water and hard water), indicating that the copper binding to the yellow perch gill must not have been 'biologically reactive.' According to 96-h LC50s, yellow perch were less sensitive to copper than were rainbow trout; however, the difference between the two species was similar in hard water (1.05 vs 4.16 microM) and soft water (approximately 0.10 vs 0.44 microM). Perch were more tolerant because they lost less sodium upon exposure to copper; yet this mechanism of tolerance was not reflected by the amount of copper at the gill surface. The influence of water chemistry on the binding properties of the gill demonstrates the dynamic nature of the gill in maintaining ionoregulatory homeostasis, a key issue in the future development of the chronic biotic ligand model.