Toxicity of acenaphthene and isophorone to early life stages of fathead minnows

Flow-through 96-hr and early-life-stage toxicity tests were conducted with acenaphthene and isophorone, using fathead minnows (Pimephalespromelas) as test animals. The 96-hr LC₅₀'s were 608g/L for acenaphthene and 145 and 255 mg/L for isophorone, depending on fish age. No-effect concentrations from early-life-stage exposures were 413g acenaphthene/L and 14 mg isophorone/L; these showed good agreement with published toxicity data.     

Toxicity of Manganese to Ceriodaphnia dubia and Hyalella azteca

Manganese is a toxic element frequently overlooked when assessing toxicity of effluents, sediments, and pore waters. Manganese can be present at toxic levels in anoxic solutions due to increased solubility under chemically reducing conditions, and it can remain at those levels for days in aerated test waters due to slow precipitation kinetics. Ceriodaphnia dubia and Hyalella azteca are freshwater organisms often used for toxicity testing and recommended for assessments of effluents and pore waters. Lethal and reproductive-inhibition concentrations of Mn were determined for C. dubia in acute 48-h tests and chronic three-brood tests using animals <24 h old and between 24 and 48 h old. Sensitivity of H. azteca to Mn was determined with 7-day-old animals in acute 96-h tests. Tests were run at three levels of water hardness to assess the amelioratory effect, which was often significant. Manganese concentrations were measured analytically at test initiation and after 96 h for calculation of toxicity and determination of Mn precipitation during the tests. Minimal amounts of Mn (≤3%) precipitated within 96 h. LC₅₀s determined for H. azteca progressively increased from 3.0 to 8.6 to 13.7 mg Mn/L in soft, moderately hard, and hard waters, respectively. The tolerance of C. dubia to Mn was not significantly different between moderately hard and hard waters, but was significantly lower in soft water. Manganese sensitivity of C. dubia was not significantly different between the ages tested. Acute LC₅₀ values for C. dubia averaged 6.2, 14.5 and 15.2 mg Mn/L and chronic IC₅₀ values averaged 3.9, 8.5 and 11.5 mg Mn/L for soft, moderately-hard and hard waters, respectively. Manganese toxicity should be considered when assessing solutions with concentrations approaching these levels. Received: 21 June 1999/Accepted: 5 October 1999     

Salinity Tolerance of Daphnia magna and Potential Use for Estuarine Sediment Toxicity Tests

Daphnia magna Straus, a common organism used for freshwater sediment toxicity tests, was evaluated to determine its tolerance to salinity and suitability for tests with estuarine water and sediments. Daphnids were exposed for 2 to 21 days to salinity in a variety of water-only tests, in tests with freshwater sediment overlain by salt water, and in tests with estuarine sediments overlain by freshwater. Daphnid age, test length, and temperature seemed to have little effect upon the range of LC50, NOAEL, and LOAEL values. LC50s for all tests ranged from 5.10 to 7.81 g/L, with a mean of 6.6 g/L salinity (measured conductivity 10.0 mS/m). The mean NOAEL and LOAEL values based on production of young were 4.6 and 6.9 g/L salinity (measured conductivity 7.1 and 10.5 mS/m), respectively. The results indicate that D. magna will survive and reproduce well in water with salinities below 4 g/L and demonstrate the potential usefulness of this organism in monitoring sediment toxicity from both freshwater and estuarine wetland sites. Received: 26 September 1996/Revised: 21 November 1996     

Acute Toxicity and Effects Analysis of Endosulfan Sulfate to Freshwater Fish Species

Endosulfan sulfate is a persistent environmental metabolite of endosulfan, an organochlorine insecticide–acaricide presently registered by the United States Environmental Protection Agency. There is, however, limited acute fish toxicity data for endosulfan sulfate. This study determines the acute toxicity (LC₅₀s and LC₁₀s) of endosulfan sulfate to three inland Florida native fish species (mosquitofish [Gambusia affinis]; least killifish [Heterandria formosa]; and sailfin mollies [Poecilia latipinna]) as well as fathead minnows (Pimephales promelas). Ninety-six-h acute toxicity tests were conducted with each fish species under flow-through conditions. For all of the above-mentioned fish species, 96-h LC₅₀ estimates ranged from 2.1 to 3.5 μg/L endosulfan sulfate. The 96-h LC₁₀ estimates ranged from 0.8 to 2.1 μg/L endosulfan sulfate. Of all of the fish tested, the least killifish appeared to be the most sensitive to endosulfan sulfate exposure. The above-mentioned data were combined with previous acute toxicity data for endosulfan sulfate and freshwater fish for an effects analysis. The effects analysis estimated hazardous concentrations expected to exceed 5, 10, and 50% of the fish species’ acute LC₅₀ or LC₁₀ values (HC₅, HC₁₀, and HC₅₀). The endosulfan sulfate freshwater-fish acute tests were also compared with the available freshwater-fish acute toxicity data for technical endosulfan. Technical endosulfan is a mixture of α- and β-endosulfan. The LC₅₀s had a wider range for technical endosulfan, and their distribution produced a lower HC₁₀ than for endosulfan sulfate. The number of freshwater-fish LC₅₀s for endosulfan sulfate is much smaller than the number available for technical endosulfan, reflecting priorities in examining the toxicity of the parent compounds of pesticides. The toxicity test results and effects analyses provided acute effect values for endosulfan sulfate and freshwater fish that might be applied in future screening level ecologic risk assessments. The effects analyses also discussed several deficiencies in conventional methods for setting water-quality criteria and determining ecologic effects from acute toxicity tests.     

Mortality, Preference, Avoidance, and Activity of a Predatory Leech Exposed to Cadmium

The effects of cadmium on the hatching success of the cocoons of the freshwater predatory leech Nephelopsis obscura were examined together with the survivorship of hatchlings, changes in 96-h LC₅₀ with biomass, preference-avoidance responses and changes in activity. The 96-h EC₅₀ for cocoons was 832.6 μg Cd/L with a decreasing bounded monotonic function best describing hatchling success as a function of Cd concentration. Exposure of cocoons to Cd had a highly significant effect on post-hatchling survivorship with survivorship of hatchlings from the 0–500-μg Cd/L concentrations not significantly different from each other but higher than survivorship of hatchlings from cocoons exposed to 1,000–4,000 μg Cd/L. Resistance to acute Cd toxicity, measured as LC₅₀, increased with leech biomass. In preference-avoidance tests large leeches (>450 mg) spent more time in 100- and 200-μg Cd/L than in control water or in 50-μg Cd/L, while small leeches (<250 mg) spent more time in 200-μg Cd/L compared to control water or 50–100-μg Cd/L. Leeches exposed to 100- and 200-μg Cd/L exhibited a significant decrease in activity compared to the leeches in the control and 50-μg Cd/L treatments. Received: 14 February 1996/Revised 24 June 1996     

The acute and chronic toxicity of cadmium to different life history stages of the freshwater crustaceanAsellus aquaticus (L)

Different life-history stages of the freshwater isopod crustaceanAsellus aquaticus were exposed to a range of cadmium concentrations using a semi-static toxicity testing procedure. Median lethal concentrations (96-hr LC50) ranged from 80 g Cd/L for juveniles to >2,000 g Cd/L for embryos. Pre-treatment of eggs with cadmium did not increase their tolerance to the metal as juveniles. The responses of each stage are discussed in relation to the use of macroinvertebrate toxicity test data in predicting the hazardous effects of pollutants.     

Determining Toxicity Trends in the Ozonation of Synthetic Dye Wastewaters Using the Nematode Caenorhabditis elegans

The nematode Caenorhabditis elegans was used in 72-h toxicity tests to evaluate the influence of ozonation on the toxicity of three synthetic azo dye wastewaters (two reactive dyes and one acid-based dye). The two reactive dye wastewaters contained high concentrations of NaCl (89–112 g/L) in addition to potentially toxic dye components. To determine the contribution of NaCl to toxicity, simulated dye wastewater samples with and without NaCl were tested. Samples were collected at various times during ozonation (t = 0, 8, 32, 64 min); nematodes were exposed to the samples for 72 h. The influence of ozonation on toxicity varied between dye wastewater types. For the acid-based dye wastewater, toxicity increased as duration of ozonation increased. For the reactive dyes without NaCl, toxicity did not appear to be influenced by ozonation. For the reactive dyes with NaCl, mortality was 100% with or without ozonation. Range-finding experiments with NaCl in water and NaCl in dye wastewaters suggested an additive toxic interaction between NaCl and the dyes in wastewater to the nematodes. The duration of ozonation for acid-based dyes and the relatively high NaCl concentrations for the reactive dyes appear to influence effluent toxicity in the ozonated dye wastewaters. Received: 17 July 1997/Accepted: 6 November 1997     

Toxicity of alum sludge extracts to a freshwater alga,protozoan, fish,and marine bacterium

Alum sludges from ten water treatment plants throughout North America were subjected to a battery of toxicity tests which included the S. capricornutum growth test, the fathead minnow survival and growth test, a protozoan mortality test, and the Microtox^® test. S. capricornutum was more sensitive than any other test species to sludge extracts. Algal growth inhibition was observed in extracts obtained at pH 5 but generally not in circumneutral solutions. Alum sludge extracts prepared with natural receiving waters were toxic to S. capricornutum at all extract pH levels tested if receiving water hardness was less than 35 mg CaCO₃/L. These results indicate that water-soluble constituents from alum sludges discharged into receiving waters may affect algal growth.     

Exclusion of the Jefferson salamander,Ambystoma jeffersonianum,from some potential breeding ponds in Pennsylvania: Effects of pH,temperature, and metals on embryonic development

A field survey revealed that Al, SO₄, H⁺, and Zn were significantly higher in 40 ponds lacking successful breeding of the Jefferson salamander, A. jeffersonianum, whereas alkalinity, Cu, DOC, K, Mg, Na, and NO₃ were significantly higher in 10 ponds that supported successful breeding. In a second smaller set of ponds used for transplant studies, Al, conductivity, H⁺, and SiO₂ were significantly higher in five ponds lacking reproduction of A. jeffersonianum; alkalinity, Ca, and K were significantly higher in three ponds with successful reproduction. Survival and hatching success were significantly greater for egg masses transplanted into ponds supporting viable Jefferson salamander populations than into those that did not. Survival and hatching success were greater at 15°C than at 10°C. Low pH slowed developmental rate, consequently increasing the time until hatching. Low pH decreased hatching success of the embryos at 10 and 15°C. Copper was acutely toxic to embryos at pH 4.50 (96 h LC₅₀=315 g/L); chronic exposure levels in the field were much lower (approximately 0.01 times). Since successful ponds actually contained more Cu than unsuccessful ones, Cu does not appear to be toxic in the field. Aluminum ameliorated the acute 96 h toxicity of pH 4.50; at [Al]'s between 250 and 500 g/L mortality at pH 4.50 was greatly reduced. This effect of Al occurred at concentrations comparable to those found in the field. Lead and zinc, at concentrations up to 2,000 g/L, had no apparent effects on the developing embryos of A. jeffersonianum. Aluminum, Pb, and Zn did not afect developmental rate, as did low pH and Cu. Based on these findings, low pH and its interaction with Al are likely to be major factors responsible for the success or failure of the Jefferson salamander in breeding ponds in Pennsylvania. Further investigation is needed into interations among pH, metals, dissolved organics, and non-toxic cations to further clarify the mechanisms of toxicity of the complex mixture of which pond water consists.     

Influence of Dissolved Organic Matter on Acute Toxicity of Zinc to Larval Fathead Minnows (Pimephales promelas)

We conducted laboratory toxicity tests in support of the development of a biotic ligand model (BLM) to predict acute toxicity of zinc (Zn) to fathead minnows (Pimephales promelas). To test the effect of dissolved organic matter (DOM) on Zn toxicity, we exposed larval fathead minnows to Zn in water containing elevated concentrations of dissolved organic carbon (DOC) in 96-h static-renewal toxicity tests. We tested DOM isolated from four surface waters: Cypress Swamp, Delaware; Edisto River, South Carolina; Suwannee River, Georgia; and Wilmington, Delaware, wastewater treatment effluent. The DOM isolates from the Edisto River and Wilmington wastewater treatment effluent contained elevated concentrations of NaCl (20–110× control NaCl) due to the use of a Na⁺-exchange resin to remove Ca²⁺ and Mg²⁺ during the DOM isolation process. Therefore, we also performed Zn toxicity tests in which we added up to 20 mM NaCl to exposure solutions containing Cypress Swamp and Suwannee River DOM. A threshold concentration of 11 mg DOC/L was needed to decrease Zn toxicity, after which the 96 h Zn LC50 was positively correlated with DOC concentration. Elevated NaCl concentrations did not alter Zn toxicity in the presence of DOM. In conjunction with data from other studies with fish and invertebrates, results of this study were used to calibrate Version 2.1.1 of the Zn BLM. BLM-predicted LC50s for our exposure waters containing elevated DOM concentrations were within the range of acceptable deviation relative to the observed LC50s (i.e., 0.5–2× observed LC50s); however, BLM-predicted LC50s for our exposure waters containing < 1 mg DOC/L were 2–3× lower than the observed LC50s (i.e., the BLM over-predicted the toxicity). Therefore, the current composite-species BLM for Zn could be improved for fathead minnows if that species were modeled separately from the other species used to calibrate Version 2.1.1.     

Acute and chronic toxicities of arsenic(III) to fathead minnows,flagfish, daphnids,and an amphipod

Acute and chronic toxicities of arsenic (III) (As) to four species of freshwater organisms were determined. All tests were flow-through exposures except the daphnid (Daphnia magna) tests which were static concentration renewal exposures. Acute exposures of fathead minnows (Pimephales promelas), flagfish (Jordanella floridae), and an amphipod (Gammarus pseudolimnaeus) to As resulted in 96-hr LC₅₀ or EC₅₀ estimates of 14,100, 14,400, and 874 g/L, respectively. Daphnids were exposed to As with and without food resulting in 96-hr EC₅₀ estimates of 4,340 and 1,500 g/L, respectively. Chronic exposures of 28 to 31 days duration were made for fathead minnows, flagfish, and daphnids. The chronic limit ranges (highest tested exposure concentration having no adverse effect and the lowest tested exposure concentration having an adverse effect) based upon the most sensitive measured parameters of body length and wet weight were 2,130 to 4,300 g/L for fathead minnows and 2,130 to 4,120 g/L for flagfish. Daphnids had chronic limits of 633 to 1,320 g/L based upon survival and the measured parameters of reproduction and body length. Calculation of an acute test/chronic test ratio for fathead minnows, flagfish, and daphnids (fed and unfed) resulted in a range of values from 1.64 to 4.80.     

The acute and chronic toxicity of ammonia to marine fish and a mysid

The acute toxicity (96-hr LC50) of un-ionized ammonia to mysids (Mysidopsis bahia) and larval inland silversides (Menidia beryllina) was influenced by pH and salinity in a species specific manner. With mysids, NH₃ was most toxic at pH 7.0 and less toxic at pH 8.0 and 9.0. In contrast, NH₃ toxicity to inland silversides was greatest at pH 7.0 and 9.0 and lowest at pH 8.0. A drop in salinity from 31 g/kg to 11 g/kg uniformly increased toxicity to mysids over this pH range. In contrast, in silversides at 11 g/kg, NH₃ toxicity was less at pH 7.0, greater at pH 8, and slightly less at pH 9, relative to the toxicity at 31 g/kg. Temperature had no significant effect on the acute toxicity of un-ionized ammonia with acclimated mysids tested at 18, 25 and 32.5°C, but did have a small effect with acclimated larval sheepshead minnows (Cyprinodon variegatus) tested at 13, 25 and 32.5°C. The chronic toxicity value (the geometric mean of the highest no-effect concentration and lowest effect concentration) at pH 8.0, 25°C and 31 g/kg salinity is 0.061 mg NH₃/L for inland silversides and 0.232 mg NH₃/L for mysids; the acute: chronic ratio is 21.3 and 7.2, respectively.Contribution No. 893 of the U.S. Environmental Protection Agency, Environmental Research Laboratory, Narragansett, RI 02882, USAAlthough the information in this document has been funded wholly or in part by the United States Environmental Protection Agency, it does not necessarily reflect the views of the Agency and no official endorsement should be inferred.     

Environmental Effects of Sodium Acetate/Formate Deicer, Ice Shear™

The environmental impacts of Ice Shear™, an alternative highway deicer, have been evaluated using standard laboratory tests; biochemical oxygen demand (BOD) tests, chemical oxygen demand (COD) tests, acute rainbow trout bioassays, and phytotoxicity tests were used. Ice Shear consists of equimolar sodium acetate and sodium formate. The organic matter of the deicer can be readily degraded microbiologically in the natural environment with a slow rate of degradation at lower temperatures but an increased rate at higher temperatures. At elevated temperatures, highway runoffs of the deicer may reduce the level of dissolved oxygen in the receiving waters to cause an adverse impact. However, the apparent activation energy calculated for the BOD rate of Ice Shear is low (8.78 kcal mole⁻¹), indicating that the temperature variation may not significantly influence the biodegradation of the deicer compound. Ice Shear appears relatively harmless to aquatic animals, showing a high 96-h LC₅₀ value (16.1 g/L) derived for rainbow trout (Oncorhynchus mykiss). Ice Shear causes minimal toxicity to representative roadside vegetation; herbaceous (e.g., sunflowers, beans, and lettuce) and woody (e.g., pine seedlings) plants. Rather, the deicer at low concentrations (less than 2 g/kg soil) seems to work as a fertilizer, promoting the yield of biomass. The test results indicate that Ice Shear poses minimal environmental disturbance in both aquatic and terrestrial ecosystems. Received: 4 October 1997/Accepted: 17 March 1998     

Toxicities of butoxyethanol ester and propylene glycol butyl ether ester formulations of 2,4-dichlorophenoxy acetic acid (2,4-D) to juvenile salmonids

Continuous-flow toxicity tests were conducted to determine acute toxic effects of butoxy-ethanol ester (BOEE) and propylene glycol butyl ether ester (PGBEE) formulations of 2,4-D on juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead-rainbow trout (Salmo gairdneri). A chronic toxicity test with chinook salmon egg-to-fry was conducted to determine effects of BOEE on survival and growth. The hydrolysis in water of 2,4-D esters to 2,4-D acid was influenced by the presence of fish. Median lethal concentrations (96-hr LC50 values) indicated that PGBEE (170 to 355 g/L) was slightly more toxic (37 to 57%) than BOEE (303 to 525 g/L). The LC50 values also indicated that chinook salmon were generally more sensitive than steelhead-rainbow trout and that fry and smolts were equally sensitive to the 2,4-D esters. Static tests substantially underestimated BOEE toxicity when compared to dynamic tests. Based on reduced survival and growth of chinook salmon alevins and fry, the estimated maximum safe chronic exposure concentration under these test conditions is 40 g/L BOEE.     

Effects of cadmium,cobalt, copper,and nickel on growth of the green alga Chlamydomonas reinhardtii: The influences of the cell wall and pH

Comparative studies of the toxicity of Cd, Co, Cu, and Ni to walled (UTCC 11) and wall-less (UTCC 12) strains of Chlamydomonas reinhardtii were made in order to test the hypothesis that the cell wall affords some protection against metal toxicity. The wall-less strain was consistently more sensitive than the walled strain to all four metals, indicating that the cell wall plays a role in conferring metal tolerance. Between-strain differences were most striking for Cu and for Co. The effect of hydrogen ion concentration (pH 5 and 6.8) on metal toxicity was also determined for the two strains. Having established that both strains grew equally well at pH 5 or 7 in the absence of added metal, it was necessary to correct for the changes in metal speciation due to pH in the medium used for the tests. Speciation of each metal at each pH was determined by mathematical (GEOCHEM) modeling of the medium and the calculated free (ionic) metal concentration was used to express toxicity. In addition, the concentration of ionic metal that reduced final cell density to 30% of that in control solution (EC₃₀) was used as an indicator of relative metal toxicity. For both strains, all metals were less toxic at pH 5 than at pH 7, supporting previous observations. The results are discussed in terms of the possible mechanisms by which the cell wall could protect the cell from metal toxicity, and the relevance of the results to more general considerations of metal tolerance mechanisms in plants.     

Salinity Tolerances of Selected Macroinvertebrates of the Sabie River,Kruger National Park,South Africa

Salinization has been identified as the most important problem facing the managers of South African freshwaters. Laboratory-based toxicity tests were conducted to assess the tolerance of selected macroinvertebrates to elevated salt concentrations. Since the Kruger National Park is the focus of river research in South Africa, and the Sabie River is the least mineralized river in the park, 96-h acute toxicity tests were conducted using Sabie River water and an ephemeropteran mayfly Tricorythus sp. found in the river. Experiments were conducted in flowing water systems known as raceways. The tolerance of the mayfly to two sodium salts, sodium chloride and sodium sulphate, was assessed at a range of selected conductivity levels/concentrations. The results indicated that mortality cannot be linked only to conductivity or total dissolved solid (TDS) concentrations, but also to the nature of the salt. Sodium sulphate was considerably more toxic to Tricorythus sp. than sodium chloride. Causes of mortality and implications for the development of water quality guidelines for the natural aquatic environment are discussed. Received: 1 April 1996/Revised: 21 July 1996     

Acute and Chronic Toxicity of Azinphos-Methyl to Two Estuarine Species, Mysidopsis bahia and Cyprinodon variegatus

The acute and chronic toxicity of azinphos-methyl (Guthion) was evaluated for two estuarine species in the laboratory. Mysids (Mysidopsis bahia) and sheepshead minnows (Cyprinodon variegatus) were selected as the representative invertebrate and vertebrate estuarine test species, respectively. The toxicological endpoints determined for each species included the 96-h LC50, the no-observed-effect concentration (NOEC), the maximum acceptable toxicant concentration (MATC), and the acute-to-chronic ratio. The 96-h LC50 value derived for sheepshead minnows (2.0 μg/L) was seven times higher than the 96-h LC50 value (0.29 μg/L) derived for mysids. The MATCs were 0.024 μg/L and 0.24 μg/L for the mysid and the sheepshead minnow, respectively. The estimated acute-to-chronic ratios were 12 for mysids and 8.3 for sheepshead minnows. Received: 29 July 1996/Revised: 28 November 1996     

Acute toxicity of pure pentachlorophenol and a technical formulation to three species ofDaphnia

The acute toxicity of a technical formulation of pentachlorophenol (PCP) and pure pentachlorophenol to three age classes ofDaphnia magna, and adultD. pulex andD. galeata mendotae was determined by static toxicity tests. The influence of a number of factors on toxicity of PCP was also examined. The 48-hr LC50 estimates for adult daphnids of the three species exposed to pure PCP were 1.78, 4.59 and 0.51 mg/L, respectively, while those for the technical formulation were 2.57, 3.66 and 0.33 mg/L, respectively. There was little difference in toxicity between the technical and pure PCP; however, toxicity of both forms of PCP was influenced by duration of exposure, age (and/or size) and species of test organism and pH of the test solution.Pentachlorophenol caused a toxic response over a very narrow range of concentrations, with the greatest response occurring immediately between 0 and 24 hr. Pure PCP was equally toxic to all age classes ofD. magna but susceptibility to technical PCP decreased with maturation.D. g. mendotae was ten times more sensitive thanD. pulex to PCP. Pure PCP was significantly more toxic toD. magna at pH 5.5 than 7.0 with mean 48-hr LC50 values of 0.082 and 1.78 mg PCP/L, respectively.At 12°C, the toxicity of both forms of PCP toD. g. mendotae andD. pulex did not differ significantly from that at 20°C; however, technical PCP was significantly more toxic toD. magna at 12°C for an exposure duration of 48 hr. There was no effect of test container size (100, 250, 600 and 1,000 mL) on the toxicity of PCP toD. magna at 20°C with the lower pH of 5.5, suggesting that adsorption to glassware was not a factor in availability of PCP to test organisms. Beaker size had no effect on the toxicity of PCP toD. pulex at 20°C with test solutions having a pH of 7.0-8.0.     

Assessment of the freshwater annual fish Cynopoecilus melanotaenia as a toxicity test organism using three reference substances

This study presents a preliminary evaluation of the use of the Brazilian fish Cynopoecilus melanotaenia as a test organism in toxicity tests. The cryptobiotic stage presented by the eggs of fish C. melanotaenia can overcome the difficulty of continuously keeping cultures and recruiting healthy animals in sufficient numbers to be used in toxicity tests. In order to determine the applicability of this species as a test organism, three different reference substances were evaluated in 96-h acute toxicity tests: Copper sulfate (CuSO4 x 5H2O), sodium dodecil sulfate (C12H25NaO4S), and sodium chloride (NaCl). Sensitivity ranged as follows: copper sulfate (0.05-0.13 mg/L), sodium dodecil sulfate (10.7-19.0 mg/L), and sodium chloride (1.44-1.96 g/L). We conclude that C. melanotaenia shows potential as a test organism in toxicity tests; however, further research should be conducted with other substances and should be compared with the research on other species before we can reach more conclusive results.     

The Influence of Salinity and Dissolved Organic Carbon on the Toxicity of Copper to the Estuarine Copepod, <Emphasis Type="Italic">Eurytemora affinis</Emphasis>

The objectives of this study were to determine the influence of salinity (2.5, 5, 15, and 25 ppt) at dissolved organic carbon (DOC) concentrations of 1.3–3.3 mg/L and DOC concentrations of 2, 4, 6, and 8 mg/L at a fixed salinity of 10 ppt on the acute toxicity (96-h LC50s) of copper to the sensitive estuarine copepod, Eurytemora affinis. For both salinity and DOC experiments, various other chemical constituents such as DOC, Ca²⁺, Cl^-, Mg²⁺, Na⁺, K⁺, SO₄^2-, hardness, alkalinity, salinity, pH, temperature, and dissolved oxygen were measured at selected copper concentrations at test initiation and test termination. Dissolved copper, copper speciation, and organic copper complexation were measured at various test conditions during the salinity and DOC experiments. Ninety-six-hour dissolved copper LC50 values for the four salinities ranged from 58 μg/L (25 ppt) to 104 μg/L (5 ppt) with intermediate values of 71 μg/L (2.5 ppt) and 68 μg/L (15 ppt). The 58, 68, and 71 μg/L LC50 values were not significantly different. Copper LC50 values at 5 ppt were higher than at both 15 and 25 ppt. The isosmotic salinity of E. affinis is approximately 5–10 ppt, which was a likely factor for why the LC50 value increased for copper at 5 ppt. The dissolved copper 96-h LC50s for E. affinis increased from 76 to 166 μg/L as DOC increased from 2 to 8 mg/L. This result is not surprising and is consistent with reported values for other saltwater species.