Piscicidal and anti-acetylcholinesterase activity of Euphorbia royleana stem bark extracts against freshwater common predatory fish Channa punctatus

The present paper deals with the piscicidal activity of different solvent extracts of Euphorbia royleana stem bark against freshwater predatory fish Channa punctatus, which is commonly present in shrimp and carp culture ponds. The rank of order of toxicity of different solvent extract was: diethyl ether (LC(50) (96h) 31.76mg DW/L) > chloroform (LC(50) (96h) 56.26mg DW/L) > methanol (LC(50) (96h) 56.80mg DW/L) > acetone (LC(50) (96h) 65.77mg DW/L). There was a significant (P < 0.05) negative correlation between LC values and exposure periods, thus increase in exposure time. The LC(50) values of diethyl ether extract of E. royleana stem bark decrease from 81.78mg DW/L (24h) to 31.76mg DW/L (96h). Similar trend were also observed in case of chloroform, methanol and acetone extracts. Exposure of sub-lethal doses (40% and 80% of LC(50)) of the diethyl ether extract for 24h or 96h caused significant inhibition in the activity of enzyme acetylcholinesterase (AChE) in liver and muscle tissue of fish C. punctatus. There was a significant recovery observed in the activity of enzyme acetylcholinesterase in both the tissues of fish after 7th day of the withdrawal of treatment. Thus, the diethyl ether extract of E. royleana stem bark can be used for control of unwanted predatory fish C. punctatus from fish culture ponds. Their toxicological action is due to their anti-acetylcholinesterase enzyme activity, reversibility in their action is advantageous factor for their use as environmentally safe piscicide in aquatic bodies.     

Cadmium tolerance in the Nile tilapia (Oreochromis niloticus) following acute exposure: assessment of some ionoregulatory parameters

The Nile tilapia (Oreochromis niloticus) can tolerate very high levels of waterborne cadmium. It has one of the highest 96 h LC50 recorded for a freshwater teleost fish (14.8 mg/L Cd; hardness 50 mg/L CaCO(3)). Cadmium is known to perturb ion balance in teleost fishes. However, in an acute time course experiment, plasma Na(+) concentrations were unaffected, and plasma Ca(2+) values only decreased after 96 h exposure in a dose-independent manner. Branchial Na(+)/K(+)-ATPase activity and alpha-subunit protein level expression in crude gill homogenates were not affected by Cd exposure during this period. Branchial chloride cell numbers, identified as Na(+)/K(+)-ATPase immunoreactive cells using immunohistochemistry, decreased 24 h after exposure but recovered thereafter. Histopathological changes did not follow a consistent pattern of variation with exposure time, and the alterations noted in gill epithelium were basically nonspecific to cadmium. Because of its tolerance, it can be concluded that the tilapia O. niloticus would not be a suitable test organism to evaluate sublethal toxicity of cadmium and the realistic impact of this pollutant in the environment. However, it certainly could contribute significantly to our understanding of the toxic mechanism of cadmium exposure in aquatic organisms. This is the first work to investigate the effect of waterborne pollutants on Na(+)/K(+)-ATPase alpha-subunit protein expression in fish gills.     

Acute toxicity of synthetic pyrethroid cypermethrin to freshwater catfish Heteropneustes fossilis (Bloch)

Lethal concentrations of cypermethrin, dissolved either in water or acetone, were determined for freshwater catfish Heteropneustes fossilis at different hours of exposure by static bioassays. Up to 48 hours, there was no difference between LC(50) values of aqueous and acetone solublized cypermethrin. Seventy-two-hour LC(50) values of aqueous cypermethrin and acetone solublized cypermethrin to H. fossilis were 0.67 and 1.27 microg/L, respectively. Lethal values remained unchanged beyond 72 hours. The fish exposed to even lower concentration of cypermethrin (0.5 microg/L) showed hyperactivity.     

Hazard/Risk Assessment of Pyridaben: I. Aquatic Toxicity and Environmental Chemistry

The toxicity and environmental fate of the insecticide-miticide, pyridaben were investigated using both standardized laboratory procedures and outdoor studies with natural water. Outdoor studies provide a more realistic exposure scenario to aquatic organisms and any toxicity is a response to actual exposure concentrations resulting from the natural degradation and dissipation of the chemical. This paper describes the environmental chemistry/fate and aquatic toxicity of pyridaben. The subsequent paper describes the results of the outdoor aquatic toxicity studies and the use of the water-effect ratio in hazard/risk assessment. Environmental fate studies indicate that pyridaben has a low water solubility and high K_d and K_oc values, which favors partitioning from water onto soil and sediment. Pyridaben is stable to hydrolysis but has a short photolysis half-life in water (<30 min) and soil (11 d). Furthermore, pyridaben has a short half-life in soil (12 to 14 d) when applied in the field to citrus crops. Laboratory studies with constant 48- to 96-h exposures to pyridaben show it is acutely toxic to fish (Lepomis macrochirus, Pimephales promelas, Oncorhynchus mykiss, Cyprinodon variegatus) and invertebrates (Daphnia magna, Mysidopsis bahia). Invertebrates are more sensitive (lower LC50s) than fish to pyridaben, and most mortalities occur <24 h for fish and <72 h for invertebrates. Chronic laboratory studies indicate that the MATCs for pyridaben and D. magna, M. bahia and P. promelas were 0.12, 0.15 and 0.39 g/L, respectively. Acute-to-chronic ratios for pyridaben are low for fish and invertebrates, indicating a low potential for residual activity. Chronic toxicity to aquatic organisms is not an issue after application in the field because exposures tend to be brief.     

Toxicity of perfluorooctane sulfonate and perfluorooctanoic acid to plants and aquatic invertebrates

Acute toxicities of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were tested on four freshwater species and three plant species. PFOS was more toxic than PFOA for all species tested in this study. Similar time-response patterns of PFOS and PFOA toxicity were observed for each tested species. Values of the 48-h LC(50) of PFOS for all test species ranged from 27 to 233 mg/L and values of the 96-h LC(50) for three of the species ranged from 10 to 178 mg/L. Values of the 48-h LC(50) of PFOA for all test species ranged from 181 to 732 mg/L and values of the 96-h LC(50) for three of the species ranged from 337 to 672 mg/L. The most sensitive freshwater species to PFOS was green neon shrimp (Neocaridina denticulate) with a 96-h LC(50) of 10 mg/L. Of the aquatic organisms tested, the aquatic snail (Physa acuta) always has the highest resistance to PFOS or PFOA toxicity over each exposure period. Both PFOS and PFOA had no obvious adverse effect on seed germination for all three plant species. Five-day EC(50) of root elongation was more sensitive to LC(50) of seed germination in this study. Based on EC(10), EC(50), and NOECs, the 5-day root elongation sensitivity of test plants to both PFOS and PFOA was in the order of lettuce (Lactuca sativa) > pakchoi (Brassica rapa chinensis) > cucumber (Cucumis sativus). Based on the results of this study and other published literature, it is suggested that current PFOS and PFOA levels in freshwater may have no acute harmful ecological impact on the aquatic environment. However, more research on the long-term ecological effects of PFOS and PFOA on aquatic fauna are needed to provide important information to adequately assess ecological risk of PFOS and PFOA.     

Comparative study on two freshwater invertebrates for monitoring environmental lead exposure

Two freshwater invertebrate organisms, Biomphalaria glabrata and Lumbriculus variegatus, were tested as potential experimental animal models to assess Pb exposure using acute laboratory bioassays. Since long, the enzyme delta-aminolevulinic acid dehydratase (ALA-D) has been recognised as a useful biomarker of Pb exposure and effect. Therefore, determinations of ALA-D activity were performed in the whole body soft tissues of pigmented and non-pigmented gastropods B. glabrata and in the oligochaete L. variegatus. The organisms were exposed to varying concentrations of Pb for 48 h. Levels of Pb in the invertebrates were also analysed. Highly significant negative correlations were found between the enzymatic activity and the levels of Pb exposure, and also between the enzymatic activity and the metal incorporated by the invertebrates. No significant differences were found in the enzyme activity nor in the resulting metal accumulation based on gastropod pigmentation. The values of Pb concentration that produce 50% of inhibition on the enzyme activity (EIC50) were 0.023 and 0.029 mg Pb/L for pigmented and non-pigmented B. glabrata, respectively. A much higher value was found for L. variegatus (0.703 mg Pb/L). The non-observed effect concentration (NOEC) on enzyme activity for the oligochaetes was 0.05 mg Pb/L, about twice the EIC50 calculated for the gastropods. These data showed that both pigmented and non-pigmented B. glabata were much more sensitive organisms than the oligochaetes. The differences in enzyme inhibition could be attributed, at least partly, to differences in the metal body burden found between the organisms, since levels of Pb accumulated by B. glabrata were approximately three times higher compared to those observed in L. variegatus. Therefore B. glabrata showed to be a more suitable and reliable bioindicator organism for assessing Pb contamination in aquatic ecosystems, especially at low levels of metal exposure.     

Toxicity evaluation of single and chemical mixtures of roundup,Garlon-3A, 2,4-D,and syndets surfactant to channel catfish (Ictalurus punctatus), bluegill sunfish (Lepomis microchirus), and crawfish (Procambarus spp.)

The acute toxicity of individual and mixtures of three herbicides (2,4-D, Garlon-3A, and Roundup) and a chemical additive (Syndets surfactant) was evaluated using three species of freshwater organisms (channel catfish, bluegill sunfish, and crawfish). Among the three herbicides, Roundup was more toxic to catfish and bluegill than Garlon-3A and 2,4-D. The order of toxicity in fish (Roundup > Garlon-3A > 2,4-D) was reversed in bioassays with crawfish, indicating a significant difference in interspecies (vertebrate vs invertebrate) biological variability. Adjusted 96 h LC₅₀'s were 14.5, 13.0, and 21,632.8 mg/L for Roundup, 109.5, 91.0, and 6,397.5 mg/L for Garlon-3A, and 181.2, 266.3, and 750.1 mg/L for 2,4-D, for catfish, bluegill, and crawfish, respectively. For Syndets surfactant, LC₅₀ values of 1.9 mg/L (bluegill), 2.3 mg/L (catfish), and 15.2 mg/L (crawfish) were recorded, indicating that this chemical additive was much more toxic than the three herbicides. Bioassays with herbicide mixtures resulted in combined toxic effects that were slightly antagonistic and/or additive. Lethal concentrations of herbicide mixtures were found to be lower than recommended field formulations, but it was anticipated that such hazardous amounts would be rarely reached in roadside ditches where the presence of large volumes of water is likely to provide dilutions to levels that may not pose a threat to aquatic life. ©1997 by John Wiley & Sons, Inc. Environ Toxicol Water Qual 12 : 237–243, 1997     

Toxicity of nitrite to three species of freshwater invertebrates

Nitrite is a compound with a high toxicity to aquatic animals. Several anthropogenic pollution sources are increasing the concentrations of this component of the nitrogen cycle. Despite this toxicity, there is little available literature on its effects on freshwater invertebrates. Laboratory bioassays were performed to obtain data on the lethal effects of nitrite to three species of freshwater invertebrates: the planarian Polycelis felina and the amphipods Echinogammarus echinosetosus and Eulimnogammarus toletanus. The LC(50), LC(10), and LC(0.01) values (mg/L NO(2)--N) at 24, 48, 72, and 96 h were calculated for each species. E. toletanus and E. echinosetosus were the most sensitive species, with 96 h LC(50) values of 2.09 and 2.59 mg/L NO(2)--N, respectively. In contrast, the planarian P. felina showed a higher tolerance to nitrite, with a 96 h LC(50) value of 60.0 mg/L NO(2)--N. The obtained results were compared with the reported nitrite data for other freshwater invertebrates. This study may contribute to a more appropriate assessment of the ecological risk of this compound in freshwater ecosystems.     

The relative importance of waterborne and dietborne arsenic exposure on survival and growth of juvenile rainbow trout

Previous work demonstrated reduced growth of rainbow trout receiving diets containing environmentally relevant concentrations of arsenic, but did not address the relative and combined potency of waterborne and dietborne exposures. In the current study, juvenile rainbow trout were exposed for 28d to a range of arsenic concentrations in water and in a live oligochaete diet, separately and in combination. In clean water, fish fed worms previously exposed to arsenate at 4 or 8mg As/L showed pronounced reductions in growth, but fish exposed to these same water concentrations and a clean diet experienced less or no effect. Increasing waterborne arsenate to 16 or 32mg As/L had substantial effects on both growth and survival, and simultaneous exposure via both routes intensified growth effects, but not mortality. Growth reduction was strongly correlated to total arsenic accumulation in the fish tissue, regardless of the route of exposure, but mortality was better correlated to waterborne arsenic concentration. The relative concentration of total arsenic in fish viscera and in the remaining carcass was not a useful indicator of exposure route. Speciation analysis showed that most arsenate was converted to arsenite within the worms, but organoarsenic species were not found. The greater toxicity of dietborne exposure when fish and prey were exposed to the same waterborne arsenate concentration emphasizes the need to address dietborne exposure when assessing the aquatic risks of arsenic contamination. This is of particular concern because risk from dietary exposure may occur at even lower water concentrations than used here when prey organisms are exposed for longer periods and via multiple routes.     

Toxicity of the molluscicidal plant, Ambrosia maritima L., to aquatic non-target organisms

The toxicity of the molluscicidal plant, Ambrosia maritima L., has been evaluated in fish, crustacea and algae. The LC50 for fries of the guppy, Lebistes reticulatus, was respectively 650 and 450 mg/litre using a powder or an ether-methanol-hexane extract from the leaves of the plant. This concentration is much higher than the molluscicidal concentration (LC90) of 35 to 70 mg/litre, which is used in the field (irrigation canals in Egypt). Preliminary tests showed that juveniles of L. reticulatus and Tilapia aurea were as sensitive as the fries. Using the same extract of A. maritima the LC50 for Daphnia magna was 766 mg/litre and no toxic effects could be observed in algae Selenastrum capricornutum at 1 g/litre. It can be concluded that A. maritima has a very low toxicity to aquatic non-target organisms. It is not toxic when used at the molluscicidal concentration of 35 to 70 mg/litre.     

Acute toxicity of vanadium to the threespine stickleback, Gasterosteus aculeatus

Vanadium is widely distributed, occurring in many types of minerals, coal, and petroleum. Anthropogenic sources of vanadium originate from the production, processing, and wastes of these materials. The aquatic toxicity of vanadium to fish species is not well characterized. This study focused on the three-spined stickleback, Gasterosteus aculeatus, a small and widely distributed euryhaline species of fish. The three-spined stickleback is used as an effluent-monitoring species in both Canada and the United States. Five 96-h static renewal acute toxicity tests were performed in moderately hard water with adult fish. The geometric mean and range of the five 96-h LC(50)s based on measured concentrations of total vanadium in the test solution were 3.17 and 2.35-4.07 mg V/L, respectively. A conservative estimation of a safe concentration of vanadium that would not affect survival of adult three-spined sticklebacks over a 96-h exposure period in moderately hard water is approximately 0.30 mg V/L. A comparison with other fish species previously tested suggests that the three-spined stickleback is intermediate in sensitivity to vanadium. Information reported from this study may be useful in effluent toxicity identification evaluations and ecological risk assessments related to vanadium.     

Chronic toxicity of glutaraldehyde: differential sensitivity of three freshwater organisms

The biocide, glutaraldehyde, is a potential environmental contaminant due to its widespread use in medical applications, off-shore oil extraction, and pulp mill processing. It has also been proposed as a candidate for treating the ballast water of vessels, which could result in a substantial increase in environmental release. To assess the potential for environmental impacts associated with glutaraldehyde, three standard chronic toxicity bioassays were performed: 96-h phytoplankton growth bioassays using Pseudokirchneriella subcapitata (formerly, Selenastrum capricornutum), three-brood reproduction bioassays using Ceriodaphnia dubia, and an embryo-larval bioassay using steelhead trout, Oncorhynchus mykiss. For the green alga, P. subcapitata, significant decreases in growth were observed at glutaraldehyde concentrations greater than or equal to 1.0 mg L(-1). Embryos of O. mykiss demonstrated a similar sensitivity with exposures of 2.5 mg L(-1) resulting in a 97% reduction in hatch rate. In most cases, this failure to hatch was due to the inability of the embryo to leave the chorion and not to early embryo mortality. In contrast, reproduction and mortality rates in C. dubia were not as sensitive to glutaraldehyde: decreased reproduction was detected at 4.9 mg L(-1) (the lowest observed effect concentration), and is similar to concentrations causing acute mortality in adults (4.7 mg L(-1) for the estimated LC(50), or 50% lethal concentration). These data indicate that both algae and fish embryos may be particularly sensitive to long-term glutaraldehyde exposure; however, this is predicated on whether glutaraldehyde concentrations will achieve high enough environmental concentrations and for a sufficient period of time to elicit such effects.     

Age-altered susceptibility in hexavalent chromium-exposed Daphnia schodleri (Anomopoda: Daphniidae): integrated biomarker response implementation

Daphnia schodleri is a naturally occurring cladoceran in Mexican freshwater bodies and its relative big size and short life cycle allow its use in toxicological bioassays. Generally, life stages at opposite sides of a normal distribution are considered to be the most susceptible and/or sensitive because of several sub-individual level processes, such as ageing, in which antioxidant activity decreases and reactive oxygen species (ROS) cannot be totally neutralized. Most aquatic populations are structured by organisms of different ages, in which physiological and biochemical responses differ (in magnitude) from each other. According to these statements, seven age groups of D. schodleri (0, 3, 5, 7, 14, 21, and 28 d) were exposed to Cr (VI) in both acute and non-lethal bioassays. Results from acute bioassays were used to estimate the chromium LC(50) values for every age group, which ranged from 0.12 to 0.61 mg L(-1), with a normal pattern distribution. Antioxidant enzymatic activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) was assessed in organisms exposed to two sublethal Cr(VI) concentrations (0.032 and 0.0064 mg L(-1)). Results showed that neonates' antioxidant activity increased with respect to their controls; nevertheless, the same pattern was not seen in the other age groups. Moreover, GPx activities followed a decreasing pattern with respect to their control groups in organisms 3-d and older. In addition, GR activities were barely modified by chromium exposure of neonates, but not in the other age groups; CAT was only modified in younger daphnids. Once the biomarker responses were normalized, it was possible to observe that enzyme participation differed during the life cycle of this cladoceran and, as a result of their decreasing antioxidant activity, relatively old organisms could have lower capability to deal with pro-oxidant toxicants such as Cr(VI).     

Acute toxicity of copper to the threespine stickleback, Gasterosteus aculeatus

This study focuses on characterizing the acute toxicity of copper in freshwater to the threespine stickleback, Gasterosteus aculeatus, a small and widely distributed euryhaline fish. The threespine stickleback is used as an effluent monitoring species in both Canada and the United States, yet in some locations natural populations are listed as threatened or endangered. Four 96-h static renewal acute toxicity tests were performed in moderately hard water using U.S. EPA methods with adult fish (mean wet weight = 0.41 g/fish). The geometric mean of the 24-, 48-, 72- and 96-h LC(50)s based on measured concentrations of total copper (estimated dissolved copper in parentheses) in the test solutions were 382.2 (366.9), 278.7 (267.6), 256.6 (246.3), and 227.2 (218.1) microg Cu/L, respectively. Conservative estimates of acute toxicity thresholds, made using LC1 values, for adult threespine sticklebacks over 24-, 48-, 72- or 96-h exposure periods in moderately hard water are approximately 114.3 (109.7), 78.3 (75.2), 67.0 (64.3), and 52.4 (50.3) microg Cu/L, respectively. Test results were normalized to a range of water hardness from very soft to very hard using two U.S. EPA methods, the water hardness and the Biotic Ligand Model normalization procedures. Subsequently, interspecies sensitivity comparisons were made with aquatic animal species used in both the current and proposed U.S. EPA copper water quality criteria documents. Information reported in this study may be useful in effluent toxicity identification evaluations, ecological risk assessments and criteria development where copper is a concern.     

Ecotoxicological effects of jute retting on the survival of two freshwater fish and two invertebrates

Severe deterioration of water quality occurs during jute retting in ponds, canals, floodplain lakes, and other inland water bodies in the rural areas of West Bengal in India. Attempts were made to evaluate changes in the physicochemical parameters of water caused by jute retting, and their impact on the survival of two species of freshwater fish (Labeo rohita and Hypophthalmicthys molitrix) and two species of freshwater invertebrate (Daphnia magna, a Cladocera, and Branchiura sowerbyi, an Oligochaeta). Results showed that jute retting in a pond for 30 days resulted in a sharp increase in the BOD (>1,000 times) and COD (>25 times) of the water, along with a sharp decrease in dissolved oxygen (DO). Free CO₂, total ammonia, and nitrate nitrogen also increased (three to five times) in water as a result of jute retting. Ninety-six-hour static bioassays performed in the laboratory with different dilutions of jute-retting water (JRW) revealed that D. magna and B. sowerbyi were not susceptible to even the raw JRW whereas fingerlings of both species of fish were highly susceptible, L. rohita being more sensitive (96 h LC₅₀ 37.55% JRW) than H. molitrix (96 h LC₅₀ 57.54% JRW). Mortality of fish was significantly correlated with the percentage of JRW.     

Acute toxicity, behavioral changes, and histopathological effects of deltamethrin on tissues (gills, liver, brain, spleen, kidney, muscle, skin) of Nile tilapia (Oreochromis niloticus L.) fingerlings

Deltamethrin, a synthetic pyrethroid contaminating aquatic ecosystems as a potential toxic pollutant, was investigated in the present study for acute toxicity. The purpose of this study was to evaluate LC(50) values of deltamethrin on Nile tilapia (Oreochromis niloticus L.) fingerlings and investigate histopathological responses of fish exposed to deltamethrin. The 48 h LC(50) value for Nile tilapia fingerlings was estimated as 4.85 microg/L using static test system. In addition, behavioral changes at each deltamethrin concentration were observed closely. All fish, exposed to 5 microg/L deltamethrin revealed severe morphological alterations in the gills and liver. In the gills hyperemia, fusion of secondary lamellae and telangiectasis were observed; whereas hydropic degenerations in liver were observed in all examined fish. The results are significant for reporting acute deltamethrin toxicity in terms of behavioral and histopathological changes: Deltamethrin is highly toxic to fingerlings.     

Fluoride sensitivity in freshwater snail,Bellamya bengalensis (Lamarck, 1882): An integrative biomarker response assessment of behavioral indices,oxygen consumption,haemocyte and tissue protein levels under environmentally relevant exposure concentrations

There is limited information on fluoride toxicity and risk overview on ecotoxicological risks to aquatic invertebrate populations particularly molluscan taxa. This necessitated the assessment of toxicity responses in the freshwater snail, Bellamya bengalensis exposed to environmentally relevant concentrations of sodium fluoride. Under lethal exposures (150, 200, 250, 300, 400 and 450 mg/l), the median lethal concentrations (LC₅₀) were determined to be 422.36, 347.10, 333.33 and 273.24 mg/l for B. bengalensis at 24, 48, 72 and 96 h respectively. The rate of mortality of the snails was increased significantly with elevated concentrations of the toxicant. The magnitude of toxicity i.e., toxicity factor at different time scale was also higher with increased exposure duration. Altered behavioural changes i.e., crawling movement, tentacle movement, clumping tendency, touch reflex and mucous secretion in exposed snail with elevated concentrations and exposure duration. Similarly, oxygen consumption rate of the treated snail also lowered significantly during 72 and 96 h of exposure. Under 30-day chronic exposures (Control-0.00 mg/L; T1–27.324 mg/L; T2–54.648 mg/L), protein concentrations in gonad and hepatopancreas of exposure groups was significantly lowered. Chronic exposures also revealed lowered haemocytes counts in exposure groups. The potential for loss of coordination, respiratory distress and physiological disruption in organisms exposed to environmentally relevant concentrations of fluoride was demonstrated by this study. The estimation and magnitude of toxicity responses are necessary for a more accurate estimation of ecological risks to molluscan taxa and invertebrate populations under acute and chronic fluoride exposures in the wild.     

Lethal and sublethal responses of an aquatic insect Culex quinquefasciatus (Diptera: Culicidae) challenged with individual and joint exposure to dissolved sodium selenate and methylmercury chloride

Pollutants rarely occur alone in the natural environment, and few studies have focused on the potential interactions between metals or metalloids. In this study an aquatic insect, the southern house mosquito (Culex quinquefasciatus: Diptera), was used to test the individual and joint effects of dissolved sodium selenate (Se) and methyl mercury chloride (MeHg). We conducted ovipositional preference tests and 14-day chronic toxicity studies to determine lethal and sublethal responses of C. quinquefasciatus to a range of Se and MeHg concentrations and mixtures. No evidence was found for female ovipositional preference in field trials using artificial ponds. Larvae were more sensitive to MeHg than Se, with LC(50) values of 30 microg/L (CI = 28-31 microg/L) and 11 mg/L (CI = 10-12 mg/L) respectively. In addition, larval survival was significantly reduced at concentrations as low as 25 microg/L of MeHg and 8 mg/L of Se. A synergistic interaction was observed in the toxicity of the Se-MeHg mixtures to C. quinquefasciatus larvae. Larval mosquito survival was significantly reduced at 7.5 microg/L MeHg + 2.75 mg/L Se and an LC(50) value of 9 microg/L MeHg + 3.4 mg/L Se was determined for a fixed ratio mixture. The rate of growth of the larvae was analyzed using a Growth Index that provided a sensitive measure of the developmental effects of toxicant exposure. Sodium selenate at concentrations as low as 2 mg/L caused a significant decrease in growth between larvae in treatment versus control solutions after only 4 days. Similarly, MeHg at concentrations as low as 25 microg/L and a Se-MeHg mixture of 3 microg/L MeHg plus 1.1 mg/L Se caused significant growth reductions after only 2 and 3 days, respectively. These are the first reported survival and developmental data for an aquatic insect exposed to MeHg and Se-MeHg mixtures.     

Measurement of the aquatic toxicity of volatile nitrosamines.

The acute toxicity of N-nitrosodimethylamine (DMN) and N-nitrosodiethylamine (DEN) was determined for three groups of aquatic organisms: algae, invertebrates, and fish. Toxicity of DMN and DEN to algae was assessed as a repression in the growth rate of either Selenastrum capricornutum or Anabaena flos-aquae in static bioassay tests. DMN and DEN concentrations of 1-10 ppm depressed algal growth in all cases. Invertebrate toxicity was determined in 96-h static bioassay tests with Dugesia dorotocephala and Gammarus limnaeus. The data indicated that these organisms are not highly susceptible to nitrosamine toxicity. The 96-h LC50s for D. dorotocephala were 1365 and 1490 ppm for DMN and DEN, respectively. Similar studies with G. limnaeus indicated LC50s of 330 and 500 ppm for DMN and DEN, respectively. Fish toxicity was also determined in 96-h statis bioassays with the fathead minnow (Pimephales promelas). Acute toxicities were calculated as LC50s of 940 and 775 ppm for DMN and DEN, respectively. Algae were calculated as LC50s of 940 and 775 ppm for DMN and DEN, respectively. Algae were quite sensitive to relative low levels of volatile nitrosamines, but higher organisms (invertebrates and fish) were relatively insensitive.     

Acute spill‐mimicking exposure effect of hexavalent chromium on the pituitary‐ovarian axis of a teleost,Channa punctatus (Bloch)

Acute exposure to hexavalent chromium (as 10, 20, and 40 mg/L potassium dichromate for 96 h) adversely affected the pituitary‐ovarian axis of a teleost Channa punctatus. The toxic impact of metal exposure on fish ovary was revealed in the form of increased percentage of atretic follicles, significantly in 20 mg/L and 40 mg/L exposure groups. The follicular atresia mostly occurred in vitellogenic (stage II and stage III) oocytes. Reduction of serum level of 17β‐estradiol was also significant in 20 mg/L and 40 mg/L exposure groups. The increase of LH‐immunointensity of pituitary gonadotrophs (LHβ‐immunoreactive cells) and their hypertrophy was evident, significantly in fish of 40 mg/L exposed group. Thus, the present acute metal spill‐mimicking laboratory study clearly demonstrated that short‐term exposures to high doses of hexavalent chromium may disrupt reproduction of the fish and affect their population. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 733–739, 2014.