Do laboratory salinity tolerances of freshwater animals correspond with their field salinity?

The degree to which laboratory derived measures of salinity tolerance reflect the field distributions of freshwater biota is uncertain. In this paper we compare laboratory-derived acute salinity tolerance (LC(50) values) of freshwater macroinvertebrates (range 5.5-76 mS/cm) and fish (range 2.7-82 mS/cm) from southeastern Australia with the salinity from which they have been collected in the field. Only 4% of the macroinvertebrates were collected at salinity levels substantially higher than their 72-h LC(50) obtained from directly transferring animals from low salinity water to the water they were tested (direct transfer LC(50)). This LC(50) value was correlated with the maximum salinity at which a species had been collected. For common macroinvertebrates, the maximum field salinity was approximated by the direct transfer 72-h LC(50). For adult freshwater fish, 21% of species were collected at salinities substantially greater than their acute direct transfer LC(50) and there was a weak relationship between these two variables. Although there was a weak correlation between the direct transfer LC(50) of early life stages of freshwater fish and the maximum field salinity, 58% of the field distribution were in higher than their LC(50) values. In contrast, LC(50) determined from experiments that acclimated adult fish to higher salinity (slow acclimation) provided a better indication of the field distribution: with only one fish species (7%) being in conflict with their maximum field salinity and a strong positive relationship between these variables. This study shows that laboratory measures of acute salinity tolerance can reflect the maximum salinity that macroinvertebrate and fish species inhabit and are consistent with some anecdotal observations from other studies.     

Impact of cypermethrin on stream fish populations under field-use in biotech-soybean production

The impact of biotech-soybean technology on freshwater ecosystems is being evaluated in the Rolling Pampas region, Argentina. The effect of cypermethrin, the main soybean insecticide, on low-order temperate-stream fish populations was investigated for two consecutive crop cycles under field-use conditions in biotech-soybean production. Cypermethrin was unable to induce mortality or behavioral effects on any of the fish species resident in a first-order stream across a crop field (pulsed acute exposure scenario) sprayed according to conventional practices. No spatially or temporally dependent effects were observed on population parameters (size-class structure, abundance, survival, sex and immature/mature ratio, condition factor) of resident or caged Cnesterodon decemmaculatus after spraying or rainfall events, not even one year after, at the beginning of the next crop cycle. Although cypermethrin was "very highly toxic" to C. decemmaculatus in laboratory water (96h-LC(50)=0.43microg/l), its toxicity was reduced in filtered (78%) and unfiltered (92%) stream water. Changes in LC(50) values were mainly correlated with the OC content of each water fraction (r(2)=0.99; p<0.01; n=9), showing that both DOC and TOC contributed proportionally to toxicity reduction. Protective effects of stream water (12-fold reduction LC(50) values) explained the lack of effects on fish populations in the field, despite cypermethrin water concentrations after spraying reached values comparable with the 96h-LC(50). Therefore, cypermethrin under field-use conditions in transgenic-soybean production represents a low risk of acute exposure for fish populations inhabiting low-order temperate-streams rich in TOC. The relationship between LC(50) and TOC could be a convenient way to improve risk estimation based on laboratory toxicity testing.     

Ecotoxicological assessment for receiving waters with the premetamorphic tadpoles acute assay

The toxicity of receiving waters was evaluated by means of the young tadpoles assays. The sentinel organism was Bufo arenarum, an indigenous anuran species. The assayed water samples were taken from a highly polluted urban watercourse (Reconquista River, Buenos Aires, Argentina), characterized by high concentration of nitrites, phosphates and heavy metals. The toxicity of water samples was assessed performing the pass-fail test and by means of the NOEC and LC(50); TUs (toxic units) were also calculated. The effect of the addition of a positive control (Cd) on the toxicity of the river water samples was also examined. Water samples of three sites, characterised by their different degree of pollution, were assayed. The lethal response had a clear cut correspondence with the water quality of the sample evaluated by means of physicochemical parameters. In most cases, the dilution of the samples resulted in a significant reduction of their toxicity to TU values compatible to those stated by the USEPA for industrial effluents. It was concluded that (a) the used Bufo arenarum bioassay was an adequate method for assessing the toxicity of natural polluted water samples and (b) the three considered endpoints showed no important differences after 48 or 96 h of exposure, therefore we concluded that it may not be necessary to extend the assay for a longer period than 48 h.     

Investigation of acute toxicity of chlorpyrifos-methyl on Nile tilapia (Oreochromis niloticus L.) larvae

Chlorpyrifos-methyl, a wide-spectrum organophosphorus insecticide and potential toxic pollutant contaminating aquatic ecosystems, was investigated for acute toxicity. Larvae of the freshwater fish Nile tilapia (Oreochromis niloticus L.) were selected for the bioassay experiments. The experiments were repeated three times and the 96 h LC50 was determined for the larvae. The static test method for assessing acute toxicity was used. Water temperature was maintained at 25+/-1 degrees C. In addition, behavioral changes at each chlorpyrifos-methyl concentration were observed for the individual fish. Data obtained from the chlorpyrifos-methyl acute toxicity tests were evaluated using Finney's probit analysis statistical method. The 96 h LC50 value for Nile tilapia larvae was calculated to be 1.57 mg/l.     

Sublethal effect of silver and chromium in the green mussel Perna viridis with reference to alterations in oxygen uptake, filtration rate and membrane bound ATPase system as biomarkers

Perna viridis is an ideal animal for studying the impairment caused by the effects of heavy metals that are often detected in coastal areas. Preliminary bioassay tests revealed that the lethal (LC(100)), median lethal (LC(50)) and sublethal (LC(0)) concentration of silver and chromium to P. viridis were 6.5, 4.0, 2.0 mg l(-1) and 4.5, 2.5, 1.0 mg l(-1), respectively. Toxic effect of silver and chromium was evaluated in the green mussel P. viridis, with reference to oxygen consumption, filtration rate and ATPase system in laboratory experiments. These parameters were selected as the end point of sublethal stress. Oxygen consumption and filtration rates were calculated as a measure of decline in the dissolved oxygen level and algal concentration (feed) in the aquaria water, respectively. Silver and chromium affects both oxygen consumption and filtration rate significantly (P<0.01) at 96 h when compared to control. The activity of ATPases system in the gills, hepatopancreas, ovary and muscle of mussels were inhibited by silver and chromium indicating that metals exerted significant toxic effect. The inhibition of Na(+)K(+) ATPase, Ca(2+) ATPase and Mg(2+) ATPase in the mussels were significant (P<0.05) for silver and highly significant (P<0.01) for chromium, which indicates that chromium was more toxic to mussels when compared to silver. The assessment of oxygen consumption, filtration and ATPases system can thus be used as a valid biomarker in aquatic ecotoxicology studies.     

Toxicity of uranium and copper individually, and in combination, to a tropical freshwater macrophyte (Lemna aequinoctialis)

Copper (Cu) and uranium (U) are of potential ecotoxicological concern to tropical freshwater biota in northern Australia, as a result of mining activities. Few data are available on the toxicity of U, and no data are available on the toxic interaction of Cu and U, to freshwater biota. This study determined the toxicity of Cu and U individually, and in combination, to a tropical freshwater macrophyte, Lemna aequinoctialis (duckweed), in a synthetic soft water (27 degrees C; pH, 6.5; hardness, 40 mg CaCO3 l-1, alkalinity, 16 mg CaCO3 l-1), typical of many fresh surface waters in coastal northern Australia. The growth rate of L. aequinoctialis decreased with increasing Cu or U concentrations, with the concentration of Cu inhibiting growth by 50% (EC50) being 16+/-1.0 microg l-1, with a minimum detectable effect concentration (MDEC) of 3.2 microg l-1. The concentration of U inhibiting growth by 50% (EC50) was 758+/-35 microg l-1 with a MDEC of 112 microg l-1. The EC50 value for the exposure of L. aequinoctialis to equitoxic mixtures of Cu and U was significantly (P0.05) higher than one toxic unit (1.35; 95% confidence interval, 1.18-1.52), indicating that the combined effects of Cu and U are less than additive (antagonistic). Therefore, inhibition of the growth rate of L. aequinoctialis was reduced when Cu and U were present in equitoxic mixtures, relative to individual metal exposures. Since non-additive (e.g. antagonistic) interactions of metal mixtures cannot be predicted using current mixture models, these results have important potential implications for the protection of freshwater ecosystems through the derivation of national water quality guidelines.     

Comparative study on the susceptibility of freshwater species to copper-based pesticides

Copper compounds have been intentionally introduced into water bodies as aquatic plant herbicides, algicides and molluscicides. Copper-based fertilizers and fungicides have been widely used in agriculture as well. Despite the fact that copper is an essential element for all biota, elevated concentrations of this metal have been shown to affect a variety of aquatic organisms. Nonetheless, comparative studies on the susceptibility of different freshwater species to copper compounds have seldom been performed. This study was conducted to compare toxicity of copper-based pesticides (copper oxychloride, cuprous oxide and copper sulfate) to different freshwater target (Raphidocelis subcapitata, a planktonic alga and Biomphalaria glabrata, a snail) and non-target (Daphnia similis, a planktonic crustacean and Danio rerio, a fish) organisms. Test water parameters were as follows: pH = 7.4 +/- 0.1; hardness 44 +/- 1 mg/l as CaCO3; DO 8-9 mg/l at the beginning and > 4 mg/l at the end; temperature, fish and snails 25 +/- 1 degrees C, Daphnia 20 +/- 2 degrees C, algae 24 +/- 1 degrees C. D. similis (immobilization), 48-h EC50s (95% CLs) ranging from 0.013 (0.011-0.016) to 0.043 (0.033-0.057) mg Cu/l, and R. subcapitata (growth inhibition), 96-h IC50s from 0.071 (0.045-0.099) to 0.137 (0.090-0.174) mg Cu/l, were the most susceptible species. B. glabrata (lethality), 48-h LC50s from 0.179 (0.102-0.270) to 0.854 (0.553-1.457) mg Cu/l, and D. rerio (lethality), 48-h LC50s 0.063 (0.045-0.089), 0.192 (0.133-0.272) and 0.714 (0.494-1.016) mg Cu/l, were less susceptible than Daphnia to copper-based pesticides. Findings from the present study therefore suggest that increased levels of copper in water bodies is likely to adversely affect a variety of aquatic species.     

Quantitative structure-toxicity relationships of organophosphorous pesticides to fish (Cyprinus carpio)

This study was conducted to determine the relationships between 1381 chemical and structural parameters of 43 organophosphorus pesticides (OPs) and their toxicity to fish, Cyprinus carpio, using ChemOffice 8.03 and Dragon 2.1. By multivariate linear regression and intervariable regression analyses, various equations have been derived to calculate the lethal toxicity value, LC(50), for 43 OPs found in fish with different levels of toxicity. Results show that for all selected OPs, especially those of low toxic OPs (LC(50)< 2.5 mM), the equation, LC(50) = 56.259 - 13.071 lg K(ow)+17.510 MATS8P-17.455 Mor24u - 0.085 MW + 1.706 (lg K(ow))(2) + 2.306 (Mor14e)(2) + 6.849 Mor20 m (n = 43, F = 36.815, r = 0.942, r(adj)(2) = 0.862, SE = 2.899, p < 10(-6)), could account for 86.2% of the variability of the toxic effect. The steric and electronic characteristics and the hydrophobicity of OPs, in particular, are among the most important parameters determining the toxicity of OPs to fish. For the OPs with high toxicity, different structural parameters were introduced into the following two equations: LC(50)=3.795-1.195 (H1p)(2)-0.037 U-2.225 MATS3v-19.593 Tcon (n = 16, F = 56.820, r = 0.977, r(adj)(2) = 0.937, SE = 0.143, p < 10(-6)), where LC(50) is less than 2.5 mM, and LC(50) = 0.341-0.561 (HOMA)(2) + 0.231 HOMA (n = 3,r(adj)(2) = 1), where LC(50) is less than 0.3 mM. These results suggest that chemical and structural parameters could be useful in modeling chemical reactivity within homologous series of OP compounds and elucidating possible mechanisms associated with different levels of toxicity to fish.     

Dioxins, metals, and fish toxicity in ash residue from space heaters burning used motor oil

Ash residue, generated from burning used motor oil, is a complex and ubiquitous waste stream. Ash samples were collected from space heaters and analyzed for dioxins (N=10), expressed as toxic equivalents (TEQ), and heavy metals (N=9). TEQ averaged 148-164 ng kg(-1) (standard deviation [SD] 385-416 ng kg(-1)), depending on methods used for non-detects (NDs) and toxic equivalency factors (TEFs). It is notable that median TEQ (2.89-3.49 ng kg(-1)) was about 50 fold lower, reflecting the influence of several high end values on the mean. The proportion of NDs among 17 polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in each sample averaged 38.2% (range 0-94.1%). Total metals averaged 103,000 mg kg(-1) (SD 26,600 mg kg(-1)), with Zn, Cu, and Pb contributing 89.3%, 6.4%, and 3.0% of the total, respectively. Rainbow trout bioassays resulted in median mortalities of 3.2% and 42.0% (respective SD 25.3% and 43.2%) at ash concentrations of 10 and 100 mg l(-1), respectively. Nominal concentrations of several metals (e.g., Cu, Zn) in the fish bioassay exceeded their reported median lethal concentrations (LC50s) for the test species. Multiple regressions (Bonferroni P<0.05) demonstrated that most of the variance in fish mortality could be accounted for by pH, metals (e.g., As, Cd, Pb), and TEQ. Mean TEQ concentration in used oil ash ranked on the high end of TEQ content in other environmental matrices, including wood ash, cement kiln dust, biosolids, and soils. Overall, these results suggest that suitable disposal methods are needed for ash generated from burning used motor oil.     

Toxicokinetics,toxicity and lethal body residues of two chlorophenols in the oligochaete worm,Lumbriculus variegatus,in different sediments

Bioavailability, toxicokinetics and toxicity (LC(50)) of water- and sediment-associated 2,4,5-trichlorophenol (2,4,5-TCP) and pentachlorophenol (PCP) were measured in Lumbriculus variegatus Müller in a set of experiments. The critical body residue approach was applied by measuring also the lethal body residues (LBR(50)). Freshwater and three different sediments with various sediment organic carbon (SOC) concentrations were used as exposure media. SOC decreased the bioavailability of both chlorophenols, and the uptake rates decreased by 81% and 91% for 2,4,5-TCP and PCP, respectively, in the sediment with a SOC of 6.9% compared to those in sediment with a SOC of 0.5%. SOC appeared to be an important factor controlling the bioavailability as after the carbon normalisation the difference between the sediments was much smaller. The 96-h LC(50) values for instance for PCP were 145.3 microg/l in freshwater, and 6.8 and 8.1 microg/g dry weight in sediments with SOC concentrations of 0.5% and 2.4%, respectively. The LBR(50) values, were practically the same in freshwater and sediments: between 1.0 and 1.6 and from 0.4 to 0.9 micromol/g wet weight for 2,4,5-TCP and PCP, respectively, demonstrating the usefulness of this method for accurate, and more comparable, measurement of toxicity of chemicals with the same mode of toxic action in varying conditions. L. variegatus expressed a dose-response sediment avoidance behaviour but the PCP tissue concentrations were not affected by this behaviour.     

Comparative study on the environmental risk induced by several pyrethroids in estuarine and freshwater invertebrate organisms

The acute toxicity of permethrin, resmethrin, and cypermethrin to four species of aquatic non-target invertebrate organisms, found in estuarine and freshwater ecosystems, was evaluated. Artemia franciscana and Brachionus plicatilis larvae, as estuarine organisms, and Brachionus calyciflorus and Thamnocephalus platyurus larvae, as freshwater organisms, were exposed for 24 h to concentrations of these pyrethroids, and the LC(50) values were compared. The freshwater organisms were more sensitive to these pyrethroids than estuarine organisms tested. A. franciscana larvae were more tolerant organisms than B. plicatilis larvae. The freshwater organisms tested have demonstrated to be a good alternative to the standard acute toxicity assays using Daphnia, although Brachionus plycatilis larvae were more sensitive to these pyrethroid insecticides than T. platyurus. Analysis of 24 h LC(50) values of these pyrethroids, determined by static bioassays, revealed that the rank order of toxicity was: permethrin相似文献   

Is an assessment factor of 10 appropriate to account for the variation in chemical toxicity to freshwater ectotherms under different thermal conditions?

Ecotoxicity tests are often conducted following standard methods, and thus carried out at a fixed water temperature under controlled laboratory conditions. Yet, toxicity of a chemical contaminant may vary in a temperature-dependent manner, depending on the physiology of the test organism and physicochemical properties of the chemical. Although an assessment factor of 10 (AF10) is commonly adopted to account for variability in toxicity data related to temperature in the development of water quality guidelines and/or ecological risk assessment, no one has ever rigorously assessed the appropriateness of AF10 to account for potential variation in temperature-dependent chemical toxicity to aquatic organisms. This study, therefore, aims to address this issue through a meta-analysis by comparing median lethal concentration data for nine chemicals (cadmium, copper, nickel, lead, silver, zinc, arsenic, selenium and DDT) on a range of freshwater ectothermic animal species at different temperatures, and to assess whether AF10 is under- or over-protective for tropical and temperate freshwater ecosystems. Our results reveal varying extents of interaction between temperature and different chemicals on organisms and the complexity of these interactions. Applying AF10 sufficiently protects 90 % of the animal species tested over a range of temperatures for cadmium, copper, nickel, silver, zinc and DDT in the tropics, but it is insufficient to adequately encompass a larger temperature variation for most studied chemicals in temperate regions. It is therefore important to set specific AFs for different climatic zones in order to achieve the desired level of ecosystem protection.     

Quantitative structure-toxicity relationship study of lethal concentration to tadpole (Bufo vulgaris formosus) for organophosphorous pesticides

In the present study more than 1,000 structural parameters of 41 organophosphorus pesticides (OPs) were calculated using the software ChemOffice 8.03 and Dragon 2.1. Then, with multivariate linear regression and best subset regression analyses, different equations were derived to calculate the lethal toxicity, LC(50), for these 41 organophosphorous pesticides found in tadpoles (Bufo vulgaris formosus). An equation was developed for all selected OPs, especially those with relatively low toxicity levels (LC(50)>4.5mM) that accounted for 89.09% of the variability in the toxic effect. The equation indicated that the main contributions to OPs toxicity with tadpoles were the electrostatic contribution qH(+) (maximum net positive H atomic charge), spatial autocorrelation (MATS7 m) and hydrophobicity (lgK(ow)), with the two former being the most important parameters. For OPs with high toxicity, however, different structural parameters were introduced. The following equation was developed with LC(50)<4.5mM. These equations implied that with different levels of toxicity there could have different mechanisms in the tadpole. Furthermore, the results showed that molecular structural parameters had a particular value in modeling chemical reactivity within a homologous series of compounds.     

Piscicidal effect of some common plants of India commonly used in freshwater bodies against target animals

Mortality caused by the aqueous extracts of leaf and stem bark of four plants belonging to family Euphorbiaceae and Apocynaceae against freshwater fish Channa punctatus has been reported. It was found that dilute aqueous solutions of leaf and stem bark were active in killing the fishes. The toxic effect of stem bark of all the plants were time as well as dose dependent. There was significant negative correlation between LC50 and exposure periods. Thus, the LC50 values of stem bark extracts of Euphorbia royleana, Jatropha gossypifolia, Nerium indicum and Thevelia peruviana were decreased from 0.050 g/l (24 h) > to 0.020 g/l (96 h); 4.61 g/l (24 h) > to 4.34 g/l (96 h); 0.097 g/l (24 h) > to 0.041 g/l (96 h) and 4.05 g/l (24 h) > to 3.17 g/l (96 h), respectively. It has been suggested that these plant products cannot be used directly in freshwater bodies, without their detailed studies on long-term effects on non-target organism as well their structure activity relationship.     

Investigation of acute toxicity of permethrin on guppies Poecilia reticulata

Permethrin, a synthetic pyrethroid pesticide and potential toxic pollutant contaminating aquatic ecosystems, was investigated in the present study for acute toxicity. Guppy fish (Poecilia reticulata) were selected for the bioassay experiments. The experiments were repeated 3 times and the 48-h LC(50) was determined for the guppies. The static test method of acute toxicity test was used. Water temperature was regulated at 20+/-1 degrees C. In addition, behavioral changes at each permethrin concentration were observed for the individual fish. Data obtained from the permethrin acute toxicity tests were evaluated using the probit analysis statistical method. The 48-h LC(50) value for guppy was estimated as 245.7 microg/l. Values in the range of 0.05-97.0 microg/l have been reported for various other fish species.     

Acute toxicity of heavy metals towards freshwater ciliated protists

The acute toxicity of five heavy metals to four species of freshwater ciliates (Colpidium colpoda, Dexiotricha granulosa, Euplotes aediculatus, and Halteria grandinella) was examined in laboratory tests. After exposing the ciliates to soluble compound of cadmium, copper, chromium, lead, and nickel at several selected concentrations, the mortality rate was registered and the LC50 values (with 95% confidence intervals) were calculated. Large differences appeared in sensitivities of the four species to the metals. H. grandinella showed the highest sensitivity for cadmium (0.07 mg l(-1), LC50) and lead (0.12 mg l(-1), LC50), whilst E. aediculatus showed the highest sensitivity for nickel (0.03 mg l(-1), LC50). The comparison with data obtained with other species indicate that Halteria grandinella and Euplotes aediculatus are excellent and convenient bioindicator for evaluating the toxicity of waters and wastewaters polluted by heavy metals. The short time (24 h) and simplicity of the test procedure enable this test to be used in laboratory studies.     

The freshwater planarian Polycelis felina as a sensitive species to assess the long-term toxicity of ammonia

Behavioural endpoints are a good link between physiological and ecological effects. However long-term behavioural endpoints are not uniformly studied over all different organism groups. For example behaviour has been scarcely studied in planarians. Unionized ammonia (NH₃) is one of the most widespread pollutants in developed countries, and is known to alter animal behaviour. In this study a long-term (30 d) bioassay was conducted to assess the effect of this pollutant on survival and behavioural activity (e.g. locomotion activity) of the freshwater planarian Polycelis felina. One control and three environmentally-realistic concentrations of unionized ammonia (treatments of 0.02, 0.05, and 0.09 mg N-NH₃ L⁻¹) were used in quintuplicate. The behaviour of planarians was measured after 0, 10, 20 and 30 d of ammonia exposure. Mortality was recorded every 2 d. Unionized ammonia increased mortality in the two highest NH₃ concentrations and the locomotory activity was depressed in all treatments after 20 d of exposure. Behavioural effect was observed at concentrations 20 times lower than the short-term LC50 for this species. Previous studies proposed safe concentrations of unionized ammonia of 0.01-0.10 mg N-NH₃ L⁻¹ to aquatic ecosystems, but our study has shown that these concentrations will affect planarians. Because planarians play a key role in streams (as predator/scavenger), safe concentrations should be below 0.02 mg N-NH₃ L⁻¹ to protect this species in the freshwater community. Our results can contribute to improve the knowledge about ammonia toxicity to freshwater ecosystems, we recommend that safe concentrations of unionized ammonia should be based on very sensitive species.     

Comparative study of the effects of MCPA, butylate, atrazine, and cyanazine on Selenastrum capricornutum

The herbicides MCPA, butylate, atrazine and cyanazine are extensively used in Canadian agriculture and information regarding their effects on indigenous biota is scarce. Phytotoxicity assessments were conducted in the laboratory on the common green alga Selenastrum capricornutum using both the active ingredient of the herbicides and their formulated products (for MCPA and butylate). Endpoints determined after the 96 h exposure included algal population growth inhibition (IC50-cell counts), percent lethality (LC50-flow cytometry derived) and photosynthetic electron transport inhibition (EC50-fluorescence induction). Pesticide formulations had greater toxic effects than the active ingredient alone. The 96 h IC50 (50% Inhibition Concentration) and LOEC (Lowest Observable Effects Concentration) using cell counts of S. capricornutum were 18.4 and 8.9 mg l(-1) respectively for MCPA-active ingredient and for MCPA-formulated, these were 0.62 and 0.0062 mg l(-1) respectively. Those for butylateactive ingredient were 61.0 and 8.3 mg l(-1) and for butylate-formulated 1.46 and 0.17 mg l(-1), respectively. The triazines active ingredient, which are photosynthetic inhibitors, had greater effects than either the MCPA or butylate. The IC50 for cyanazine and atrazine were 0.059 and 0.026 mg l(-1), respectively. By comparing the IC50 and LC50 values for the tested active ingredients, it was found that the effects of atrazine were algicidal, whereas those of cyanazine, butylate and MCPA were algistatic.     

Endosulfan and diazinon toxicity to the freshwater rotifer Brachionus calyciflorus.

The acute toxicity of endosulfan and diazinon to the freshwater rotifer Brachionus calyciflorus was determined after 24 hours exposure to these toxicants. The mean 24 hr-LC50 values were 5.15 and 29.22 mg/L for endosulfan and diazinon respectively. Based on these results, four sublethal concentrations were chosen to determined the median lethal time (LT50) at each concentration of toxicant tested. We also used a control with the solvent (acetone). The concentration tested were 1/5, 1/4, 1/2 and 2/3th LC50 (24hr) for both pesticides. We found a decrease in the median lethal time (LT50) with increasing pesticide concentrations. The LT50 values ranged from 6.49 to 3.48 days after endosulfan treatment, and from 6.96 to 2.49 days after diazinon exposure. No effects on survival were observed in control animals exposed to the solvent.     

Acute toxicity and genotoxicity of five selected anionic and nonionic surfactants

The results of four toxicity bioassays of selected anionic and nonionic surface active agents were presented. Three widely used anionic surfactants that belong to alkyl sulphates (AS), alkylbenzene sulphonates (LAS) and alkylpolyoxyethylene sulphates (AES) as well as nonionic surfactants: polyoxyethylene alkyl ethers (AE) and polyoxylethylene alkylphenyl ethers (APE) were tested. Three different toxicity assays to aquatic organisms: Physa acuta Draparnaud, Artemia salina and Raphidocelis subcapitata were applied. Additionally, the genotoxicity test with Bacillus subtilis M45 Rec- and H17 Rec+ strains was performed. The obtained results showed that none of the surfactants studied was genotoxic at the concentration 1000 mg l(-1). On the basis of toxicity tests to aquatic organisms all tested anionic surfactants were harmful (LC50 between 10 and 100 mg l(-1)), whereas nonionic ones were toxic (LC50 between 1 and 10 mg l(-1)) or even highly toxic (LC50 below 1 mg l(-1)). Moreover, the bigger was the molecular weight of the tested compound, the higher toxicity was observed.