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Lethal Concentration Values (lethal + concentration_value)
Selected AbstractsAcute and chronic toxicity of mercury to early life stages of the rainbow mussel, Villosa iris (Bivalvia: Unionidae)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2005Theodore W. Valenti Abstract Mercury (Hg) contamination is receiving increased attention globally because of human health and environmental concerns. Few laboratory studies have examined the toxicity of Hg on early life stages of freshwater mussels, despite evidence that glochidia and juvenile life stages are more sensitive to contaminants than adults. Three bioassays (72-h acute glochidia, 96-h acute juvenile, and 21-d chronic juvenile toxicity tests) were conducted by exposing Villosa iris to mercuric chloride salt (HgCl2). Glochidia were more sensitive to acute exposure than were juvenile mussels, as 24-, 48-, and 72-h median lethal concentration values (LC50) for glochidia were >107, 39, and 14 ,g Hg/L, respectively. The 24-, 48-, 72-, and 96-h values for juveniles were 162, 135, 114, and 99 ,g Hg/L, respectively. In the chronic test, juveniles exposed to Hg treatments ,8 ,g/L grew significantly less than did control organisms. The substantial difference in juvenile test endpoints emphasizes the importance of assessing chronic exposure and sublethal effects. Overall, our study supports the use of glochidia as a surrogate life stage for juveniles in acute toxicity tests. However, as glochidia may be used only in short-term tests, it is imperative that an integrated approach be taken when assessing risk to freshwater mussels, as their unique life history is atypical of standard test organisms. Therefore, we strongly advocate the use of both glochidia and juvenile life stages for risk assessment. [source] Aquatic toxicity of triclosanENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2002David R. Orvos Abstract The aquatic toxicity of triclosan (TCS), a chlorinated biphenyl ether used as an antimicrobial in consumer products, was studied with activated-sludge microorganisms, algae, invertebrates, and fish. Triclosan, a compound used for inhibiting microbial growth, was not toxic to wastewater microorganisms at concentrations less than aqueous solubility. The 48-h Daphnia magna median effective concentration (EC50) was 390 ,g/L and the 96-h median lethal concentration values for Pimephales promelas and Lepomis macrochirus were 260 and 370 ,g/L, respectively. A no-observed-effect concentration (NOEC) and lowest-observed-effect concentration of 34.1 ,g/L and 71.3 ,g/L, respectively, were determined with an early life-stage toxicity test with Onco-rhynchus mykiss. During a 96-h Scenedesmus study, the 96-h biomass EC50 was 1.4 ,g/L and the 96-h NOEC was 0.69 ,g/L. Other algae and Lemna also were investigated. Bioconcentration was assessed with Danio rerio. The average TCS accumulation factor over the five-week test period was 4,157 at 3 ,g/L and 2,532 at 30 ,g/L. Algae were determined to be the most susceptible organisms. Toxicity of a TCS-containing wastewater secondary effluent to P. promelas and Ceriodaphnia was evaluated and no observed differences in toxicity between control and TCS-treated laboratory units were detected. The neutral form of TCS was determined to be associated with toxic effects. Ionization and sorption will mitigate those effects in the aquatic compartment. [source] Influence of UV Radiation on Four Freshwater Invertebrates,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2000Alina Cywinska ABSTRACT Laboratory tests confirmed a negative and variable response of the following four species to artificial UV radiation: Cypridopsis vidua, an ostracode; Chironomus riparius, a midge larvae; Hyalella azteca, an amphipod; and Daphnia magna, a daphnid. Severe damage occurred at UV-B irradiance ranging from 50 to 80% of incident summer values. Under constant exposure to UV and photosynthetically active radiation (PAR) the acute lethal response was recorded at 0.3, 0.8, 0.8 and 4.9 W m,2 UV-B for D. magna, H. azteca, C. riparius and C. vidua, respectively. Sublethal UV-B damage to invertebrates included impaired movement, partial paralysis, changes in pigmentation and altered water balance (bloating). A series of UV-B, UV-A and PAR treatments, applied separately and in combination, revealed a positive role for both UV-A and PAR in slowing down UV-B damage. Mean lethal concentration values of the species typically more tolerant to UV and PAR (Cypridopsis, Chironomus) decreased conspicuously when both UV-A and PAR were eliminated. For UV-B,sensitive species (Hyalella, Daphnia) these differences were notably smaller. We suggest that this gradation of sensitivity among the tested species demonstrates potential differences in repairing mechanisms which seem to work more efficiently for ostracodes and chironomids than for amphipods and daphnids. Manipulations with a cellulose acetate filter showed that lower range UV-B (280,290 nm), produced by FS-40 lamps, may cause excessive UV damage to invertebrates. [source] Evaluations of lactic acid bacteria as probiotics for juvenile seabass Lates calcariferAQUACULTURE RESEARCH, Issue 2 2008Sirirat Rengpipat Abstract Lactic acid bacteria (LAB) were isolated from adult, wild-caught and farmed seabass (Lates calcarifer) intestines for evaluation as possible probiotics using the well agar diffusion method. Five LAB isolates (designated as LAB-1,5) were found to inhibit Aeromonas hydrophila, a known seabass pathogen. Median lethal concentrations (LC50) of A. hydrophila on juvenile seabass were measured in aquaria. Median lethal concentration values of 7.76, 7.47 and 7.26 log10 CFU mL,1 for 72, 96 and 120 h, respectively, were found. Juvenile seabass (0.6±0.2 g) were cultured in aquaria and fed individual LAB-1,5 fortified feeds with 7 log10 CFU g,1 LAB. Seabass fed LAB-4 fortified feed had significantly greater growth (P<0.05) than fish fed other feeds. Seabass fed LAB-4 also had greater survival, but this was non-significant (P<0.05). Challenge tests of LAB-4 fed seabass with A. hydrophila at ,7 log10CFU mL,1 yielded significantly greater survival compared with control seabass (P<0.05). Aeromonas hydrophila infections in seabass were confirmed by observing disease manifestation and by immunohistochemistry techniques. LAB-4 was preliminarily identified using lactic acid analysis, biochemical and physical characteristics. It was further identified using 16S rDNA sequencing. LAB-4 was identified as Weissella confusa (identity of 99%). GenBank accession number for the 16S rDNA sequence for LAB-4 was AB023241. [source] | ||||||||||