An assessment of the potential of the microbial assay for risk assessment (MARA) for ecotoxicological testing

Rapid microscale toxicity tests make it possible to screen large numbers of compounds and greatly simplify toxicity identification evaluation and other effect directed chemical analyses of effluents or environmental samples. Tests using Vibrio fischeri (such as Microtox?) detect toxicants that cause non-specific narcosis, but are insensitive to other important classes of contaminants. The microbial assay for risk assessment (MARA) is a 24 h multi-species test that seeks to address this problem by using a battery of ten bacteria and a fungus. But there has been little independent evaluation of this test, and there is no published information on its sensitivity to pesticides. Here, we assess the performance of MARA using a range of toxicants including reference chemicals, fungicides and environmental samples. Mean MARA microbial toxic concentrations and IC₂₀s (20% Inhibitory concentrations) indicate the toxicant concentrations affecting the more sensitive micro-organisms, while the mean IC₅₀ (50% Inhibitory concentration) was found to be the concentration that was toxic to most MARA species. For the two fungicides tested, the yeast (Pichia anomalia) was the most sensitive of the ten MARA species, and was more sensitive than the nine other yeasts tested. The test may be particularly valuable for work with fungicides. Mean MARA IC₅₀s were comparable to values for nine other yeast species and the lowest individual IC₅₀s for each toxicant were comparable to reported IC₅₀s for Daphnia magna, Selenastrum capricornutum and Microtox? bioassays. MARA organisms exhibited more variable sensitivities, with the most sensitive organism being different for different samples, enhancing the likelihood of toxicity detection and giving a toxicity “fingerprint” that may help identify toxicants. The test, therefore, has great potential and would be valuable for ecotoxicological testing of pollutants.     

A rapid and simple toxicity assay based on growth rate inhibition of Pseudomonas fluorescens

A simple and rapid test, based on growth rate inhibition (GRI) of Pseudomonas fluorescens, is described for toxicity screening and assessment. The test involves challenging standardized suspensions [0.2 optical density (OD) at 600 nm] of exponentially growing cells with various concentrations of a toxicant at 33°C and monitoring changes in the growth rate by OD measurements after 0.5, 1.0, 1.5, and 2.0 h. The toxicity end point is measured as the effective concentration of a test sample that causes 50% inhibition of growth rate (EC₅₀) during each designated time period. Several metal salt solutions, organic compounds, and complex effluents were screened using this test and data compared with those obtained using the Microtox® assay. Results indicated that the P. fluorescens GRI test could be used as a valuable part of a battery of short-term bioassays for toxicity screening and assessment.     

Toxicology evaluation of Atlantic Canadian seafood processing plant effluent

The purpose of this study was to carry out an acute aquatic toxicity assessment on select effluent samples from Atlantic Canadian seafood processing plants. Raw effluent acute aquatic toxicity for the flatfish and salmon effluents was assessed using the acute lethality test and Microtox? test. The effectiveness of dissolved air flotation treatment (DAF) in removing acute toxicity from these effluents was evaluated using the Microtox? test. The salmon effluent failed the acute lethality test using rainbow trout while the flatfish effluent showed acute toxicity in the Microtox? test with a 50% inhibiting concentration (IC₅₀) of 38.84%. Subsequent treatment by DAF of the flatfish and salmon effluents increased IC₅₀ values by 20% and 26% respectively. The findings of this study indicate that all of the processing effluents sampled showed characteristics that could potentially degrade effluent receiving waters and acute toxicity was demonstrated in the two raw finfish effluents. Application of DAF treatment was successful in significantly increasing Microtox? IC₅₀ values, thereby reducing acute toxicity, but failed to entirely remove acute toxicity. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

Effect of the test media and toxicity of LAS on the growth of <Emphasis Type="Italic">Isochrysis galbana</Emphasis>

In this paper, the toxicity of linear alkylbenzene sulfonate (LAS) was evaluated in the marine microalga Isochrysis galbana using data of growth inhibition toxicity tests at 96-h exposure time. Toxicity was examined in standard conditions and by means of the modification of two variables of the test media: (1) the dilution water and (2) the content of nutrients in the test medium. For this purpose, a total of 10 toxicity test were designed: five dilution waters, four natural marine waters and one synthetic seawater; each in two different nutritive conditions, saturated nutrient concentration (SC) by the addition of modified f/2 nutritive medium, and natural nutrient concentration (NC), i.e., without the addition of f/2. At threshold toxicity levels, the dilution waters used in the test and the nutrient concentrations did not affect the toxicity of LAS. At IC₅₀ concentrations, the toxicity of LAS is influenced by both variables: under SC conditions, the toxic effect of LAS diminishes, obtaining in all the tests IC₅₀ > 10 mg/L LAS. Under NC conditions, IC₅₀ concentrations ranging between 3.15 and 9.26 mg/L LAS have been obtained.     

Rapid test for toxicity in wastewater systems

A test employing sewage bacteria was developed for rapid screening of chemical toxicity in wastewater systems. The procedure entails incubation of sewage samples with 2–(p–iodophenol)–3–(p–nitrophenyl)–5–phenyl tetrazolium chloride (INT) followed by concentration of bacteria on membrane filters, dissolution of the filters with concomittant extraction of INT-formazan in dimethylsulfoxide, and spectrophotometric determination of the INT-formazan. Preliminary results indicate that the test is sensitive to both heavy metals and toxic organics. Chemical concentrations inhibiting 50% of the response in controls (IC₅₀'s) for Ni^{+ +}, Zn^{+ +}, Cu^{+ +}, Hg^{+ +}, phenol, 3,4-dichlorophenol, sodium dodecyl sulfate, tetrachloroethylene and formaldehyde were 4.8, 3.9, 0.59, 0.07, 1531, 74, 156, and 11.6 mg/l, respectively. IC₅₀ values obtained with sewage from different collection systems or with sewage from the same system sampled on different days were in good agreement.     

Acute toxicity evaluation of olive oil mill wastewaters: A comparative study of three aquatic organisms

Acute toxicity of olive mill wastewaters (traditional and continuous processes) collected from different regions of Portugal was evaluated using three test species (Vibrio fischeri formerly Photobacterium phosphoreum, Thamnocephalus platyurus, and Daphnia magna) and correlated with several physical and chemical parameters. Acute toxicity of these effluents, expressed in LC₅₀ or EC₅₀, ranged from: 0.16 to 1.24% in Microtox test, 0.73 to 12.54% in Thamnotoxkit F test, and 1.08 to 6.83% in Daphnia test. These values reflect the high toxicity of the olive mill wastewaters to all test species. Statistical analysis of the results shows a high correlation between the two microcrustacean bioassays. Microtox test did not correlate significantly with the other bioassays used. A significative correlation (p≤0.05) could also be established between L(E)C₅₀ obtained in the microcrustacean tests and some physicochemical parameters of the effluent. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 263–269, 1999     

Evaluation of the agar plate method for rapid toxicity assessment with some heavy metals and environmental samples

The use of the agar plate method as a screening test for detecting the toxicity of chromium and copper and of effluents from the tannery industry was evaluated. The bacteria Bacillus cereus and Escherichia coli were used as test organisms. The toxicity of chromium and copper on B. cereus was demonstrated at concentrations as low as 2 and 0.5 μg/spot, respectively. A linear relationship between the chromium concentration (μg/spot) and the diameter (mm) of the clear inhibition zone on the agar plates was observed between 2 and 20 μg for B. cereus and between 10 and 50 μg for E. coli. For copper the linear relationship was between 0.5 and 50 μg/spot for B. cereus and 5 and 50 μg/spot for E. coli. Bacillus cereus was more sensitive than E. coli to these tests. Results with tannery wastes showed that the method is applicable to detect environmental contaminants and the procedure is a convenient and economical tool for screening toxicity of chemical compounds and industrial wastewaters. © 1996 by John Wiley & Sons, Inc.     

Acute toxicity assessment of industrial effluents with a microplate-based Hydra attenuata assay

The acute toxicity potential of ten industrial plants located in Toyama Prefecture (Japan) was appraised with a microplate-based assay developed with the freshwater cnidarian Hydra attenuata. Three measurement end points (LC₅₀, EC₅₀, and TC or “threshold concentration”) were determined based on specific morphological changes displayed by Hydra under conditions of progressive intoxication. Four effluents were shown to be lethal toward Hydra while eight induced sublethal toxicity responses, LC₅₀s varied from 18.8 to > 100% v/v, while EC₅₀s ranged from 15 to > 100% v/v. Similarly, lethal and sublethal TCs ranged from 17.7 to > 100% v/v and from 8.8 to > 100% v/v, respectively. Statistical analyses performed on all toxicity data for the ten effluents confirmed that the sublethal end points (EC₅₀s and sublethal TCs), previously unreported to assess complex wastewaters, proved to be more sensitive than the lethal end points (LC₅₀s and lethal TCs). This was also reflected by lethality to sublethality ratios, which ranged from 1 to 2.6 (LC₅₀/EC₅₀ comparisons) and from 1.1 to 5.4 (LC₅₀/TC comparisons) within a 96 h exposure period. Similar statistical analyses undertaken on 24, 48, 72, and 96 h toxicity data failed to show any significant time-related differences, thereby suggesting that an exposure time as short as 24 h would not diminish test sensitivity. Since Hydra displayed an apparent increase in sensitivity toward a few effluents with time of exposure, however, we would nevertheless recommend a 96 h time frame for this microtest. A correlation was also observed between conductivity and Hydra responses, highlighting a possible link to the presence of toxic metal ions. Based on our study, this simple and cost-effective microassay appears valuable as a (sub)lethal toxicity screening tool for effluents. Additional studies are planned with chemicals and other environmental matrices to better circumscribe its scope of usefulness. © 1997 by John Wiley & Sons, Inc. Environ Toxicol Water Qual 12: 53–60, 1997     

Toxicity assessment of industrial effluents from S. Paulo state,Brazil, using short-term microbial assays

Microorganisms have demonstrated several attributes that make them attractive for use in quick screening of effluents and chemicals for toxicity. The aim of this study was to evaluate the acute toxicity and mutagenicity of industrial effluents from São Paulo State using short-term microbial bioassays. Samples of industrial effluents and receiving waters were analyzed for acute toxicity by the Microtox system, a motility test using Spirillum volutans, growth inhibition of Pseudomonas fluorescens, and dehydrogenase assay; for mutagenicity, these samples were analyzed by Salmonella typhimurium (Ames test), Escherichia coli WP₂, and Saccharomyces cerevisiae reversion mutation assays. Among the acute toxicity assays carried out in this study, the Microtox and S. volutans tests showed good sensitivity and general good agreement with the Daphnia similis assay, which demonstrates that these tests are potentially useful as toxicity indicators for the industrial effluents and receiving waters considered. In relation to mutagenicity assays, good results were obtained with the three methods tested. The detection of mutagens in the industrial effluents considered indicates that some constituents of these waste waters discharged in receiving waters can cause adverse biological effects and could be deleterious from a public health standpoint. The data of this research emphasize the importance of acute toxicity and mutagenicity assays as supplementary approaches for a rapid and efficient action in water pollution control, and for evaluation of potential toxic chemical effects.     

Ecotoxicological assessment of effluents in the Basque country (Northern Spain) by acute and chronic toxicity tests using Daphnia magna straus

Acute pass/fail, multi-concentration tests, and 3-brood chronic toxicity tests with Daphnia magna Straus (Cladocera, Crustacea) were used to characterise industrial and municipal effluents from various sources. The effluents that “passed” the pass/fail tests had 48-h EC₅₀ values >100% and reproduction No Observed Effect Concentration (NOECs) ≥100%, except for one effluent that had a reproduction NOEC of 31.6%. The acute multi-concentration toxicity tests allowed a rapid classification of effluents from Very Toxic (48-h EC₅₀<25%), to Non-Toxic (48-h EC₅₀ >100%). The acute-to-chronic ratio (ACR: 48-h EC₅₀ divided by the NOEC for reproduction) in the studied effluents ranged from 5 to about 100. From these results, we propose a step-wise protocol for assessing effluent toxicity. First, effluent is evaluated by means of simple and rapid pass/fail acute toxicity tests, to discriminate Non-Toxic from potentially Toxic effluents, thus facilitating the establishment of priority actions. Second, 48-h EC _x is estimated to classify effluents on a toxicity scale from Non-Toxic to Very Toxic. Third, chronic multi-concentration tests are used to calculate reproduction NOECs. These parameters combined with data on effluent chemical composition, chemical and hydrological characteristics of receiving waters, and biological quality criteria can be jointly used for more rational regulatory practices and risk assessment of effluents.     

Enzyme biosynthesis versus enzyme activity as a basis for microbial toxicity testing

A toxicity assay based on inhibition of β-galactosidase biosynthesis was compared to a similar assay based on inhibition of β-galactosidase activity. In both tests, Escherichia coli grown in a minimal medium was exposed to isopropyl-β-thiogalactoside to induce β-galactosidase biosynthesis. The induction step preceded contact of cells with the toxicant in the enzyme activity assay, whereas in the enzyme biosynthesis test, the inducer was added following contact of cells with the toxicant. Relative sensitivity was judged on the basis of responses to the heavy metals Hg²⁺, Cu²⁺, and Cd²⁺, and the organics 3,4-dichlorophenol, formaldehyde, Hydrothol, phenol, sodium dodecyl sulphate, and toluene. Comparison of these results to the IC₅₀s achieved with other microbial systems, Daphnia bioassay, and fish bioassay indicates that the enzyme activity test was moderately sensitive to heavy metals but was insensitive to organic toxicants. The test based on inhibition of enzyme biosynthesis was sensitive to both heavy metals and toxic organics.     

Water quality of the river nile. III. Toxicity assessment of six industrial effluents polluting the river nile

Six different industrial effluents were chemically and physically characterized. Their toxicity was evaluated using biotests with Selenastrum capricornutum strain NIVA-CHL1. The growth of the test alga showed either inhibition or stimulation. Two of the effluents were highly inhibitory with EC₅₀ values ranging between 1 and 10% (v/v) effluent concentrations. Others showed low growth inhibitory effects (50% < EC₅₀ < 100%). EC₅₀ values derived from the growth parameters, algal dry weight, cell count, growth rate, and area under the growth curve were almost similar for those two effluents exhibiting highly inhibitory effects. The toxicity values, calculated from algal dry weight and cell count showed, a strong positive linear relationship (r = 0.97 at p < 0.0001). The potential toxicity of some effluents was partly related to their high content of heavy metals. Changes in mean cell volume of the test alga may be used as an indicator for the potential effects of toxic effluents on the overall cellular activities. The results emphasized the indispensable role of algal bioassays among the basis of relevant and quantitative information about the biological impacts of the investigated effluents on the receiving waters. © 1993 John Wiley & Sons, Inc.     

Microbiological and Toxicological Effects of Perla Black Bean (Phaseolus vulgaris L.) Extracts: In Vitro and In Vivo Studies

Abstract: We investigated the microbiological and toxicological effects of three Perla black bean extracts on the growth and culture of selected pathogenic microorganisms, the toxicity over Vero cell lines and an in vivo rat model. Three different solvents were used to obtain Perla black bean extracts. All three Perla black bean extracts were tested for antibacterial and antiparasitic activity and further analysed for intrinsic cytotoxicity (IC₅₀). Methanol Perla black bean extract was used for acute toxicity test in rats, with the up‐and‐down doping method. All Perla black bean extracts inhibited bacterial growth. Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella oxytoca, Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis and Listeria monocytogenes showed inhibition, while Escherichia coli and Enterobacter aerogenes did not. Acidified water and acetic acid Perla black bean extract were tested in parasites. The best IC₅₀ was observed for Giardia lamblia, while higher concentrations were active against Entamoeba histolytica and Trichomonas vaginalis. The Vero cells toxicity levels (IC₅₀) for methanol, acidified water and acetic acid Perla black bean extract were [mean ± S.D. (95% CI)]: 275 ± 6.2 (267.9–282.0), 390 ± 4.6 (384.8–395.2) and 209 ± 3.39 (205.6–212.4) µg/ml, respectively. In vivo acute toxicity assays did not show changes in absolute organ weights, gross and histological examinations of selected tissues or functional tests. The acetic acid and methanol Perla black bean extract proved to exhibit strong antibacterial activity and the acidified water Perla black bean extract exerted parasiticidal effects against Giardia lamblia, Entamoeba hystolitica and Trichomonas vaginalis. The three Perla black bean extracts assayed over Vero cells showed very low toxicity and the methanol Perla black bean extract in vivo did not cause toxicity.     

Neuropathy target esterase in mouse whole blood as a biomarker of exposure to neuropathic organophosphorus compounds

The adult hen is the standard animal model for testing organophosphorus (OP) compounds for organophosphorus compound‐induced delayed neurotoxicity (OPIDN). Recently, we developed a mouse model for biochemical assessment of the neuropathic potential of OP compounds based on brain neuropathy target esterase (NTE) and acetylcholinesterase (AChE) inhibition. We carried out the present work to further develop the mouse model by testing the hypothesis that whole blood NTE inhibition could be used as a biochemical marker for exposure to neuropathic OP compounds. Because brain NTE and AChE inhibition are biomarkers of OPIDN and acute cholinergic toxicity, respectively, we compared NTE and AChE 20‐min IC₅₀ values as well as ED₅₀ values 1 h after single intraperitoneal (i.p.) injections of increasing doses of two neuropathic OP compounds that differed in acute toxicity potency. We found good agreement between the brain and blood for in vitro sensitivity of each enzyme as well for the ratios IC₅₀(AChE)/IC₅₀(NTE). Both OP compounds inhibited AChE and NTE in the mouse brain and blood dose‐dependently, and brain and blood inhibitions in vivo were well correlated for each enzyme. For both OP compounds, the ratio ED₅₀(AChE)/ED₅₀(NTE) in blood corresponded to that in the brain despite the somewhat higher sensitivity of blood enzymes. Thus, our results indicate that mouse blood NTE could serve as a biomarker of exposure to neuropathic OP compounds. Moreover, the data suggest that relative inhibition of blood NTE and AChE provide a way to assess the likelihood that OP compound exposure in a susceptible species would produce cholinergic and/or delayed neuropathic effects. Copyright © 2016 John Wiley & Sons, Ltd.     

Cyst-based toxicity tests. VII. Evaluation of the 1-h enzymatic inhibition test (fluotox) with Artemia nauplii

The newly developed 1-h enzymatic inhibition bioassay (Fluotox) was applied to toxicity testing with the larvae of the brine shrimp Artemia. The method consists of visual observation of in vivo inhibition of an enzymatic process using a fluorigenic enzyme substrate. The 1-h Fluotox test and the conventional 24- and 48-h LC₅₀ toxicity tests were conducted in parallel on 8 different organic and inorganic chemicals. A good correlation was found between the 1-h EC₅₀ and the 24- and 48-h LC₅₀ data with r² s of 0.94 and 0.93 for each respective regression. Addition of the enzyme substrate did not influence the toxicity of the chemicals in the 24- and 48-h tests. The repeatability of the Fluotox test compares favorably with that of the conventional 24-h acute test; coefficients of variation (CV) ranged from 8 to 34% and from 1 to 39%, respectively. Investigations on the applicability of the Fluotox procedure for testing in brackish waters revealed that lowering the salinity from 35 to 15 ppt did not affect the fluorescence and mortality responses in the controls. The same decrease in salinity had no significant influence on the 1-h EC₅₀s except for NaLS and acetic acid. The ratio between the 1-h EC₅₀s at 35 and 15 ppt varied from 0.46 to 2.18 depending on the chemical. However, the same decrease in salinity significantly influenced (p < 0.05) the 24-h LC₅₀s (except NaPCP) and the 48-h LC₅₀ (except formaldehyde). In general, the ratio of the LC₅₀ values obtained at 35 and 15 ppt varied from 0.30 to 2.21 and from 0.48 to 2.53 for the 24- and 48-h exposures, respectively. In view of several inherent advantages such as rapidity, experimental simplicity, low cost of performance, and the use of dry cysts as biological starting material (which eliminates the maintenance of live stock culture) the 1-h Artemia Fluotox test offers promising potential for numerous ecotoxicological applications. © by John Wiley & Sons, Inc.     

Developmental toxicity and structure-activity relationships of chlorophenols using human embryonic palatal mesenchymal cells

The chlorophenols (CPs) comprise a major class of widely distributed and frequently occurring environmental contaminants. Previous studies have demonstrated the adverse effects of CPs on embryonic and fetal development. HEPM (human embryonic palatal mesenchymal) and MOT (mouse ovarian tumor) cell lines have been utilized in complementary bioassays for the detection ofteratogens, but not the CPs. In this study, our objectives were 2-fold: (1) to determine if the HEPM assay could be used to complement other bioassay systems of nonhuman origin i.e.. Hydra attenuata (HA) and rat whole embryo culture (WEC), in the evaluation of the developmental toxicity of CPs, and (2) to delineate the ability of the HEPM assay to evaluate structure-activity relationships of pentachlorophenol (C₅P), 2,3,4,5-tetrachlorophenol (C₄P), 2,3,5-trichlorophenol (C₃P), 3,5-dichlorophenol (C₂P), 4-monochlorophenol (CP), phenol, and CP derivatives (i.e., acetates, sodium phenates and anisoles). HEPM cells were seeded into each well of a 24-well plate and cultivated for 24 h. The medium was replaced with fresh medium containing various concentrations of test chemicals dissolved in dimethyl sulfoxide (DMSO, 0.1%). After culturing for 72 h, the medium was removed, cells were trypsinized, and cell number determined. The HEPM cell growth inhibition assay demonstrated a linear relationship between the IC₅₀ values of the CPs and degree of chlorine substitution. The IC₅₀ values of C₅P, C₄P, C₃P, C₂P, CP, and phenol were 18.8, 21.5, 27.5, 63.0, 150.0 and 470.0 μM, respectively. A clear structure-activity relationship was observed between toxicity of CPs and the degree of chlorine substitution. The rank order of CP toxicity from the HEPM assay (i.e., C₅P>C₄P>C₃P>C₂P>CP>phenol) is in excellent agreement with previous in vitro and in vivo studies. However, contrary to published reports, the HEPM assay predicted that all CPs were teratogenic (false positives). These findings suggest that the HEPM cell growth inhibition bioassay may be useful to discriminate between subtle differences in structure-activity and, in combination with other bioassays, might facilitate the rapid detection and prioritization of diverse cytotoxins, including various developmental toxicants. Importantly, conclusions about the teratogenicity of a test chemical (via HEPM testing) should be approached with caution and confirmed with other teratogen-sensitive systems.     

Investigations into the mechanism of paraquat toxicity utilizing a cell culture system

Paraquat (PQ) and diquat (DQ) produced a dose-dependent inhibition of cellular proliferation in the P388D₁, “macrophage-like” cells in culture. DQ (IC₅₀ = 1.92 × 10^?5m) was not significantly more potent than PQ (IC₅₀ = 1.05 × 10^?4m). The dose-response lines did not deviate significantly from parallelism. Both herbicides had no effect on lipid peroxidation. Ferric pyrophosphate, a known stimulator of lipid peroxidation, produced a dose- and time-dependent stimulation. The effects produced by ferric pyrophosphate indicated that the absence of an effect due to PQ or DQ was not due to an insensitivity of the system. In addition, increasing the oxygen tension did not enhance the toxicity (as measured by cell growth) of PQ. There was no indication of PQ-induced membrane damage as indicated by the leakage of the cytoplasmic enzyme, lactate dehydrogenase. The effect of PQ and DQ on macromolecular synthesis was evaluated as a possible mechanism by which cell growth may have been inhibited. Both herbicides produced a dose- and time-dependent inhibition of DNA synthesis. DQ, but not PQ, inhibited RNA synthesis. Neither PQ nor DQ altered protein synthesis. The inhibition of DNA synthesis did not appear to be due to an alteration of the availability of the precursors. Mitochondrial function, as measured by oxygen consumption, was not affected, suggesting that the inhibition of DNA synthesis was not due to an alteration of energy metabolism. Cyclic nucleotide levels were also not affected, suggesting that the inhibition of cell growth and DNA synthesis was not due to an alteration of cellular control processes. These results suggest that inhibition of macromolecular synthesis may be involved in the molecular mechanism of toxicity of PQ.     

Acute toxicity to Daphnia magna of effluents containing Cd,Zn, and a mixture Cd‐Zn,after metal removal by Chlorella vulgaris

Daphnia magna was used as a test organism for assessing the toxicity remaining in simulated effluents containing cadmium, zinc, and a cadmium‐zinc mixture, after these metals were removed with suspended and immobilized Chlorella vulgaris cultures. The percentage of removal was higher (84.7%) for cadmium in the metal mixture with immobilized cultures. The LC₅₀ value was lower for the residual cadmium (single and in the mixture) in the effluent after treatment with suspended cultures. The acute toxicity response observed in D. magna, indicates that zinc has an antagonistic effect on cadmium toxicity. According to the results, the treatment system can modify the Cd acute residual toxicity. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 160–164, 2000<     

Effect of suspended solids concentration and filament type on the toxicity of chlorine and hydrogen peroxide to bulking activated sludge

Toxic inhibition of three communities of filamentous microorganisms by chlorine and hydrogen peroxide was investigated in relation to the total suspended solids concentration of bulking acitvated sludges. The filament communities studied were dominated by type 1701, Sphaerotilus natans, and the combination of type 021N and Thiothrix spp., respectively. Activity of filamentous and gross biomass was assessed separately using the malachite green-INT (MINT) test. The effectiveness of toxicants was characterized in terms of the concentration required to inhibit 50% of microbial dehydrogenase activity (IC₅₀). IC₅₀s were found to be proportional to total suspended solids concentration. Values for filamentous biomass were generally lower than those for gross biomass. Relative sensitivity (ratio of gross IC₅₀ to filamentous IC₅₀) did not vary significantly over the practical range of total suspended solids concentraton. This parameter was unaffected by the nature of the toxicant in S. natans and type 021N/Thiothrix dominated sludges, but was toxicant specific in type 1701 dominated sludge. Overall, S. natans and type 1701 were the least sensitive of the filament types studied. Bulking caused by these organisms has been successfully cured by toxicant addition in numerous past instances. It is therefore expected that type 021N, Thiothrix, and most other types of filamentous bulking can also be controlled by this technique.     

Acute toxicity test of CuO nanoparticles using human mesenchymal stem cells

Despite the growing interest in nanoparticles (NPs), standardized procedures for the evaluation of their toxicity have not been defined. The risk of human exposure is rapidly increasing and reliable toxicity test systems are urgently needed. In vitro methods are ideal in toxicology research because they can rapidly provide reproducible results while preventing the use of animals. Recently, a new test for acute toxicity based on the use of human bone marrow mesenchymal stem cells (hBMMSCs) has been developed and successfully tested in our laboratory following the Interagency Coordinating Committee on the Validation of Alternative Methods guidelines. Along these lines, the aim of this study is to evaluate the acute cytotoxicity of copper oxide (CuO) NPs using the new toxicity test based on hBMMSCs. Our results show that CuO NPs are much more toxic compared to micrometer ones. Specifically, CuO NP exposure exhibits a significant cytotoxicity at all the concentrations used, with an IC₅₀ value of 2.5?±?0.53?µg/ml. On the other hand, CuO microsized particle exposure exhibits a very low cytotoxicity at the same concentrations, with an IC₅₀ value of 72.13?±?16.2?µg/ml.