Microtox test system

The Microtox test system utilizes a strain of naturally occurring luminescent bacteria - Vibrio fischeri. Exposure to a toxic substance causes a disruption of the respiratory process of the bacteria resulting in reduced light output. The effective concentration (EC50) is determined as the concentration of a toxicant that causes a 50% reduction in light output over a prescribed period of time (typically 5, 15, or 30 min). The test is fast, fairly simple to conduct, uses small sample sizes, and is relatively inexpensive. Results correlate well with those from other toxicity bioassays such as fish and Daphnia. The test is used... 

Johnson, B.T. 1998, Microtox Toxicity Test System—New Developments and Applications. In Microscale Testing in Aquatic Toxicology Wells, P.G., Lee, K., Blaise, C., Eds CRC Press Washington, D.C. pp. 201-218. 

Doherty, F.G. (2001) A review of the Microtox toxicity test system for assessing the toxicity of sediments and soils, Water Quality Research Journal of Canada 36 (3), 475-518. 

Hauser, B., Schrader, G. and Bahadir, M. (1997) Comparison of acute toxicity and genotoxic concentrations of single compounds and waste elutriates using the Microtox/Mutatox test system, Ecotoxicology and Environmental Safety 38 (3), 227-231. 

The Microtox test can be used in field studies and in mobile laboratories.7-8 54 This is especially important in unexpected and rapidly developing environmental threats, when continuous inspection of pollution levels is necessary.68 Since the test is instantly applicable, and because the results are obtained within an hour of the sample being delivered to the laboratory, this type of assay has become very popular worldwide. But despite the aforementioned advantages, this system is not perfect. The most important shortcomings are... 

Effluent test results support the use of Microtox as part of a test battery. Uniform response of sublethal effects to 50 effluents from pulp and paper mills was obtained with the Microtox test compared to the results with fish and algae, which varied greatly with age and genetic variation within the population. Microtox has also been used to detect other sublethal effects (e.g., chronic toxicity). For example, the bacterial response can be used to quantify the stress on the immunological defense systems of mussels exposed to toxins in polluted rivers or wastewaters. In... 

We developed the first expert system that incorporates a working set of rules for a type of QSAR referred to as a linear solvation energy relationship or LSER (13-17) to predict LSER variable values from SMILES string formalism. The program also uses these LSER results and information about toxicity to predict acute toxicity to four representative organisms the fathead minnow (Pimephales promelas), the crustaceans Daphnia magna and Daphnia pulex. and Photobacterium phosphoreum. the luminescent agent in the Microtox test. 

Bioassav Data Sets and Multiple Linear Regression Equations The expert system predicts the acute toxicity of a chemical to four representative aquatic organisms and reports toxicity as either EC50--is the effective concentration at which either 50% of the animals (Daphnia pul ex or D. magna) were immobilized or 50% of the luminescence (the Microtox test) was diminished--or LC50, the lethal concentration for 50% of the fish (fathead minnows) in the study. 

The Microtox acute toxicity test is based upon measuring metabolic inhibition using a standard suspension of luminescent bacteria. Since bioluminescence is a direct measure of metabolic activity in these wganisms, measuring the rate of light output is a simple way to measure metabolic inhibition (toxicity). The test system has been in use for over 10 years and is the subject of many reports, reviews and application studies as well as being... 

The key to implementation is a continuous flow of relevant and speedy toxicity information. Timely information cannot be provided by many toxicity tests, especially those which require some days to obtain results. For effective system control, toxicity information is required in minutes and the use of reliable technology is now available to provide this monitoring information, especially if on-line techniques are used. The Microtox test is now available in an on-line mode [32] which allows for an analysis to be conducted automatically ew cy 30 mins. This test system can (qjerate unattended for 7 d. This ensures that the operator will know what is happening, rather than what has happened, and thus be able to take effective corrective action when toxicity monitoring indicates a biological event outside of acceptable limits. 

A novel extension of the Microtox Acute Test has resulted in the development of a new test system which uses a dark strain of luminescent bacteria to measure genotoxicity of chemicals or environmental samples. 

Research and development efforts over the last 2 years have provided new and useful infraination about the genetics and physiology of the light producing mechanism in the luminescent bacterium Vibrio fischeri. These research and development efforts, along with years of experience gained from the development and application of the Microtox Acute Toxicity Test, has resulted in the development of a new Microtox Chronic Toxicity Test System using luminescent bacteria [57]. 

Bacterial or enzymatic toxicity tests are used to assay the activity of organic compounds including solvents. A survey of environmental bacterial or enzymatic test systems is given by Bitton and Koopman. The principles of these test systems are based on bacterial properties (growth, viability, bioluminescence, etc.) or enzymatic activities and biosynthesis. The toxicity of several solvents were tested in bacterial or enzymatic systems, e.g., pure solvents such as phenol in growth inhibition assays (Aeromonas sp.), solvents in complex compounds such as oil derivates, solvents in environmental samples such as sediments or solvents used in the test systems.The efficiency of several test systems, e.g., Microtox tests or ATP assays, vary, e.g., looking at the effects of solvents. ... 

Jung, K., Bitton, G. 1997. Use of Ceriofast for monitoring the toxicity of industrial effluents Comparison with the 48-H acute Ceriodaphnia toxicity test and Microtox . Experimental Toxicology and Chemistry 16 2264-2267. Kahru, A., Borchardt, B. 1994. Toxicity of 39 MEIC chemicals to Bioluminescent photobacteria (The Biotox test) Correlation with other test systems. 22 147160. 

Environment Canada recently developed an evaluation system based on effluent toxicity testing, capable of ranking the environmental hazards of industrial effluents [185]. This so-called Potential Ecotoxic Effects Probe (PEEP) incorporates the results of a variety of small-scale toxicity tests into one relative toxicity index to prioritize effluents for sanitation. In the index no allowance has been made for in-stream dilution, therefore the acmal risk for environmental effects is not modeled. The tests performed on each effluent are the following bacterial assay [V.fisheri (P. phosphoreum), Microtox], microalgal assay S. capricornutum) crustacean assay (C. dubiay, and bacterial genotoxicity test E. coli, SOS-test). 

The Microtox equipment includes a self-calibrating analyzer which incorporates a photomultiplier tube, a data collection and reduction system, and software. The temperature-controlled analyzer maintains the test organisms and samples at a standard temperature of 15°C. It also detects the light intensity at 490 nm, the wavelength emitted by the bacteria. 

To further validate the treatment technology, the contaminated groundwater was subjected to tests for toxicity and teratogenicity before and after treatment (sampled before carbon treatment). As determined by Microtox , embryonic Menidia beryllina, Mysydopsis bahia, and Ceriodaphnia dubia bioassays, these indicators of potential threat to human health and the environment were significantly reduced. This data shows that the treatment system was effective in removing the hazardous properties of the waste material, while simultaneously demonstrating that no metabolic byproducts or toxic intermediates were created by the microbial biotransformation of the waste constituents. 

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