Multiple bioassay measurements

The results of bioassay measurements or air sampling are used to calculate the magnitude of an intake, and the route of intake is determined from knowledge of the exposure scenario or can sometimes be inferred by the results of multiple bioassay measurements. 

The date of the intake may be definitely known if an incident occurred that resulted in the bioassay measurement(s) being made. Otherwise, a review of records and an interview of the individual should be performed. A review of radiation work permits may indicate when an individual had the potential for an intake of the material of concern even if no intake was suspected at the time, or an interview of the individual may reveal a particular occurrence that could have resulted in the intake. If multiple bioassay measurements are made over a period of time, it may be possible to fit a plot of the data and back-calculate the date of the intake. If none of these are possible, the default assumption is to assume the intake occurred at the midpoint between the positive measurements and any previous bioassay measurements that would have detected the material. Use of the midpoint strikes a balance between conservatively estimating the intake and overconservatism. 

Chief among the knowledge gaps that currently impede progress is a lack of information about cumulative exposure scenarios. Comparatively few studies have measured multiple chemicals in one and the same sample, and consequently, information about how many pollutants co-occur, and at what levels, is patchy. Viable concepts for cumulative exposure assessment strategies need to be developed, and the experiences that have occurred in the areas of bioassay-directed fractionations and with the toxicity identification evaluation (TIE) concepts no doubt provide valuable stimuli. 

Complete information on pollution available. If all contaminants present in the sample have been analysed using conventional physical or chemical methods, the application of bioassays provides further information e.g. on toxicity interactions and bioavailability. It has to be emphasised that for multiple contamination, bioassays reveal an overall combined toxicity response to the bioavailable part of each contaminant present in the mixture. The identification of the bioavailable fraction of a particular substance by relating the measured effect to the measured concentration of the chemical is only possible for a single substance contamination (only one toxic chemical present). Although it may be tempting for risk assessors, the response of multiple pollution cannot be used to calculate the bioavailable fraction (percentage of the total concentration of a compound) of a particular chemical from the mixture, unless toxicant... 

Potency. Binding assays for quantitation use the binding of at least two molecules to form an interaction that withstands multiple washing steps, and they are the least variable [75]. Cell-based bioassays for potency use a cell line mixed with a sample to generate a cellular response that is quantified [75]. They have more variability [75] and are tricky to use to measure potency because the CV often is >30% [2]. Whole animal assays for potency are time-consuming and highly variable [75], and they have the typical disadvantages of in vivo tests in that they are expensive, inaccurate, slow, and raise animal ethics issues [19]. 

Whole-organism bioassays are based on the measurement of the biological response (acute or chronic toxicity) of a test organism to contaminants present in a water sample (e.g., drinking, ground, surface, or wastewater effluent) in a standardized test usually conducted in the laboratory. Several test species covering most of the different trophic levels in freshwater and/or estuarine/marme environments may be employed, the use of multiple test species and trophic levels being usually recommended because each species shows specific sensitivity to different chemicals or classes of compounds. " ... 

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