Bioassays limitations

The radiological hazard of tritium to operating personnel and the general population is controlled by limiting the rates of exposure and release of material. Maximum permissible concentrations (MPC) of radionucHdes were specified in 1959 by the International Commission on Radiological Protection (79). For purposes of control all tritium is assumed to be tritiated water, the most readily assimilated form. The MPC of tritium ia breathing air (continuous exposure for 40 h/wk) is specified as 185 kBq/mL (5 p.Ci/mL) and the MPC for tritium in drinking water is set at 3.7 GBq/mL (0.1 Ci/mL) (79). The maximum permitted body burden is 37 MBq (one millicurie). Whenever bioassay indicates this value has been exceeded, the individual is withdrawn from further work with tritium until the level of tritium is reduced. 

Toxicologists tend to focus their attention primarily on c.xtrapolations from cancer bioassays. However, tlicrc is also a need to evaluate the risks of lower doses to see how they affect the various organs and systems in the body. Many scientific papers focused on tlic use of a safety factor or uncertainty factor approach, since all adverse effects other than cancer and mutation-based dcvclopmcnUil effects are believed to have a tlu cshold i.e., a dose below which no adverse effect should occur. Several researchers have discussed various approaches to setting acceptable daily intakes or exposure limits for developmental and reproductive toxicants. It is Uiought Uiat an acceptable limit of exposure could be determined using cancer models, but today tliey arc considered inappropriate because of tlircsholds. ... 

Stauber JL, Davies CM (2000) Use and limitations of microbial bioassays for assessing copper bioavailability in the aquatic environment. Environ Rev 8 255-301... 

The advantages of combining toxicity testing with chemical analysis when dealing with complex mixtures of environmental chemicals are clearly evident. More useful information can be obtained than would be possible if one or the other were to be used alone. However, chemical analysis can be very expensive, which places a limitation on the extent to which it can be used. There has been a growing interest in the development of new, cost-effective biomarker assays for assessing the toxicity of mixtures. Of particular interest are bioassays that incorporate mechanistic... 

Some Chemical Considerations Relevant to the Mouse Bioassay. Net toxicity, determined by mouse bioassay, has served as a traditional measure of toxin quantity and, despite the development of HPLC and other detection methods for the saxi-toxins, continues to be used. In this assay, as in most others, the molar specific potencies of the various saxitoxins differ, thus, net toxicity of a toxin sample with an undefined mixture of the saxitoxins can provide only a rough approximation of the net molar concentration. Still, to the extent that limits can be placed on variation in toxin composition, the mouse assay can in principle provide useful data on trends in net toxin concentration. However, the somewhat protean chemistry of the saxitoxins makes it difficult to define conditions under which the composition of a mixture of toxins will remain constant thus, attaining a reproducible level of mouse bioassay toxicity is difficult. It is therefore useful to review briefly some of the chemical factors that should be considered when employing the mouse bioassay for the saxitoxins or when interpreting results. Similar concepts will apply to other assays. 

Bioassay with mosquito larvae for the detection of insecticide residues in fresh and processed fruits and vegetables is feasible, subject to the limitation that the untreated natural product is in itself nontoxic to the larvae at the dilutions tested. 

Horwitz claims that irrespective of the complexity found within various analytical methods the limits of analytical variability can be expressed or summarized by plotting the calculated mean coefficient of variation (CV), expressed as powers of two [ordinate], against the analyte level measured, expressed as powers of 10 [abscissa]. In an analysis of 150 independent Association of Official Analytical Chemists (AOAC) interlaboratory collaborative studies covering numerous methods, such as chromatography, atomic absorption, molecular absorption spectroscopy, spectrophotometry, and bioassay, it appears that the relationship describing the CV of an analytical method and the absolute analyte concentration is independent of the analyte type or the method used for detection. 

The main advantage of this technique is the rapidity of response and the possibility of performing many bioassays with different algal strains at the same time. The disadvantage is that the kind of response is qualitative. This limitation can be overcome by selecting for liquid inhibition bioassays, the strains that give a positive response in paper disk bioassay (i.e. the strains sensitive to the allechemical(s) tested). 

A word of caution should be made with respect to estimating tenability for human exposures. Experimental LC values are determined using rat lethality as the bioassay. Judgement should be exercised for human tenability, with limits set considerably lower than FED summation at unity. An FED limit of, perhaps, 0.3 may be more appropriate for assessment of the potential escape of humans. 

In the light of these limitations, effective additional tools able to assess the biological responses of the pesticides present, as well as their interaction with the other chemicals, have to be introduced to complete the evaluation of waste-waters. Bioassays on water samples provide a direct functional response that can relate to the negative effects of a single pesticide and overall toxic properties of the complex mixture of compounds present in a sample [16]. 

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