Comparative and Genetic Effects

Comparative toxicology is the study of the variation in toxicity of exogenous chemicals toward different organisms, either of different genetic strains or of different taxonomic groups. Thus the comparative approach can be used in the study of any aspect of toxicology, such as absorption, metabolism, mode of action, and acute or chronic effects. Most comparative data for toxic compounds exist in two areas—acute toxicity and metabolism. The value of the comparative approach can be summarized under four headings  

Selective toxicity. If toxic compounds are to be used for controlling diseases, pests, and parasites, it is important to develop selective biocides, toxic to the target organism but less toxic to other organisms, particularly humans. 

Experimental models. Comparative studies of toxic phenomena are necessary to select the most appropriate model for extrapolation to humans and for testing and development of drugs and biocides. Taxonomic proximity does not necessarily indicate which will be the best experimental animal because in some cases primates are less valuable for study than are other mammals. 

Environmental xenobiotic cycles. Much concern over toxic compounds springs from their occurrence in the environment. Different organisms in the complex ecological food webs metabolize compounds at different rates and to different products the metabolic end products are released back to the environment, either to be further metabolized by other organisms or to exert toxic effects of their own. Clearly, it is desirable to know the range of metabolic processes possible. 

Laboratory micro ecosystems have been developed, and with the aid of Relabeled compounds, chemicals and their metabolites can be followed through the plants and terrestrial and aquatic animals involved. 

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For next development of allelopathy utilization, especially such ways as breeding for stronger allelopathic potential is very hopeful. Hybridization could be a promising method of breeding. However, allelopathic activity was identified as a quantitative trait and therefore this characteristic is affected by both genetic effects and environmental conditions. The main disadvantage of the application of allelopathy is considerable variability in the dependence on environment. Therefore all results achieved in laboratory should be compared with effects of allelopathic crops in field conditions. 

The failure to find non additive genetic effects in the large twin registry sample remains a puzzle and will be resolved only when we are able to test this sample with instruments comparable to those used in the other studies. As an aside it is worth mentioning that the two instruments used to derive the factor scales make use of quite different methods of measurement (paired comparisons vs. a Like, Indifferent, Dislike format) and utilize different content. Each instrument, however, yielded the same results. 

In vitro enzymatic polymerizations have the potential for processes that are more regio-selective and stereoselective, proceed under more moderate conditions, and are more benign toward the environment than the traditional chemical processes. However, little of this potential has been realized. A major problem is that the reaction rates are slow compared to non-enzymatic processes. Enzymatic polymerizations are limited to moderate temperatures (often no higher than 50-75°C) because enzymes are denaturated and deactivated at higher temperatures. Also, the effective concentrations of enzymes in many systems are low because the enzymes are not soluble. Research efforts to address these factors include enzyme immobilization to increase enzyme stability and activity, solubilization of enzymes by association with a surfactant or covalent bonding with an appropriate compound, and genetic engineering of enzymes to tailor their catalytic activity to specific applications. 

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