Selective toxicity Defined

To select and define the target analytes for the residue analysis of crops in a field trial, applicants should consider metabolites/degradation products of the test materials by conducting plant and animal metabolism studies and by assessing toxicity of the metabolites/degradation products. 

Viruses present a more difficult problem of chemotherapy than do higher organisms, e.g. bacteria, for they are intracellular parasites that use the metabolism of host cells. Highly selective toxicity is, therefore, harder to achieve. Identification of differences between viral and human metabolism has led to the development of effective antiviral agents, whose roles are increasingly well defined. 

The compounds were first tested against two panels of human tumour cell lines. The primary cell panel consisted of cells from tumours representative of different tissue types and with different chemosensitivities to cisplatin . Differential cytotoxicity, as opposed to non-selective toxicity, was used as an indicator of potential antitumour activity of test compounds . The second panel was disease-oriented and consisted of cell lines established from human ovarian tumours. This panel included two pairs of cisplatin-sensitive and cisplatin-resistant hnes, with defined mechanisms of resistance (CHl/CHl-R, A2780/A2780-R), and also two inherently resistant cell hnes (HX62 and SK-OV-3). This panel has been used to identify agents with the abihty to circumvent cisplatin resistance . ... 

Ryanodine and 9,21-dehydroryanodine are the principal insecticidal components and toxicants among 11 identified ryanoids in the botanical insecticide ryania. Their biological activity is attributed to block of the calcium release channel, which is conveniently measured as inhibition of pH]ryanodine binding in muscle and nerve preparations. Structure-activity relationships based on 10 natural ryanoids and 45 of their derivatives help define the conformation of the ryanodine binding site and the structural requirements for insecticidal activity and selective toxicity. 

Reversibility of combination with receptors. The majority of drugs and other selectively toxic agents combine very loosely with their receptors. They can usually be easily washed off the receptors, which then cease to register the adverse effects produced by the agent. It is comparatively rare for agents to form covalent bonds with their receptors (covalent bonds are defined in Section 8.0), but those that can do so inflict a change that is difficult to reverse. 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

Specificity, this can be thought of as an extreme form of selectivity (see Selectivity) where, in this case, no increase in the concentration of the molecule will be sufficient to activate the other processes). This term is often used erroneously in that the extremes of concentration have not been tested (or cannot be tested due to chemical, toxic, or solubility constraints in a particular system) to define what probably is only selectivity. 

The Danish List of Undesirable Substances is a list of chemicals of concern that the government believes should be avoided to the extent feasible in commerce. Using a systematic analysis, substances are selected automatically if they meet some clear and defined criteria, for example, problematic classifications, because they are imder suspicion for being PBT/vPvB (Persistent, Bioaccumulative, Toxic/very Persistent, very Bio accumulative) or endocrine-disrupting. 

RCRA was passed to manage nonhazardous and hazardous wastes and underground storage tanks, with an emphasis placed on the recovery of reusable materials as an alternative to their disposal. This act introduced the concept of the separate management of hazardous and nonhazardous wastes, and defined procedures to identify whether a waste is hazardous or nonhazardous. A waste exhibits the characteristic of toxicity, classified as a hazardous material, if the concentration of any of 39 selected analytes in the Toxicity Characteristic Leaching Procedure (TCLP) extract exceed regulatory action levels. 

The tables were designed to encompass processes included in most models of the various media of concern. Although selected processes are not rigorously defined for each media (e.g., sorption/desorption in air refers to toxicant-particulate interactions), the goal was to provide a concise ranking table for each level of analysis. 

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