Toxicants factors affecting activity

Various factors affect the activities of the enzymes metabolizing xenobiotics. The activities of these enzymes may differ substantially among species. Thus, for example, the possible toxicity or carcinogenicity of xenobiotics cannot be extrapolated freely from one species to another. There are significant differences in enzyme activities among individuals, many of which appear to be due to genetic factors. The activities of some of these enzymes vary according to age and sex. 

These results have suggested that mineral dusts that are inert in a particulate form may have biological activity when they occur in a fibrous form. Factors affecting fiber toxicity include length, diameter, respirability resistance to chemical dissolution in biological fluids, and durability. "... 

Several factors affect the extent of hazard associated with pesticide use. The compound used, the type of formulation, and the application equipment are important. Acute toxic hazards of active ingredients may be categorized but it must be recognized that the type of operation will also influence the hazard to the operator. For example, it has been stated that the application of parathion to fruit orchards by a power airblast sprayer is twice as hazardous to the operator as the application of dust to row crops with a boom duster (4 ). 

A second important factor affecting the kidneys sensitivity to chemicals is its ability to concentrate the tubular fluid and, as a consequence, as water and salts are removed, to concentrate any chemicals it contains. Thus a nontoxic concentration in the plasma may be converted to one that is toxic in the tubular fluid. The transport characteristics of the renal tubules also contribute to the delivery of potentially toxic concentrations of chemicals to the cells. If a chemical is actively secreted from the blood into the tubular fluid, it will accumulate initially within the cells of the proximal tubule or, if it is reabsorbed from the tubular fluid, it will pass into the cells in relatively high concentration. 

In allelopathy studies a central goal is to isolate, identify, and characterize allelochemicals from the soil. However, since it is essentially impossible to simulate exact field conditions, experiments must be designed with conditions resembling those found in natural systems. Indcrjit (1996) argued that allelopathic potential of phenolics can be appreciated only when we have a good understanding of i) species responses to phenolic allelochemicals, ii) methods for extraction and isolation of active phenolic allelochemicals, and iii) how abiotic and biotic factors affect phenolic toxicity. 

Several factors affect the selection of the buffer solution, such as the optimum pH the buffer anionic or cationic species (which can interfere in the subsequent purification steps) the pH variation with ionic strength or temperature the buffer reactivity with the proteins in solution the biological activity (e.g. phosphates can inhibit or activate a protein in biological reactions) the interaction of the buffer with other components the buffer permeation in biological membranes the toxicity the light absorption at 280 nm the cost (especially if used in large-scale processes) and the protein solubility. 

A wide variety of organic and inorganic compounds inhibit microbial activity by interfering with the uptake of metabolites and enzymic reactions (Davis and Feingold, 1962 Pelczar and Reid, 1958). In particular, the heavy metals are extremely toxic to the heterotrophs but are tolerated at higher levels by Desulfovibrio spp. due to their precipitation as metal sulphides (see p. 343). Other factors affecting the activity of sulfate-reducers are discussed in Chapter 6.1. 

Age, Sex, Inducers and Inhibitors of Metabolism. The ability of an organ to activate a specific toxin is one explanation of organ-selective toxicity. Factors such as age, sex, circadian rhythms, nutritional status, and exposure to chemicals are known to affect xenobiotic metabolizing enzymes, and therefore might affect organ-specific toxicity of metabolically activated toxins. Several of these factors have striking effects on the organ-specific toxicity produced by IPO. 

The role of GSH in DEB toxicity provides a plansible background to envisage oxidative stress-dependent GSH depletion and, especially, decreased GST activity as possible contributory factors affecting the detoxification potential of cells and in vidual susceptibihty to DEB toxicity. This view was corroborated by a study in which pretreatment with phorone, a well-known intracellular glutathione depletor, was foimd to enhance DEB cytotoxicity, consistent with an active role played in vivo by the GSH-detoxifying system. 

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