Processing effect lethality

A second area of concern associated with steam quality is superheating. This is a phenomenon related to the phase equilibria of steam under pressure (Fig. 1). In some circumstances it is possible at a fixed pressure to increase the temperature of steam above its equilibrium temperature. It is then referred to as superheated or supersaturated steam. Superheated steam is not as effectively lethal to microorganisms as saturated steam—the biochemical mechanisms of lethality are similar to those of dry heat. If supersaturated conditions prevail, the lethality of the process will be much lower at any specified temperature than that which would be expected from saturated steam. Supersaturation may arise from autoclave problems or load problems or both. For instance, the steam in the chamber may pick up heat from a jacket running at loo high a temperature or pressure, or condensation of the steam may be impeded by veiy dry cellulosic materials in the toad. 

Most drugs can be expected to have potentially lethal effects, as their usefulness depends on their ability to infiuence physiological processes. However, the dose level at which toxic effects manifest should be significantly higher than those required to produce a pharmaceutical response, so that a good safety margin exists between therapeutic and toxic levels. 

The lethal effects of dry heat on microorganisms are due largely to oxidative processes which are less effective than the hydrolytic damage which results firm exposure to steam. Thus, dry heat sterilization usually employs higher temperatures in the range 160-180°C and requires exposure times of up to 2 horns depending upon the temperatrrre employed (section 10). 

To provide a better understanding of toxic impacts on aquatic ecosystems, cause-effect relationships between changes in biodiversity and the impact of environmental pollution as causative factor as well as the underlying processes. This included the assessment of sub-lethal effects in vitro and in vivo as early warning strategies and of their strength to predict potential hazards to the ecosystem. 

The toxic effect produced by a chemical agent on a susceptible organism depends on the nature and magnitude of its interactions with the vital processes which it disrupts (which may be termed its intrinsic toxicity) and on the amounts which reach the sites of interaction. Both these determinants of toxic effect are expressions of biophysical and physico-chemical factors. The effectiveness of the lethal interaction which is equivalent to the intrinsic toxicity... 

Differential effects on uptake and excretion. If the tissue in which the lethal process occurs is separated from the source of the toxicant and from an excretory or detoxifying... 

Iron(n) is known to decompose hydrogen and dialkyl peroxides to free radicals by reductive cleavage of the 0—0 bond and early investigations established the parasite s sensitivity to these species. When treated with radiolabelled C-artemisinin, the hemin-hemozoin fraction of the lysed malaria-infected erythrocytes was shown to contain a radiolabel, though the mechanism of incorporation is not clear. Meshnick and coworkers demonstrated that uninfected cells did not contain radiolabelled proteins whereas six radiolabelled proteins were isolated from cells infected with the Plasmodium falciparum (P. falciparum) strain of the parasite. It was suspected that one of the alkylated proteins was the Histidine Rich Protein (HRP) that was known to bind multiple heme monomers and therefore thought to be instrumental to the parasite s detoxification process. Moreover, iron chelators were found to inhibit the lethal effects of peroxides on the parasite. ... 

Despite widespread use as an Insecticide, nematoclde, and Intermediate In chemical processes, the toxic potential of PS has not been fully evaluated. Absence of lethal effects may well be explained by Its powerful odor, which alerts workers to Its presence In contaminated areas. Anlmal-toxlclty data suffer from variations In the methods used. One long-term study of carcinogenicity In rats was unsatisfactory because of high early mortality. 

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