Chemical sensitivity human body

In nonindustrial settings, MCS substances are the cause of indoor air pollution and are the contaminants in air and water. Many of the chemicals which trigger MCS symptoms are known to be irritants or toxic to the nervous system. As an example, volatile organic compounds readily evaporate into the air at room temperature. Permitted airborne levels of such contaminants can still make ordinary people sick. When the human body is assaulted with levels of toxic chemicals that it cannot safely process, it is likely that at some point an individual will become ill. For some, the outcome could be cancer or reproductive damage. Others may become hypersensitive to these chemicals or develop other chronic disorders, while some people may not experience any noticeable health effects. Even where high levels of exposure occur, generally only a small percentage of people become chemically sensitive. 

Sensitivity The ability of a chemical analysis to detect low levels of the analyte. Also, any abnormal reaction of the human body to chemical substances. 

Most chemical agents are essentially cumulative in their effects. The reason is that the human body detoxifies them very slowly or not at all. For example, a 1-h exposure to HD or CG followed within a few hours by another 1-h exposure has about the same effect as a single 2-h exposure. Continued exposure to low concentrations of HD may cause sensitivity to very low concentrations of HD. Other chemical agents also have cumulative effects. For example, an initial exposure to a small (less than lethal) amount of Sarin (GB) would decrease cholinesterase levels a second quantity less than the FDS0... 

Hydroxyapatite (HAP), the molecular formula of which is Ca5(P04)3(0H) or Caio(P04)6(OH)2, is the major inorganic constituent in bone, teeth, etc. in the human body. HAP has essentially the same chemical composition and crystalline structure as those of human bone and so has good bio-compatibility. For a long time, it has been widely used as a sclerotin material in setting broken bone, filling teeth, etc. [215]. In addition, HAP can also be used as a food additive and moisture-sensitive element, etc. 

The existing methods available for scientifically defensible risk characterization are not yet ideal since each step has an associated uncertainty resulting from data limitation and incomplete knowledge on exact mechanism of action of the toxic chemical on the human body. For noncancer end points, safety factors or uncertainty factors are applied since these effects are assumed to have a threshold below which no adverse effect is expected to be observed. US EPA has used the concept of a reference concentration (RfC) to estimate acceptable daily human exposure from HAPs. The RfC was adapted for inhalation studies based on a reference dose (RfD) method previously used for oral exposure assessment. The derivation of the RfC differs from that for the RfD in the use of dosimetric adjustment to extrapolate the exposure concentration for animals to a human equivalent concentration. Both are estimates, with uncertainty spaiming perhaps an order of magnitude, of a daily exposure to the human population, including sensitive subgroups, which would be without appreciable risk of deleterious effects over a lifetime. 

The assessment of adverse health effects such as acute and chronic toxicity, carcinogenicity, reproductive toxicity, but also skin sensitization require in depth scientific knowledge of the processes in the human body that absorb, distribute, biotransform (or metabolize), or excrete the foreign chemicals but also endogenous compounds and the events associated with the toxicities in... 

For assessing noncancer health risks, the relevant toxicity value for each contaminant is expressed as a reference dose (RfD), which is derived from experimental or epidemiological data. An RfD is the daily exposure level or dose (usually expressed in units of milligrams of chemical per kilogram body weight per day) for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk of deleterious effects. RfDs can be calculated for a subchronic exposure duration (2 wk to 7 yr) or for a chronic exposure duration (7 yr to a lifetime). A daily exposure at or below the RfD is not likely to be associated with health risks, but as the amount of chemical that an individual is exposed to increases above the RfD, the probability that an adverse effect will occur also increases (Cicmanec et al. 1996). Unlike control... 

Chemical reactions that occur in living systems are often extremely sensitive to pH. Many of the enzymes that catalyze important biochemical reactions are effective only within a narrow pH range. For this reason, the human body maintains a remarkably intricate system of buffers, both within cells and in the fluids that transport cells. Blood, the fluid that transports oxygen to all parts of the body, is one of the most prominent examples of the importance of buffers in living beings. 

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