Contaminants endogenous exogenous

So from a simple mass transport point of view, hair is less susceptible to contamination by exogenous mechanisms than urine by endogenous mechanisms. But then hair, but not urine, is cleansed by normal hygienic practices and by special laboratory wash procedures. The latter are further strengthened by special kinetic analysis of the wash data. And, finally, the deposition of exogenous drugs onto hair, unlike their accumulation in urine, is not associated with the formation of metabolites. 

Bacteria involved in SSI are either acquired from the patient s normal flora (endogenous) or from contamination during the surgical procedure (exogenous). 

If an analytic method lacks sufficient specificity, chemical interferences will result in an erroneously high reported concentration. If a measured chemical is introduced as an artifactual contaminant during sample collection or analysis, reported concentrations will also be overestimated. For example, credibly estimating human exposure to phthalates was hindered by the difficulties involved in avoiding specimen contamination with these ubiquitous chemicals the problem was resolved by focus on the much less prevalent metabolic product, the phthalate half-ester (Silva et al. 2004). Alternatively, a chemical measured as a marker of exogenous exposure may be identical with a chemical formed by an unrelated endogenous metabolic pathway. In each of those cases, a rigorous laboratory-method validation should detect the problem before data are reported. More subtly, the measured biomarker of exposure may be chemically identical with a dietary... 

The biological starting material contains other proteins, DNA and RNA, either from the medium or secreted by the host cell, and endotoxins. Endogenous and exogenous viruses, mycoplasma, bacteria, and proteins responsible for transmissible degenerative encephalopathies (TDE) must also to be considered as serious contaminants present in biological starting material. 

The evidence from this laboratory and from others reviewed in this chapter reinforces and extends the serious concern that external contamination of hair by drugs of abuse can easily occur. Any interpretation of hair analysis data should consider the prospect that the sample could have been externally contaminated. The pharmacokinetics of the incorporation of drugs into many tissues has been well elaborated. However, substantial additional information on the mechanisms for incorporation of drugs into hair, the decontamination of hair, the differentiation between exposure to exogenous and endogenous drugs, and the meaning of the presence of metabolites in the hair are needed before hair analysis can be employed in many forensic applications. 

The main issue in hair testing is the avoidance of exogenous interpretive false positives, i.e., positives caused by external contamination of hair by drugs present in the environment, e.g., smoke, powder. This type of false positive is not the major issue for urinalysis where endogenous interpretive false positives are the main concern. But, the effective avoidance by urinalysis of exogenous false positives due to specimen contamination in the laboratory depends critically on the exclusion of drugusing personnel, and this can best be achieved by evasion-proof hair analysis. However, when such false positives occur, or when urinalysis labs are unable to guarantee that they have taken effective measures to exclude such contamination, then very little can be done to remedy the problem. For, in contrast to hair, the collection of a new urine specimen identical to the first one is not possible. 

If one now adds to these safety features against exogenous false positives the ability to collect a second hair sample, safer endogenous cutoff levels, the trilevel reporting system (negative, contaminated, or positive), as well as the subversion-proof nature of the hair test, one can readily appreciate that hair analysis is a safer procedure than urinalysis. One also recognizes that hair analysis, unlilce urinalysis, is not a stand-alone test. 

Given the almost constant exposure of humans to toxic chemicals (via air pollution, water pollution, or food contamination) and the filtration function of the kidneys, one could easily argue that the kidneys are almost constantly exposed to mixtures of toxic chemicals and that the uptake of additional xenobiotic chemicals creates new mixtures. As we have already seen earlier, many single chemicals have been shown to be renal toxins. Whether the observed nephrotoxic effects of any of these chemicals are because of its interactions with endogenous or other exogenous chemicals is unknown. What is known is that exposures to some chemical mixtures are toxic to the kidneys of test animals and humans. Examples of studies demonstrating mixture effects follow ... 

Unfortunately, higher amoimts of some minerals in seaweed have been the result of pollution of the seawater or natural environment. Thus, many studies were conducted with respect to the contamination of seaweed by heavy metals. Because of their high sorption capacity, they were also probed for their utilization as biosorbents to remove heavy metals from the environment and to elucidate mechanisms of metal biosorption by seaweeds (Davis et al., 2003 Murphy et al., 2008 Suzuki et al., 2005). Further, these conclusions could be utilized for the understanding of the uptake mechanisms by seaweed. Finally, endogenous and exogenous factors have participated on the variability of seaweed mineral composition. 

Wounds can be classified into acute wounds and chronic wounds. While acute wounds take only a few weeks to heal, chronic wounds require several months to heal completely. Chronic wounds include venous leg ulcers and pressure sores. Wounds are not usually sterile. A wound may bear a level of 100,000 microorganisms per gram of tissue. Beyond this number, the wound may become infected. In some wounds the pathogens may be able to colonise (critical colonisation) and this is considered to be detrimental for wound healing. Wound bacteria can be acquired from the patient s own endogenous flora or from exogenous microbial contamination... 

Successful RNA preparation depends on the inhibition of both endogenous RNase activity liberated on cell lysis and contamination of preparations by exogenous RNases. In this method treatment of equipment and solutions with diethyl pyrocarbonate (DEPC), a strong inhibitor of RNases, is used to prevent degradation of samples. In addition working quickly and keeping preparations on ice whenever possible will help to minimize problems with RNase activity. 

Occupational medicine and environmental medicine are independent specialties. However, they have many common points with respect to hair analysis. In most cases it is not necessary to solve the problem of endogenous or exogenous contamination in order to be able to assess exposure to a damaging substance by means of hair analysis analysis before and after cleaning is sufficient to provide an indication concerning the amount of exposure. 

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