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 heated to body temperature (i.e., 37°C)? For TLV purposes, should solubility be based upon body temperature? b.

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Should the TLV documentation specify that analytical procedures use extraction media heated to body temperature?

HEALTH EFFECTS From a health perspective, the solubility of a metal or metal compound is not the only consideration of interest. Ultimately, the most important consideration is the extent to which such soluble metals accumulate in body fluids or target organs, leading to toxic levels of the metal ion. This is of more concern than solubility in water, acids, or alkalies per se. Further complicating the solubility issue is the fact that the term “soluble” may have different meanings among industrial hygienists and chemists. Chemists generally use the term “soluble” as defined by the CRC Handbook of Chemistry and Physics [5]. According to the Handbook, a material is considered soluble if a saturated solution in water (at 25 o C) contains more than 1% (m/v); any material in which 1 percent or less is dissolved is considered insoluble. Unfortunately, a material listed as insoluble, using the CRC definition, could still dissolve in body fluids and produce a significant tissue concentration which is biologically detrimental. The point is that an occupational exposure limit (OEL) for an “insoluble”compound may not be sufficient to protect exposed workers. When asked in an informal poll to choose a solvent in which to measure the relative solubility of metals, industrial hygienists chose, in order of preference, water, body fluids, and a petroleum solvent [1]. Body Fluids. When considering the biological effect of the solubility of a material, we should ideally first consider body fluids. However, body fluids vary considerably in pH. For example, the pH of the stomach is acidic, the pH in the intestine is alkaline, the pH of blood serum is approximately neutral, some macrophages are highly acidic, and the pH of saliva is slightly acidic. Furthermore, body fluids contain a variety of solutes, including salts and polypeptides (proteins). Polypeptide molecules can wrap around metal ions in solution and often contain functional groups that can chelate metals. Polypeptides have strong chelating ability in body fluids and will account for the considerable difference between the solubility of a metal in body fluids versus that same metal in water. Metals, in turn, are bound to different proteins, depending upon where in the body they are located at a given time. In passing through the body, a metal ion is bound by different polypeptides. For each of them, a different reaction may be involved. Some reactions may increase or decrease the toxicity of the metal ion. Because of the effect of proteins, pH, and other solutes in body fluids, the solubility of a metal compound in body fluids will be quite different than the metal’s solubility in water [9].

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SAMPLING CONSIDERATIONS Filter Reactivity. The filter medium used must not react with the airborne particulate collected by the sampler so as to change the chemical form of the captured sample. This can occur if a soluble compound reacts with the filter material or a contaminant therein to produce an insoluble or less soluble compound. An example of this problem has been observed with silver, where a soluble silver compound, AgNO3, can react with chloride in some mixed cellulose ester (MCE) or polyvinyl chloride (PVC) filters to form AgCl, which is much less

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NIOSH Manual of Analytical Methods