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 Table 1 except for CrVI and Fe. Nevertheless, the sample preparation protocol described in this International Standard is certainly applicable to these other two metallic elements as well. The ISO “soluble”metals method [3] calls for treatment of collected workplace filter samples in 5 mL of deionized water (or ammonium citrate leach solution in the case of Ni) and mechanical agitation in a water bath at 37 ± 2 oC for 60 min. Undissolved material is thereafter separated from the sample solution using a suction filtration apparatus or a syringe filter, and ensuring use of filtration materials that are unreactive towards the soluble metal compounds of interest. After filtration, the sample solution is acidified with nitric acid in order to stabilize the dissolved metallic elements within the extracted sample. This test sample is then ready for analysis by ICP-AES (or ICP-mass spectrometry if very low detection limits are required). Of course other analytical techniques, e.g., atomic absorption spectrometry [19,20] or electrochemical analysis [22,23] can be used as analytically equivalent alternatives.

7. SUMMARY The exposure standards for some metals vary up to a factor of 500 to take into account the increased solubility and bioavailability of some compounds. Even compounds generally considered by chemists as being “insoluble” may have sufficient solubility in body fluids to be of biological importance. Exposure standards for soluble metals such as ACGIH TLVs are not specific with regard to extraction fluid, fluid temperature, agitation and other factors affecting solubility. Since these factors significantly affect solubility, some standardization or adoption of an operational definition is necessary if there is to be reproducibility among laboratories conducting soluble metal analyses. In some countries (e.g., nations in the European Union), the national requirements provide this specificity. In other instances, including exposure monitoring standards in the United States, formal national guidelines are not available.

Therefore, adherence to international extraction guidelines or methods such as those described in ISO standards is necessary to produce measurements that are reproducible with other laboratories, and have utility to the laboratory client when exposure standards or national guidelines are vague. ISO 15202 has the advantage over other guidelines and standards in that it has had input from more than (don’t forget that “O” members also have input) 13 participating countries (Table 2). Thus the use of ISO 15202 is encouraged until either exposure standards or national guidelines provide better specificity.

Laboratories cannot recover soluble metal data if inappropriate sample media are used. Sample stability is a problem that must be addressed when sampling for silver (Ag), chromium (Cr) and other soluble metal compounds. Although the ISO procedure has not been validated for all soluble metal species, the standard recommends that method validation be carried out using representative soluble metal compounds for target elements. ISO 15202 provides guidance on sample media selection for soluble metals that can be a useful guide for industrial hygienists and other laboratory clients.