ABSTRACT ABSTRACT In laboratory studies microbiocidal properties of chromium in coatings depended on the following exposure conditions: atmospheric vs. immersion, hexavalent chromium concentration and the target organism. INTRODUCTION Chromium is used in wood preservation, leather tanning, corrosion inhibitors and corrosion resistant coatings. Factors regulating chromium toxicity are quite specific. Health effects on humans are largely determined by the chromium oxidation state. In general, redox-active hexavalent chromium (Cr) is more water-soluble, enters living cells more easily and is more toxic and carcinogenic than trivalent chromium (Cr). Cr most often occurs as chromate (CrO4). Because of these properties, Cr can be used as a biocide. The oxidation state of chromium is used to make decisions about the use of the element in many applications. For example, Cr used in treated wood is regulated as a preservative and not as a biocide since Cr in the treated wood is reduced to Cr within hours to days, depending on temperature and wood species. To minimize the potential risk to individuals handling treated wood, several fixation techniques have been developed to speed the reduction, including high temperatures. “Cr should not be detected when treated wood leaves the storage facility.” According to the World Allergy Organization, Cr can be used in the leather tanning process, because most of the Cr is reduced to Cr before the leather goods are sold. However, residual Crleft over from the tanning process can cause skin reactions in sensitive individuals. Cr is also used in corrosion-inhibiting coatings. The formation of a chromate conversion coating involves Cr reduction to Cr followed by formation of an insoluble Cr - Cr mixed oxide with reversible binding of Cr. Cr is incorporated into the chromate conversion coating at about 1/3 concentration of Cr and Cr can be released. Release into solution is pH dependent, with higher pH favoring desorption.