Nickel release from 304 and 316 stainless steels in synthetic sweat. Comparison with nickel and nickel-plated metals. Consequences on allergic contact dermatitis

Abstract

Release of nickel from nickel or nickel-plated metals, is often responsible for allergic contact dermatitis. However, the effect of nickel-bearing stainless steels is not well known. In this paper AISI 304, 316 and 430 type stainless steels, as well as nickel and nickel-plated materials, are investigated. Three tests were carried out: electrochemical tests and leaching experiments in sodium chloride (0.05 M) and synthetic sweat solutions, and clinical patch tests on 50 patients already sensitive to nickel. Results of the leaching experiments show that nickel and nickel-plated samples release nickel in an amount much larger than 0.5 μg cm −2 week −1, in sodium chloride and synthetic sweat solutions of neutral or acidic pH (6.6 and 4.5 respectively), while AISI 304, 316L and 430 grades release nickel in very small amounts ( <0.03 μgcm −2week −1 ) in those solutions. These differences are attributed to the corrosion resistance of these stainless steels in chloride solutions, due to the protective effect of their chromium-rich passive films; for those materials, no localised corrosion is observed in the experimental solutions, even at pH 4.5, while pitting occurs on nickel and nickel-plated steel. However, complementary studies show that, for resulphurised stainless steels (for instance free-machining steels), the MnS inclusions may dissolve, mainly at acidic pH. In this case nickel release becomes larger. Thus, stainless steels AISI 304, 316 and 430, should not cause any allergic contact dermatitis. This was confirmed by the clinical patch tests which showed that 96% of the patients were intolerant to the nickel-plated samples, while low sulphur containing stainless steel samples elicited no reactions in the patients. Conversely, resulphurised stainless steel (AISI 303), led to reactions in 14% of the patients. In addition, it was shown that the dimethylglyoxime test was not relevant for selecting materials which cause no contact dermatitis. A new test was then proposed, in accordance with the present results.