The cobalt spot test – further insights into its performance and use

BACKGROUND: A spot test was recently developed for easy and rapid testing to detect whether cobalt is available on surfaces in contact with skin. OBJECTIVES: To explore the potential use of the cobalt spot test as a tool for skin dose assessment, and to verify the sensitivity under laboratory conditions. METHODS: A cobalt dilution series (cobalt standards mixed with cobalt spot test reagent solution) was prepared to determine the threshold for colour change. Defined doses of cobalt were applied to the fingers of 5 volunteers. Acid wipe sampling was used to measure the recovery of applied cobalt skin doses on one hand, and cobalt-exposed areas on the other hand were spot tested. RESULTS: A weak colour gradient was visible from approximately 1 to 1.5 µg cobalt/ml in the dilution series. For a skin dose of 0.125 µg cobalt/cm(2) , 80% of the cobalt dose was collected by acid wipe sampling. Spot tests gave positive results in all cases (n = 5). CONCLUSIONS: The cobalt spot test can be used to show cobalt on the skin. More experience is needed to understand and describe the most suitable test conditions.