Effect of microwave heating on leaching of lead from old ceramic dinnerware

When samples of pre-1950s U.S.-made ceramic dinnerware, purchased in antique shops and flea markets, were filled with 4% acetic acid or 0.5% citric acid and heated in a microwave oven for 2–5 min, lead was leached in amounts of up to 5 mg per dish. Concentrations of lead in the leachates were not significantly correlated with, and could not be predicted from, concentrations in leachates measured during 24-h room temperature acid leaching tests. Unsafe lead concentrations (>3 μg/ml) were found in microwave leachates of dishes with uranium-containing glazes, with copper-containing glazes, and with floral over-the-glaze decals. This evidence suggests that use of such dishes to microwave common foods could result in the ingestion of dangerously large amounts of lead.