Hot leaching of ceramic and enameled cookware: collaborative study

A hot leach method published by the World Health Organization for determining Pb and Cd in ceramic and enameled ware was collaboratively studied in 14 laboratories. The method consisted of heating a solution of 4% acetic acid at the boil for 2 h in 6 samples of specially glazed ceramic ware and 6 samples of special enameled ware. The acid was allowed to cool and stand in contact with the ware for an additional 22 h. At the end of the 2 h heating period and again at the end of the 24 h period, the leach solution was assayed by atomic absorption spectrophotometry for Pb and Cd. Ruggedness testing before the collaborative study revealed that: (1) the quantity of metal released increased as the average leach temperature approached the boiling point, (2) the quantity of Pb and Cd released from enameled ware increased linearly with time during 7 h of boiling, (3) the concentration of acid could be varied from 2 to 6% with no apparent effect on the amount of metal released, and (4) the room temperature (RT) contact period lasting from 22 to 120 h (after the 2 h heating period) did not increase the amount of metal released. The quantities of Pb and Cd measured by the collaborators at the end of 2 h of heating and after 24 h of total contact were essentially identical. The amounts of Pb and Cd were not related to the quantity of acid solution required to restore the leach solution volume to its initial value after boiling. The collaborative results showed that the period of standing at RT is not necessary and probably can be eliminated from the method. The modified method, which requires analysis of the leach solution immediately after the 2 h heating period, has been adopted interim official first action by AOAC.