Although food contact polymers do not normally contain lead, it is suspected that lead may be leached from some microwavable plastic ware items made in Thailand with lead-containing pigments. The purpose of this study was to examine relationships with regard to lead leached from microwavable plastic ware. Four factors were studied: pH, heat level, extraction time, and number of repeated extractions. A total of 243 samples of microwavable plastic ware items locally manufactured in Thailand were used. This study used three pH values (3.5, 4.5, and 6.5) and three heat levels (levels 3, 6, and 9 [170, 500, and 850 W, respectively]). Acetic acid was used both as the extracting agent and for adjusting the pH. Samples were collected at each level at 1, 3, and 5 min, and the amount of leached lead was measured with an atomic adsorption spectrometer. The results of this study show that pH, heat, and extraction time affected the amount of lead leaching from microwavable plastic ware. The amount of lead leaching increased with decreasing pH but increased with increasing heat level and extraction time. On the basis of these three factors, the results of this study indicate that the pH of the extractant (r = −0.592, P < 0.01), the heat level of extraction (r = 0.293, P < 0.01), the extraction time (r = 0.226, P < 0.01), and the number of extractions (r = −0.153, P < 0.01) are related to lead leaching from microwavable plastic ware. The relationship between the pH of the extractant, the heat level of extraction, and the extraction time significantly moderated lead leaching from microwavable plastic ware (R2 = 0.511, P < 0.001). For all factors, the amount of lead leaching was lower than the permissible level of 1 mg/liter specified by the Minister of Public Health. In conclusion, a combination of high acid, prolonged heating, and extraction time accelerated the amount of lead leaching from microwavable plastic ware, but the incidence of lead leaching was negligible.

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