Studies of Leaching of Metals from Food Ceramics

In this study the leaching potential of food ceramic wares available in New Zealand has been done using ICP-MS analysis. A survey of ceramic wares purchased in New Zealand markets ranging from historical (antique) Victorian eras (Wilemen bone china and Chapman), mid - 20th century (Alfred Meakin), 1960-1980’s New Zealand-made (Crown Lynn) and modern day ceramic wares manufactured in China, India and Thailand was carried out with respect to their elemental compositions, ceramic composition and leaching potential. All these ceramic wares were found to contain various amounts of heavy metals in their glazes used for imparting special colours, texture and smooth finishes. Structural characterisation of these ceramic wares was carried out using different techniques such as solid state magic angle spinning NMR, Fourier transform infrared (FTIR), scanning electron microscopy (SEM) coupled to energy dispersive X-ray analysis (EDX), and X-ray fluorescence (XRF) to determine which elements were present in the bulk of ceramics clay sourced-body and in the glazes. The results of the XRF analysis informed the inductively coupled plasma mass spectroscopy (ICP-MS) studies by providing a list of elements to follow. In general XRF identified a number of heavy metals of interest in all the ceramic wares such as lead and cadmium in Victorian era Wileman and Chapman, mid-20th century Alfred Meakin and especially in the Crown Lynn wares. Barium was predominantly the heavy metal of interest in all modern ceramic wares that are predominantly used by many people in New Zealand. Cobalt, chromium, tin and zinc were present in all the ceramic wares. However, cadmium was significantly present in the red coloured modern ceramic wares. These ceramic wares were subjected to leaching tests to detect whether various elements of relevance such as lead, cadmium, barium, cobalt and chromium migrated to any great extent into liquids exposed to these ceramic wares. Leaching studies were done following the ASTM 738 -94 standard test methods for specific metals leaching into 4% acetic acid solutions after a 24 hour exposure time. The lead leached from Victorian era Wileman bone chinaware studied with 4% acetic acid leaching solution was found to exceed the standard safe limits of lead as given by the FDA (3 µg/mL) and European Council Directive 84/500/EC (4mg/L). The Victorian era Chapman and the New Zealand made Crown Lynn ceramic wares leached lead with 4% acetic acid leaching solution but was below the standard safe limit. However, the modern day ceramic wares manufactured in China, India and Thailand analysed in this research were found to leach extremely low levels of barium being well below the oral reference dose (RFD) for barium given by the US Environmental protection agency (EPA) as 0.07 mg/kg/day, i.e. 4 mg/person/day. Ceramic teacups were exposed to other leachate solutions based on the normal domestic use and all the leachate solutions were analysed with ICP-MS. These leachate solutions which were exposed to the ceramic teacups for a ten minutes leaching test included: orange juice at room temperature, hot tea at 80 - 95 oC, hot water at 80 - 95 o C, cold water at 4 oC and Coca Cola at room temperature in which some of the Crown Lynn teacups studied were found to be continuously leaching lead in all the tested solutions at varying conditions i.e. pH of the leaching solutions, its temperature and duration of exposure to the leaching solution have influence in migrating the metals from these ceramic teacups tested. However, the level of lead leached from these ceramic teacups was well below the standard safe limits of lead leached from ceramic wares

A cursory study of the bulk and glaze composition plus metal leaching properties of a selection of antique, vintage and present day food and drink ceramic wares using XRF, FTIR, ²⁷Al, ²⁹Si, ³¹P MAS NMR and ICP-MS for providing a characterisation of the types of domestic ceramic ware used in New Zealand currently

The ceramic utensils used for eating and drinking such as plates, cups, bowls and other items have been a fundamental part of many societies since ancient times. The word “ceramics” is itself derived from the Greek word κεραμικός (“Keramikos”)¹ meaning “of or for pottery”. The art of making ceramics dates back thousands of years with evidence of pottery from 20,000 years ago² being reported recently from Xianrendong Cave in China. Ceramics manufacture depends on a source of various materials, namely clay, e.g. kaolinite, silica and feldspar.³ When these clay and mineral materials are mixed and soaked in water with removal of the excess water, a wet clay is produced which can then be fashioned into the desired shapes using moulds. Water is then removed via drying and the articles fired at temperatures up to 1170 °C during which complex chemical transformations occur in the clay with physical changes in the added silica and feldspar. Kaolinite (Al₂Si₂O₅(OH)₄ ) is converted via a series of precursor compounds to mullite (Al₆Si₂O₁₃) and cristobalite (SiO₂). The feldspar acts as a flux with the alkali metal ion content (Na₂O, K₂O and CaO) causing a lowering of the melting point of the silica early on in the firing process. This melt effectively forms a glass which then draws the individual particles of the fired mixture together and additionally reacts with them so giving the ceramic body strength (when it cools) and reducing porosity