Rare earth elements residues in Pu'er tea commercially available in Guangzhou city

Objective To detect rare earth element residues in Pu'er tea commercially available in Guangzhou city and to provide basic data for assessing risk of rare earth element exposure due to Pu'er tea consumption among residents.Methods A total of 418 Pu'er tea samples were collected from super markets,wholesale markets,retail stores,catering units,and online sellers in Guangzhou city from 2013 to 2015.The concentrations of the total rare earth oxides in the samples were determined with inductively coupled plasma-mass spectrometry (ICP-MS) using Agilent 7700 Series according to GB 5009.94-2012.Results There were 169 (40.43%) of the samples being detected with over standard concentration of total rare earth oxides and the average content of total rare earth oxides was 1.95 mg/kg for all the samples,with a median of 1.75 mg/kg,a 95% quantile content of 3.75 mg/kg,and a variation range from 0.33 mg/kg to 6.70 mg/kg.The ratios of the samples with the total rare earth oxides of 2.0-3.0,3.1-4.0,4.1-5.0,and 5.1-10.0 mg/kg were 28.23%,8.38%,1.91%,and 1.91%,respectively.The qualification rates of raw tea and caky tea were higher than those of cooked tea and loose tea and the qualification rate of the tea processed within the 5 years was higher than that of the tea processed 5 or more years ago.Conclusion A higher proportion of Pu'er tea commercially available in Guangzhou city was detected with over standard concentration of total rare earth oxides and the concentration of total rare earth oxides differed by the type,retailer,and the year of processing of the tea.More attentions should be paid to the monitoring on rare earth elements in cooked tea,brick tea,tuocha,and the tea processed 5 or more years ago.