Determination of Lead in Saudi Arabian Imported Green Tea by ICP-MS

Lead (Pb) in nine different Saudi Arabian imported green tea samples originated from China has been determined using inductively coupled plasma mass spectrometry (ICP-MS). Tea infusion and microwave acid digestion procedures are used for sample pre-treatment. The concentrations range of lead (total) in the analyzed green tea samples is 0.231 – 6.340 mg/kg. The total concentration of lead released 3% – 19% into tea infusions with boiling water. The calculated average daily intakes of lead in tea infusions was low and within the bounds of safety (≤0.009 mg/day).


Introduction
Tea is the most popular beverage in the world. It is made from the processed leaves of Camellia sinensis plants and originates from China. The three most popular types of tea (green, oolong, and black) are distinguished on the basis of degree of fermentation. The leaves of green tea are dried and roasted but not fermented for green tea product 1 . Many studies have concluded that tea has numerous beneficial effects on health including the prevention of many diseases such as certain types of cancer, Parkinson's diseases, myocardial infarction and coronary artery disease 2,3 .
The contaminations of tea by heavy metals may pose a serious threat to human, because they remain in environment and pass to food chain 4 . Lead (Pb) is one of the most common environmental contaminants due to its wide use in petroleum, mining, paint and pigments, ceramics and weapons industries. Its accumulation in the body may cause several pathological states, including brain damage, kidney failure and serious developmental, learning and behavioral problems in children [5][6][7] . Therefore, lead content of tea has become public health issue. The concentration of lead in different tea leaves and tea infusion samples have been studied, but there is still not enough information on its allowable standard limits 4,8,9 . In the present study, lead has been determined in nine imported green tea samples using ICP-MS. Tea infusion and microwave acid digestion procedures were used for sample pretreatment. The data obtained will provide information on lead toxic levels in these samples when compared to U.S. Agency for Toxic Substances and Disease Register (ATSDR) daily average intake of lead by consumption of food, ≤ 0.009 mg/day 10 .

Experimental
PerkinElmer SCIEX Inductively coupled plasma mass spectrometer (ICP-MS), model ELAN 9000, with S10 auto-sampler, DELL pc with perkin elmer software system control, MDS SCIEX Canada, was used for the detection of lead, its operating conditions 11,12 given in Table 1. Multiwave 3000 acid digestion system, Anton paar GmbH, Graz, Austria, Milli-Q academic, RiOs 8, water purification system ( ≥18.2 MΩ), Millipore, France and Beckman Coulter, Allegra X-12 centrifuge, 3500 RPM, USA were used in this study.

Reagents, standards and samples
Nine different imported Chinese green tea samples were collected from Saudi Arabian markets for the analysis. Lead standard solution (1000 µg/mL) supplied by PerkinElmer was used for preparation of standard calibration curve. Rhodium standard solution (1000 µg/mL) supplied by PerkinElmer was used for preparation of internal standard. FAPAS soya flour quality control test material, T0770 and soya flour external proficiency testing samples, T07109, Food & Environment Research Agency (fera), York, U.K, were used for precision and accuracy of the method. Distilled and de-ionized water was obtained using Milli-Q academic (RiOs 8), Millipore, France and nitric acid 69.0-70.0 % for trace element analysis from Baker, Inc., NJ, USA, were used throughout.

Procedures
All standards were made by appropriate dilution of 1000 mg/L stock solution of lead with 1.0 % (v/v) HNO 3 . A series of lead standards in 1.0 % (v/v) HNO 3 was prepared to contain lead at 0, 10, 50 and100 µg/L. All quality control, external proficiency testing, green tea samples were digested into multi-wave digestion system using 25% (v/v) nitric acid. Infusion was prepared from 2.0 g of tea sample in 100 mL boiled distilled and de-ionized water. Matrix matched calibration standards, quality control, external proficiency testing and green tea samples were prepared by adding 200 µL of each into 10 mL diluent (diluent was prepared by adding 10 µL of rhodium as an internal standard into 1L of 1.0 % (v/v) HNO 3 ). Reagent blank was prepared similarly by adding 200 µL of distilled de-ionized water. Blank, standards and samples were mixed, centrifuged and carried out in the ICP-MS auto-sampler for measurements. Data acquisition parameters were, peak hopping using mass 208 amu, 50 ms dwell time, 20 sweeps per reading, 1 reading per replicate and 3 replicates. The total analysis time per solutions was 40 s.

Results and Discussion
The analytical standard calibration curve obtained for lead gave correlation coefficient values better than 0.9999 in all cases. The linearity of the method in an aqueous matrix was obtained The precision of the method was tested using FAPAS soya flour quality control sample, T0770. The Inter-day precision data for lead obtained from twenty determinations are in agreement with ± 17% correlation of variation (CV) value. The mean concentration of lead, standard deviation and satisfactory range are shown in Table 2. For accuracy, one external proficiency testing, FAPAS, soya flour, T07130, was analyzed, and three tea samples were analyzed by both KFSHRC, Saudi Arabia and Food and Environment Research Agency (fera), UK for comparison. The percent difference values range from 0 -13 as shown in Table 3.  The concentration range for lead in the nine different imported Chinese green tea samples is 0.231 -6.340 mg/kg with acid digestion and 0.041 -0.265 mg/kg using the infusion procedure. The total concentration of lead in tea samples released 3% -19% into tea infusions. Concentration of lead in green tea products and their infusions and lead percentage release are shown in Table 4. The calculated average daily intakes of lead from green tea infusions, based on 2 g of tea in 100 mL and three cups/day was low for all cases, ≤ 0.002 mg/day and within the bounds of safety 10 (ATSDR 1999). Average daily intakes of lead from green tea infusions and recommended reference dose are presented in Table 5.

Conclusion
The method is accurate, precise and applied successfully for monitoring lead content in some Saudi Arabian marketed green tea products originated from China. The calculated average daily intakes of lead from green tea infusions was low and within the bounds of safety.