Chemical Speciation and Characterization of Trace Metals in Dry Camellia sinensis and Herbal Tea Marketed in Nigeria

Abstract

Background. Trace metals from anthropogenic activities have been found to occur in tea brands and pose potential human health risks to consumers. Objectives. The present study assessed the concentrations of trace metals in green, black and herbal tea brands using a modified Community Bureau of Reference sequential extraction method. Methods. Fifteen (15) Camellia sinensis and eight (8) herbal tea samples commonly consumed in Nigeria were collected and analyzed for trace metals. The concentrations of cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) in extract fractions were analyzed using microwave plasma atomic emission spectroscopy (MP-AES). Results. Trace metals were detected in all of the samples investigated. The concentrations of trace metals in 4 stages (soluble/exchangeable/carbonates bound fraction, reducible fraction, oxidizable fraction, residual fraction) of sequential and pseudo-total metal extraction procedures are presented. The concentrations of Cd, Cr, Cu, Mn, Ni, Pb, V, and Zn in the exchangeable/carbonate bound fraction for green tea ranged between 0.27–1.47, ND-0.33, ND-0.44, 7.05–33.04, 0.23–0.69, ND-0.51, ND-0.16 and 0.18–1.99 mg/kg, ND-0.73, 0.15–0.36, 0.36–0.59, 1.38–30.07, 0.15–0.54, 0.05–0.76, 0.15–0.34 and 0.27–0.77 mg/kg and 0.54–0.64, 0.25–0.41, 0.35–0.47, 18.72–23.98, 0.30–0.55, 0.15–0.21, 0.15–0.23 and 0.30–0.48 mg/kg for hebal tea, respectively. Conclusion. The metal content in the investigated tea indicated low to enhanced concentrations. Locally produced black teas recorded relatively low trace metal contents compared to the green and herbal tea samples. The most bioavailable trace metal was Mn, while Zn was most preferably bound to the residual fraction. Cadmium, Cr, Cu, Ni, Pb, and V were distributed at varied concentrations among other extractable phases. Daily consumption of the investigated tea products may expose consumers to potentially toxic metals as well as essential elements. Competing interests. The authors declare no competing financial interests.