Concentrations and Diffusion Characteristics of Heavy Metals in Green Tea Samples from Urban Markets in Guizhou Province
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Abstract:
In order to investigate the distribution characteristics of heavy metals in tea, the green tea samples of five production and processing areas commercially available from urban markets in Guizhou Province were collected for monitoring the contents of heavy metals such as Pb, Cr, Cd, Hg, Cu, Zn, Mn, Ni and As. The effects of brewing temperature, brewing time and brewing times on heavy metal leaching rate of tea were investigated. The results were as follows: the content of Cr, Mn, Ni, Cu, Zn, As, Cd, Hg and Pb were 3.98~4.63, 320.04~526.74, 17.43~25.74, 15.00~23.15, 27.68~42.23, 1.12~1.34, 0.72~1.06, 0.11~0.13 and 1.20~1.45 mg/kg, respectively. The contents of Cr, Cd, Pb, Hg and As in green teas of five areas were all lower than national standard. The diffusion rate of heavy metals in green tea was positively correlated with the brewing time and brewing temperature (p<0.05), and negatively correlated with the brewing times (p>0.05). Zn and Mn were shown to have the highest diffusion rate in tea infusion after three times of brewing, which were 78.73%~87.04% and 74.87%~81.27%, respectively; followed by Hg (32.25%~45.84%); and Ni was the lowest (7.78%~11.58%). The diffusion rate in tea infusion was ordered as: Zn>Mn>Hg>As>Cd>Pb>Cr>Cu>Ni. When the brewing temperature was 80 ℃ and the brewing time was 40 min, the diffusion rate of heavy metals in green tea was the largest. After 80 ℃ and 40 min, the diffusion rate of heavy metals increased gradually.
