Determination of heavy metals in Iranian and imported black tea
Tea (camellia sinesis) is one of the most popular beverages all over the world. It has originated from China long time ago. About 75% of the estimated 2.5 million metric tons of dried tea that are manufactured annually are processed as black tea which are consumed by many countries (Nas et al., 1993). Currently, consumption of tea as a soft drink is very popular in Iran and its production in 2006 was about 78,000 tons. Various reports have discussed the potential health implications of trace metals in tea, particularly since the tea bush is known to accumulate trace metals (Bosque et al., 1990 and Anonymous, 1999), cadmium, lead, nickel, and aluminum (Al), hereinafter referred to as toxic heavy metals and may pose a serious threat to plant, animal, human and environmental health, because they are not degradable by bio-process and remain in environment and passes to food chain. It is globally accepted that some heavy metals such as Fe, zinc, copper, and manganese (Mn); hereinafter referred to as macro-elements; are essential for healthy growth and development within certain permissible limits. Macro-elements are of great biological importance despite their small contribution to the body weight, although excess intake of them can cause chronic toxicity in human. The determination of these elements in beverages, water, food, plant and soil is thus of outermost important tasks. One of the major food sources of these metals is green leafy vegetable (McLaren, 1991). Several attempts have been made to assess tea quality by chemical analysis. However, to date, few works has been performed to determine the metal contents of tea due to the analytical difficulties associated with both the separation of such components and their quantitative measurements. Metallic constituents of tea leaves are normally different according to the type of tea (green or black) and geological source (Marcos et al., 1996).