Selenium enrichment of tea from some areas of China

The levels of selenium (Se) in soils and rocks and Se enrichment of tea as well as factors affecting Se extraction rate from tea were studied. The Se content for 133 tea samples varied from 0.021 to 0.774 mg kg(-1) with a minimum value of 0.017 mg Se kg(-1) while some other teas had a maximum value of 4.32 mg Se kg(-1). The Se content of tea was ina logarithmic normal distribution, and its geometric mean value was 0.120 mg Se kg(-1). The Se content of soil parent materials and rocks were highly correlated with the Se content in tea leaves. Rock stratum rich in Se occurred in Paleozoic siliceaus shales and carbonaceous-siliceaus shales of the Permian, Ordovician, and Cambrian periods. Total Se extraction rate of tea in three extractions was 25.6% (black tea and green tea were 24.9% and 26.2%, respectively), and the extraction rate for the first, second, and third times were 50.9%, 27.3%, and 21.8% of the total Se extracted, respectively.