Study On Pb Concentration Of Tea Leaves And Its Sources At Different Tea Gardens In West Lake District

As we all know, lead (Pb) is very dangerous to human health. Westlake Longjing tea from the West Lake District of Hangzhou, China, is one of the highest quality green teas, and is often called the national drink of China. However, the ever-increasing accumulation of lead (Pb) in Westlake Longjing tea has been continually reported in the recent decades, while the exact Pb sources still remain unclear. Our purpose is to investigate the key factors that account for the concentration increase of Pb accumulated in Longjing tea based on a broad regional scale.Eighty-one tea leaves, and the corresponding soil and air samples where the tea plants grow in and around respectively, were collected from three typical Longjing tea gardens for illustrating the sources of Pb that accumulated in Longjing tea. The sampling lines were arranged with the proximity to the traffic area. Pb concentrations in the tea leaves, soil and air samples were determined respectively. The results showed that the Pb concentration in the young tea leaves, ranged from 0.5 to 2.74 mg kg^-1 with an average of 1.18 mg/kg. 8.75% of the samples exceeded 2 mg kg^-1 (The former maximum permissible concentration for Pb in China). The regional differences and seasonal variation of Pb concentration were found for young tea leaves, with the order of Longwu > Meijiawu > Longjing and spring > summer (p <0.05) respectively.Simple statistical analysis and spatial geostatistics was further applied for the investigation of the potential relationship of Pb levels among tea leaves, and the relevant soil and air samples. The significant positive correlation was found only for the Pb concentration between tea leaves and air samples (r = 0.34, p <0.01). A similar geographic distribution tendency of Pb between young tea leaves and air was also revealed by further geographic spatial analysis taking Longwu as a case. The concentration of soil available Pb has a very significant positive correlation with the concentration of soil organic matter, The significant negative correlation between the Pb concentration of old tea leaves and soil organic matter. It showed that the Pb of young tea leaves came mainly from the transfer of Pb in the air and in old tea leaves. The accumulation of new leaves Pb concentration at roadside tea garden come mainly air source.Washing procedures were also conducted to trace the removable possibility and rates of Pb in tea leaves. The results from washing experiment showed that a substantial portion of Pb in tea leaves could be removed by washing, and the removable rates of Pb existed an obvious decrease with the increasing distance from the traffic area. An average reduction of Pb concentration in tea was 24.83%, ranging from14.91 % to35.79%.Greenhouse cultivation was also conducted at the Tea Research Institute, Chinese Academy of Agricultural Sciences. Results showed that the Pb concentration of tea leaves and Pb concentration in the air all decreased with the increasing distance from Meiling South Road. The pot tests of external sources of lead absorption of tea seedling showed that the lead content in different parts of all the tea seedling was: root >stem>leaves, in the treatment groups of different lead concentrations. Regardless of roots, stems or leaves, the lead content presented: 450 treatment group>250treatment group>125 treatment group> CK treatment group. Under the low pH condition, the higher Pb concentration, the more Pb was absorbed by the tea roots.