Jin Chong Wei, Zheng Shao Jian, He Yun Feng, Zhou Gen Di, Zhou Zhong Xian
MOE Key Lab of Environment Remediation and Ecosystem Health, College of Environmental and Resources Science, Zhejiang University, Hangzhou 310029, People's Republic of China.
Chemosphere. 2005 May;59(8):1151-9. doi: 10.1016/j.chemosphere.2004.11.058. Epub 2005 Jan 1.
The consumption of heavy metals is detrimental to human health and most countries restrict the concentration of metals such as lead (Pb) in food and beverages. Recent tests have detected high Pb concentrations in certain commercial brands of tea leaves and this finding has raised concerns for both producers and consumers. To investigate what factors may be contributing to the increase in Pb accumulation in the tea leaves we collected tea leaves and soils from tea producing areas and analyzed them for Pb concentration, pH and organic matter content. The result showed the Pb concentration of 47% investigated tea leaves samples was beyond 2 mg kg(-1), the permissible levels given by China. The total Pb concentration in the surface and subsurface soil layers averaged 36.4 and 32.2 mg kg(-1), respectively which fall below of the 60 mg kg(-1) limit provided for organic tea gardens in China. The pH of the tea garden soils was severely acidic with the lowest pH of 3.37. Soils under older tea gardens tended to have a lower pH and a higher Pb bioavailability which was defined as the amount of lead extracted by CaCl2 solution than those under younger tea gardens. We found that the concentration of bioavailable Pb and the percentage of bioavailable Pb (bioavailable Pb relative to total Pb concentration) were positively correlated with soil H+ activity and soil organic matter content, and the organic matter accumulation contribute more effects on Pb bioavailability in these two factors. We conclude that soil acidification and organic matter accumulation could contribute to increasing Pb bioavailability in soil and that these could increase Pb uptake and accumulation in the tea leaves.
重金属的摄入对人体健康有害，大多数国家都对食品和饮料中的铅（Pb）等金属浓度进行限制。最近的检测在某些商业品牌的茶叶中发现了高铅浓度，这一发现引起了生产者和消费者的担忧。为了调查哪些因素可能导致茶叶中铅积累的增加，我们从茶叶产区采集了茶叶和土壤，并分析了它们的铅浓度、pH值和有机质含量。结果显示，47%的被调查茶叶样品的铅浓度超过了中国规定的2毫克/千克的允许水平。表层和亚表层土壤层中的总铅浓度平均分别为36.4毫克/千克和32.2毫克/千克，低于中国有机茶园规定的60毫克/千克的限值。茶园土壤的pH值呈强酸性，最低pH值为3.37。老茶园的土壤往往pH值较低，铅的生物有效性较高，生物有效性定义为氯化钙溶液提取的铅量，比年轻茶园的土壤高。我们发现，生物可利用铅的浓度和生物可利用铅的百分比（生物可利用铅相对于总铅浓度）与土壤H+活性和土壤有机质含量呈正相关，在这两个因素中，有机质积累对铅生物有效性的影响更大。我们得出结论，土壤酸化和有机质积累可能导致土壤中铅的生物有效性增加，进而增加茶叶对铅的吸收和积累。
