Distribution Trends of Cadmium and Lead in Timberline Coniferous Forests in the Eastern Tibetan Plateau

Ji Luo,Wenbo Shi,Peihao Peng,Qian Xu,Xiyi Lai,Longyu Jia,Danli Yang,Wei Li

doi:10.3390/app11020753

Abstract

The concentrations of Pb and Cd in the needles and twigs of fir and spruce collected from 26 sites in the Eastern Tibetan Plateau were measured and analyzed in this study. The mean concentrations of Cd and Pb were 0.034 and 1.291 mg/kg, respectively, in the needles and 0.101 and 2.511 mg/kg, respectively, in the twigs. These concentrations increased significantly with needle and twig age and peaked at 5 years. The twigs were significantly enriched in Pb and Cd compared with the needles. The spatial distributions of Pb and Cd were determined using the inverse-distance-weighted spatial interpolation method on the basis of the mean concentration of the elements in the needles and twigs from each site. The highest concentrations of Pb and Cd in twigs and needles were found in Yunnan Province and Gongga Mountain. They showed a tendency to decline from Yunnan Province to the northern direction, as well as from Gongga Mountain to the western area. Principal component analysis showed that Pb and Cd originated from the anthropogenic activities in this area. The mining activities and climatic factors may be the main sources of Pb and Cd in this area. Combining the HYSPLIT (The Hybrid Single-Particle Lagrangian Integrated Trajectory) model and PCA, the results implied that exterior Pb and Cd sources from Southeast Asia and the eastern developed cities in China can infiltrate the ecosystem through long-range transportation and accumulate in timberline forests, with atmospheric deposition in the Eastern Tibetan Plateau. This plateau suffers from severe Pb pollution but slight Cd contamination.

Highlights

Pb and Cd are widespread in the earth’s crust
Increased blood lead levels among people have been revealed in other countries [3,4]
Pb concentrations in needles in the present study were much higher than those measured in remote Austrian forests and even exceeded those in areas close to pollutants [15], whereas Cd concentrations were lower than those determined in remote sites in Austria [15] and France [31]. This might imply that the eastern Tibetan Plateau suffers from severe Pb pollution and the content of Cd is normal. This is consistent with the findings reported by Tang et al (2014), who found that Cd concentrations in soil were no more than the national standard while Pb concentrations were higher than the national standard in the eastern Tibetan Plateau

Summary

Introduction

Enormous amounts of Pb and Cd are emitted into the atmosphere with urbanization, rising human population, and excessive industrialization, causing severe environmental pollution [1]. Some studies have reported Pb and Cd contamination among children in China, who presented with hair loss and dysplasia due to high blood Pb levels [2]. Increased blood lead levels among people have been revealed in other countries [3,4]. Forest canopies retain high amounts of Pb and Cd because they consist of a large active surface interacting with these pollutants [7]. Unknown biological roles are displayed in plants, high accumulation of Pb and Cd produces severe toxicity, inhibits the growth of plants, and even causes plant death [8,9]

Methods

Findings

Discussion

Conclusion