Unexpected Heavy Metal Pollution in Wetland Soils Along the Yarlung Tsangbo River in Tibet, China: Assessment and Source Apportionment

The Qinghai-Tibetan Plateau (QTP), as the third pole, has recently experienced unexpected heavy metal pollution. However, few were available on heavy metal pollution and source apportionment in regions near South Asia, where the economy is currently experiencing rapid development. This paper evaluated heavy metal pollution in wetland soils along the Yarlung Tsangbo River (YTR), the largest river in the QTP. Results indicated minor contamination levels of Cu, Pb, Zn, Hg, As, Mn, and Cr. However, Cd pollution was serious and was the main pollutant. Nemero synthesis index values (PN) were relatively high and ranged from 4.54 to 10.47 caused by high loading from Cd and Zn. Roughly 92% Pb, 89% Cr, and 89% Mn were from natural sources while 86% Cd and 61% Zn were from anthropogenic sources in wetland soils along the YTR. Differences in heavy metal contents and sedimentation rates were accentuated by the metal accumulation rates of each site. Cd, Zn, and Hg accumulation rates were estimated to 0.966 mg m(-2) year(-1), 0.187 g m(-2) year(-1), and 0.061 mg m(-2) year(-1)in the 1800s and increased to 5.351 mg m(-2) year(-1), 1.144 g m(-2) year(-1), and 0.263 mg m(-2) year(-1)in the 2000s, respectively. This implied unexpected heavy metal pollution in wetland soils along the YTR basin and more attention should be paid to avoid the risk of heavy metal pollution here.