Atmospheric deposition of Cd accumulated in the montane soil, Gongga Mt., China

Gongga Mountain, the highest mountain in Sichuan Province and the eastern edge of the Tibetan Plateau, is usually regarded as the "clean" area and free from heavy metal contamination because it is far away from intensive human activities. The purpose of this study is to discover the enrichment characteristics of cadmium (Cd) in soil of Gongga Mt. and probe into its provenance. Thirty-three soil profiles were hand-dug and totally 114 soil samples were collected from different altitude and vegetation zone. Meanwhile seven samples of glacial debris at the foreland of Hailuogou glacier were collected to be used to determine the background of Cd. Cd and other element contents in soil samples were measured using ICP-AES and ICP-MS after acid digested. Enrichment factor (EF) together with the Cd content in precipitation samples were used to determine the source of Cd. Four soil units were divided according to the primary aspect in the field. In the surface A0 soil horizon, the Cd content varied between 0.2 and 7.86 mg/kg while in A soil horizon, it was between 0.11 and 5.61 mg/kg. The background value of Cd in Gongga Mt. was estimated at 0.22 mg/kg according to the Cd content in the deeper layer of soil profiles and glacial debris at the foreland of Hailuogou glacier. The EF of Cd was hence calculated to determine the state of Cd enrichment and its provenance. The Cd content in precipitation, relationship between Cd content and soil grain-size component, relationship between Cd content and soil organic carbon content, together with Cd EF indicated that the atmospheric deposition is the major source of soil Cd. As EF revealed, the Cd contamination in the surface soil of Gongga Mt. area has reached a serious level, especially in the coniferous zone. The atmospheric deposition is the major source of soil Cd.