Concentration and risk assessments of mercury along the elevation gradient in soils of Langtang Himalayas, Nepal

ABSTRACT

The fragile Himalayan region could be regarded as the sink for various pollutants transported from urbanized and polluted areas of South Asia. Therefore, in order to understand the concentrations, spatial distribution, pollution, and risk assessments of toxic heavy metal, mercury (Hg), surface soil samples were taken from the central Himalayas in the Langtang region. The average THg concentration in the Langtang Himalayas was 35.75 ± 24.41(ngg⁻¹), which is comparable to the Tibetan top soil values and slightly lower than world average soil values. In addition, an inverse relationship of THg with elevation were observed (i.e. decrease in concentration with increase in elevation) in the Langtang Himalayan soils. Meanwhile, THg concentrations and TOC% were significantly positively correlated at both the depths (0–10 and 10–20 cm), inferring the sorption capacity of organic carbon for Hg. The results of the geo-accumulation index (I_geo), enrichment factor (EF), and pollution index (PI) indicated limited or no pollution by Hg in the Himalayan soils. Further, surface soils had a low potential ecological risk in the region. Therefore, the Hg value from this study could be used for the further evaluation and calculation of I_geo, EF, and PI for water, soil, and aerosol in the Himalayan region as background reference value. However, Hg pollution from long-range transport and atmospheric deposition (wet/dry) in future could not be ignored in the Himalayan region.

KEYWORDS:

• soil
• mercury
• risk assessments
• background value
• Himalayas

Additional information

Funding

This study was supported by the National Natural Science Foundation of China (41630754, 41671067 and 41721091) and the Key Research Program of Frontier Sciences CAS (QYZDJ-SSW-DQC039). Dr. Lekhendra Tripathee is supported by Chinese Academy of Sciences, President's International Fellowship Initiative (PIFI, Grant No: 2016PE007).