Heavy metals in the alpine rangelands of Qinghai, China: spatial and vertical distribution, pollution sources, and soil-to-grass transfer

Abstract

Background

The alpine rangelands of Qinghai Province, China, are ecologically fragile and support key livestock production, yet they face widespread heavy metal contamination with unclear spatial patterns, pollution sources, and soil-to-grass transfer risks.

Methods

This study systematically investigated the spatial and vertical distribution, potential sources, and soil-to-grass transfer characteristics of eight heavy metals (Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb) across 27 counties and 82 rangelands in Qinghai, using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for quantification.

Results

The results showed that Cr, Ni, Zn, As, and Cd were the primary pollutants, with 53.09%, 58.02%, 54.32%, 75.31%, and 51.85% of soil samples exceeding China’s Category I soil standards, respectively, particularly in Guoluo, Yush, and Hainan Tibetan Autonomous Prefectures (TAPs). Heavy metal concentrations generally decreased with soil depth, while the 10–20 cm layer acted as a transitional zone with weak stratification. Rainfall deposition was identified as the primary source, while agricultural, industrial, and tourism activities exerted only limited local impacts. Grasses from the corresponding rangelands contained Cr and Hg levels exceeding the mandatory limits of China’s Hygienical Standard for Feeds in 100% and over 50% of samples, respectively. Transfer correlations were positive for Ni, Cu, As, Cd, and Hg (with Ni significantly correlated) and negative for Cr, Zn, and Pb.

Conclusion

This study is valuable for the control of heavy metal pollution and the ecological protection of Qinghai’s alpine rangelands.

Graphical abstract

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