Shapley additive explanations revealed the effects of climate, topography, anthropogenic activities and geochemical properties on soil cobalt, nickel and vanadium contents

Zhiqiang Bai; Fangyi Li; Shirong Zhang; Ting Li; Guiyin Wang; Xiaoxun Xu; Xiaomei Pan; Qinmei Zhong; Wei Zhou; Yulin Pu; Yongxia Jia

doi:10.1016/j.jhazmat.2025.139070

Shapley additive explanations revealed the effects of climate, topography, anthropogenic activities and geochemical properties on soil cobalt, nickel and vanadium contents

J Hazard Mater. 2025 Jun 25:495:139070. doi: 10.1016/j.jhazmat.2025.139070. Online ahead of print.

Authors

Zhiqiang Bai¹, Fangyi Li¹, Shirong Zhang², Ting Li³, Guiyin Wang¹, Xiaoxun Xu¹, Xiaomei Pan⁴, Qinmei Zhong⁵, Wei Zhou³, Yulin Pu³, Yongxia Jia³

Affiliations

¹ College of Environmental Sciences, Sichuan Agricultural University, Wenjiang 611130, PR China; Sichuan Provincial Key Laboratory of Soil Environmental Protection, Wenjiang 611130, PR China.
² College of Environmental Sciences, Sichuan Agricultural University, Wenjiang 611130, PR China; Sichuan Provincial Key Laboratory of Soil Environmental Protection, Wenjiang 611130, PR China. Electronic address: srzhang@sicau.edu.cn.
³ College of Resources, Sichuan Agricultural University, Wenjiang 611130, PR China.
⁴ Chengdu Agricultural College, Wenjiang 611130, PR China.
⁵ College of Chemistry and Environment, Southwest Minzu University, Chengdu 610041, PR China.

PMID: 40578202
DOI: 10.1016/j.jhazmat.2025.139070

Abstract

The quantification of environmental drivers for soil heavy metals is crucial for pollution control, yet their relative importance and critical thresholds remain unquantified at the macroscale. Therefore, Shapley additive explanations based on a random forest model were used to analyze environmental drivers of soil cobalt, nickel and vanadium distributions along a 4000-km transect. These results revealed that climate was the dominant factor, followed by topography, anthropogenic activities, and soil geochemical properties. Specifically, mean annual precipitation predominantly shaped the distributions of total and residual contents of these metals through weathering-leaching equilibrium (threshold approximately 670 mm), while acting synergistically with mean annual temperature (exceeding 5 °C) to promote vanadium transformation from labile to residual states. Altitude enhanced organic bound nickel and vanadium accumulation via hydrothermal and organic matter regulation. Low thresholds for population density (97 people km^-2) and electricity consumption (555017 kWh km^-2) indicated minimal anthropogenic activities could elevate carbonate bound metals through cement-derived carbonate cycling. The attenuated latitudinal trends of heavy metals were primarily attributed to biphasic effects of environmental factors and their interactive compensation. Therefore, climate dominated but synergized with other environmental drivers to collectively shape soil cobalt, nickel and vanadium distribution patterns.

Keywords: Environmental drivers; Generalized additive models; Mean annual precipitation; Random Forest; Soil heavy metal.