pH-dependent overestimation of heavy metals mobility risk in soils: Implications for soil quality assessment

Yingdong Wu; Zixin Zeng; Rong Teng; Jiang Yu; Guanlin Guo; Pengxinyue Huang; Zhi Huang; Siwei Deng

doi:10.1016/j.jhazmat.2025.140792

pH-dependent overestimation of heavy metals mobility risk in soils: Implications for soil quality assessment

J Hazard Mater. 2025 Dec 11:501:140792. doi: 10.1016/j.jhazmat.2025.140792. Online ahead of print.

Authors

Yingdong Wu¹, Zixin Zeng¹, Rong Teng², Jiang Yu³, Guanlin Guo⁴, Pengxinyue Huang⁵, Zhi Huang⁵, Siwei Deng⁵

Affiliations

¹ Department of Environmental Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, PR China; Yibin Institute of Industrial Technology, Sichuan University, Yibin 644000, PR China.
² School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Parkville, Victoria 3010, Australia.
³ Department of Environmental Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, PR China; Yibin Institute of Industrial Technology, Sichuan University, Yibin 644000, PR China; Rural Revitalization Research Center, Sichuan University, Chengdu 610065, PR China. Electronic address: yuj@scu.edu.cn.
⁴ Technical centre for soil, Agriculture and Rural Ecology and Environment, Ministry of Ecology and Environment, Beijing 100012, PR China.
⁵ Department of Environmental Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, PR China.

PMID: 41386136
DOI: 10.1016/j.jhazmat.2025.140792

Abstract

Risk Assessment Code (RAC), which treats the percentage of the Bureau Communautaire de Référence (BCR) acid-extractable fraction (P_F1) as a proxy for heavy metal (HMs) mobility, is widely used to evaluate soil HMs mobility risk. Yet it may lead to pH-dependent bias if P_F1 increases or remains constant with rising pH. However, the P_F1-pH relationship remains unclear. This study synthesizes 5151 observations from 162 studies and use nonparametric statistics, random forests, and SHapley Additive exPlanations to quantify P_F1-pH relationships for eight HMs, and assess modulation by environmental properties. Results show P_F1 increases with pH for Cr, Fe, Mn, and Pb (p<0.05); peaks near neutral pH (6.5-7.0) for Zn; shows a V-shaped trend with an inflection around neutral pH ≈ 7.0 for Cu; exhibits weak dependence for Cd and Ni. Mean annual temperature, mean annual precipitation, clay, and organic carbon modulate P_F1-pH patterns for Cu, Cd, Fe, Pb and Ni, respectively. These findings indicate RAC systematically overestimates risk under alkaline conditions, as HMs mobility declines with pH whereas P_F1 for Cr, Fe, Mn, and Pb rises. Based on these findings, we propose a conceptual fraction-environment coupling framework integrating subfraction weighting and environmental-factor correction to recalibrate RAC for more accurate soil quality assessment.

Keywords: BCR acid-extractable fraction; Mobility risk assessment; Soil heavy metals; Soil pH.