Ecological restoration mitigates heavy metal pollution in rubber monocultures: Quantifying risk reduction and anthropogenic source control

Chen, Zi-Yan

JOURNAL OF HAZARDOUS MATERIALS ADVANCES

2026

22

Shi, XM; Song, L

The expansion of rubber (Hevea brasiliensis) monocultures has fundamentally reconfigured tropical landscapes, yet the efficacy of ecological restoration in mitigating associated soil heavy metals (HMs) pollution remains insufficiently quantified. Employing a space-for-time substitution approach, this study evaluated the pollution characteristics, ecological risks, and sources of eight HMs across four forest types in Southwest China, which form two parallel restoration chronosequences from rubber monocultures (RM) towards mature rainforests (MF): a natural succession (RM-naturally restored forests, NF-MF) and an artificial restoration (RM-artificially restored forests, AF-MF). Empirical analyses revealed pronounced enrichment of Mercury (Hg) and Cadmium (Cd) within RM soils, driven primarily by legacy agrochemical inputs. Ecological restoration precipitated a substantial mitigation of potential ecological risks: relative to RM, the Nemerow Integrated Risk Index (NIRI) declined by 94.8 % in AF and 78.7 % in NF, with AF attaining risk baselines analogous to the climax rainforest reference. Source apportionment via Positive Matrix Factorization (PMF) identified anthropogenic activities-specifically agricultural practices (31.5 %) and traffic emissions (26.7 %)-as the predominant drivers of topsoil HMs accumulation, overriding natural pedogenic contributions. Furthermore, Partial Least Squares Structural Equation Modeling (PLS-SEM) elucidated a dual-pathway mechanism for this risk mitigation, demonstrating that restoration relies primarily on cutting off exogenous anthropogenic inputs, while secondarily enhancing the buffering capacity of the soil microenvironment. Consequently, a spatially differentiated Restoration-Source Control framework integrating active restoration within plantation interiors with the establishment of vegetative bio-barriers along transport corridors is proposed. These findings provide quantitative evidence that ecological restoration, when coupled with targeted source abatement, is a robust remediation strategy for HMs contamination in tropical agro-ecosystems.