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Purpose <p>Conventional urbanization-gradient assessments often assume a monotonic “distance-decay” pattern of soil pollution from urban centers to rural areas. This assumption can be misleading in topographically complex inland basins, where intensive agricultural sinks coexist with strong geogenic baselines. This study quantifies how distinct sources translate into source-specific probabilistic health risks (total hazard quotient, THQ, and total carcinogenic risk, TCR) of potentially toxic elements (PTEs) along an urbanization gradient.</p> Materials and methods <p>Farmland soils from the Sichuan Basin (China) were used as a representative inland-basin system. PCA-assisted positive matrix factorization (PCA–PMF) was applied for source apportionment. Monte Carlo simulation was coupled with exposure–risk assessment to propagate uncertainty and quantify source-specific probabilistic THQ and TCR. Sensitivity analysis (Spearman’s ρ) was used to identify dominant drivers of TCR variability.</p> Results and discussion <p>A non-monotonic spatial pattern was observed, with higher accumulation in rural areas (Cd: 0.44&#xa0;mg/kg; Zn: 104.45&#xa0;mg/kg) than in urban counterparts (Cd: 0.27&#xa0;mg/kg; Zn: 86.05&#xa0;mg/kg), indicating that intensive agricultural zones serve as primary regional sinks. PMF resolved a four-factor structure in which broad-spectrum mixed sources and natural background accounted for a homogenized TCR baseline (&gt; 70%). Agricultural inputs dominated the spatial differentiation of As (~ 40%) and Cd (~ 30%), whereas industrial point sources contributed mainly to localized Pb and Cd enrichment. Despite the higher mass loadings of As and Cd, a clear mismatch between mass loading and toxic contribution was evident. Geogenic Ni primarily drove the homogenization of carcinogenic risk, yielding a mean child TCR of 1.80 × 10⁻<sup>4</sup> and masking urban–rural risk contrasts. Sensitivity analysis further showed that TCR variability was dominated by Ni (ρ = 0.93) and Cr (ρ = 0.92).</p> Conclusions <p>Superimposed on the high TCR baseline, agricultural inputs acted as a critical incremental driver, shifting the risk cumulative distribution function (CDF) to the right and increasing the probability of extreme risks. These findings highlight the nonlinear source–risk evolution in inland agricultural landscapes and support baseline-aware risk stratification and source-targeted mitigation where strong geogenic baselines may obscure management-relevant gradients.</p> Graphical Abstract <p></p>

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Source-specific probabilistic health risk of potentially toxic elements in farmland soils across an inland-basin urbanization gradient: Sichuan Basin, China

  • 期刊论文

  • 发表日期：

    2026年5月4日

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  • Yizhou Peng,
  • Grigorieva Iya Yu

摘要

Purpose

Conventional urbanization-gradient assessments often assume a monotonic “distance-decay” pattern of soil pollution from urban centers to rural areas. This assumption can be misleading in topographically complex inland basins, where intensive agricultural sinks coexist with strong geogenic baselines. This study quantifies how distinct sources translate into source-specific probabilistic health risks (total hazard quotient, THQ, and total carcinogenic risk, TCR) of potentially toxic elements (PTEs) along an urbanization gradient.

Materials and methods

Farmland soils from the Sichuan Basin (China) were used as a representative inland-basin system. PCA-assisted positive matrix factorization (PCA–PMF) was applied for source apportionment. Monte Carlo simulation was coupled with exposure–risk assessment to propagate uncertainty and quantify source-specific probabilistic THQ and TCR. Sensitivity analysis (Spearman’s ρ) was used to identify dominant drivers of TCR variability.

Results and discussion

A non-monotonic spatial pattern was observed, with higher accumulation in rural areas (Cd: 0.44 mg/kg; Zn: 104.45 mg/kg) than in urban counterparts (Cd: 0.27 mg/kg; Zn: 86.05 mg/kg), indicating that intensive agricultural zones serve as primary regional sinks. PMF resolved a four-factor structure in which broad-spectrum mixed sources and natural background accounted for a homogenized TCR baseline (> 70%). Agricultural inputs dominated the spatial differentiation of As (~ 40%) and Cd (~ 30%), whereas industrial point sources contributed mainly to localized Pb and Cd enrichment. Despite the higher mass loadings of As and Cd, a clear mismatch between mass loading and toxic contribution was evident. Geogenic Ni primarily drove the homogenization of carcinogenic risk, yielding a mean child TCR of 1.80 × 10⁻4 and masking urban–rural risk contrasts. Sensitivity analysis further showed that TCR variability was dominated by Ni (ρ = 0.93) and Cr (ρ = 0.92).

Conclusions

Superimposed on the high TCR baseline, agricultural inputs acted as a critical incremental driver, shifting the risk cumulative distribution function (CDF) to the right and increasing the probability of extreme risks. These findings highlight the nonlinear source–risk evolution in inland agricultural landscapes and support baseline-aware risk stratification and source-targeted mitigation where strong geogenic baselines may obscure management-relevant gradients.

Graphical Abstract