Human and environmental controls on soil contamination in a dust-prone region revealed by random forest and Shapley additive explanations analysis

Accurate prediction of the spatial distribution of potentially toxic elements (PTEs) and identification of the most important environmental drivers are essential for reducing their adverse effects on human health and the environment. In this regard, the present study was conducted to predict the spatial distribution of arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), and lead (Pb) in a dust-prone area of central Iran using the RF model under 11 scenarios constructed based on human activity-based factors (HAF), land-based factors (LSF), physicochemical soil properties) PSP), meteorological factors (MF), and remote sensing auxiliary data (RSAD). The overall contribution of the influencing factors in predicting soil PTEs was determined using the SHapley additive exPlanations (SHAP) analysis. Soil PTEs and some other properties of 107 surface soil samples were measured in the laboratory. The best performance of RF in predicting As, Co, and Cr was observed under scenario VI (HAF + PSP) with the R² value of 0.59, 0.60, and 0.58, respectively. The RF under Scenario X (PSP + LSF+HAF+RSAD) showed the best performance in predicting Cd (R² = 0.67). The performance of RF for predicting Pb was weak in all scenarios (R² < 0.38). The contributions of HAF, LSF, PSP, and RSAD in predicting Cd were 54.9, 21.5, 18.3, and 5.2%, respectively. On average, the contributions of HAF and PSP to the prediction of the other three PTEs were 55.6 and 44.4%, respectively. Among these categories, distance to industries, calcium, magnesium, magnetic susceptibility, terrain ruggedness index, and distance to rivers were identified as the most important predictors. Our findings are useful for improving soil management to reduce the adverse effects of PTEs in arid environments.