Potentially Toxic Elements in Agricultural Soils of an Arid Region: Deterministic and Probabilistic Assessment of Direct Non-Dietary Exposure and Ingestion-Based Human Health Risk
Abstract
Direct contact with soil and dust may expose people to potentially toxic elements (PTEs) in cultivated soils. We analyzed As, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn in 35 agricultural soil samples from Al Ghat, central Saudi Arabia, using contamination indices alongside deterministic and probabilistic exposure assessments. The modified contamination degree (mCd) suggested low cumulative contamination overall, while the Nemerow integrated pollution index (NIPI) revealed localized enrichment at several sites. Health-risk assessment focused on soil ingestion; sensitivity analysis examined As bioavailability and Cr speciation. Pb was excluded from RfD-based HQ/HI calculations and evaluated separately using the USEPA residential soil screening level of 200 mg kg−1 as a supplementary screening reference. At As RBA = 0.6 and Cr(VI)/total-Cr = 0.10, mean child HIing and TCRing were 0.470 and 5.90 × 10−5, respectively. No site exceeded HIing = 1, whereas two exceeded TCRing = 1 × 10−4. Under the extreme upper-bound assumptions of As RBA = 1.0 and Cr(VI)/total-Cr = 1.00, the corresponding child means increased to 0.955 and 1.14 × 10−4, with 13 and 17 sites exceeding the respective screening levels. Replacing the three censored As observations with 1 mg kg−1 had little effect and left maxima and exceedance counts unchanged. Parametric As/Cr sensitivity analysis also had limited effects on upper-tail Monte Carlo estimates. Overall, estimated risks depended strongly on As bioavailability and the assumed Cr(VI) fraction, underscoring the need for site-specific speciation and bioavailability data in refined assessments.