Probabilistic dermal risk assessment for shallow groundwater users in agricultural settings of Saudi Arabia

Elevated salinity in unconfined aquifers limits residents' use of groundwater for drinking in agricultural settings in KSA. The study developed a probabilistic dermal risk assessment methodology for heavy metals exposure through washing and bathing activities in farms across the Qassim Region, which addressed the uncertainties associated with limited data and vagueness in site-specific exposure factors, such as skin surface area and body weight. Groundwater monitoring established the probabilities of Ba, Cd, Cr, Mn, and Zn levels exceeding the maximum allowable concentrations (MAC) as 0.03 mg/L, 0.003 mg/L, 0.15 mg/L, 0.01 mg/L, and 0.01 mg/L, respectively. A hazard index with a 0.99 probability of less than 1 indicates an insignificant non-cancer risk associated with dermal exposure. The study found an incremental lifetime cancer risk (ILCR) of 6E-5 for Cd and 8E-5 for Cr at median probability, less than the acceptable cancer risk of 1.0E-4. ILCR values of 3.2E-4 for Cd and 2.2E-04 for Cr at 0.9 probability remained lower than the corresponding values of 9E-4 (Cd) and 3.1E-4 (Cr) estimated for the MAC values recommended for KSA. Monte Carlo simulations highlighted Zn (59.5%), Cr (18.1%), and exposure time (10.5%) as the primary contributors to variations in non-cancer health risks to infants. Cd (60.1%) and Cr (46.2%) concentrations, along with exposure time (12.6% for Cd and 25.8% for Cr), were identified as key contributors to ILCR variations. The estimated heavy metal pollution indices at 0.95 probability indicate non-contaminated groundwater. The study offers insights into the health risks and guidelines for treating raw water at the household level, promoting agricultural sustainability in Saudi Arabia and elsewhere.