Risk Assessment of Potentially Toxic Elements in Agricultural Soils of Al-Ahsa Oasis, Saudi Arabia

Abstract

Contamination of soil with potentially toxic elements (PTEs) is receiving great attention worldwide due to its apparent toxicity and hazards to local residents. The assessments of soil PTE distribution, sources, and environmental risks are, therefore, the first steps of high-efficiency pollutant degradation and sustainable utilization. The current study used a variety of contamination indicators and multivariate methods to evaluate the environmental risk of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in Al-Ahsa soils in eastern Saudi Arabia. For analysis, 30 surface soil samples were collected from palm fields irrigated with groundwater and treated sewage water. Landsat images of Al-Ahsa indicated an increase in the total vegetative area and the residential area, and a decrease in the bare land area from 1985 to 2021. The average concentrations of PTEs (mg/kg−1) were lower than the maximum admissible concentrations and had the following decreasing order: Zn (54.43) > Cr (28.67) > Ni (14.53) > Cu (10.83) > Pb (5.23) > As (2.27) > Hg (0.35) > Cd (0.26). The enrichment factor (EF) findings confirmed that the Al-Ahsa soil is significantly enriched with Hg, moderately to severely enriched with As, and moderately enriched with Cd. The potential ecological risk index (RI) demonstrates a moderate ecological risk, with only certain parts presenting a high risk. The different PTE levels in agricultural soils may be caused partly by the various qualities of groundwater that originate from various aquifers and sewage-treated water. The results of a multivariate analysis showed that most of the anthropogenic sources of Hg, As, and Cd may come from using a lot of fertilizers and insecticides. Levels of the remaining PTEs indicated natural sources from earth crust materials.