Sulfur and potentially toxic elements in soils and various organs of oak trees (Quercus brantii Lindl.) in Zagros forests: the effect of a gas refinery

Abstract

This study aimed to measure S, As, Cr, Cu, Mn, Ni, Zn, and Pb element contents and contamination indices in various organs of Brant oaks (Quercus brantii Lindl.) and ambient soils at different spatial from the Ilam gas refinery (IGR). Soils, bark, leaf, and acorn sampling were performed in four distances at the east and west IGR directions and an uncontaminated distance as a control. The results showed that the elements in soils and tree organs at distances up to 2500 m from the IGR were significantly (p < 0.05) higher than the control distance. The mean contents of S, Cr, Cu, Ni, and As were more elevated than local and world soil quality standards. The soil samples with pollution load indices (PLI) of 4.65 had significant contamination levels. Soil samples and tree organs exhibited a varying capacity for accumulating elements, with mean contents decreasing from soil > leaf > bark > acorn. Compared to other elements, sulfur was enriched in the bark and tree leaves. The highest bioconcentration factor (BCF) was observed for Pb in the acorn (2.81) and S in the leaves (2.40). The mean metal accumulation index (MAI) decreased as leaf > acorn > bark. The oak trees can be used as potential atmospheric remediation organisms than soil contamination. Leaves are appropriate organs to regulate air pollution in surrounding semi-arid ecosystems of oil and gas refineries because of their enrichment and high accumulation rate of several elements, particularly sulfur.