Ecological risk assessment of heavy metals in the marine sediments associated with the petroleum hydrocarbon industry in the central Arabian Gulf

Heavy metal contamination of marine sediments poses a critical environmental threat in the Arabian Gulf, with documented impacts linked to regional activities of petroleum industry. Despite this, there is still very limited information and a big gap in the literature on contamination status of surface sediments. Therefore, this study aimed to address this concern by examining the spatial distribution and levels of heavy metals and metalloids within the sediments of the Qatar's Exclusive Economic Zone, focusing on the potential ecological risks and toxicological impacts, associated with the petroleum hydrocarbon industry. Sediment samples were collected from the central Arabian Gulf, representing distinctive water depths at 12 stations, spanning depths of 11 to 72 m. The multipurpose Qatar University research vessel (R/V Janan) was utilized for sampling. Samples were analyzed for metal concentrations, grain size, and total organic carbon content. The mean concentrations (mg kg⁻¹) were found in the following order: Ca (292,281) > Al (6530) > Fe (4623) > Sr (2433) > Mn (83.3) > Ni (15.5) > Cr (22) > Zn (13.1) > V (8.7) > Cu (5.7) > As (4.02) > Co (2.17) > Pb (1.43) > Cd (0.04) > Hg (0.02), with Sb levels below detectable limits of the instrument (0.0013 mg kg^-1). The results indicated that the four major metals (Al, Fe, Sr, and Mn) exhibited higher mean concentrations than the other elements. Ni, V, Pb, Cd, Hg and Sb had the lowest concentration. Ecological risk assessments revealed that, except for As, most metals presented limited pollution risk. This elevated Arsenic concentration was observed at deep-water stations and harbor areas along the southern transect. The relationships between elemental concentrations, sediment characteristics, and their Total organic carbon (TOC) contents are both evident and well-defined. Grain size fractions of sediments and TOC content contributed to low metal concentrations together with the mechanism of prevailing hydrodynamic conditions. The strong statistical correlation between the natural background elements Al, Fe, and other heavy metals indicated natural origin. The study's multiple-element risk index highlighted that anthropogenic activities associated with oil operations, and petroleum hydrocarbon extraction facilities have a minimal impact on marine sediment heavy metal concentrations. Overall, the results suggest a low-to-slight toxic pollution status in the study area. This study provides critical information for policymakers supporting efforts for sustainable marine management strategies in the Arabian Gulf's vulnerable ecosystems.