Assessment of Pollution Severity and Ecological Risks of Potentially Toxic Elements in Marine Sediments of the Northeastern Persian Gulf

The Persian Gulf is an incredibly important and sensitive ecosystem that has garnered increased attention in the 21st century due to ongoing changes in international relations. There is an evident need for marine geological studies in this area, given the development plans, limited understanding of the seabed's geological condition, abundant oil resources, environmental concerns, and pollution of potentially toxic elements along the Persian Gulf's shores. The Persian Gulf holds a significant global importance as a water body with a delicate ecological balance. Given the sensitivity of the Persian Gulf and the detrimental impacts it endures from diverse polluting industries, environmental monitoring of this region is essential. This study presents a comprehensive analysis of geochemical changes, origin, and environmental and ecological risk assessment of potentially toxic elements in 140 sediment samples collected from the Iranian waters of the northeastern Persian Gulf.

We examined 140 surface sediment samples collected from varying depths of the waters under Iran's jurisdiction in the northeastern Persian Gulf during the MG-PG-2008 cruise. Our goal was to assess the level of contamination and ecological risk posed by elements such as As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, V, and Zn. The concentrations of these elements in the sediment samples were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to provide a comprehensive understanding of their presence. Additionally, we quantified the pollution intensity in the sediments using indicators such as the geo-accumulation index (Igeo), enrichment factor (EF), and modified degree of contamination (mCd). Furthermore, we evaluated the ecological risk of potentially toxic elements in the sediment samples based on the potential ecological risk index (RI) and determined the toxicity risk of trace elements using the toxic risk index (TRI).

The sediment samples indicate significant enrichment of elements such as As, Cd, and Mo. Elements like Fe, Pb, Ni, Cr, and Mn fall into the medium enrichment category, while Cu, Zn, Ba, V, and Co are classified as having low enrichment. Comparatively, Fe, Ba, V, Zn, Pb, and Cu in the sediment samples show lower concentrations than their corresponding values in the upper continental crust. The enrichment factor (EF) values for these elements are less than 1.5, suggesting a terrestrial source for these elements. Additionally, the modified degree of pollution (mCd) values indicate very low levels of pollution at almost all stations.The ecological risk evaluation of potentially toxic elements in the surface sediments of the northeastern Persian Gulf reveals that Cd poses a medium ecological risk, while other elements exhibit a low ecological risk. The overall average ecological risk potential index (RI) at all sampling stations indicates a low level of ecological risk. Cd has the greatest influence on the ecological risk potential index, accounting for 61% of the total index, followed by As with 27%. The average toxicity risk index (TRI) suggests no toxicity risk, with Nickel being the most influential, contributing 52%, while Chromium has a 19% share.Notably, the significant enrichment of As and Cd in the northeastern Persian Gulf suggests their predominantly anthropogenic origin. This high concentration of arsenic may stem from the release of wastewater from urban and agricultural sources, various industries, gas and oil fields, and dust particles. Likewise, the presence of cadmium can be attributed to sources like oil tankers' transportation and industrial wastewater from factories.The significant correlation between aluminum, nickel, chromium, and vanadium (Al, Ni, Cr, V) indicates their terrestrial origin, mainly attributed to riverside erosion, weathering, and atmospheric precipitation. While the average enrichment of chromium and nickel can be linked to their high natural concentrations in the soil of southern Iran, industrial processes, including oil refining, can also contribute to their sediment concentrations.

The ecological risk assessment indicates medium-level risk for cadmium and low-level risk for other elements. The overall average potential ecological risk index (RI) suggests a low level of ecological risk across all sampling stations. The average toxicity risk index (TRI) indicates no toxicity risk, with nickel contributing the largest share (52%) followed by chromium (19%). Chromium and nickel concentrations in sediments are primarily of geogenic origin, evidenced by their strong correlation with aluminum. The average enrichment of these elements is attributed to their high natural concentration in the soil of southern Iran, although some man-made sources also contribute. The significant enrichment of As and Cd in sediments suggests their predominant human origin, possibly from wastewater discharge, industrial activities, and oil and gas fields. Cadmium in the Persian Gulf may originate from anthropogenic sources such as oil tanker transportation and industrial wastewater discharge.