Abstract
The Gemlik Gulf, located in the eastern part of the Sea of Marmara (Türkiye), is recognized as a relatively contaminated marine environment, influenced by a variety of natural and anthropogenic inputs. A comprehensive geochemical study was performed to examine the distribution of total mercury (THg) in surface sediments and to elucidate the possible sources contributing to its accumulation. The analysis revealed that THg concentrations ranged from 485 to 6486 ng/g, with all measured values substantially exceeding the average shale background concentration of 400 ng/g, indicating significant enrichment. According to sediment quality guidelines, none of the samples exceeded the effects range median values. The noncarcinogenic health risk posed by mercury was evaluated through hazard quotient (HQ) analysis of sediment. Ingestion-related exposure was higher than inhalation and dermal contact exposure. For both children and adults, total HQ values remained below 1, showing no considerable risk to noncarcinogenic health. The highest levels of contamination exceeding 3000 ng/g were predominantly found in specific regions of the gulf, including the mouth of Karsak Creek, the central sector of the gulf situated between the Kapaklı and Mudanya coastlines, and the northwestern and southwestern corners of the basin. The spatial distribution of THg suggests a combination of factors influencing mercury input, with the most prominent being fluvial discharges from creeks, particularly Karsak Creek, and industrial effluents from nearby urban and manufacturing zones. The distribution of concentrations higher than ~4000 ng/g THg along active faults suggests potential contributions from cold seep and possible hydrothermal activities.