Evaluating arsenic and heavy metal contamination in estuarine sediments of the Southern Caspian Sea, Iran

Abstract

Coastal and estuarine ecosystems face increasing threats from heavy metal pollution originating from industrial and agricultural activities, presenting significant environmental and public health risks. This study investigates arsenic and heavy metal contamination within surface sediments of eight major rivers discharging into the southern Caspian Sea: Gorganrud, Qarasu, Tajan, Babolrud, Sardabrud, Safarud, Cheshmeh Kileh, and Sefidrud. Twenty-four surface sediment samples, collected from upstream, river mouth, and near-shore zones, were analysed to assess spatial variations. A sediment core from Gorgan Bay, providing a ~1400-year depositional record, was also examined to understand historical trends. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to determine trace metal concentrations, along with grain size distribution and organic matter content analyses. Arsenic concentrations varied spatially, ranging from 0.3 to 18.45 mg/kg. Pollution indices, including modified contamination degree (mCd) and Pollution Load Index (PLI), revealed slight-to-moderate pollution in several rivers, while the Ecological Risk Index (RI) indicated consistently low ecological risk. Enrichment Factor (EF) analysis identified both natural and anthropogenic influences contributing to heavy metal accumulation. These results underscore the complex interplay of factors driving heavy metal contamination in the Caspian Sea estuaries, emphasising the need for long-term monitoring programs to support effective coastal management and mitigation efforts within this ecologically vital region.