Seasonal and tidal variability of trace metals and potentially toxic elements in intertidal sediments along the Thiruvananthapuram coast, southwest India

Intertidal sediments serve as important sinks for trace metals and potentially toxic elements (PTEs), reflecting both natural processes and anthropogenic inputs in coastal environments. This study investigates the spatial and seasonal distribution of major elements, trace metals, and PTEs in intertidal sediments along the southwest coast of India from Poovar to Varkala. Sixteen sediment samples were collected from eight stations representing low- and high-tide zones during the wet (August 2019) and dry (March 2020) periods. Elemental concentrations were determined using ICP-MS following microwave-assisted digestion. The analyzed elements were grouped as major elements (Mg, Al, K, Ca, and Fe), trace elements (Li, Be, B, Mn, V, Co, and Ba), and potentially toxic elements (Hg, Cr, As, Cd, Pb, Ni, Cu and Zn). Pollution indices, including contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), pollution load index (PLI), and potential ecological risk index (PERI) were applied to evaluate contamination status. Iron (Fe) was the dominant major element, while manganese (Mn) was the most abundant trace metal. Among the PTEs, chromium (Cr) showed the highest concentrations in both seasons. Two-way ANOVA indicated significant spatial and temporal variations for selected elements. Pollution indices indicated generally low contamination across most stations; however, localized enrichment of Arsenic (As) was observed, particularly at Kovalam. PLI values (<1) indicated good sediment quality, while PERI values indicated that sites had low ecological risk. Higher enrichment and contamination levels during the wet period suggest that monsoonal runoff and enhanced sediment transport influence metal accumulation in intertidal sediments.