Geochemical characteristics and ecological risk of heavy metals in Karaikkal coastal sediments, India

Abstract This study examines the presence of heavy metals (HMs) and their environmental impacts in samples collected from the surface sediments of Karaikkal Beach, located on the southeastern coast of India. To assess the textural attributes and heavy metal content in the area, 26 sediment samples were collected and analyzed using atomic absorption spectroscopy (AAS). The sediments are composed primarily of sand (98.56%), followed by silt (1.2%), clay (0.41%), and calcium carbonate, which ranges from 3.19% to 6.71%, with a mean value of 4.77% present at a significant level. Organic inputs from riverine sources were also observed to influence sediment composition, and the average organic matter concentration is 0.52%, with values ranging from 0.26% to 0.75%. The HM concentrations followed the descending order: Fe (22,434.42–36,525.69 µg/g) > Mn (230.15–395.49 µg/g) > Cr (114.33–244.63 µg/g) > Ni (13.60–24.22 µg/g) > Pb (29.89–55.96 µg/g) > Cu (22.47–36.52 µg/g) > Zn (24.14–40.69 µg/g) > Co (12.00–20.32 µg/g). Fe and Mn concentrations were primarily controlled by fluvial inputs and terrestrial influences. The derived indices such as enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), sediment pollution index (SPI), and potential ecological risk index (PERI) reveal that the coastal sediments mostly fall within the unpolluted to slightly polluted categories, indicating a low ecological threat. The origin of metal enrichment in the sediment fractions is attributed to natural geogenic sources. The sources of HMs and their inter-element associations were interpreted using principal component analysis (PCA) and a correlation matrix. These baseline data underscore the importance of continuous environmental monitoring to identify emerging pollution patterns and guide sustainable coastal management.