Spatio-Seasonal Distribution of Water Quality Parameters and Heavy Metals in Plankton along the Mangaluru Coast, Southeastern Arabian Sea

Abstract

Aquatic ecosystems are increasingly polluted by heavy metals due to urbanisation, industrialisation, and poor waste management, especially in coastal regions. These metals accumulate in plankton and marine food chains, causing ecological damage and posing serious risks to human health through bioaccumulation and biomagnification. The current study examined the relationship between heavy metal accumulation in plankton and the physicochemical properties of coastal waters throughout a one-year period, from February 2024 to January 2025. The levels of selected heavy metals (Iron, Nickel, Zinc, Lead, Cadmium, Copper, Mercury, and Arsenic) were determined in plankton collected from six sites along the Mangaluru coast using an Atomic Absorption Spectrophotometer (AAS), the Thermo Scientific iCE 3300 series. The physicochemical indices of water quality, as well as heavy metal concentrations, varied dramatically among seasons and sites. The concentration of metals in plankton was in the same order: Fe > Zn > Ni > Cu > Pb > As > Cd > Hg. Throughout the monsoon season, Fe was the most prevalent metal, with a maximum concentration of 41.42 ± 10.54 µg g⁻¹ at station S1. In contrast, Cd and Hg had relatively lower quantities, with Hg remaining undetectable throughout the pre-monsoon. Ni, Pb, Hg, and As showed significant seasonal fluctuations (p < 0.05), whereas Fe, Ni, Pb, and Cu showed significant geographical differences. The study underlines the necessity of ongoing monitoring of coastal ecosystems throughout the Mangaluru coast and underscores the impact of anthropogenic inputs and monsoon-driven processes on heavy metal dynamics.