Persistent elevated levels of dissolved lead in the Indian Ocean post-leaded gasoline ban: The impact of anthropogenic activities, sediment desorption, and dust storms

Abstract

This study examines the distribution of dissolved lead (dPb) in the Indian Ocean, based on seawater samples collected during winter monsoon GI10 (2020) and spring inter-monsoon GI09 (2021) cruises. A total of 510 samples were analyzed for dPb concentrations using HR-ICP-MS coupled with seaFAST system. The study emphasizes the spatial distribution of dPb in the Indian Ocean, identifying major sources and key influencing factors. Concentrations of dPb in the mixed layer ranged from 23 to 114 pM, with elevated values in the northern Indian Ocean. A pronounced latitudinal gradient was observed as the dPb concentration decreased from north to south. The atmospheric lead fluxes range from 35–1439 Mmol y⁻¹ in the Arabian Sea and 22–281 Mmol y⁻¹ in the Bay of Bengal, while lead contributions from continental shelf sediments vary between 1.8–2 Mmol y⁻¹ and 5.9–10.7 Mmol y⁻¹, respectively. Atmospheric deposition is the dominant source of dPb in both basins. However, the substantially higher Pb contribution from continental shelf sediments in the Bay of Bengal highlights the impact of enhanced sediment loading, primarily driven by the Ganga-Brahmaputra River system. Among the Asian countries, China and India have exhibited a substantial rise in lead emissions by coal combustion, with an increase of approximately 4.3 to 4.8 times over a last 33-year period, amounting to 12.5×10³ and 82.8×10³ tons y⁻¹ for India and China respectively in 2023, highlighting their rapid industrialization and heavy reliance on coal. Apart from coal combustion, climatic events such as the Indian Ocean Dipole (IOD), which controls dry/wet conditions, dust storms, and bushfires, play a substantial role in the addition of dPb over the southern Indian Ocean.