BENGALURU: A study by the National Institute of Oceanography, Goa, and the Academy of Scientific and Innovative Research, Ghaziabad has found higher concentration of dissolved lead (dPb) in the northern and central Indian Ocean (IO), which is much higher (23–114 pM) compared to other ocean basins such as the Atlantic and Pacific oceans, with clear a north-south decreasing gradient.
The recent study conducted by scientists Chhaya Yadav, Sunil Kumar Singh and Venkatesh Chinni states that among the Asian countries, China and India have exhibited a substantial rise in lead emissions by coal combustion, with an increase of 4.3 to 4.8 times over a last 33-year period; 12.5 and 82.8 thousand tonnes annually for India and China respectively in 2023, due to coal burning.
“Apart from coal combustion, climatic events such as the Indian Ocean Dipole, which controls dry/wet conditions and dust storms, play a substantial role in the addition of dPb over the southern Indian Ocean,” states the study during which the authors had examined the distribution dPb in the IO, based on seawater samples collected during winter monsoon and spring inter-monsoon cruises in 2020 and 2021.
Most of the dPb comes from anthropogenic sources largely through coal combustion by atmospheric deposition. “The concentration of Pb in Asian aerosols has been found to be significantly higher than in other regions because of increasing emissions from coal combustion, industrial processes, and vehicular emissions. This has led to a higher flux of Pb to the northern and central IO over the past 20 years,” stated the report published in ‘Marine Pollution Bulletin.’
Monitoring and understanding lead dynamics in the IO is crucial because of the high levels of industrial emissions and their environmental impact. Pb is a toxic metal that can cause serious health issues, with even low levels of exposure being harmful, especially in vulnerable populations, such as children and pregnant women. Studies have shown that developmental exposure to lead is linked to adult criminal behaviour, highlighting the importance of monitoring lead levels in the environment to protect human health.
Atmospheric transport is the primary pathway for lead to enter the open ocean, with surface waters near continents being most significantly affected by aerosols from pollutants or natural crustal sources. “Concentrations of dPb in the mixed layer ranged from 23 to 114 pM, with elevated values in the northern IO. A pronounced latitudinal gradient was observed as dPb concentration decreased from north to south. Substantially higher Pb contribution from continental shelf sediments in Bay of Bengal highlights impact of enhanced sediment loading, primarily driven by the Ganga-Brahmaputra river system,” the report stated.
The authors observed that in the past decade, there has been a notable shift in lead sources, with a decrease in leaded gasoline emissions and there has been an increase in industrial sources such as coal combustion for power generation and other usage such as ore and metal processing.
Anthropogenically derived metals generally have a higher seawater solubility than those derived from crustal aerosol populations.