Coal particles contaminating Mandovi river, found in oysters too: Study

Hindustan Times | Oct 31, 2019

The study suspects that the river gets the mercury most likely from coal handling at Goa’s Mormugao Port though the mercury content in oysters was found to be within permissible limits.

Traces of mercury, a neuro-toxic heavy metal, from coal particles have found their way into the Mandovi and the edible oysters harvested from the river, a study by the Indian Institute of Technology (IIT), Kharagpur, and the Goa-based National Institute of Oceanography (NIO) has found.

The study suspects that the river gets the mercury most likely from coal handling at Goa’s Mormugao Port though the mercury content in oysters was found to be within permissible limits.

Explaining the findings, Parthasarthy Chakraborty, a professor at IIT-Kharagpur who led the study, said the researchers measured levels of mercury at various points along the Mandovi and found that levels of mercury increased closer to the mouth of the river.

“Mercury found in estuaries is usually from untreated industrial effluents. In such cases the mercury levels are high upstream, where the effluent is discharged and lower downstream where the river mixes with the sea. However, in the case of the river Mandovi, it was the opposite,” he explained.

“We noticed that the levels of total mercury concentrations in the water column of the river increase downstream as the levels of suspended particles in the water increased. Upstream where the water is relatively clearer the levels of mercury were low,” Chakraborty said.

When the researchers dug deeper, they noticed that the bulk of the mercury in the water was largely on account of fine particles of suspended matter.

“A significant portion of the total mercury in the water column was found to be associated with suspended particulate matter (SPM) in the Mandovi estuary,” he said.

These fine particles that do not easily settle and remain suspended in the water were found to be similar to coal particles.

“Dark black powder was collected from the adjacent beaches of the Mandovi river. The physical appearance of the black powder looked very similar to that of the fine particles of coal. The scanning electron microscope images also support that the black powder was coal particles,” the study notes.

The concentration of mercury in this black powder was found to be around 200.5 microgram per kg similar to the concentration of mercury in a coal sample which is around 210 microgram per kg.

The sources of this coal could be from the Mormugao port, given the levels of mercury in the coal at the port and the sediment particles found in the river was similar, but the researchers insist that further studies are needed before conclusions concerning the source can be drawn.

“Further investigation is required to identify the sources of this fine black particle associated with high concentration of mercury,” the study, which was part of a Council of Scientific and Industrial Research (CSIR)-NIO project, notes.

The study also said that the coal particles in the water and their re-suspension by the wind and the tide also has the potential to contaminate the filter feeders such as edible oysters and clams that are routinely harvested from the river.

The average concentrations of bio-accumulated mercury (in oysters) during the dry season were between 76.2 microgram per kg and 46.7 in the wet season.

“However, the concentrations of mercury in the edible oysters (in this study) were below the permissible limit and thus should be safe to consume,” Chakraborty said.

Seafood is one of the primary sources of mercury contamination as fish and shellfish harvested from polluted waters are known to contain methyl mercury, an organic form of mercury that is absorbed by the body. And, coal is globally known as a significant source of mercury pollution.

Chairman of the Mormugao Port (MPT) E Ramesh Kumar refused to comment on the findings of the study.

President of the Goa Fishermen’s Union, Agnelo Rodrigues, said: “Instead of working in consonance with the state government in the best interest of Goa and the people of Goa, MPT for the last two decades has caused destruction to the environment, loss of livelihoods and has deteriorated the health of people who are residing at Mormugao taluka.”

Coal handling at Mormugao Port (MPT) is a hugely controversial issue in Goa. MPT has been handling 12 million metric tons per year of fine particulate coal that is imported via the Goa port by steel manufacturers to be transported to plants in North Karnataka. After an uproar over coal pollution, the total quantity has been capped by the Goa State Pollution Control Board (GSPCB) at around 5 million metric tons per year.

An earlier study by Chakraborty and a team of researchers from NIO had found that levels of mercury in the Arabian Sea off the coast of Goa were rising but remained within limits.