The Tamil Nadu Pollution Control Board (TNPCB) on Thursday, April 17, has submitted its report, confirming high level presence of mercury in water bodies, groundwater, and soil around Neyveli Lignite Corporation (NLC)’s thermal power stations and lignite mines in Cuddalore district.
According to the TNPCB’s report, mercury concentration in some surface water samples was up to 115 times higher than the permissible limit, and up to 62 times higher in groundwater. Other metals like nickel, lead and cadmium were also detected. The samples were collected on December 17, 2024, from areas surrounding Neyveli. The findings were submitted to the southern bench of the National Green Tribunal (NGT).
Of the 17 surface water samples tested, 15 exceeded the permissible limit of mercury levels (0.0012 mg/l to 0.115 mg/l). The highest levels were found in Buckingham Canal, 115 times above the permissible limit.
However, TNPCB said these water bodies are classified as IS 2296 Class E, meaning they are “unsuitable” for drinking or irrigation. Because of this, the board did not treat the high mercury levels as violations, they claimed.
This classification has drawn criticism as several of the affected water sources, including the Valayamadevi Combined Water Supply Scheme, Paravanar river, Walajah Lake, and Ayyan Lake are known to supply drinking water.
The World Health Organization (WHO) has identified mercury as one of the top ten chemicals of public health concern, warning that even low-level exposure can severely impact the nervous, digestive, and immune systems.
The NGT took suo motu cognisance of the issue in 2023 after Chennai-based environmental group, Poovulagin Nanbargal and Manthan Adhyayan Kendra, a research institute, submitted a study on pollution caused by NLC’s operations in Neyveli and Parangipettai.
The study found mercury levels in drinking water in North Vellur and Tholkappiar Nagar to be up to 250 times the permissible limit. Samples from nearby agricultural fields and water bodies also showed elevated levels of heavy metals like nickel, cadmium, zinc, boron, and selenium.
While TNPCB had earlier denied contamination claimed by the NGOs, its latest report submitted to NGT, now confirms the presence of toxic pollutants in the area.
Responding to the TNPCB, Poovulagin Nanbargal in its statement said, “How can water bodies used by people, such as the Valayamadevi Combined Drinking Water Project, Paravanar river, Walajah lake, and Ayyan Lake, not be considered sources of drinking water? Heavy metals like mercury do not naturally occur in water bodies, who is responsible for this contamination?” the group asked. The Tamil Nadu government needs to appoint a medical team to study the health impacts on residents, the statement added.
The NGT last heard the matter on April 16, 2025. The final hearing is scheduled for June 12, 2025.