However, officials have been restricted from a thorough clean-up because one of the land owners in the area, whose 30-rai plot was once part of the mine, refused to have the sludge removed.

Pongtheb Jaru-ampornparn, director of Environmental Management and Rehabilitation under the Department of Basic Industry and Mining, said the owner filed a lawsuit last year to keep them off his land after officials tried to remove over 100 tonnes of sludge laden with arsenic and lead from his land.

Covering 54 rai, the mine had been in operation for over two decades until five years ago.

It is located in the upper reaches of the Pattani River, which serves as a lifeline to seven communities in Tambon Koh Talu and Bannang Sata district in Yala province.

The Land Department issued a Nor Sor 3 land ownership document to the Sakol Mining Co even though the mine was located in a forest reserve. Under normal circumstances, the land should be rehabilitated and returned to the Forestry Department once mining was halted. ``The land owner has been informed the sludge is a pollution source and a possible threat to neighbouring communities,'' Mr Pongtheb said in a phone interview.

The company had denied an official request to rehabilitate the land because the sludge was believed to contain valuable minerals that could be extracted for sale. Company executives failed to return calls for clarification.

Test samples of water and soil near the mine by the Pollution Control Department (PCD) last December found a high content of lead and arsenic.

Arsenic contamination in the Pattani River was recorded at 5.2 microgrammes per decilitre (ug/dl), lower than the standard of 10 ug/dl. However, the sediment on the river bed has up to 600 milligrammes per kilogramme (mg/kg), over 50 times higher than the amount in normal soil conditions.

Lead contamination in soil and water samples was found to be within standard.

Wijarn Simachaya, director of the PCD's inland water section, advised the public to stay calm because the contamination was low and would be diluted by water. However, he warned that the situation could worsen if the sludge was not removed soon. The PCD would soon propose that the cabinet and the National Environment Board invoke article 9 of the 1992 Environment Act.

Article 9 authorises the prime minister to halt any activity on private land deemed to affect the environment. The Chuan Leekpai government had used this article to restrict inland shrimp farming in rice-growing zones.

Lead is classified as a toxic substance that attacks human limbs and restricts brain and mobility development. Arsenic is a toxic substance that causes skin cancer.