A study carried out by researchers from Mulawarman University in Balikapapan, East Kalimantan, has found unsafe concentrations of heavy metals like lead (Pb), cadmium (Cd), copper (Cu) and zinc (Zn) in fish caught in the Mahakam River delta.
Mulawarman University Community Health School vice dean Blego Sedionoto said lead concentrations of 4.02 milligrams per kilogram of fish were observed, in addition to concentrations of cadmium (1.03 mg per kg), copper (1.93 mg per kg) and zinc (97.54 mg per kg).
He said the tolerable level for lead was 0.003 milligrams per kg; 0.005 milligrams for copper; 0.3 milligrams for zinc and 0.0005 for cadmium.
He added that those who consumed fish contaminated by high concentrations of heavy metals were exposing themselves to carcinogenic substances.
The source of the heavy metals pollution is believed to be coming from the upstream section of the Mahakam River, where many coal mines operate.
According to a 2014 Greenpeace Indonesia report on coal-mining pollution in South Kalimantan, wastewater from coal mines can cause elevated levels of aluminium, arsenic, cadmium, chloride, copper, fluoride, hydrogen sulphide, iron, lead, manganese, nickel, nitrate, nitrite, phosphate, potassium, sodium, sulphate, zinc and other contaminants.
Sedionoto said the Mahakam River also contained run-off from agricultural waste products, such as pesticides. 'So coal is not the only culprit,' he added.
Separately, East Kalimantan Fisheries Agency head Iwan Mulyana said that although the office had yet to receive reports of illness related to fish consumption in the Mahakam River delta area, the elevated concentrations of heavy metals were worrying.
'I'm afraid [cases like] the Minamata syndrome could happen here in the future,' said Iwan.
Minamata disease is a neurological syndrome caused by mercury poisoning. The disease ran rampant among locals in Minamata Bay, Japan, who ate fish contaminated by methyl mercury from industrial wastewater at the Chisso Corporation chemical factory between 1932 and 1968.
According to Iwan, as the authority in the Mahakam delta area, the Kutai Kartanegara regency government needed to take firm action.
To minimize air and water pollution, Iwan said, the local government should require that coal transportation in closed containers prevented air and river pollution.
'This is the authority of the Kutai Kartanegara administration,' said Iwan.
Iwan said annual fish consumption among residents in East Kalimantan stood at 58 kg per capita, much higher than the national consumption rate of 36 kg per capita.
'This worries me, because we are all fish-lovers here,' said Iwan.
Conservationists have urged the government to take immediate action.
'The government must immediately take precautionary measures,' said East Kalimantan chapter of the Indonesian Forum for the Environment (Wahli) head, Fathur Roziqin.
'The Mahakam River is used by the local tap [water] company as a source of raw water, and residents living along the river also use the water for their washing needs,' said Roziqin.
He added that the heavy metal contamination also illustrated the poor management of the Mahakam River basin area and the negative impacts of the mining industry.