WHAT has been a source of sustenance for years has suddenly become: bane for the tribals of Bastar, Madhya Pradesh. They are being slowly poisoned through contaminated tubewells in the region. High levels of iron-oxide were found in about 1,400 villages in the country's largest district. The villagers suffer from.black scars, yellow teeth and other skin ailments, A high incidence of cancer has also been reported among them. Though non-gov'ernmental organisations have known about the contamination for long, the state government *has been turning a deaf year to their complaints.