The seeds of the forest tree strychnos potatorum used by the tribals of Andhra Pradesh for purifying water may hold the key to remove arsenic in the ground water of West Bengal and Bangladesh, scientists claim. A substance isolated from the seeds has proved to be efficient in removing arsenic, according to preliminary investigations at the All Indian Institute of Hygiene and Public Health (AIHPH) in Calcutta. The substance was isolated by a consultant to the Girijan cooperative corporation of Andhra Pradesh.