The state environment department will come out with a roadmap next month to stop use of toxic colours on idols so that the Hooghly is not polluted during immersion.

At a recent meeting of the state pollution control board, researchers and academics had expressed concern about the extent of the problem. Senior government officials and representatives of paint manufacturers attended the meeting.

“Lead, mercury, arsenic, molybdenum, nickel, cadmium and chromium are being extensively used to manufacture colours The level of lead in the Hooghly has always been above the permissible limit,” said biochemistry professor Krishnajyoti Goswami, who is also the director (east) of the National Referral Centre for Lead Poisoning in India.

“An expert committee will find ways to stop use of toxic chemicals on idols,” said environment secretary M.L. Meena, who chaired the meeting.

Teachers, researchers and officials will form the eight-member panel, which will suggest eco-friendly alternatives to toxic colours, said Biswajit Mukherjee, a senior law officer of the environment department and the convener of the committee.