GPCB Member Secretary Dr G B Soni, in a letter to the Ahmedabad-based Federation of Industries Association, pointed out that units generating ``spent acid'' as a by-product claimed they sold it to various end-users and traders. However, the board has found that the challans/invoices produced in support of the sales were often fake, he added.

The letter further said the acid was directly discharged into rivers or on land through tankers, causing severe pollution-related problems. He said the board had reported such cases to the Gujarat High Court, which has taken serious note of it.

The board has banned the sale of acidic effluents with immediate effect, asking the units generating such effluents to either consume it internally or discharge it after in-house treatment in keeping with Board norms.

Dr Soni further said in the letter that the ban applied to all old and new industrial units situated in Gujarat. The letter asked the Association to circulate the instructions to all the units concerned and advise them to comply judiciously.

Strict action, including referring the names to the Gujarat High Court, would be taken against defaulters, the letter added.

The ban, and the subsequent instructions, have caused a flutter among industries. Industry sources claim the cost of treating one litre of the acidic effluent ranges between Rs 6 and Rs 10. To save on the massive cost, they used to sell it to industries who need acidic effluents as raw material for as little as 20 paise per litre, they say.

Former president of the Nandesari Industries Association Mohan Nair said there was confusion on what constituted ``spent acid'', and the industries have sought clarification from the board. He admitted that some units were disposing of highly acidic effluents in such a manner, but claimed that only half-a-dozen units in Nandesari were selling acidic effluents.

Regional officer of the GPCB N L Kansagra said the Board authorities had received the letter.