Kolkata: The city’s iconic Howrah bridge is under threat from “acidic gutkha-laced spit", the Kolkata Port Trust (KoPT), which built and maintains it, said in a statement on Thursday.

Commissioned 80 years ago, parts of the 26,500-tonne pure steel structure will now be given a fibre glass cover to prevent corrosion.

Commuters spitting at the base of so called hangers, which support the 1,500-ft long bridge, have “damaged (them) considerably", KoPT said. The bridge, built between 1937 and 1942, is supported by 78 hangers—39 on each side.

The bases of these hangers, which were until now covered by steel plates of 6 mm thickness, were found to have eroded by 50% over three years, according to KoPT.

Some 500,000 pedestrians use the bridge everyday to cross the Hooghly river. That apart, 110,000-115,000 passenger vehicles use the bridge on weekdays.

To protect the fast corroding hanger bases, KoPT said it will cover them with “washable" fibre glass sheets. These polymer sheets being of “no resale value" are unlikely to be stolen, according to KoPT.

Fiber glass covers can also be used as advertising boards, too, to “fetch (the) required resources to fund the project," KoPT said, adding that the cost of covering the hanger bases was estimated at 15 lakh.

KoPT, which in fiscal 2013 spent 2.57 crore on maintaining the bridge, expects advertising agencies using the fibre glass billboards to clean them “periodically in their own interest".