A section of Fox St in Featherston was cordoned off on Saturday afternoon while fire crews and police assessed an iodine spill from farm suppliers RD1.
A drum of iodine teat spray, classified as hazardous, had been tipped over during the night by vandals, said Featherston chief fire officer Colin McKenna.
The spill had run across the rear entrance, over the sidewalk into the gutter and towards Waite St.
RD1 had contained the spill with sawdust, but a fire service hazard unit and police were called in to ensure safety.
Mr McKenna said it was really just a clean-up job, but precautions had to be taken.