A 69-year-old woman is recovering from a leg injury Thursday after she inadvertently sat in sulfuric acid days before while onboard a public transit bus in New Jersey, officials say.

Police told NJ.com that the woman boarded a New Jersey Transit bus in Lodi Sunday afternoon and immediately felt a pain in her leg after sitting down. The bus then was evacuated and a Bergen County Hazmat team was called to the scene to investigate.

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The website reports that authorities described the substance the woman sat on as sulfuric acid, while transit officials called it a liquid.

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The woman was treated at a local hospital and no other passengers were injured.

An investigation is now underway to determine how the liquid got there.