The gymnasium at North Plainfield Middle School has been closed after mercury was found in the floor.

Superintendent Michelle Aquino sent a letter to parents and staff.

The school district tested gym flooring in both the middle school and Somerset School.

According to the school district, their tests proved mercury was present in the floors of both gyms, but air quality tests were only at concerning levels at the middle school.

The district says the gym at North Plainfield Middle School will be closed until it is properly ventilated.