At least 20 elementary school students and three teachers tested negative for exposure to mercury after a thermometer filled with the liquid broke in a science classroom Friday, according to Baltimore fire officials.
City hazardous-materials teams and school police went to Guilford Elementary School on York Road after a teacher reported the thermometer broken and evacuated about 45 students from the classroom, according to city school officials.
Fire officials said in a news release that students may have been handling a mercury-filled thermometer that broke.
Affected students and staff were isolated for assessment and decontamination. All students tested negative for exposure and were sent home, according to a city schools spokeswoman.
The use of mercury thermometers has been banned in Maryland since 2001. City school officials said Friday that they "are aware that the mercury-containing devices have been banned from all school districts, and we make every concerted effort to remove them from all school buildings. However, at times they do reappear from hidden storage areas, and are not reported for hazardous disposal."
The school system said that it will send notes to principals Monday urging them to inspect their buildings for all hazardous waste devices and materials.
Mercury, at high levels, can damage the brain and kidneys, according to the Agency for Toxic Substances and Disease Registry.