The opening of an elementary school in Jamaica Plain may be delayed after small traces of a potentially harmful toxin were detected in the building this week, city officials said.
In a letter yesterday to the parents of students at the Hennigan Elementary School, Superintendent Carol R. Johnson wrote that traces of polychlorinated biphenyl, or PCB, were found in paint inside the building.
“Even though the amount of PCBs in the paint is nominal and is not even significant enough to meet federal reporting thresholds, we would like to take this opportunity to safely remove flaking paint and repaint in a way that does not disrupt students and staff throughout the year,’’ Johnson wrote.
She said in a telephone interview yesterday that the PCB readings were taken in preparation for a new paint job inside. The readings came back on Monday, said Matthew Wilder, a School Department spokesman.
Johnson said the Agassiz School, located in the neighborhood and closed in June, is being prepped for possible use by the roughly 700 students scheduled to begin the academic year in the Hennigan building Sept. 8.
She said that officials hope to know next week whether students will have to begin at the Agassiz.
Johnson wrote in her letter that some materials in schools built between 1950 and 1978 contained PCB.
Exposure to the substance has been shown to cause cancer and other adverse health affects, according to the US Environmental Protection Agency, which banned PCB in 1979.
Dr. Barbara Ferrer, executive director of the Boston Public Health Commission, said by phone that according to federal guidelines, building materials should have a PCB reading of less than 50 parts per million to be considered safe.
She said the average reading at the Hennigan was 5 parts per million, and the highest reading was in the low 20s.
Ferrer said workers will take steps to ensure that the Hennigan is safe after the painting is completed, including conducting an air quality test and disposing of all affected materials.
Forty of the city’s 125 schools were built between 1950 and 1978, but that does not necessarily mean that PCBs would be found in them, Wilder said.
Johnson and Ferrer both said yesterday that they could not recall a prior instance of a school opening being delayed after a PCB reading.
“We want to make sure that we expedite [the students] coming back’’ to the Hennigan, Johnson said. “We also want to make sure that everything is safe and parents can feel very comfortable about the building and its cleanup.’’
Travis Andersen can be reached at tandersen@globe.com. Follow him on Twitter @TAGlobe. 
