"These reports confirm that the environment at NWH is safe and we hope they reassure you of our commitment to your wellbeing," the email from President and CEO Ellen Moloney, and others, said.

"We are exploring opportunities for an additional third-party review for further validation of these findings," the email said.

The environmental investigations were set off by the cluster of brain tumor diagnoses.

The most recent person to be diagnosed, a Needham woman who worked at the hospital from 2005 to 2018, told the Globe earlier this month that she's concerned and confused as to how seven people who worked in the labor and delivery unit could be diagnosed with benign brain tumors.

Debbie Connolly, 58, was diagnosed with meningioma in her right frontal lobe in April, she told the Globe.

"You have to wonder, how many people have these tumors and don't know," she said.

Among the six other current or former workers diagnosed is a nurse who worked there 23 years ago and was diagnosed in 2021.

Details about the other brain tumor cases have not been released by the hospital, except that the benign tumors are of three different types, and the individuals affected included some who worked there only part-time.

The state report said "most brain tumors develop for no apparent reason and are not associated with specific risk factors," the hospital's email said.

The "most established environmental risk factor" is "high-dose exposure to ionizing radiation" and typical latency after exposure is between 10 to 50 years, the email said.

In addition to radiation surveys and reviews of calibration equipment and maintenance logs, the state investigation included air and water testing.