Newton-Wellesley Hospital announced on Thursday that a sixth staff member who works in the maternity department has been diagnosed with a benign, non-cancerous brain tumor, and hospital officials say no cause has been found at the facility.

The hospital’s Department of Occupational Health and Safety (OHS) led an investigation that included interviewing staff and measuring air and water quality, testing for radiation and chemical exposure, and more.

“While the OHS investigation is ongoing, we have found no evidence that these medical conditions were caused by the work environment,” Ellen Moloney, Mass General Brigham/Newton-Wellesley president and chief operating officer, wrote in a statement Thursday to families and patients.

The first five brain tumors were found in nurses, while the sixth involves a staff member who’s not a nurse. The tumors were reported over the span of several years, Moloney’s statement notes, and not all at once. The staff members self-reported their tumor histories.

“As always, your health, wellbeing, and safety–along with that of our employees–remain our top priority,” Moloney continues. “While there has been a great deal of misinformation shared on social media and in other forums, we want to make sure you have the facts.”