An investigation has been launched after five nurses working on the same hospital floor developed brain tumours. Eleven employees from the fifth-floor maternity unit near Boston, Massachusetts, identified health concerns, five of whom had benign tumours, reported NBC 10 Boston.

A nursing union is now carrying out an independent investigation after accusing the hospital of attempting to prematurely make the issue "go away". Mass General Brigham Newton-Wellesley Hospital found "no environmental risks" in its investigation, which it said was in collaboration with government and health and safety officials. A Massachusetts Nurses Association spokesperson, Joe Markman, said: "The hospital only spoke to a small number of nurses, and their environmental testing was not comprehensive."

He added: "The hospital cannot make this issue go away by attempting to provide a predetermined conclusion.

"Right now, the best way we can help is to complete an independent, scientific investigation. That effort is underway and may take additional weeks.

The union indicated that nurses came forward with workplace health concerns, which led to the discovery of those with tumors.

Two nurses have the most common benign type of tumour called a meningioma, according to the hospital in Newton, about 10 miles west of Boston.

The hospital said its investigation ruled out disposable masks, the water supply, nearby x-rays, and chemotherapy treatment on the floor below.

"The investigation found no environmental risks which could be linked to the development of a brain tumour," said associate chief medical officer Jonathan Sonis, and Sandy Muse, chief nursing officer, in a joint statement.

They added: "Based on these results, we can confidently reassure our dedicated team and all our patients that there is no environmental risk at our facility."