Boston ? Six Harvard University medical researchers were poisoned in August after drinking coffee that was laced with a chemical preservative, according to university officials.

In an internal memo first reported in the Boston Herald’s Sunday editions, the school said the coffee came from a machine near their lab that later tested positive for sodium azide, a common preservative used in labs.

The six reported symptoms after drinking the coffee Aug. 26, ranging from dizziness to ringing in the ears, and one passed out. They were treated at Beth Israel Deaconess Medical Center and later released.

The memo does not say whether officials believe the poisoning was intentional.