NO police charges will be laid over the poisoning of 11 people at a Bunbury fast food store in May.

Police spokesman Gerry Cassidy said today that the investigation into caustic soda on chips at the Bunbury Chicken Treat on May 22 had been closed.

He said there was no evidence of criminality for charges to be laid. But the City of Bunbury’s health department may still pursue charges under the Food Act.

Five children aged under 10 were among the 11 people who needed hospital treatment after eating the Chicken Treat chips laced in the cleaning chemical.

Caustic soda, or sodium hydroxide, is commonly used as a detergent or drain cleaner and causes chemical burns in contact with the skin, and can induce permanent blindness if it contacts eyes.

Staff were interviewed, as forensic tests were carried out at the Blair Street outlet, which was closed for several days.

In a statement at the time, Chicken Treat said it "deeply regrets'' the incident.