CHICAGO – A government agency has quitted plans for a study related to the treatment of autism, that critics had called an unethical experiment on children.

The National Institute of Mental Health (NIMH) said that the study of the treatment, called chelation has been aborted. The agency has decided to test other possible therapies for autism and associated disorders, the statement said.

“There will be parents who are disappointed,” said Richard Nakamura, the scientific director of NIMH. “We recognize that for children there is a thread line for the risk-benefit ratio. You have to be pretty assured of the overall safety of the procedure.”

The study had been suspended because of safety matters, after another study published last year regarding a drug used in the treatment to permanent brain dysfunction in rats.

Chelation clears heavy metals and is used to treat lead poisoning and study is based on the fringe theory that vaccines with mercury triggers autism, a theory rejected by modern science. Mercury has not been used in childhood vaccines since 2001, except for certain flu shots.

The study included 120 autistic children, participant ages 4 to 10 and providing half a chelation drug and the other half a placebo. The three months test would calculate before-and-after blood mercury levels and autism symptoms.

Autism is a collection of disorders that unable a person to communicate and interact with others. Most doctors believe there is no cure.

Several scientists second the decision. Dr. Paul Offit, chief of infectious diseases at the Children’s Hospital of Philadelphia, appreciate the decision of cancellation.

“Suppose that a child suffers a severe side effect from chelation,” said Offit, author of “Autism’s False Prophets,” a new book on autism research. “Without any evidence it’s helpful, I think it’s unethical.”