The FBI told District of Columbia Fire Department officials early last month, however, the irradiated mail makes people sick, according to the fire department.
Grassley asked the Office of Compliance, responsible for enforcing labor and employment law on Capitol Hill, to investigate complaints of headaches, skin rashes, dry mouth and skin irritation from 73 staff members after handling the mail.
"An independent review can help shed light on what kind of health risks might exist and if they exist, how to solve them," Grassley said.
According to Grassley, health officials at the Attending Physician's Office in the Capitol have attributed some of the complaints to colds, flu or dry air.
The Senate Sergeant at Arms has put together a task force to investigate the issue, but some staff members on Capitol Hill said task force members have mostly questioned the link between the mail and the health concerns.
But some adverse health impact of handling irradiated mail is becoming common knowledge in Washington since the process was put in place last fall to kill possible anthrax spores in the mail.
On Jan. 9, the Washington Fire Department took a 42-year-old woman and a 37-year-old woman to the hospital after 11 workers handling mail at the Commerce Department complained of feeling ill.
Fire Department Spokesman Alan Etter said Monday at the time, officials on an FBI terrorism task force told him the irradiation process had reacted with plastic materials in mail delivered to the department. Etter said FBI officials indicated they had seen this type of thing before in Washington.
"At the time, the FBI terrorism task force said they had had issues this and that this was a problem in D.C.," Etter said. "A lot of people seem to think this is happening."
An FBI spokesman would not comment on this story.