This is believed to be the first such case in California, reports Correspondent Juan Fernandez of CBS Station KCBS-TV.
Andrew Andris Blakis was taken into custody at his home in Los Angeles.
On July 1, Blakis was conducting tests at the Gillespie Neuroscience Research Facility at UCI. He was working in an enclosed area with radioactive material called P32 Isotope.
During the test, Blakis' lips began tingling so he stopped working and swept the area with a Geiger counter, which is a standard safety procedure for the lab.
He found that some of the material had escaped and allegedly assumed that someone had put the material there.
In alleged retaliation, Blakis allegedly smeared some of the compound on the chair of co-worker Jingtong Zuo. However, no evidence exists that Zuo had placed the P32 around the workstation.
Zuo sat in her contaminated chair for a day and a half before she discovered the radioactive material during a safety check.
"This was a revenge kind of thing, but no evidence exists that she tried to harm him," said a prosecutors' spokeswoman, Tori Richards.
Since the incident, Blakis has resigned his job. It's estimated that Zuo was exposed to an average yearly dose of radiation during that time period. Zuo is not experiencing any symptoms of radiation poisoning, but the long-term effects are unclear.