Border guards at Kiev's Borispol Airport said the passenger's luggage was flagged with a radioactivity detector during a routine check of bags arriving on a flight from Frankfurt Tuesday, RIA Novosti reported.
"Two plastic containers with 12 grams of clay soil were found during an inspection of personal belongings. The acceptable level of radiation was exceeded by about a factor of two," Ukraine's State Border Guard Service said.
The passenger told law enforcement personnel the soil was from the Fukushima nuclear disaster site in Japan and that he was taking it to a university in the Ukrainian city of Zhitomyr for study.
Radiation has been leaking from the Fukushima Daiichi Nuclear Power Plant since the March 2011 earthquake and subsequent tsunami knocked out its cooling systems and damaged its containment structure.