Authorities across Asia stepped up checks this week on Japanese imports after radioactive contaminants showed up in food and water in quake-stricken Japan following blasts at a nuclear plant last week.

Experts are most worried about three radioactive substances — iodine-131, caesium-134 and caesium-137 — all of which can cause various types of cancer years later.

Caesium-137 is of particular concern as it can stay in the environment and potentially cause havoc for hundreds of years. It takes 30 years for this contaminant to lose its power by half — what experts refer to as a “half life.”