tjeir --> their(people's)
Sansai (Japanese mountain vegetables) and mushrooms are food but also communication tool for villagers. But now, radiation is a problem. It depends on each Sansai and mushrooms how much radioactive cesium they consume. Even in the highly affected areas, some Sansai(or mushroom) consume very low cesium. But some other Sansai collect lots of cesium.
Evacuation life continues for almost 4 years, not just 1 or 2 years. It's just too long.