http://www.utexas.edu/courses/sami/dieda/socio/chernobyl.htm--snip
Cesium 137 intruded into Sámi life foremost by contaminating their food supplies. Through rainfall following the explosion, radioactive fallout permeated freshwater lakes and inland forests, thereby contaminating fish, wild game, berries and other plants (Stephens, 1995). Most detrimental was the contamination of lichen, the main winter staple of Scandinavia’s reindeer. Lichens have no root system so they extract nutrients directly from the air, thereby acting as virtual radioactive sponges, absorbing incredible amounts of airborne cesium 137 and passing it straight onto the deer. Lichen is an extremely slow-growing plant, taking 30 years to regrow completely (Vitebsky). Thus, radioactivity in affected lichen may not drop to safe levels short of 20 to 30 years after contamination. The effects of the contaminated lichen were not fully realized until after the first post-Chernobyl autumn slaughter season; then scientists began to measure levels of radioactivity in slaughtered reindeer.