Effective half-lives of 134Cs and 137Cs in reindeer meat and in reindeer herders in Finland after the Chernobyl accident and the ensuing effective radiation doses to humans.

Monitoring of 137Cs in reindeer herders and in reindeer meat in Finnish Lapland began in the early 1960s and has continued until today. The monitoring of 137Cs in reindeer herders and in reindeer meat in the Halla area began after the Chernobyl accident. In this study, reindeer herders together with reindeer meat samples were monitored for gamma-emitting radionuclides from two separate areas in the Finnish reindeer management area, Northern Finland and the Halla area. The effective half-lives determined for 137Cs in reindeer meat were from 3.0 ± 1.7 to 5.1 ± 0.5 y. For 134Cs, the observed effective half-lives in reindeer meat were from 1.3 ± 0.2 to 1.5 ± 0.1 y. The effective half-lives among male and female reindeer herders in Northern Finland were 5.5 ± 1.3 and 4.4 ± 0.9 y, respectively, for the body-burden of 137Cs. In the Halla reindeer herding cooperative, located to the south of Finnish Lapland in the province of Kuusamo, the effective half-lives in the reindeer herders were shorter, about 1-2 y. The 134Cs × 137Cs-1 ratios decreased more rapidly in reindeer meat and also in humans in the Halla area than in Northern Finland. This implies faster removal of Chernobyl-derived cesium from the reindeer-man food chain in the Halla area. The contribution of Chernobyl fallout (percent) in reindeer meat was 70% and 80% in the Paistunturi and Ivalo cooperatives, respectively, and 50% and 80% in the western and eastern part of Halla cooperative, respectively. In humans, the contribution of Chernobyl fallout to 137Cs in whole-body content was 60% in Northern Finland and 80% in the Halla area. The mean committed effective doses of Cs for reindeer herders in Finnish Lapland decreased from 0.36 mSv y-1 in 1987 to 0.053 mSv y-1 in 2005.