Concentration of radioactive materials in small mammals collected from a restricted area in Fukushima, Japan since 2012
Fukushima Daiichi Nuclear Power Plant was struck by a huge earthquake and tsunami, which ultimately released a large amount of radioactive material owing to steam explosion in March 2011. This accident affected extensive area and resulted in soil contamination, which would prevail over a long period. The contaminants included various types of nuclear materials, among which cesium (134,137Cs) has a particularly long half-life. Organisms living in the contaminated area are presumably exposed to radiation caused by the presence of these radioactive contaminants in their environment, in addition to internal exposure owing to the intake of these contaminants through the food web. The purpose of our data collection is to monitor accumulation of radioactive materials in small mammals for a long period and to predict its effects. Reasons for focusing on small mammals include: i) mammals are the most sensitive to radiation, ii) small mammals have a smaller home range compared to large mammals; therefore, accumulation of radioactive materials in small mammals is considered to reflect the condition of the surrounding environment, and iii) among the small mammals, rodents are used as laboratory animals and provide a lot of information, from which we can expect to acquire much knowledge based on investigations. The dataset contains measurements of 134,137Cs and potassium (40K) concentrations in small terrestrial mammals collected in areas contaminated with radioactive contaminants from the Fukushima Daiichi Nuclear Power Plant accident. We established two fixed study sites and three temporary sites inside the zone from which humans were evacuated owing to high levels of radiation. Annual monitoring of Cs contamination in small mammals was started in 2012 at the fixed study sites. Until 2016, we collected 547 individuals of four species (Apodemus speciosus, A. argenteus, Microtus montebelli, and Urotrichus talpoides). Cs concentrations in each individual were measured using high-purity germanium detectors against a ground body after removing the internal organs and the head. Our data provide valuable information about temporal changes in 134Cs and 137Cs concentrations in small mammals following the Fukushima Daiichi Nuclear Power Plant accident. The study is continuing and the present dataset will be updated in the future.