Radiation doses and decontamination effects in Minamisoma city: airborne and individual monitoring after the Fukushima nuclear accident.

ABSTRACT

After the Fukushima accident, airborne monitoring was implemented to measure airborne radiation. We examined the relationships between airborne and individual radiation monitoring and clarified the use of airborne monitoring to evaluate the effects of decontamination on residents' received doses. We used the air dose rate data from four airborne monitors conducted between 2013 and 2016, and the dose data from four individual monitors (in which a total of 18 392 adults and 3650 children participated), conducted in Minamisoma City during the same period. We examined the Pearson correlation coefficients between the airborne and individual monitoring data and estimated exposure ratios (ERs; ratios of individual dose to air dose rates) among adults and children. We also estimated the effects of decontamination on residents' doses based on airborne monitoring data, adjusting this for timing and dosing through propensity score matching, which were then compared to individual monitoring data. There were significant correlations between airborne and individual monitoring doses among adults and children, and more than 80% of residents showed a good estimation-observation agreement within a factor of two. The median of ERs was 0.304 and 0.250 among adults and children, respectively. There was a significant difference between the two. Effects of decontamination on residents' doses estimated from airborne monitoring were significantly lower than those estimated from individual monitoring. These findings suggest that airborne monitoring can be used to estimate representative radiation doses within residential areas. It may be a useful tool for enhancing communication among stakeholders and supporting individual and policy decisions; however, it is less sensitive for evaluating individual effects of decontamination than individual monitoring. Combined use of airborne and individual monitoring also showed a lower median of ERs in children than in adults and in a Japanese government's model, possibly due to prioritised decontamination for children and differences between their behavioral patterns.