Fundamentals of wildlife dosimetry and lessons learned from a decade of measuring external dose rates in the field.

Methods for determining the radiation dose received by exposed biota require major improvements to reduce uncertainties and increase precision. We share our experiences in attempting to quantify external dose rates to free-ranging wildlife using GPS-coupled dosimetry methods. The manuscript is a primer on fundamental concepts in wildlife dosimetry in which the complexities of quantifying dose rates are highlighted, and lessons learned are presented based on research with wild boar and snakes at Fukushima, wolves at Chornobyl, and reindeer in Norway. GPS-coupled dosimeters produced empirical data to which numerical simulations of external dose using computer software were compared. Our data did not support a standing paradigm in risk analyses: Using averaged soil contaminant levels to model external dose rates conservatively overestimate the dose to individuals within a population. Following this paradigm will likely lead to misguided recommendations for risk management. The GPS-dosimetry data also demonstrated the critical importance of how modeled external dose rates are impacted by the scale at which contaminants are mapped. When contaminant mapping scales are coarse even detailed knowledge about each animal's home range was inadequate to accurately predict external dose rates. Importantly, modeled external dose rates based on a single measurement at a trap site did not correlate to actual dose rates measured on free ranging animals. These findings provide empirical data to support published concerns about inadequate dosimetry in much of the published Chernobyl and Fukushima dose-effects research. Our data indicate that a huge portion of that literature should be challenged, and that improper dosimetry remains a significant source of controversy in radiation dose-effect research.

Airborne radiometric survey of a Chernobyl-contaminated mountain area in Norway - using ground-level measurements for validation.

An airborne radiometric survey can be an efficient way to investigate contamination of large areas after nuclear accidents. In the current study, a helicopter borne gamma ray spectrometry survey was carried out in a vast mountainous area in Norway, where the contamination from the 1986 Chernobyl accident still affects animal husbandry more than 30 years after the fallout occurred. The 137Cs activity densities provided by the aerial survey was validated using various independent ground-based measurements - including soil samples and in situ measurements (at 1 m above ground). Despite considerable small-scale heterogeneity, demonstrated by the ground-based measurements, strong correlations were obtained between the results from the aerial survey - after introducing more detailed instrument calibration and spectre analysis - and the ground-level data. Adjusted R2 values were around 0.9, and linear correlation coefficients close to unity.