Nonparametric estimation of thresholds for radiat

Authors: Tatiana G Sazykina A I Kryshev K D Sanina

Publish Date: 2009/06/17

Volume: 48, Issue: 4, Pages: 391-

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Abstract

Databases on effects of chronic lowLET radiation exposure were analyzed by nonparametric statistical methods to estimate the threshold dose rates above which radiation effects can be expected in vertebrate organisms Data were grouped under three umbrella endpoints effects on morbidity reproduction and life shortening The data sets were compiled on a simple ‘yes’ or ‘no’ basis Each data set included dose rates at which effects were reported without further details about the size or peculiarity of the effects In total the data sets include 84 values for endpoint “morbidity” 77 values for reproduction and 41 values for life shortening The dose rates in each set were ranked from low to higher values The threshold TDR5 for radiation effects of a given umbrella type was estimated as a dose rate below which only a small percentage 5 of data reported statistically significant radiation effects The statistical treatment of the data sets was performed using nonparametric order statistics and the bootstrap method The resulting thresholds estimated by the order statistics are for morbidity effects 81 × 10−4 Gy day−1 20 × 10−4–10 × 10−3 reproduction effects 60 × 10−4 Gy day−1 40 × 10−4–15 × 10−3 and life shortening 30 × 10−3 Gy day−1 10 × 10−3–60 × 10−3 respectively The bootstrap method gave slightly lower values 21 × 10−4 Gy day−1 14 × 10−4–32 × 10−4 morbidity 41 × 10−4 Gy day−1 30 × 10−4–57 × 10−4 reproduction and 11 × 10−3 Gy day−1 79 × 10−4–13 × 10−3 life shortening respectively The generic threshold dose rate based on all umbrella types of effects was estimated at 10 × 10−3 Gy day−1This work was performed within the framework of the Norwegian Research Council Project “Impact Assessment of elevated levels of natural/technogenic radioactivity on wildlife of the North” INTRANOR leading by the Norwegian Radiation Protection Authority whose support and useful discussions are gratefully acknowledged

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