Radioactive contamination in feral dogs in the Chernobyl exclusion zone: Population body-burden survey and implications for human radiation exposure

Abstract

This report describes a two-year effort to survey the internal 137Cs and external β-emitter contamination present in the feral dog population near the Chernobyl nuclear power plant (ChNPP) site, and to understand the potential for human radiation exposure from this contamination. This work was performed as an integral part of the radiation safety and control procedures of an animal welfare oriented trap-neuter-release (TNR) program. The measurement program focused on external contamination surveys using handheld β-sensitive probes, and internal contamination studies using a simple whole-body counter. Internal 137Cs burden was measured non-invasively during post-surgical observation and recovery. External β contamination surveys performed during intake showed that 21/288 animals had significant, removable external contamination, though not enough to pose a large hazard for incidental contact. Measurements with the whole-body counter indicated internal 137Cs body burdens ranging from undetectable (minimum detection level ∼100 Bq/kg in 2017, ∼30 Bq/kg in 2018) to approximately 30,000 Bq/kg. A total of 33 animals had 137Cs body-burdens above 1 kBq/kg, though none posed an external exposure hazard. The large variation in the 137Cs concentration in these animals is not well-understood, could be due to prey selection, access to human food scraps, or extended residence in highly contaminated areas. The small minority of animals with external contamination may pose a contamination risk allowing exposures in excess of regulatory standards.

Fig 1. Methods and photos.

(a) Diagram of experimental approach. (b) Diagram of experimental hardware and systems. Native dogs were collected and initially triaged before being measured. Numbered, thermoluminescent dosimeter-equipped ear tags (c) were place on dogs during the TNR campaign as part of a related study.

Fig 2. Understanding the Chernobyl region of interest.

(a) Map of Chernobyl exclusion zone (2016) and 10 km radius inner circle. (b) Exploded view of points of interest (orange circles) within 10 km radius inner circle centered on the ChNPP (red diamond), colored by ¹³⁷Cs contamination (2014). (Access: https://harvard-cga.maps.arcgis.com/home/index.html).

Fig 3. Dosimetry and analysis of wild dogs.

(a) 21/288 animals surveyed as part of the 2017 and 2018 programs had external contamination above the threshold (100 cpm on Ludlum 26-2, equivalent to 95 Bq per 100 cm² area, ⁹⁰Sr). The distribution of this contamination is shown here. (b) Scatter plot of the animal body-burden as a function of body mass for the 2017 (peach) and 2018 (purple) campaign. Animals in 2017 with activity less than 100 Bq/kg are excluded. Animals in 2018 with activity less than 30 Bq/kg are excluded. External contamination is shown in this plot using squares, the size of which is correlated to the reported measurement in counts per minute using the Ludlum 26-2 probe on contact.