Abstract
Purpose Animals are exposed to environmental ionizing radiation (IR) externally through proximity to contaminated soil and internally through ingestion and inhalation of radionuclides. Internal organs can respond to radioactive contamination through physiological stress. Chronic stress can compromise the size of physiologically active organs, but studies on wild mammal populations are scarce. The effects of environmental IR contamination on organ masses were studied by using a wild rodent inhabiting the Chernobyl exclusion zone (CEZ). Material and methods The masses of brain, heart, kidney, spleen, liver and lung were assessed from bank voles (Myodes glareolus) captured from areas across radioactive contamination gradient within the CEZ. Relative organ masses were used to correct for the body mass of an individual. Results Results showed a significant negative correlation between IR level in the environment and relative brain and kidney mass. A significant positive correlation between IR and relative heart mass was also found. Principal component analysis (PCA) also suggested positive relationship between IR and relative spleen mass; however, this relationship was not significant when spleen was analyzed separately. There was no apparent relationship between IR and relative liver or lung mass. Conclusions Results suggest that in the wild populations even low but chronic doses of IR can lead to changes in relative organ mass. The novelty of these result is showing that exposure to low doses can affect the organ masses in similar fashion as previously shown on high, acute, radiation doses. These data support the hypothesis that wildlife might be more sensitive to IR than animals used in laboratory studies. However, more research is needed to rule out the other indirect effects such as radiosensitivity of the food sources or possible combined stress effects from e.g. infections.
Highlights
Radioactive disasters and nuclear fallouts are a major global concern
Body and internal organ mass were measured from 221 bank voles and ambient radiation level was recorded from each trapping location
A Principal component analysis (PCA) with original organ masses (Supplementary Table 4) produced a single principal component (PC) accounting over 50% of variation, likely representing the overall individual size
Summary
Radioactive disasters and nuclear fallouts are a major global concern. Long-lived radioactive compounds, such as cesium137 (Cs137) and strontium-90 (Sr90) from Fukushima and Chernobyl, have spread far in landscape scale and due to their long half-life (approximately 30 years) the effects persist for decades (Askbrant et al 1996; IAEA 1996; Baba 2013). Due to its water solubility, Cs137 has high mobility and enters the body through the diet and drinking water (Murakami et al 2015). Both Cs137 and Sr90 can enter the body as radioactive particles from soil and air (Chesser et al 2001). The rate of accumulation from external sources is usually expressed as dose rate of Sieverts per hour (Sv/h) and annual radiation dose from natural sources on average is 2.4 mSv/year (approximately 0.27 mSv/h) (IAEA 2010). The ambient radiation levels measured from the Chernobyl area can exceed 300 mSv/h, accumulated doses could potentially cause cellular damage (Waselenko et al 2004). Given the risks of future radiation-related accidents (Wheatley et al 2016), studies investigating the potential environmental and health consequences of chronic exposure to chronic low doses (less than 2 Gy/year) of radionuclides especially in natural conditions are warranted
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