Birds living around the site of the Chernobyl nuclear accident have 5% smaller brains, an effect directly linked to lingering background radiation. The finding comes from a study of 550 birds belonging to 48 different species living in the region, published in the journal PLoS One.
Impaired brain development is linked to oxidative stress because of the high lipid content of brains. Large-brained individuals must be capable of continuously supplying the brain with high levels of oxygen for neuronal ion pumping, synthesis of neurotransmitters and protection from toxic compounds. This makes brain maintenance a highly oxidizing process that requires large amounts of antioxidants, in particular glutathione. Therefore, any environment with low antioxidant levels and/or high rates of use of antioxidants will provide a challenge to normal brain development. One such extreme environment is Chernobyl because high levels of background radiation increase oxidative stress cause high rates of use of antioxidants, and hence reduce levels of circulating and stored antioxidants.
Evidence for developmental errors in the nervous systems of people exposed to radiation is widespread, including reduced head size and brain damage. Low levels of ionizing radiation cause changes in both central and autonomous nervous systems and can cause radiogenic encephalopathy. Electroencephalographic studies revealed changes in brain structure and cognitive disorders. Indeed Yablokov et al. summarized an extensive literature on the effects of radiation on cognitive performance as a consequence of the Chernobyl disaster. However, psychological effects of radiation from Chernobyl have recently been attributed to post-traumatic stress rather than developmental errors, and increased levels of neural tube defects in contaminated areas may be ascribed to low-dose radiation, folate deficiencies or prenatal alcohol teratogenesis. Surprisingly, studies of high school performance and cognitive abilities among children from contaminated areas in Scandinavia that were in utero during the Chernobyl disaster show reductions in high school attendance, have lower exam results and reduced IQ scores compared to control groups. These cognitive effects are assumed to be due to developmental errors in neural tissue caused by radiation during early pregnancy. These differences in Scandinavia cannot readily be attributed to changes in social conditions during recent decades. Such social changes have characterized the now independent countries formerly belonging to the Soviet Union, where negative effects of post-traumatic stress have been suggested to account for psychological problems among children living in contaminated areas near Chernobyl.
Here, we tested whether brain size was reduced in birds living in areas differing in background radiation level due to fallout from Chernobyl. A second objective was to test whether brain size increased with age, as expected if there is viability selection against reduced brain size. The key advantage of this study stems from the fact that any observed differences in brain mass in birds associated with radiation cannot be attributed to post-traumatic stress as suggested for humans.
Study sites
We captured 546 birds using 35 12 m mist nets in woodland that exhibit severe reductions in species richness and density of invertebrates and vertebrates in eight different sites around Chernobyl, Ukraine during 25 May – 5 June 2010. 35 mist nets was the maximum that we were able to monitor in the areas with highest density. Each site was used for capture on two consecutive days thus ensuring a similar capture effort in all sample sites. Because the density of birds has been found to decrease with increasing background radiation level, we expected to catch fewer individuals at sites with high level background radiation. In addition, we captured barn swallows at farms where we have followed the population since 1991. Capture of birds was conducted under permission from the authorities of the Chernobyl Exclusion Zone.
Source: Møller AP, Bonisoli-Alquati A, Rudolfsen G, Mousseau TA (2011) Chernobyl Birds Have Smaller Brains. PLoS ONE 6(2). Available at: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016862
Contact: anders.moller@u-psud.fr