animal survival, atomic bomb, background radiation, Belarus, bird deaths, bird mortality, birds, blindness, cataracts, cataracts and radiation, cataracts in animals, cataracts in children, cataracts in humans, cause of cataracts, Chernobyl, elevated background radiation, Hiroshima, Nagasaki, nuclear disaster, nuclear power, radiation, robins, seeing impaired, Ukraine
European Robin (Erithacus rubecula) by Pierre Selim via wikimedia
Very sad. Bird eyes with cataracts:
(k) robin (Erithacus rubecula), significant haze on cornea
Photographs of selected eyes from Chernobyl birds.
From: Mousseau TA, Møller AP (2013) “Elevated Frequency of Cataracts in Birds from Chernobyl” http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0066939
Lucky for us some few are still doing serious academic research. If animals can’t see well, with some exceptions, they can’t find food and die, or can more easily be killed by predators. The frequency and severity of cataracts increases with background radiation. In the abstract below “reduced fitness” means they are unfit for survival! Overall, increasing radiation was related to fewer birds, suggesting “effects of radiation on other diseases, food abundance and interactions with other species. There was no increase in incidence of cataracts with increasing age…”. Cataracts in humans at Chernobyl and elsewhere are also discussed:
Mousseau TA, Møller AP (2013) “Elevated Frequency of Cataracts in Birds from Chernobyl”
Radiation cataracts develop as a consequence of the effects of ionizing radiation on the development of the lens of the eye with an opaque lens reducing or eliminating the ability to see. Therefore, we would expect cataracts to be associated with reduced fitness in free-living animals.
We investigated the incidence of lens opacities typical of cataracts in more than 1100 free-living birds in the Chernobyl region in relation to background radiation. The incidence of cataracts increased with level of background radiation both in analyses based on a dichotomous score and in analyses of continuous scores of intensity of cataracts. The odds ratio per unit change in the regressor was 0.722 (95% CI 0.648, 0.804), which was less than odds ratios from investigations of radiation cataracts in humans. The relatively small odds ratio may be due to increased mortality in birds with cataracts. We found a stronger negative relationship between bird abundance and background radiation when the frequency of cataracts was higher, but also a direct effect of radiation on abundance, suggesting that radiation indirectly affects abundance negatively through an increase in the frequency of cataracts in bird populations, but also through direct effects of radiation on other diseases, food abundance and interactions with other species. There was no increase in incidence of cataracts with increasing age, suggesting that yearlings and older individuals were similarly affected as is typical of radiation cataract.
These findings suggest that cataracts are an under-estimated cause of morbidity in free-living birds and, by inference, other vertebrates in areas contaminated with radioactive materials.
Citation: Mousseau TA, Møller AP (2013) Elevated Frequency of Cataracts in Birds from Chernobyl. PLoS ONE 8(7): e66939. doi:10.1371/journal.pone.0066939
Editor: Jordi Moya-Larano, Estacion Experimental de Zonas Áridas (CSIC), Spain
Received: December 10, 2012; Accepted: May 11, 2013; Published: July 30, 2013
Copyright: © 2013 Møller, Mousseau. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Financial support was received from the US National Science Foundation, the University of South Carolina, the North Atlantic Treaty Organization Collaborative Linkage Grant program, the Civilian Research and Development Foundation, the Fulbright Program, the National Geographic Society, and the Samuel Freeman Charitable Trust. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Cataract is a disease of the eye characterized by an opaque lens that under normal conditions focus images on the retina to allow perception of visual information. Such opacities result in a reduction in vision and even complete loss of eyesight, and cataracts are the single-most common cause of blindness in humans. The lens of the eye has for a long time been considered sensitive to ionizing and non-ionizing radiation , . Cataracts are a frequent outcome of exposure to radiation [e. g. 3]–. The underlying mechanism by which ionizing radiation causes cataracts is the ionization of water and the production of free radicals such as hydroxyl and hydrogen radicals. These free radicals can damage DNA and cause damage or errors in lens protein formation and hence contribute to cataract formation. The lenses are almost entirely composed of proteins that can be oxidized with subsequent aggregation and precipitation causing opacities in the lenses that form the basis of cataracts. Lens proteins show little turnover throughout the life of an individual thereby making them particularly susceptible to oxidative stress. Dose thresholds of 0.5–2.0 Gy for acute exposure and 5.0 Gy for protracted exposure for radiation cataract are assumed in the literature . However, to date the most extensive epidemiological study of 8607 Chernobyl Ukrainian liquidators involved in clean-up at the Chernobyl nuclear power plant showed a post-exposure level of dose of only 0.12 Gy, and despite the low level of dose there was a statistically significant dose response for stage 1 cataract (the initial stage of cataracts) and posterior subcapsular cataracts (located in the subcapsular region of the ocular lens) . Threshold exposure estimates showed that values greater than 700 mGy caused a significant risk of detectable opacities, which is a much greater risk than what is recommended in radiation protection guidelines . Studies of atomic bomb survivors have shown a clear linear dose-response for the frequency of cataracts without a threshold and this is much lower than the threshold of 2–5 Gy usually assumed by the radiation protection community . A similar conclusion was reached for a study of radiological technologists . Thus there is evidence consistent with low or no thresholds , and this documented greater susceptibility to radiation than proposed by radiation protection authorities is consistent with a recent assessment showing that to generally be the case .
The eye lens is almost entirely composed of proteins whose oxidation and subsequent aggregation and precipitation generate the opacities characteristic of cataracts . Some cases of cataracts in humans have a genetic basis , although the main causes of human cataracts are agents that produce oxidative stress (i.e., the imbalance between levels of reactive oxygen species and state of the antioxidant and repair machinery) such as ultraviolet radiation and smoking, as well as accumulation of effects of free radicals with aging , . Accordingly, Galván et al.  showed elevated levels of cataracts in wild birds with pheomelanin-based plumage coloration, apparently linked to the effects of oxidative stress. Cataracts are a rare phenomenon in wild animals  because any deterioration in vision will likely very soon be followed by death due to predation or lack of ability to find adequate and sufficient food for survival.
The objectives of this study were to determine (1) the relationship between the incidence of cataract and background radiation, using a large database of more than 1100 free-living birds captured at Chernobyl during 2011–2012. In other words, we assessed the reliability of the rate of cataracts as a biomarker of radiation exposure. Because the lifespan of most free-living animals with impaired vision is bound to be short due to elevated risk of predation and inability to find sufficient amounts of food, field estimates of prevalence of cataracts are by definition conservative. Therefore, the second objective of this study was (2) to determine whether the abundance of different species of birds decreased the most in species that showed a stronger impact of radiation on the incidence of cataracts. Finally, we tested (3) if the frequency of cataracts increased with age as expected from human studies showing accumulation of free radicals with age –. Because many birds can be aged reliably as either yearlings or older individuals , we included a categorical age variable and the interaction between level of background radiation and age as predictors of the extent of cataracts.”
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The main findings of this study of cataracts in free-living birds in the Chernobyl region were that (1) the intensity and the incidence of cataracts increased with level of background radiation, (2) the slope of the relationship between abundance of breeding birds and background radiation decreased with increasing incidence of cataracts, but also through direct effects due to other diseases, food abundance or interspecific interactions in different species of birds, and (3) there was no increase in incidence of cataracts with increasing age.
Radiation cataracts are a frequent outcome of exposure to ionizing radiation –. While many studies have shown that atomic bomb survivors, workers in radiation facilities and people exposed to radiation following nuclear accidents suffer from elevated risk of developing cataracts , , , there are to the best of our knowledge no previous studies of animals. Cataracts in free-living birds in this study increased in a dose-dependent manner with level of background radiation with no evidence of a threshold. Individuals with opacities in one lens were much more likely to also develop opacities in the lens of the other eye, thereby increasing the risk of death for the individual. Here we have shown that radiation level in a mixed model accounted for an intermediate effect of 0.28, while a logistic regression based on dichotomous data showed an effect of a similar magnitude (0.30). The odds ratio for birds was 0.284 (95% CI 0.186, 0.431). This odds ratio is low compared to estimates for humans ranging from 1.25 (1.06–1.47)  over 1.30 (1.24–1.55)  to 1.54 (1.11–2.14) . The odds ratio estimated for birds is bound to be conservative given the elevated risk of death experienced by individuals with cataracts. Although it may seem intuitively obvious that individual birds with cataracts suffer from reduced fitness, the magnitude of that cost has so far never been quantified in birds or other taxa.
Population size of birds can be assessed from point counts ,  and mist net captures . Birds and other organisms have severely depressed breeding population sizes in the most contaminated areas surrounding Chernobyl both in Ukraine and in Belarus , , . Some of these effects may arise because of antioxidant deficiency , or because of excess mortality due to a variety of health reasons . Studies of humans have shown that a great diversity of disease conditions has developed as a consequence of exposure to radiation from Chernobyl , . If that was also the case in birds, as our data suggests, we should expect that the species with the strongest negative effects of radiation on abundance of breeding birds were the species with the highest frequency of disease. Thus we predicted a negative relationship between slope of the relationship between abundance and radiation and incidence of cataracts. This was indeed the relationship that we found. Obviously, we cannot ascertain that cataracts are the direct cause of these population declines, nor can we estimate the exact contribution of cataracts to this reduction. However, given that cataracts are associated with a dramatic increase in risk of mortality in birds, it seems likely that species with high frequencies and degree of cataracts will suffer from elevated levels of mortality. Furthermore, Galván et al.  have shown that bird species with pheomelanic coloration are more likely to develop cataracts than species without such coloration, and such species also show much stronger population declines from background radiation than expected , consistent with our predictions. We estimated the direct effects of background radiation, but also the indirect effects through cataracts, relying on path analysis (Figure 5). This resulted in an estimated indirect contribution of cataracts by 4.0% and a direct contribution of radiation by 23.4% to population levels. Therefore, radiation had a direct effect that was six-fold greater than the indirect effect of cataracts. However, again, we must emphasize that the indirect effect is bound to be an under-estimate given the likely elevated probability of mortality among individuals with cataracts. Possible direct effects of radiation on abundance include effects on other diseases , abundance of food  and interspecific interactions , .
Most human cases of cataracts are reported in people older than 40 years –. However, radiation cataracts can affect even young children, as shown in a study of people exposed to radiation from Chernobyl in Belarus  and studies of children treated with radiation therapy for cancer –. In addition, recent reports indicated that health care technicians who use radiation for medical treatment are at much higher risk of cataract irrespective of sex or age . Here we were able to age more than half of all birds as either yearlings or older individuals using well-established external age criteria . When entering age as a categorical predictor of cataracts in our statistical models together with the level of background radiation and species, we found only weak and non-significant effects of age on the incidence and the severity of cataracts. Hence radiation exposure rather than age was the main predictor of cataract. This conclusion must be drawn cautiously because high mortality rates among individuals with cataracts may have significantly reduced the fraction of old individuals that are more likely to develop cataracts.
In conclusion, we have shown increased incidence of cataracts in free-living birds inhabiting areas with elevated levels of background radiation around Chernobyl. Cataracts were associated with depressed breeding population sizes in contaminated areas.” (We have added bold for emphasis) Entire article with details of research methods, references, images, etc. is here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0066939