Almost four decades have passed since the accident at the Chernobyl nuclear power plant (Ukraine). During this time, and to the surprise of many, this place has become one of the largest nature reserves in Europe. Over the last eight years we have worked to understand the situation of the fauna in the area affected by this environmental disaster.
Radiation is capable of damaging cells and, in extreme exposures, can even cause the death of organisms. But the situation at Chernobyl has changed a lot since the accident. Less than 10% of the radioactive material released in 1986 remains there today. The most dangerous isotopes, such as iodine, disappeared many years ago.
Male Eastern San Antonio Frog (Hyla of the east). Ukraine, June 2019.
German Orizaola
These factors may explain the great abundance and diversity of animals that live in Chernobyl today. However, it is essential to examine whether organisms experience damage that we do not see. For example, if they accumulate damage that ends up reducing their life expectancy.
The frogs of Chernobyl
Since 2016 we have been studying the populations of the eastern San Antonio frog (Hyla of the east) in Chernobyl, visiting the area for several weeks each spring. Taking advantage of the breeding season, we capture males during the night and take them to our laboratory.
In addition to the Chernobyl exclusion zone, we work in other areas of northern Ukraine without radioactive contamination. These places serve as controls to compare our results there with those of the party affected by the accident.
Field work in the Chernobyl Exclusion Zone (Ukraine). May 2018.
German Orizaola
For years we have examined the morphology, physiological and immune status, and many other traits of these frogs. Our works have shown the apparent good health of amphibians in Chernobyl. In addition, we discovered an example of rapid evolution in frogs, which are darker than those in other areas without radiation. This is possibly due to the protective role of melanin against radiation.
The long-term effect of radiation on these animals remained to be investigated. That is why we analyzed the relationship between radiation, age and aging of frogs.
How long does a frog live?
We can calculate the age of an amphibian by counting the growth lines on its bones. Just like tree rings, each year of a frog’s life is marked. We know that some species in high mountain areas can live more than 20 years. Other species, however, barely reach 2 years.
In our work in Chernobyl we examined about 200 specimens over three years. We found a maximum age of 9 years in male eastern San Antonio frogs. The majority of individuals we studied were between 3 and 4 years old.
Male Eastern San Antonio Frog (Hyla of the east) in our laboratory in Chernobyl (Ukraine). May 2019.
German Orizaola
In addition, we wanted to know if radiation affected the rate of aging of the frogs. To do this, we measured telomere length, a marker associated with the rate of aging. These are DNA sequences found at the end of chromosomes. Their function is to protect the genetic material and they become shorter with each division of the cell.
To complete our study, we also examined the levels of stress-related hormones in these frogs. We measure the blood content of corticosterone, a hormone that participates in the regulation of metabolism and the activation of the stress response.
In all frogs we also calculated the levels of radiation absorbed by each individual. We measure the level of cesium in your muscles and strontium in your bones. This is one of the most detailed studies on current radiation exposure in animals from Chernobyl. It allows us to precisely relate the traits we measured with radiation exposure in the frogs studied.
Field work with reactor 4 of the Chernobyl nuclear power plant in the background. May 2019.
German Orizaola
The aging of Chernobyl frogs
Our work reveals that living in Chernobyl does not affect the age or rate of aging of the frogs studied.
The average age of the individuals we captured was 3.6 years and was similar in individuals with a higher level of radiation and in those from areas without radiation. These values are normal for the species and similar to those of other populations far from Chernobyl.
We also did not observe any effect of radiation on the rate of aging of the frogs. We did not detect any relationship between the radiation absorbed by the frogs and the length of their telomeres. This remained fairly constant throughout all the radiation levels studied.
Furthermore, levels of the hormone corticosterone were not affected by the absorbed radiation. The Chernobyl frogs don’t seem to be stressed either.
These results suggest that the radiation levels present today at Chernobyl are not sufficient to cause chronic damage to these organisms. These investigations are essential to dismantle the myth that the Exclusion Zone is hell for life. Instead, studies like ours show that it has become a highly relevant refuge for Europe’s threatened fauna.
