Antinuclear

A few years ago, on one of her first visits to Chernobyl, Katherine Raines went to the Red Forest, a radioactive cemetery of pine trees scorched by the nuclear accident in 1986. She was curious to see if there were bees living in the area. Research on the effect of chronic exposure to ionizing radiation on insects is limited, and some of the findings are controversial, but most experts support the idea that bees and other invertebrates are relatively resilient to radioactive stress.

Raines, a radioecologist at the University of Stirling in Scotland, didn’t spend long in that forest. In one spot there, her personal radiation dosimeter measured an environmental level of ionizing radiation of 200 microsieverts (µSv) per hour; more than a few hours of that exposure could have increased her cancer risk. But even during that brief visit, she did see bees. Whether they were living there or just visiting, Raines says, is hard to tell.

Back in the UK, Raines and colleagues recreated the same levels of radiation in a specialized facility. Boxes each containing a bumble bee colony made up of a queen, workers, and brood were placed at different distances from a radiation source, creating a gradient where bees in each box received a fairly steady dose of between 20 and 3,000 micrograys (µGy) per hour. (The two kinds of units, sieverts and grays, are essentially equivalent measures of the amount of exposure to radiation; sieverts factor in the type of radiation and account for the sensitivity of the exposed tissue. Bees at the site Raines visited in the Red Forest would experience around 200 µGy per hour.) The bees stayed in their artificial homes for four weeks before being moved outdoors into the university gardens for around one month, until the colonies were no longer viable—that is, once the queen had died and only a few workers remained. 

The limited lab studies previously carried out by other groups had suggested that bees and other insects should be safe below 400 µGy per hour. So, Raines says, she was shocked when she found that even those colonies exposed to lower rates showed signs of a negative effect of radiation, especially on reproduction. Bumble bee colonies experiencing just 100 µGy per hour, for example, had reduced their production of queens by almost half, dramatically impairing the chances of successfully founding new colonies. According to the study, the overall effect was stronger than the one-fourth reduction observed in colonies exposed to a popular pesticide. 

This work “sheds new light on the importance of chronic low-dose radiation exposure in a nonmodel species [with] profound relevance for the natural world,” says Timothy Mousseau, an ecological geneticist at the University of South Carolina who was not involved in this research. But he adds that it is hard to determine how some of these results, based on experimental manipulations in an artificial setting, can translate “to what’s actually going on in Chernobyl” for these important pollinators. 

Mousseau and his colleague Anders Pape Møller (now at CNRS in France) have been doing field studies since 2000 to assess the abundance of wildlife populations living in the Chernobyl Exclusion Zone (CEZ), a 2,600 square-kilometer area surrounding the nuclear power plant. Their results have shown a negative correlation between radiation levels—which vary a great deal within the zone—and wildlife abundance. Insects were no exception: the team observed fewer bumble bees in the most contaminated areas, a relationship that held even within a range of extremely low radiation levels (from 0.01 to 1 µGy per hour)

Those studies have been criticized, partly over the accuracy of their estimations of radiation levels. Mousseau and Møller have collaborated with some of their critics to reanalyze some of their data, and maintain that there has been wildlife reduction in the CEZ due to radiation. ………

Researchers who spoke to The Scientist about the study agree that further work is needed to conclusively demonstrate the effects of radiation on bumble bees. ……. Raines is now gathering more data. The next stage of her research, she says, will be to look at the interaction between parasite load, which reduces longevity, and radiation exposure—both in lab-kept bees and in bees she sampled on one of her visits to deserted agricultural land around Chernobyl. “It would be ideal to directly relate lab and field [data].”       https://www.the-scientist.com/notebook/insects-might-be-more-sensitive-to-radiation-than-thought-68366