The United Nations Scientific Committee on the Effects of Atomic Radiation oversaw a study by an international team of scientists, who evaluated the results of a 2011 environmental assessment of the area near the power plant and published their results earlier this year (Environ. Sci. Technol. Lett., 2014, 1, 198–203).The UN committee compiled data for the year following the accident; relevant reports and scientific papers provided additional data. Radiation effects were inferred by comparing compiled dose–response relationships.
Radiation exposures were evaluated for the first 3 months after the accident, during which short-lived isotopes played a significant role, and for a later phase (3–12 months), in which exposure was dominated by longer-lived isotopes. Radionuclide concentrations were measured over time and geographic area. The researchers used kinetic models to calculate how concentrations varied over time in the whole collection of organisms for each area (biota). They determined cumulative doses using calculations.
Adult butterflies collected in September 2011 showed more severe abnormalities than those collected in May 2011, indicating that cumulative radiation exposure had caused deterioration in the overall butterfly population. However, dosimetry uncertainties and other confounding factors complicate the interpretation of these observations. The recorded dose rates were much too low to cause the kinds of abnormalities the researchers observed, and when they tried to replicate the conditions in the laboratory, they needed ten times the radiation exposure to reproduce the same effects that they saw in the field. Other scientific data do not support the appearance of the observed effects at the dose rates recorded.
The research team noted that localized effects might have contributed to the abnormalities they saw in the butterflies. They also observed declines in some bird populations and exposures of macroalgae that exceeded corresponding benchmarks, which supports this possibility.
The team concluded that because the highest exposure levels lasted only a short time, there was likely no damage to the integrity of plant and animal populations overall. However, individual organisms in relatively contaminated areas might have been damaged during the weeks immediately after the accident. Especially at risk were individual members of species that are especially sensitive to radiation, that stay in one place rather than moving around, or that live in areas that received high doses of radiation.
This is a lay-audience summary of my writeup on The American Chemical Society’s website.