19 March 2014

Radiation risk from Chernobyl forest fire smoke worries ecologists

by Will Parker

Radiation damage to microbes around the site of the Chernobyl nuclear disaster has dramatically slowed the decomposition of fallen leaves and other plant matter in the area, according to a study published in the journal Oecologia. The resulting build-up of dry, loose material is a fire hazard that poses the threat of spreading wind-borne radioactivity, the study suggests.

Study authors Tim Mousseau, from the University of South Carolina, and Anders Moller, from the University Paris-Sud, based their work on extensive research in the contaminated area surrounding the Chernobyl nuclear facility. Mousseau says they focused their research on the Red Forest, the most contaminated part of the Chernobyl Exclusion Zone.

"We were stepping over all these dead trees on the ground that had been killed by the initial blast," Mousseau exaplined. "Some 15 or 20 years later, these tree trunks were in pretty good shape. If a tree had fallen in my backyard, it would be sawdust in 10 years or so."

The researchers set out to assess the rate at which plant material decomposed as a function of background radiation, placing hundreds of samples of uncontaminated leaf litter (pine needles, oak, maple and birch leaves) in mesh bags throughout the area. The locations were chosen to cover a range of radiation doses, and the samples were retrieved after nine months outdoors.

An analysis of the weight loss of each leaf litter sample after those nine months showed that higher background radiation was associated with less weight loss. The response was proportional to radiation dose, and in the most contaminated regions, the leaf loss was 40 percent less than in regions in Ukraine with normal background radiation levels.

The researchers concluded that the bacteria and fungi that decompose plant matter in normal ecosystems are hindered by radioactive contamination.

"It's another facet of the impacts of low-dose-rate radioactive contaminants on the broader ecosystem," Mousseau says. "We've looked at many other components, namely the populations of animals in the area, and this was an opportunity for broadening our range of interests to include the plant and microbial communities."

Worryingly, the results show the potential for further spread of radioactivity. "This litter accumulation that we measured, which is likely a direct consequence of reduced microbial decomposing activity, is like kindling. It's dry, light and burns quite readily. There's been growing concern by many different groups of the potential for catastrophic forest fires to sweep through this part of the world and redistribute the radioactive contamination that is in the trees and the plant biomass," Mousseau explained. "That would end up moving cesium and other contaminants via smoke into populated areas."

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Source: University of South Carolina