By Victoria Gill
Science reporter, BBC News
Chernobyl is largely human-free but still contaminated with radiation
Two decades after the explosion at the Chernobyl nuclear power plant, radiation is still causing a reduction in the numbers of insects and spiders.
According to researchers working in the exclusion zone surrounding Chernobyl, there is a "strong signal of decline associated with the contamination".
The team found that bumblebees, butterflies, grasshoppers, dragonflies and spiders were affected.
They report their findings in the journal Biology Letters.
Professor Timothy Mousseau from the University of South Carolina, US, and Dr Anders Moller from the University of Paris-Sud worked together on the project.
The two researchers previously published findings that low-level radiation in the area has a negative impact on bird populations.
"We wanted to expand the range of our coverage to include insects, mammals and plants," said Professor Mousseau. "This study is the next in the series."
Professor Mousseau has been working for almost a decade in the exclusion zone. This is the contaminated area surrounding the plant that was evacuated after the explosion, that remains effectively free of modern human habitation.
The team counted insects and spider webs in the 'unique' exclusion zone
For this study they used what Mousseau described as "standard ecological techniques" - plotting "line transects" through selected areas, and counting the numbers of insects and spiders webs they found along that line.
At the same time, the researchers carried hand-held GPS units and dosimeters to monitor radiation levels.
"We took transects through contaminated areas in Chernobyl, contaminated land in Belarus, and in areas free of contamination.
"What we found was the same basic pattern throughout these areas - the numbers of organisms declined with increasing contamination."
According to Professor Mousseau, this technique of counting organisms is "particularly sensitive" because it can account for the changing pattern of contamination across the zone.
"We can compare relatively clean areas to the more contaminated ones," he explained.
Thriving or dying?
But some researchers have challenged the study, claiming that the lack of human activity in the exclusion zone has been beneficial for wildlife.
Dr Sergii Gashchak, a researcher at the Chornobyl Center in Ukraine, dismissed the findings. He said that he drew "opposite conclusions" from the same data the team collected on birds.
"Wildlife really thrives in Chernobyl area - due to the low level of [human] influence," Dr Gashchak told BBC News.
"All life appeared and developed under the influence of radiation, so mechanisms of resistance and recovery evolved to survive in those conditions," he continued.
"After the accident, radiation impacts exceeded the capabilities of organisms. But 10 years after the accident, the dose rates dropped by 100 to 1,000 times."
Professor Mousseau responded that his aim is to use the site to discover the true ecological effects of radiation contamination.
"The verdict is still out concerning the long-term consequences of mutagenic contaminants in the environment," he said.
"Long-term studies of the Chernobyl ecosystem offer a unique opportunity to explore these potential risks that should not be missed."