Date Published: January 26, 2017
Publisher: Public Library of Science
Author(s): Yumiko Ishii, Seiji Hayashi, Noriko Takamura, Hideyuki Doi.
To understand radiocesium transfer in the forest insect food web, we investigated the activity concentrations of radiocesium in forest insects in the Fukushima and Ibaraki Prefectures approximately 1.5–2.5 years after the Fukushima Dai-ichi Nuclear Power Plant. We analyzed 34 species of insects sampled from 4 orders and 4 feeding functional groups (herbivore, carnivore, omnivore, and detritivore) from three sites in each prefecture. 137Cs activity concentrations were lowest in herbivorous species and were especially high in detritivorous and omnivorous species that feed on forest litter and fungi. Radiocesium activity concentrations in any given species reflected the degree of contamination of that species’ primary food sources since radiocesium activity concentrations were found to be the lowest in leaves and grass and the highest in litter, bark, and fungi. This study confirmed that litter and other highly contaminated forest components such as fungi, decaying wood, bryophytes, and lichens serve as sources of 137Cs transfer into the forest insect community.
The forest ecosystems of Fukushima and its adjacent prefectures were severely contaminated with radionuclides after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on 11 March 2011 [1,2]. For decades to come, the most biologically important radionuclide will be radiocesium because of its long half-life (30.1 years for 137Cs, 2.1 years for 134Cs) [2,3]. Many studies have reported that most of the Chernobyl radiocesium fallout still resides in surface layers in bioavailable form and continues to be a major potential source for transfer into living organisms even several decades after deposition [4,5]. Similarly, in Fukushima, radiocesium is expected to remain in the litter and upper soil layers of the forest floor for the long term .
Understanding the movement of 137Cs through ecosystems is essential for the management of radiation contamination and risk assessment in forest environments. This study investigated 137Cs transfer in forest insect communities in areas contaminated by the Fukushima Dai-ichi Nuclear Power Plant Accident. The results showed that 137Cs activity concentrations were lowest in herbivores and highest in carnivores, detritivores, and omnivores. The level of contamination in each of the four functional feeding groups of insects reflected the level of contamination of the materials and organisms that constitute their diets. Detritorivorous species had the highest levels of contamination, confirming findings of previous studies that these species play a significant role in 137Cs transfer into the forest ecosystem via consumption of highly contaminated forest litter. The nonuniform distribution of 137Cs in the forest environment is not only because of litter but also because of other forest components that may have high levels of 137Cs contamination, including fungi, decaying wood, bryophytes, and lichens. Insect species that have high CR values or that live in highly contaminated substrates, such as dung beetles, camel crickets, and lichen moths, would be appropriate species for monitoring radiocesium activity concentrations or for studies of radiation effects on wildlife.