Monitoring Radiocesium Contamination of the Web Spider Nephila clavata (Nephilidae: Arachnida) in Fukushima Forests

Abstract

We investigated the relationships between radiocesium activity in the soil and litter and radiocesium concentration in the web spiders collected at two forest sites in Kawamata-cho, Fukushima Prefecture. Changes in radiocesium contamination levels of the web spider over two years (2012-2013) were also monitored. At both sites, the aggregated transfer coefficient（T_ag）of radiocesium from the soil into spiders in 2013 was approximately 0.005, and the radiocesium contamination level of spiders depended on the contamination level of the soil. Compared to the web spiders collected in 2012 (1.5 y after the accident), the concentration of ¹³⁷Cs in spiders collected in 2013 (2.5 y after the accident) decreased by 40-50％, which was lower than that expected based on the physical attenuation of ¹³⁷Cs. Although the mean level of ¹³⁷Cs contamination in spiders decreased, highly ¹³⁷Cs contaminated spiders were still collected in 2013, and this implies a need for a long-term monitoring of radiocesium contamination of the spider.