Using the larvae of caddisfly as a biomonitor to assess the spatial distribution and effective half-life of radiocesium in riverine environments in Fukushima, Japan

The environmental monitoring survey using this organisms was called “Caddisfly Watch” and this activity has involved both scientists and local people for collecting them. A simple method is needed for the continuous monitoring of radiocesium (137Cs) contamination in riverine environments after the 2011 accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in Japan. In a program called “Caddisfly Watch”, we used larvae of the caddisfly Stenopsyche marmorata (Trichoptera: Stenopsychidae) to monitor the spatial distribution and estimate effective half-life (Teff) of 137Cs pollution in riverine environments. Caddisfly larvae showed that the highest concentration of 137Cs among several aquatic organisms and no apparent variation between growth stage. In addition, caddisfly larvae reflected 137Cs concentrations in suspended particulate matter in their gut, and that showed no seasonal variation, better reproducibility, and significant correlation with those in sediment. Results indicate that caddisfly larvae can be used as a biological sampler of suspended particulate matters. The Teff values of 137Cs concentrations in caddisfly larvae estimated by single component decay function model showed significant fit. The Teff values in Kuma, Maeda, downstream Niida, upstream Niida, Ohkawa, and Ukedo river showed 2.8, 5.7, 3.1, 6.7, 0.6, and 4.8 years (34, 68, 38, 80, 6.9, and 58 months), respectively. The results of declining trend in this study were similar to those in previous reported in Fukushima. Further continuous observations using this simple approach of “Caddisfly Watch” make it possible to predict the future of the contamination with radioactive Cs in the river environment.