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

The environmental monitoring survey using this organisms was called“Caddisfly Watch”and this activity hasinvolved both scientists and local people for collecting them.A simple method is needed for the continuous monitoring of radiocesium (137Cs) contamination in riverineenvironments after the 2011 accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in Japan. In aprogram called“Caddisfly Watch”, we used larvae of the caddisflyStenopsyche marmorata(Trichoptera: Steno-psychidae) to monitor the spatial distribution and estimate effective half-life (Teff)of137Cs pollution in riverineenvironments. Caddisfly larvae showed that the highest concentration of137Cs among several aquatic organismsand no apparent variation between growth stage. In addition, caddisfly larvae reflected137Cs concentrations insuspended particulate matter in their gut, and that showed no seasonal variation, better reproducibility, andsignificant correlation with those in sediment. Results indicate that caddisfly larvae can be used as a biologicalsampler of suspended particulate matters. TheTeffvalues of137Cs concentrations in caddisfly larvae estimated bysingle component decay function model showed significantfit. TheTeffvalues in Kuma, Maeda, downstreamNiida, 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 re-ported in Fukushima. Further continuous observations using this simple approach of“Caddisfly Watch”make itpossible to predict the future of the contamination with radioactive Cs in the river environment