The activity concentrations and concentration factors of radio-cesium 137 (¹³⁷Cs) in chironomid larvae in Lake Kasumigaura two years after the Fukushima Accident

Abstract

　Approximately two years after the accident at the Fukushima Daiichi Nuclear Power Plant on 11 March 2011, radiocesium (¹³⁷Cs) concentrations were measured from lake water and benthic macroinvertebrate (mainly composed of chironomid larvae: Chironomus plumosus and Tanypus nakazatoi) samples from the three stations in pelagic zone of Lake Kasumigaura. The larvae of C. plumosus were collected in sufficient numbers at the three stations, whereas the larvae of T. nakazatoi were collected in sufficient numbers at Tsuchiura-iri only. We determined the difference in the activity concentrations of ¹³⁷Cs in chironomid larvae between the two species and among the three stations, and calculated their concentration factors (CF). The activity concentration of ¹³⁷Cs in T. nakazatoi (12.3 Bq kg^-1) was within the range of that observed in C. plumosus (5.5 – 20.7 Bq kg^-1). The activity concentration of ¹³⁷Cs of T. nakazatoi was lower than that of C. plumosus at Tsuchiura-iri. The concentration factors of T. nakazatoi and C. plumosus were 630 and 380 – 1060, respectively.