Novel application of mosses transplanted in bags as biointerceptors of airborne radioactive dusts after the Fukushima Dai-ichi Nuclear Power Station accident

Nine years after the Fukushima Dai-ichi Nuclear Power Plant accident, in line with the strong efforts to devise ever more effective methods to monitor airborne radioactive dusts, in the present study we proposed for the first time the use of mosses transplanted in bags as biointerceptors of ¹³⁴Cs and ¹³⁷Cs in the evacuated zone of the Fukushima territory and according to a standardised protocol. The work aimed to investigate the ability of the moss transplants to accumulate radiocaesium and therefore to act as radiocaesium biointerceptors. To this purpose, the activity concentrations of radiocaesium were measured in moss bags filled with 3 widely studied moss species (Sphagnum palustre, Hypnum cupressiforme, Hypnum plumaeforme) and exposed for 3, 6 and 9 weeks at 5 residential sites within Fukushima area. The levels of radiocaesium found in moss bags were evaluated as function of different parameters (e.g. exposure time, site conditions, moss species). The moss bags were able to accumulate ¹³⁷Cs in all exposure sites and periods, with Sphagnum palustre acting as the most performant moss species. The ¹³⁷Cs activity concentrations (from 28 to 4700 Bq kg^-1), could be explained by the Cs deposition levels and decontamination status of each exposure site, highlighting the sensitivity of the moss bags to discriminate among exposure sites according to their contamination level. Autoradiography and electron microscopy analysis of the distribution and the chemical composition of the particles entrapped by moss surfaces revealed a prevalence soil-derived radiocaesium. The linear dependency of Cs accumulation with the exposure time allowed a radiocaesium quantitative assessment by using location-specific (LF) and species-specific (SF) factors, with the latter susceptible to an “universal” applicability in future biomonitoring studies with the same experimental design.