Abstract
The Fukushima accident emitted radioactive substances into the environment, contaminating litter, algae, sand substrate, aquatic invertebrates, and fish in freshwater streams. Because these substances have substantial effects on stream ecology over many years, it is necessary to clarify the diffusion and decay mechanisms of radiocesium. The transfer coefficient differed among aquatic invertebrate groups, likely due to the differences in habitat. The ecological half-life of cesium was longer where the air dose rate was lower. The transfer coefficient was also higher in areas with lower air dose rate. The radiocesium concentration in algae was inversely related to stream current velocity in the radiocesium-contaminated area. However, this relationship was not observed in the lower air dose rate area: the radiocesium concentration in algae in the rapid-velocity areas tended to be higher than that in the slow-velocity areas. This reverse trend would lead to a longer period of freshwater contamination. The radiocesium concentration would continue to decrease in highly contaminated areas, but it would be difficult to reduce the radiocesium concentration in less-contaminated areas because different contamination mechanisms are at work. Controlling the water flow is key to regulating radiocesium concentration in freshwater ecosystems.
Highlights
The Fukushima accident emitted radioactive substances into the environment, contaminating litter, algae, sand substrate, aquatic invertebrates, and fish in freshwater streams
There were no differences in values for air or water temperature, pH, or dissolved oxygen (DO) among the four sites, whereas the electrical conductivity (EC) and dose rate on the sampling dates differed significantly among sites (Table 1)
The radiocesium concentration was higher in Ephemera japonica and Lanthus fujiacus and lower in Perlidae Gen. spp. and Corydalidae
Summary
The Fukushima accident emitted radioactive substances into the environment, contaminating litter, algae, sand substrate, aquatic invertebrates, and fish in freshwater streams. This relationship was not observed in the lower air dose rate area: the radiocesium concentration in algae in the rapid-velocity areas tended to be higher than that in the slow-velocity areas This reverse trend would lead to a longer period of freshwater contamination. Dissolved cesium-134 and cesium-137 in running water that is not adsorbed into the soil and particles is readily taken up by microbes, algae, plankton and plants These transport pathways of cesium-134 and cesium-137 will eventually lead to uptake by aquatic invertebrates and freshwater fishes at higher trophic levels in the food web[5,9,10,11]. There are few studies focusing on radioactive contamination in freshwater biota such as algae and aquatic invertebrates
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