Accumulation of cesium by aquatic plants and algae

Abstract

A huge activity of radioactive matter including biophilic elements such as cesium, strontium and iodine were released into the environment from the Fukushima 1st Nuclear Power Plant (F1NPP) which was destroyed by the Great East Japan Earthquake in 2011. It is indispensable for rehabilitation to decontaminate and collect radionuclides spread on soils and water in the huge area. However, the amount and concentration of those radionuclides released were very small and low in comparison with those activities. Chemical processes sometimes require high energy and high cost for removing such low concentration of radionuclides from the environment. On the other hand, biological processes such as bioremediation and phytoremediation are thought to be useful because plants and algae have an ability to absorb and concentrate such radionuclides into bodies and cells. Cesium is reported to be easily absorbed by plants and algal cells via potassium transport systems as an analogue of potassium. On the basis of such knowledge, this study for screening was performed to find organisms possessing very high ability to accumulate radioactive cesium specifically and also radioactive strontium and iodine. After testing 188 strains of various aquatic plants and algae, several strains were found to show a high ability to accumulate cesium in the cells by the removal of the radioactivity from medium. High cesium-accumulating strains were different from strains which have high ability to remove strontium and iodine, suggesting strains are specific to each element. The best strain for cesium accumulation coded as nak 9 was found to be a eustigmatophycean microalga Vacuoliviride crystalliferum which was a novel genus and species. This chapter focuses on the cesium uptake mechanism by plant and algal cells, the screening process how to find most effective strains which are useful for phytoremediation and the analysis of cesium absorption profiles. Morphological properties of the alga are also described.