Analysis of Rare Earth Elements in Pteridophytes from the Historical Mining Area, Southwestern Japan

Abstract

Recent studies have shown that various fern species can accumulate REEs in the soil and may be utilized as indicator plants. Athyrium yokoscense, commonly called hebino negoza in Japan, is a pteridophyte that is used as an indicator of metal-contaminated soils in Japan. Mining and mineral processing increase the potential of mine minerals to oxidize and change their chemical form. A study on the biogeochemical behavior of REEs in the mine area needs to be conducted due to the significant use of REEs as an essential material for various applications in the world. The REE content in sediment and pteridophytes under different mining areas was analyzed by inductively coupled plasma-mass spectrometry. The concentration of REEs contained in Athyrium yokoscense was analyzed and then compared to sediment to determine the ability of the plant to absorb and accumulate rare earth elements in the mine area. Sediment and plant samples were collected from three mining areas: Ikuno mine, Akenobe mine, and Tada mine. Athyrium yokoscense plants were collected and digested with hydrogen peroxide (H2O2) and nitric acid (HNO3) at a ratio of 2:5. Sediment samples were taken and digested by the alkali fusion method using lithium tetraborate and then processed using the conventional column method. The present study determined that the concentration of REEs varies in every location, and light REEs tend to be more abundant in sediments than heavy REEs. The amount that can be transferred to ferns also varies. Athyrium yokoscense in the ex-mining area accumulates proportionately more LREEs than HREEs, specifically in the Athyrium yokoscense leaves. The characteristic of the element significantly contributes to the accumulation of REEs in pteridophytes.