Source, environmental significance of rare earth elements in the soil-water system of Hunan integrated rice-fish farming base

The concentrations of rare earth elements (REE) in soils and waters in rice paddies from the three Fishing Breeding areas at the Yuping (YP), Heye (HY), and Jinggang (JG) villages in Hunan province (China) were analyzed using the ICP-MS techniques in this study, with purpose to understand the possible anthropogenic impacts on soil-water environment of the study areas based on characterizing the REE enrichment styles in the soils-waters systems. The results showed that concentrations in average of the total REE (ΣREE) in soils of YP, HY, and JG areas were 293.74, 339.93, and 272.98 μg·g-1 respectively. The enrichment factor (EF values) showed that REE was slightly enriched in the HY soils (1 Igeo −1 and 0.34—3.31 μg·L−1 respectively. The North American Shale Composition (NASC) normalization showed that soils from the three rice-fish base generally displayed the light REE (LREE) enrichment patterns, while REEs in waters of the YP rice-fish base were in patterns of slightly middle REE (MREE) enrichment, while the waters of the HY rice-fish base were in flat patterns with a Eu anomaly. The REE distributional patterns in soils and waters, speciations of REEs in soils, and correlations between REE and major elemental concentrations in soils suggested that REEs in the soil-water systems of the areas were contributed from the soil bedrocks. The transportation coefficient calculation suggested that REEs were integratedly transformed from the soils to the waters correspondingly. The triangular plots of rare earth element ratios and the above REE distributional patterns suggested that the dissolved REEs in waters of the rice paddies were contributed from the exchangeable and carbonate-associated REEs in soils. Therefore, the soil-water systems of the three rice-fish bases were less impacted by anthropogenic activities, and they were less possibly to be enriched with and contaminated by REEs. Thus, the soil-water systems of the study areas are favorable for the high quality fishing.