Geochemical Characteristics and Factors of Transfer and Accumulation of Rare Earth Elements in Rock-Soil-Tea of the Mengku Tea Region in Yunnan Province, China

Abstract

Rare earth elements (REEs) in tea are usually determined by the soil, but their transfer characteristics and influencing factors have been rarely studied and reported. In order to determine the transfer and accumulation characteristics of REEs, rock, soil, and tea samples were collected in the Mengku tea region. Levels of 15 REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) in samples were determined by inductively coupled plasma atomic emission spectrometry (ICP-MS). The results showed that light rare earth elements (LREEs) were easily enriched in rock, soil, and tea. The average total concentration of REEs in investigated rocks was 199 mg·kg−1, which was lower than the element abundance of China’s continental crust but higher than the standard value of element abundance in the upper continental crust (UCC). The average total REE concentration in the investigated soil was 225 mg·kg−1, which was lower than the background value of soil in Yunnan Province. The chondrite-normalized levels of Ce and Eu in rocks and Eu in soil showed negative anomalies, while Ce levels in soil showed slightly positive anomalies. The total amount of REEs in tea was relatively low and the chondrite-normalized values of Eu in tea showed significantly positive anomalies. Eu anomalies in tea were closely correlated with soil pH (pH < 5, negative anomalies; pH > 5, positive anomalies). K, Na, Ca, and Mg were the main factors affecting the transfer of REEs. LREEs were mainly enriched in tea through Na+ channels. Mg and K affected the differentiation and enrichment of heavy rare earth elements (HREEs) in tea. Calcium showed a significantly positive correlation with Eu in tea. The human health risk assessment showed that the risk of drinking tea to the human body was far below the reference value. Ce, Y, and La in tea were the main elements that affected non-carcinogenic risk and carcinogenic risk.