Distribution of rare earth elements, thorium and uranium in streams and aquatic mosses of Central Portugal

The distribution of 14 rare earth elements, Th and U was studied in streams of the study area at 21 sites. Aquatic mosses are known to accumulate even metabolically nonessential or toxic metals in concentrations much higher than their aqueous environment due to their unique morphology and physiology. Thus, the capacity of metal amplification in four aquatic mosses (Fontinalis squamosa, Brachythecium rivulare, Platyhypnidium riparioides and Thamnobryum alopecurum) was also evaluated as a potential bioindicator/biomonitoring tool. Thirteen REEs (0.001–2.81 μg L⁻¹) and U were detected in the stream water. Mean content of lighter rare earth elements (LREEs) was higher than that of heavier rare earth elements (HREEs). Fourteen REEs and two actinides were detected in moss samples, including Yb and Th which were below detection level in water samples. LREE uptake (0.17–12.2 mg kg⁻¹) was greater than HREE uptake (0.02–0.78 mg kg⁻¹) in all mosses. Uptake of LREEs was observed in the order: B. rivulare >T. alopecurum >F. squamosa >P. riparioides and that of HREEs in the order: T. alopecurum >B. rivulare >F. squamosa >P. riparioides. Mean U content (0.68–1.62 mg kg⁻¹) in the mosses was found in the order: B. rivulare >F. squamosa >T. alopecurum >P. riparioides. Th content ranged from 0.4 to 2.36 mg kg⁻¹ in the order: B. rivulare >T. alopecurum >P. riparioides >F. squamosa. One-way ANOVA indicated a statistically significant difference (P ≤ 0.01) in mean concentrations of all elements (individually) in moss samples except for U. Highest bioconcentration factors of six REEs each were observed in B. rivulare (La, Ce, Sm, Eu, Tb and Dy) and T. alopecurum (Nd, Gd, Ho, Er, Tm and Lu). The highest BCFs for Pr and U were obtained in F. squamosa and P. riparioides, respectively. These species hold promise for biomonitoring studies in the future.