Yttrium and rare earth elements fractionation in salt marsh halophyte plants.

Salt marshes act as natural deposits of different metals (e.g. heavy-metals), while halophyte plants are known to retain and accumulate them in the different tissues. Scarce data exists on accumulation, partition and fractionation of YREE in these plants. To study the relationship between halophyte plants and YREE, contents of these metals were determined by ICP-MS in sediment, and in the different plants organs, from Rosário's salt marsh, in Tagus estuary (SW Europe). Results show significant differences (p < 0.001) in YREE contents between sediments. In non-colonised sediment Y was lower (5.0-18 mg·kg-1) compared to the Sarcocornia fruticosa and Spartina maritima sediment cores (19-26 and 20-26 mg·kg-1, respectively). The same was observed for ΣREE, with lower values in non-colonised sediment (32-138 mg·kg-1), while colonised ones presented higher contents (146-174 and 151-190 mg·kg-1, for S. fruticosa and S. maritima, respectively). These significant differences (p < 0.05) are explained by the sediments' nature. Yttrium and ΣREE Al-normalised ratios in non-colonised sediment ranged from 1.5 to 2.3 and 11 to 13, respectively. The colonised sediments revealed significant higher ratios (particularly for ΣREE/Al ratios; p < 0.001), varying from Y/Al: 1.8-2.3 and ΣREE: 13-16 for S. fruticosa, and Y/Al: 1.4-2.3 and ΣREE: 12-18, for S. maritima. Results suggest that these plants may promote YREE enrichment in the sediments. No differences in fractionation patterns among sediments and in both species roots were found, but fractionation was different from those in the sediment, with similar middle-REE (MREE) enrichment and no light-REE (LREE) and heavy-REE (HREE) fractionation. No evidence of YREE transfer to aboveground organs was observed. Different fractionation patterns in stems and leaves were registered, with clear enrichment of LREE relative to HREE and an increase in the MREE enrichment. Therefore, these plants showed low ability to accumulate and translocate YREE but may promote its enrichment in the sediments.