Location and speciation of gadolinium and yttrium in roots of Zea mays by LA-ICP-MS and ToF-SIMS

Increasing production of rare earth elements (REE) might lead to future contamination of the environment. REE have been shown to accumulate in high concentrations in roots of plants. Plant experiments with Zea mays exposed to a nutrient solution containing gadolinium (Gd) or yttrium (Y) with 10 mg L⁻¹ Gd or Y were carried out to investigate this accumulation behaviour. Total concentrations of 3.17 g kg⁻¹ and 8.43 g kg⁻¹ of Gd and Y were measured in treated plant roots. Using a novel combination of laser ablation mass spectrometry and time-of-flight secondary ion mass spectrometry, imaging of location and concentration of Gd and Y was carried out in root thin sections of treated roots. Single spots of elevated REE concentration were found at the epidermis, while inside the cortex, weak signals of Gd⁺ and Y⁺ were aligning with the root cell structures. The composition of Gd-containing secondary ions proves an REE-oxide phase accumulated at the epidermis, limiting REE availability for further uptake. - Highlights: • Imaging of Gd in thin root sections via LA-ICP-MS and ToF-SIMS. • High concentrations of Gd and Y were found at the epidermis of root. • Identification of oxygen containing species of Gd by ToF-SIMS analysis. • Explanation for the hindered transfer of Gd in plants.