Accumulation and toxicity of lanthanum and neodymium in horticultural plants (Brassica chinensis L. and Helianthus annuus L.)

The dose‐response of two horticultural plant species (Brassica chinensis L., and Helianthus annuus L.) to two light Rare Earth Elements (REEs), namely lanthanum and neodymium, in‐vitro, was investigated. The phytotoxicity of the studied REEs was determined by measuring the aboveground and belowground biomass of the plant parts, and the chlorophyll production. Based on these measurements, inhibition concentration causing 50 % decrease (IC50) in plant biomass and total chlorophyll were calculated. Moreover, the available ionic species of La and Nd in the media for plant uptake were predicted using Visual MINTEQ. The concentration of these elements were measured in different plant tissues to assay the ability of these plants to hyperaccumulate La and Nd. It was observed that La and Nd, at lower dosages (<～100 mg/kg), had hormetic effects, respectively, on the shoot and root of H. annuus L. Also, Nd had stimulatory effects on the number of leaves and chlorophyll content of B. chinensis L. However, these two elements were toxic to both plants at higher media concentrations. Between the two plant species, H. annuus L. was more resistant to the studied REEs when compared to B. chinensis L. IC50 values of La for the roots and shoots of both plant species (139–201 mg/kg) were markedly smaller when compared to IC50 values of Nd (222–333 mg/kg). Thus, between the two assayed elements, La was more toxic to the plants. Translocation factors for La and Nd were not high enough to consider the plant species as hyperaccumulators.