Rare earth elements (REEs) comprise 17 elements of the lanthanide series, which cooccur naturally as mixtures in mineral deposits. Due to similar physical and chemical properties, their use in technology is accelerating. For singular exposures, toxicity has been determined for some REEs but quantitative understanding of mixture ecotoxicity and interactions of REEs is limited. Toxic effect concentrations for tomato and durum wheat were determined for three REEs, Cerium, Neodymium, and Europium, in singular and ternary mixture exposure exposures. Singular thresholds revealed Ce as the most toxic element, with all REE thresholds (EC10) ranging from 23- 596 mg/kg-1 based on total soil concentrations. Mixture toxicity was often found to be the same as individual toxicities, or slightly less than depending on concentration descriptors (ie. Internal vs external exposure) and plant specie. Internal tissue concentrations may serve as a better predictor of toxicity compared to external concentrations for both singular and mixture exposures.