Do essential elements (P and Fe) have mitigation roles in the toxicity of individual and binary mixture of yttrium and cerium to Triticum aestivum?

Essential elements can affect the bioavailability, uptake, and toxicity of metals. However, hardly any research has focused on the roles of essential elements on the toxicity of rare earth metals. Here we examined how P and Fe modified the individual and binary toxicity of Y and Ce to Triticum aestivum, respectively. Standard root elongation tests were used to quantify the toxicity of both single and binary mixtures at three levels of P addition (1, 5, and 10 μM) and Fe addition (0.1, 1, and 5 mM). Our results showed that both P and Fe can alleviate individual toxicity of Y or Ce irrespective of the dose indicators as suggested by the enhanced EC50 values. Both P and Fe might mitigate Y/Ce toxicity by limiting Y/Ce uptake into roots and improving nutritional status of wheats, whereas P can also decrease free Y/Ce ion activities in the exposure media. As for the mixture toxicity of Y and Ce, only improved P, but not Fe can exhibit approximately additive mixture toxicity, which can be adequately predicted by the simple Concentration Addition model. Our results suggested the important roles of P and Fe in assessing Y and Ce toxicity accurately.