Toxicity assessment of coal ash after 50 years of weathering: the integration of multielement analysis and biological endpoints

Coal ash disposal poses a significant environmental risk due to the potential leaching of toxic elements into surrounding ecosystems. Here, we analysed the phytotoxic effect of two coal ash disposal sites after 50 years of weathering to evaluate whether coal ash remains toxic after long-term disposal and whether vegetated areas are less toxic than bare ones. To analyse that, a combination of multielement analysis of coal ash and eluates and two bioassays-seed germination and Allium test-was used. Multielement analysis revealed that some samples exceed the World Health Organization's drinking water thresholds; however, biological responses did not consistently align with the total element concentrations. Seed germination was inhibited in 7 out of 12 samples, most strongly in soil and bare ash eluates from both sites. The Allium-based cytogenetic assay showed high mitotic inhibition and genotoxicity in most eluates. Correlation analyses linked Al, As, and V with increased chromosomal aberrations. However, the potential for synergistic or antagonistic interactions among elements complicates the straightforward predictions of toxicity based on concentration alone. Overall, these results advocate for the integration of biological endpoints with chemical data and highlight the persistent toxicity of coal ash even after 50 years of weathering.