Evaluation of genotoxicity of coal fly ash in Allium cepa root cells by combining comet assay with the Allium test

Fly ash is a by-product of coal-fired electricity generation plants. Its utilization and disposal is of utmost importance. Using onion (Allium cepa) root tip system, the present study was carried out to evaluate the potential toxic and genotoxic effects of fly ash, collected from a thermal power plant in West Bengal, India. Prior to testing, the collected fly ash sample was mixed with sand in different proportions. Allium bulbs were allowed to germinate directly in fly ash and after five days the germinating roots were processed for the Allium test. Additionally, the Allium test was adapted for detecting DNA damage through comet assay. The results from the Allium test indicate that fly ash at 100% concentration inhibits root growth and mitotic indices; induces binucleated cells as a function of the proportion, but is not toxic at very low concentration. In the comet assay, a statistical increase for DNA strand breaks was found only at higher concentrations. The sample was analyzed by flame atomic absorption spectrometer for Zn, Pb, Cu, Ni, Cd and As, whose presence could partly be responsible for the toxicity of fly ash. The study concludes that the classical Allium test can give a more comprehensive data when done in combination with the comet assay, which is faster, simpler and independent of mitosis. Also when fly ash is used for other purposes in combination with soils, it should be judiciously used at very low concentrations in order to protect the ecosystem health from any potential adverse effects.