Global DNA methylation in earthworms: a candidate biomarker of epigenetic risks related to the presence of metals/metalloids in terrestrial environments

In this work, possible relationships between global DNA methylation and metal/metalloid concentrations in earthworms have been explored. Direct correlation was observed between soil and tissue As, Se, Sb, Zn, Cu, Mn, Ag, Co, Hg, Pb (p < 0.05). Speciation results obtained for As and Hg hint at the capability of earthworms for conversion of inorganic element forms present in soil to methylated species. Inverse correlation was observed between the percentage of methylated DNA cytosines and total tissue As, As + Hg, As + Hg + Se + Sb (β = −0.8456, p = 0.071; β = −0.9406, p = 0.017; β = −0.9526, p = 0.012 respectively), as well as inorganic As + Hg (β = −0.8807, p = 0.049). It was concluded that earthworms would be particularly helpful as bioindicators of elements undergoing in vivo methylation and might also be used to assess the related risk of epigenetic changes in DNA methylation.