Researchers at SCK CEN, in work package 2 (exposure) of RadoNorm, published their latest research on Influence of earthworms on the mobility and bioavailability of metals, metalloids and radionuclides in historically contaminated soil in Applied Soil Ecology. Nathalie Vanhoudt, Jean Wannijn, Robin Nauts, Axel Van Gompel, Kristel Mijnendonckx and Nathalie Impens authored this study, evaluating the impact of earthworms on the mobility of metal(loid)s and radionuclides in soil and their transfer to vegetation, and studying the pathways through which earthworms work. Soil from a Belgian field, historically contaminated with metal(loid)s and radionuclides, was used and microcosm systems were applied to mimic the natural interactions between soil, earthworms (Lumbricus terrestris) and vegetation (Lolium perenne).

The results show that earthworms, due to their important role in soil organic matter dynamics, significantly increased the concentration of most elements in the pore water with already partial translation towards plant uptake within the growth period studied. This could be a direct consequence of decreased soil pH and increased humification. The latter also lead to higher nutrient concentrations in pore water that were depleted in the root zone due to high accumulation by plants. Indications were also found for earthworm-induced effects on the soil microbial activity. This illustrates the interplay between organisms and abiotic factors that drive the mobility and bioavailability of elements in the soil. It demonstrates the influence earthworms have on the (bio)availability of metal(loid)s and radionuclides in an aged, historically contaminated site, making them more mobile by increasing their concentrations in the pore water. Earthworm activity can increase leaching of metal(loid)s and radionuclides and enhance dispersion into the environment and transfer to other biota and the food chain. As such, it supports the general message that biologically induced release or remobilisation of pollutants in the soil should be considered in the context of risk assessment and site management strategies.

More RadoNorm publications can be found on the RadoNorm website.