Cadmium accumulation in organisms from a spruce plantation amended with wood ash - an environmental risk?

Recycling of wood ash from power plants to forest plantations returns plant nutrients lost at harvest. However, wood ash contains a considerable amount of cadmium (Cd) that may accumulate in the forest food web, and eventually threaten environment and human health. We examined the short-term (6-24 months) uptake of Cd in a range of organisms from different trophic levels in the forest food web. We amended twelve field plots in a Norway spruce plantation with wood ash in different concentrations (0, 3, 4.5 and 6 t ha-1), and subsequently measured Cd concentration in three vascular plant species, three metazoan groups, a lichen, and fruiting bodies of four ectomycorrhizal fungal species. Cd content varied significantly between the major taxonomic groups; metazoans contained most and vascular plants least, but also within the groups, most pronouncedly for ectomycorrhizal basidiomycetes. In vascular plants, metazoans as well as fungi, we found some examples that Cd content correlated significantly with wood ash amendment, however most organisms were unaffected, and no group of organisms contained more Cd than allowed for comparable food items. We therefore conclude that with the wood ash dosages used here, the environmental risk of Cd accumulation is slight, at least in the forest system that we examined.