Does wood ash application increase heavy metal accumulation in forest berries and mushrooms?

A number of experiments have been established at the Finnish Forest Research Institute during the last few decades to study the effect of wood ash application on soil substrate, ground vegetation and stand growth on drained mires and mineral soil forests. In this study, the plots of 23 experiments were sampled to determine whether ash application significantly increases heavy metal accumulation in forest berries and mushrooms. Both short-term (between 2 months and 4 years) and long-term effects (between 10 and 52 years after application) were studied. The heavy metal concentrations (Al, Fe, Mn, Zn, Cr, Cu, Cd, As, Ni, Pb, Ti, V and Mo) were measured using ICP-AES. No significant increase in heavy metal accumulation in the cloudberry (Rubus chamaemorus), cowberry (Vaccinium vitis-idaea) and bog whortleberry (Vaccinium uliginosum) or in the caps and stipes of russule (Russula paludosa), rufous milk-cap (Lactarius rufus), northern milk-cap (Lactarius trivialis), velvet bolete (Suillus variegatus) and in-rolled paxil (Paxillus involutus) was usually observed. In contrast, in the older experiments (13–52 years), the concentrations were often lower than those in the controls, except for As. Cd concentrations in cloudberry, bog whortleberry, in-rolled paxil and rufous milk-cap occasionally decreased significantly. The results indicated that this ash-induced decrease in heavy metal accumulation may be a long-term effect. The concentrations of Al, Fe, As, Ni and Ti in the mushrooms were occasionally very high in the younger ash experiments (2–14 months after application); probably it was a case of surface contamination by heavy metal-rich ash residue, rather than active metal uptake. It was concluded that the heavy metals brought into the ecosystem by ash application are unlikely to be accumulated in any considerable amounts in forest berries and mushrooms.