Harmful substances such as heavy metals and radioactive substances can accumulate in wood ash, although the amount can vary greatly. The accumulation of radioactive substances is highest in wood pellet ash. For this reason, among others, wood pellet ash should not be used to fertilise gardens.

Wood is a relatively fast-growing raw material and is considered an environmentally friendly, CO2-neutral fuel. The combustion process only produces ash as a waste product.  For the different wood fuels (wood pellets, wood chips, logs and wood briquettes) specially designed combustion equipment is available, which is optimally adapted to the fuel used.

Heating with wood pellets is subsidised by the federal government, the federal states and the municipalities. In recent years, more and more households have been heating with pellet boilers. Nationwide, there are more pellet boilers than other biomass boilers .In Austria, only by-products from the sawmill industry and no bark are used for pellet production. During heating, the organic component of the wood is burnt, while the mineral, non-combustible part remains as ash. Plant ashes from biomass furnaces can be valuable secondary raw materials. Their possible use on agricultural and forestry land is described in more detail in the "Guideline for the proper use of plant ashes". This guideline can be found at the bottom of this page under Downloads.

As a result of the Chernobyl reactor accident (1986), among other things, radioactive caesium and strontium were spread across several European countries, including Austria. These radioactive substances are absorbed by the vegetation. Radioactive caesium and strontium have a half-life of around 30 years and can therefore still be found in plants (e.g. trees) and wild animals in the affected areas. . If wood from these regions is used for heating, radioactive caesium and strontium may accumulate in the ashes.

The radioactivity in the wood itself is harmless from a radiation protection point of view and therefore poses no health risk to the population. However, the amount of radioactive substances that accummulates in the wood ash may vary greatly and could be relevant from a radiation protection perspective.

However, we still do not recommend scattering the wood pellet ash in the garden or on a vegetable patch. This is because, in addition to radioactive substances, the ashes may also contain non-combustible and potentially harmful minerals, salts, heavy metals and organic pollutants.

The disposal of ashes from private households is regulated differently in each federal state and often also in each municipality. In most of Austria it is mandatory to dispose of the cooled ash in the residual waste.

Detailed technical information on the project can be found in the final report, which can bee downloaded here.