Phytotoxicity Assessment of Ashes Generated From Household Combustion of Conventional Fuels, Mixed Fuels, and Municipal Waste

ABSTRACT The main aim of the study was to assess the toxicity of ash generated in household furnaces through the combustion of materials most commonly burned in individual households. The toxicity tests were conducted using plant bioassays with cress ( Lepidium sativum ), mustard ( Sinapis ) and sorghum ( Sorghum ) seeds. The research material consisted of ash ( n = 15) obtained from the combustion of: ( i ) conventional or alternative fuels (i.e., hard coal, wood: pine, birch, spruce, and wood pellets), ( ii ) mixed fuels (hard coal mixed with wood—different types), and ( iii ) mixes of conventional fuels and selected fractions of municipal waste (i.e., paper, plastics, textiles). The research method involved measuring the length of the root and shoot sections of the plants after their exposure (24, 48, 72, 96, 120, 144, and 168 h of growth) to a given type of ash, followed by calculating the growth inhibition index ( I ). The phytotoxic effect appeared as inhibited growth and development of both roots and shoots. The measurements showed that ash produced from combusting pure coal and mixed municipal waste created the most toxic conditions for germinating seeds ( I ≅ 90%–98%). Ash from wood pellets was the only material that exhibited the least harmful effects on the test organisms ( I < 50%). The study showed that ash from household furnaces exhibits toxic properties and does not provide a suitable environment for plant development. The toxic character of the ash is determined by its chemical composition, which is influenced by: the type and composition of the raw materials used as fuels, the technologies applied in thermal decomposition systems, and the combustion parameters in heating boilers.