Wood distillate as an alternative bio-based product against lichens on sandstone

The use of traditional biocides to halt or reduce biodeterioration is increasingly deterred, due to risks for human health and the environment, as well as for potential interference with stone materials. Alternative and ecofriendly substances are needed to limit these issues. Here we aim to evaluate the devitalization of lichens by a new bio-based product: wood distillate (also known as pyroligneous acid), a by-product of the use of plant biomass to produce bioenergy by pyrolysis without the addition of synthetic chemicals. We compared cellulose poultice applications of wood distillate at a concentration of 10% and two common chemical biocides against four epilithic lichen species on Pietra Serena, a sandstone widely used in Europe. The efficiency of devitalization was measured in terms of lichen vitality expressed by chlorophyll a fluorescence emission FV/FM and F0. Furthermore, we evaluated the effects of wood distillate on physical properties of the stone material of relevance for its conservation, including colour, resistance to dissolution, and surface hardness. Wood distillate was as effective as chemical biocides in devitalizing the thalli and did not cause any relevant interference with the assayed sandstone, although a limited dissolution of its calcite cement was detected.