Evaluation of fungal growth according to ammonia treated fly ash and characterization of microbial volatile organic compounds release

Most concrete materials are currently produced using industrial byproducts, such as fly ash, because of the associated economic benefits. However, ammonia used in denitrification systems reacts chemically with SO₃. The resulting ammonium-sulfate compounds are adsorbed by the fly ash, and can be used by fungi as a nutrient source. In this study, we isolated and identified fungal species that grow on fly-ash concrete surfaces and revealed that these fungi belonged to Fusarium spp., Necatria mauritiicola, and Aspergillus niger. All the fungal strains isolated from fly-ash concrete surfaces showed slow growth and weakened development of aerial mycelia. With the exception of A. niger, supplementation with fly ash positively influenced the growth of these species on minimal medium (MM) without NaNO₃, but not on MM without sucrose. Mortar supplemented with fly ash supported increased growth rates of all the fungal isolates examined in this study. Based on volatile compound profiles of isolated fungal strain obtained through headspace collection and analysis on GC-MS, volatile organic compounds, such as acetic acid, alcohol, butanol, and methane were identified. Most of these compounds could cause eye and skin irritation. In particular, 1-octen-3-ol, styrene, dimethyl disulfide, and benzene derivatives were identified as particularly harmful in humans. The information obtained in our study can help modify the production of concrete to avoid the use of materials promoting fungal contamination.