Screening of municipal effluents with the peroxidase toxicity assay

Abstract The peroxidase (Per) reaction is a quick and inexpensive biosensor for the screening of environmental contaminants and wastewaters. The purpose of this study was to screen various municipal wastewaters before and after 7 different types of treatment processes using this sensor to identify potential sites under stress by urban pollution. The following wastewater samples before (influent) and after the commonly applied treatments (effluent) were tested using the Per activity test: advanced biofiltration, biofiltration, aerated lagoons, secondary aeration sludge, trickling filter, secondary membrane filtration, and primary. The influents and effluents were collected for 3 days and concentrated to 500 X on a reverse-phase (C18) extraction cartridge. The ethanol extracts were examined for dissolved organic carbon, plastic-like materials, polyaromatic hydrocarbons and polystyrene nanoplastics. The samples were then tested using the Per reaction alone and in the presence of DNA to detect DNA binding agents. The results show that population size tended to increase Per activity and 60% of the effluents decreased Per activity leading to H 2 O 2 persistence and toxicity. More advanced treatments (biofiltration, membrane biofiltration, secondary aeration) produced stronger changes from the corresponding untreated influents corroborating their performance in reducing toxicity. The addition of DNA during the Per reaction revealed that population size had no influence and that 60% of treated effluents restored Per activity suggesting release of genotoxic compounds in the aquatic environment from treated wastewaters. The toxic implications of the continuous release of wastewaters in aquatic ecosystems are discussed in the light of emerging contaminants such as nanoplastics.