Interactions between nanoparticles and flame retardants in wastewater treatment aggregates

Emerging contaminants (ECs) (a heterogeneous group of chemicals) are "of natural origin or synthetically produced" chemicals that have been recently investigated in the environment and are posing inauspicious effects to the ecosystem. There are many different sources of ECs, including industrial wastes, municipal (domestic) wastewater, agricultural, hospital or laboratory wastewaters. Some of these contaminants include pesticides, food additives, pharmaceuticals, industrial by-products, dyes, paint, pigments, personal care products (PCPs), endocrine disrupting chemicals (EDCs), veterinary products (VPs), flame retardants (FRs) and engineered nanoparticles (ENPs). The presence of emerging contamination in the aquatic environment, soil and sediments, landfills and surface water is mainly due to the disposal of effluents from wastewater treatment plants (WWTPs). Brominated flame retardants (BFRs), are the chemicals added as additives in electrical and electronic equipment (EEE), upholstered furniture, building insulation, textile and plastic products to achieve fire safety standards and to provide fire protection. Most of them are persistent, bioaccumulative and toxic (PBT). They are widely detected in WWTPs together with engineered nanoparticles (ENPs) such as TiO₂, ZnO, Fe and Ag which have been employed in numerous applications like UV filters, cosmetics, paints, textiles, surgical equipment. As the co-occurrence of BFRs and ENPs, it is necessary to understand their interaction mechanisms in WWTPs apart from investigating their individual fate and behavior. Such information is currently lacking in the literature. In this study, we conducted a comprehensive review on the interaction mechanisms of ENPs with BFRs during the dissolution, adsorption, aggregation, sedimentation and transformation processes in a WWTP. The released pathways of the ENPs and BRFs from consumer's end use to aquatic environments were summarized. Emission phenomenon of semi volatile organic compound (BFRs) based on mass transfer modelling concepts has also been discussed. The interactions between ENPs and BFRs could influence their fate in WWTPs which is discussed in the review. This review aims to shed light on this knowledge gap and provide further insights in understanding the fate of ENPs in WWTPs. (author)