Emerging contaminants in biosolids: Presence, fate and analytical techniques

Emerging contaminants (ECs) represent a small fraction of the large chemical pollution puzzle where a wide variety of potentially hazardous chemicals reach the environment, and new compounds are continuously synthesized and released in wastewater treatment plants and ultimately in effluent and biosolids. ECs have been classified into various categories; however, this article focuses on the fate of major categories, namely pharmaceutical and personal care products (PPCPs), per-and poly-fluoroalkyl substances (PFAS), flame retardants, surfactants, endocrine-disrupting chemicals (EDCs), and microplastics (MPs). These ECs when discharged to sewer and downstream wastewater treatment plants can undergo further transformations and either degrade, persist or convert into by-products which have the potential in some cases to be more hazardous. Because of potential dangerous impacts of the availability of these contaminants in the environment, information on the fate and behavior of these pollutants is highly important to develop new strategies, such as the regulation of chemicals imported into Australia and Australian consumer goods and environmental policies to mitigate them in a sustainable way. Moreover, advanced technologies are required for the detection and identification of novel contaminants emerging in the environment at ultra low levels. The application of chromatographic techniques coupled with mass spectroscopy has provided attractive breakthroughs to detect new emerging contaminants. However, it is crucially important to understand the sensitivity and robustness of these analytical techniques when dealing with complex matrices such as biosolids. In addition, most of the literature was focused on selected compounds or a family of compounds and the existing reviews have paid less attention to examine the formation of metabolites during the wastewater treatment process and their impacts on the ecosystem. This review presents an overview of the presence of different classes of ECs around the world, their quantification from different sources like wastewater (influents or effluents), sludge and biosolids. In addition, the transformation of ECs during the treatment process, the formation of intermediate products and their impacts on the environment are also critically discussed. Three major steps of ECs analysis include sample preparation, extraction and clean-up, and analysis; hence, different methods employed for extraction and clean-up, and analytical techniques for identification are thoroughly discussed, their advantages and limitations are also highlighted. This comprehensive review article is believed to enhance the understanding of ECs in sewage sludge and would be useful to the readers of the relevant communities and various stakeholders to investigate potential technologies to maximize destruction of ECs.