Bioremediation of environmental media contaminated with emerging organic contaminants: biodegradation pathways, by-products, indicators, and end-points

Due to their widespread production and subsequent release into the environment and their associated ecological and public health risks, emerging organic contaminants (EOCs) continue to attract global research and societal focus. Bioremediation is ecofriendly and sustainable compared to chemical and physical methods; thus, it has been extensively reported in literature. A mechanistic understanding of the bioremediation of EOCs, particularly the biodegradation mechanisms, by-products and their health risks, and indicators and end-points, is critical for the uptake and upscaling of the bioremediation technology. However, currently missing on the bioremediation of EOCs is a critical analysis of (1) the biodegradation pathways, (2) the nature, ecotoxicology, and human health hazards of biodegradation by-products, and (3) indicators and endpoints of bioremediation. Therefore, this review addresses this gap and contributes novel insights on the bioremediation of various EOCs. The biodegradation mechanisms, including evidence on metabolic pathways, are presented. Several microbial species, including fungi and bacteria, and their consortia and associated enzymes such as laccases, control the biodegradation of EOCs. Consequently, several biodegradation by-products are produced, and their ecotoxicology and human health hazards relative to parent compounds are discussed. Notably, the ecotoxicity of some of the by-products is similar to, and sometimes even higher than that of the parent compounds. A critique of conventional bioremediation indicators and endpoints, and their capacity to capture the efficacy of bioremediation across ecological scales is presented. Further, future perspectives are presented to guide future research. Addressing these gaps is critical for the advancement and application of bioremediation technology.