Degradation or humification: rethinking strategies to attenuate organic pollutants.

The fate of organic pollutants in environmental matrices can be determined by degradation and humification. The humification process represents a promising strategy to remove organic pollutants, particularly those resistant to degradation. In contrast to the well-studied degradation process, the contribution and application prospects of the humification process for organic pollutant removal has been underestimated. The recent progress in synthesizing artificial humic substances (HS) has made directed humification of recalcitrant organic pollutants possible. This review focuses on degradation and humification of organic matter, especially recalcitrant organic pollutants. Challenges in understanding the contribution, underlying mechanisms, and artificial synthesis of HS for removing organic pollutants are also critically discussed. We advocate further investigating the humification of organic pollutants in future studies. Degradation and humification synergistically determine the environmental fate of organic pollutants. In contrast to previous studies focusing on degradation processes, humification represents a promising but underestimated strategy for removing recalcitrant organic pollutants. In degradation processes, reduced organic matter is utilized as electron donors to support oxidative respiration, or as fermentation substrates to produce volatile fatty acids. By contrast, recalcitrant oxidized organic matter needs to be reduced prior to subsequent degradation. Many pathways are identified for the generation of humic substances (HS), in which microbes play key roles in providing HS precursors and in subsequent polymerization. Artificial HS synthesis open a new avenue for removing organic pollutants under controlled conditions, largely dependent on the progress in construction of new chemical bonds. [ABSTRACT FROM AUTHOR]