Insights into the influence on 2,4,6-trichlorophenol microbial reductive dechlorination process by exposure to microplastics

As a newly emerging pollutant, the adverse effects of ubiquitous microplastic on ecosystems and living have attracted increasing attention, however, the microplastic intervention influencing anaerobic biotransformation behaviors of chlorinated aromatics remains poorly understood. Here, the significantly altered 2,4,6-trichlorophe-nol microbial reductive dechlorination activities were found by single-and multi-exposure to microplastics. Single contact with five different types of microplastics showed diverse dechlorination performance, that PET was the most promoted (kT of 0.037 h(-1)) and PP was the largest inhibited (kT of 0.01 h(-1)) compared to control (kT of 0.023 h(-1)). The microplastic size was negatively correlated with dechlorination activities, with 1.8-1.9 times decreased kT as the particle size decreased from 1000 mu m to 75 mu m. The higher the concentration, the more promoted effects by PET and the more inhibited effects by PP on dechlorination performance, with the respective kT of 0.052 h(-1) and 0.006 h-1 under 2.0 g/L condition. Bio-enrichment on hydrophilic surfaces of microplastics (e.g. PET) was speculated to be responsible for the favored dechlorination activity, while adsorption of chlorophenols posed little influence. However, the overall inhibited 2,4,6-TCP dechlorination performance was found under all conditions by extending exposure cycles. The obvious bacterial succession that the abundance of some absolute anaerobic fermentator (Dysgonomonas) or dechlorinator (Desulfitobacterium) was greatly decreased, while, some facultative anaerobic genera (Comamonas, Pseudomonas) that held microplastic degradation potential were enriched. The increased positive correlations among networks were found and the more simplified molecule network as the size of microplastics became larger. The study provided significant theoretical support for understanding anaerobic biotransformation process of CAs influenced by the microplastic intervention.