Environmental Behavior of 2,4,6-Trichlorophenol in the Sediment-Overlying Water System with the Presence of Tubificid Worms

To investigate the influence of bioturbating organisms on the migration and degradation of chlorophenols in freshwater sediments, simulated experimental systems were established, with tubificid worms employed as the model bioturbator and 2,4,6-trichlorophenol (TCP) as a representative chlorophenol contaminant. The results showed that tubificid worms significantly promoted the removal of TCP in sediments, with this effect mainly concentrated in the surface sediment layer (0–2 cm) and limited impact on deeper sediment layers (2–6 cm). The removal efficiency was higher in the low-concentration TCP group than in the high-concentration group. TCP in the overlying water was predominantly in the dissolved phase, and the presence of tubificid worms reduced the TCP concentration in the aqueous phase, resulting in a greater amount of removal. The bioturbation of tubificid worms altered the physicochemical characteristics of the system, increasing the turbidity of the overlying water, decreasing its pH, elevating the redox potential across different sediment depths, and improving the organic matter conditions. Tubificid worms also modified the bacterial community structure in both the overlying water and the sediment. The core mechanism by which tubificid worms accelerate TCP removal is through promoting the migration of TCP from the sediment to the overlying water, while concurrently regulating the bacterial community structure in the overlying water to enhance the degradation capacity of chlorophenols in this layer. This highlights the important role of bioturbators in aquatic ecosystems, and ignoring their presence may lead to an erroneous underestimation of the system’s self-purification capacity.