Degradation kinetics of prometryn and formation of disinfection by-products during chlorination.

Prometryn is a herbicide that is widely used and frequently detected in aqueous environment and soil. Prometryn is chemically stable, biologically toxic, and easily to accumulate in living bodies, which can cause accumulate in the environment and acute and chronic toxicity to living creatures. In this study, factors affecting the degradation kinetics of prometryn chlorination were studied, including solution pH, bromide and ammonium concentrations, and temperature. Prometryn reacted quickly with aqueous chlorine following the pseudo-first-order kinetics. The maximum pseudo-first-order rate constant (kapp) appeared at pH 5 with the observed rate constant (kobs) as 190. 08 h-1; the minimum value of kapp reached at pH 9 with kobs as 5.26 h-1. The presence of Br- and increase of temperature both accelerated the degradation rate of prometryn during chlorination. The activation energy was calculated as 31.80 kJ/mol. Meanwhile 6 disinfection by-products (DBPs) were detected, namely: chloroform (CF), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), dichloroacetone, trichloronitromethane (TCNM), and trichloroacetone. Solution pH significantly affected the formation and distribution of DBPs. CF was the most formed carbonated DBP (C-DBP) with the maximum of 217.9 µg/L at pH 8, and its formation was significantly higher in alkaline conditions. For nitrogenated DBPs (N-DBPs), the yields of DCAN and TCAN were significantly higher in acidic conditions, while the maximum of TCNM achieved in neutral conditions. Because the toxicity of N-DBPs is higher than that of C-DBPs, the pH should be controlled in neutral or slight alkaline conditions during prometryn chlorination to effectively control DBP formation and reduce the related toxicity.

[Distribution and Environmental Risk of Pharmaceutically Active Compounds in the Traditionally Aqueous Phase of Effluent-receiving Rivers].

Colloid media are not only an important "sink" for pollutants in the aquatic environment, but also a crucial regulating unit for the biogeochemical cycle of pollutants. In this study, the distribution and environmental risk levels of ten typical pharmaceutically active compounds (PhACs) in the water phase of effluent-receiving rivers were investigated using cross-flow ultrafiltration, solid-phase extraction, and liquid chromatography-tandem mass spectrometry as the pretreatment and analysis methods. The results showed that the total concentrations of the ten PhACs in the dissolved phase and colloidal phase ranged from 27.2 to 168.1 ng·L-1 and 164.5 to 751.1 ng·g-1, respectively. Ibuprofen (IPF), roxithromycin (ROX), and erythromycin (ETM) are the dominating pollutants in the dissolved phase and colloidal phase, accounting for more than 80% of the total concentration. Strong adsorption properties for ROX, ketoconazole, ETM, and sertraline were found in the colloid phase, their colloid/water distribution coefficients (lgKcol) ranged from 3.2 to 4.0, and the percentage of PhACs absorbed to the colloidal phase reached 21.1%-34.5%. The risk assessment of acute and chronic toxicity to algae, daphnia, and fish showed that only IPF presented a high chronic risk to fish, while the risk levels of the other PhACs were at or below medium risk. It is worth noting that, in comparison with their acute risk, most PhACs have chronic negative effects on higher aquatic organisms.