Metformin as an Emerging Pollutant in the Aquatic Environment: Occurrence, Analysis, and Toxicity.

The use of human and veterinary drugs has led to the accumulation of pharmaceuticals in various aquatic environments at progressively increasing levels, exhibiting strong ecological risks. Metformin is widely used as a first-line prescription drug for the treatment of type 2 diabetes mellitus as well as a livestock drug. Unlike other drugs, metformin is not metabolized in the body, and almost all of its intake is excreted and released into the aquatic environment via urine and feces, causing adverse effects on aquatic ecosystems. This review provides an overview of the occurrence and detection of metformin in the aquatic environment and its toxic effects on different aquatic organisms (fish, daphnia, rotifers, chlorella). Metformin has been documented in a variety of aqueous environments such as wastewater, surface water, and groundwater as well as drinking water. The wide distribution of metformin in the aqueous environment calls for the development of more accurate detection methods. This paper reviews detection methods for metformin in the aqueous environment and evaluates their advantages and disadvantages. Toxicity studies have shown that metformin can cause adverse reactions in fish, such as oxidative stress, genotoxicity, disruption of intestinal flora, and morphological alterations; it also affects the growth and reproduction of small aquatic organisms. Knowledge gaps in the field of metformin research were assessed, and future research priorities were identified.

The occurrence, distribution and removal of adsorbable organic halogens (AOX) in a typical fine chemical industrial park.

Coastal water quality in China has been impacted by direct discharge of industrial wastewater, and various kinds of AOX pollutants have been detected in the seawater and sediment. As the dominant pollution source of Hangzhou Bay, a typical fine chemical industry park "HSEDA" was selected as the study area in this research. The AOX in both wastewater and sludge phases from 22 large-scaled enterprises were simultaneously investigated. The results quantitatively illustrated the AOX flows from engineered wastewater and sludge treatment systems to natural environment. It can be seen that industrial enterprises discharged at least 160 t AOX every year, and about 105.4 t/a AOX eventually entered the natural environment. The dye manufacturing industry, which accounted for more than 60% of the total AOX emission load in HSEDA, was identified as the AOX pollution-intensive sector. The occurrence, characteristic pollutants and fate of AOX in dye wastewater were discussed, on the basis of which the improvements of cleaner production and wastewater treatment technologies have been put forward.

Ozone oxidation of 2,4,6-TCP in the presence of halide ions: Kinetics, degradation pathways and toxicity evaluation.

2,4,6-Trichlorophenol (2,4,6-TCP) is extensively consumed in industrial production and may cause environmental damages. The effect of halide ions on the decomposition of 2,4,6-TCP has often been overlooked. In this study, the bromide ion was found to have a stronger negative impact on 2,4,6-TCP degradation than chloride ion in the O3 system, and led to the formation of adsorbable organic halogens (AOX). Kinetic modeling demonstrated that the concentration of various radicals was largely depended on the solution pH, and stronger basicity not only contributed to the mineralization of 2,4,6-TCP, but also inhibited the formation of halogenated by-products. Combining the intermediate identification and quantum chemical calculation, the degradation pathways of 2,4,6-TCP during ozone oxidation process were proposed. The toxicity test and ECOSAR simulation demonstrated that the acute toxicity of some 2,4,6-TCP degradation intermediates was relatively higher than their parent compound. With high concentrations of halide ions, the ozone-treated solution showed greater toxicity than the originator 2,4,6-TCP solution. These results illustrate that the ozone treatment of the halide-containing wastewater may cause potential ecological hazards and its application needs to be more cautious.