Oxytetracycline induced the redox of iron and promoted the oxidation of As(III)

Oxygen adsorption and activation control the photochemical activity of common iron oxyhydroxide polymorphs in mediating oxytetracycline degradation under visible light

The natural minerals with semiconducting properties possess photochemical activity through generating reactive oxygen species (ROSs) and affect the fate of adsorbed organic pollutants. Iron oxyhydroxides occur in different polymorphic structures under various geological and climatic conditions in natural environment. However, the difference in their photoactivity has not been well understood. This work elucidates the mechanism of light-induced generation of ROSs by common iron oxyhydroxide polymorphs, including goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhyte (δ-FeOOH), and the degradation of oxytetracycline (OTC) mediated by them. Under visible light irradiation, all these iron oxyhydroxide polymorphs generated superoxide radicals (O2-•), hydroxyl radicals (•OH), and H2O2. Among the ROSs, O2-•, whose concentrations in the photochemical systems of α-, β-, γ- and δ-FeOOH reached 4.25 × 10-4 ± 5.67 × 10-5, 2.29 × 10-4 ± 2.55 × 10-5, 6.2 × 10-4 ± 8.5 × 10-5 and 7.65 × 10-4 ± 5.67 × 10-5 μmol/L, respectively, played a dominant role in the degradation of OTC. The corresponding rate of OTC degradation in these photochemical systems were 0.054 ± 0.010, 0.015 ± 0.001, 0.338 ± 0.073, and 0.404 ± 0.016 min-1, respectively. A good linear relationship was observed between the steady-state concentrations of O2-• and OTC degradation rates in the photochemical systems of iron oxyhydroxide polymorphs. O2-• was primarily generated by the electron reduction of O2 on the conduction bands (CBs) of iron oxyhydroxide polymorphs, which was controlled by the surface adsorption and activation of O2. H2O2 and surface Fe2+ on iron oxyhydroxide polymorphs synergistically contributed to •OH generation through Fenton reaction. The generation of surface Fe2+ was determined by the geometrical configuration, crystallinity, and surface oxygen vacancies of iron oxyhydroxide polymorphs. These findings demonstrate the photochemical generation of ROSs in the presence of major iron oxyhydroxide polymorphs was primarily controlled by O2 adsorption and activation, leading to different activity in mediating the degradation of adsorbed organic pollutants.

Multimedia distribution, partitioning, sources, comprehensive toxicity risk and co-occurrence network characteristics of trace elements in a typical Chinese shallow lake with high antibiotic risk

Although the combined pollution of trace elements and antibiotics has received extensive attention, the fate and toxicity risk of trace elements with high antibiotic risk are still unclear. The multimedia distributions, partitioning, sources, toxicity risks and co-occurrence network characteristics of trace elements in surface water (SW), overlying water (OW), pore water (PW) and sediment (Sedi) samples of 61 sites from Baiyangdian (BYD) Lake were investigated. The trace elements in the SW and OW are derived mainly from traffic and agricultural sources, and those in PW and Sedi samples are primarily from lithogenic and industrial sources. The total toxicity risk index (TRI) of nine trace elements (ΣTRI) in Sedi samples showed a very high toxicity risk (18.35 ± 8.84), and a high combined pollution toxicity risk (ΣΣTRI) was observed in PW (149.17 ± 97.52) and Sedi samples (46.37 ± 24.00). The co-occurrence network from SW to PW became more vulnerable. Generally, total antibiotics and TP may be keystones of trace elements in water and sediment. The high antibiotic risk significantly influenced ΣΣTRI in water samples but not in Sedi samples. The findings provide new implications for the monitoring and control of combined antibiotic-trace element pollution in shallow lakes.