RESUMEN
A practical metal-free and additive-free approach for the synthesis of 6/7/8-membered oxacyclic ketone-fused isoxazoles/isoxazolines tetracyclic or tricyclic structures is reported through Csp3-H bond radical nitrile oxidation and the intramolecular cycloaddition of alkenyl/alkynyl-substituted aryl methyl ketones. This convenient approach enables the simultaneous formation of isoxazole/isoxazoline and 6/7/8-membered oxacyclic ketones to form polycyclic architectures by using tert-butyl nitrite (TBN) as a non-metallic radical initiator and N-O fragment donor.
RESUMEN
Air pollution and climate change are closely linked because many greenhouse gases (GHGs) and air pollutants come from the same source. Perfluorinated compounds (PFCs) are new pollutants that have received high attention in recent years, as they are not only harmful to human health, but also important contributors to climate change. Therefore, PFCs are the key gases for the coordinated governance of air pollution and climate change. With the geographical shift of fluoropolymer production, the main emitters of perfluorooctanoic acid and its salts (PFOA/PFO) moved from North America, Europe and Japan to emerging Asian economies, especially China. In this study, industrial sources of PFOA/PFO in the Chinese atmosphere were identified, and its atmospheric emissions, carbon dioxide equivalent (CO2e) emissions and environmental risks were assessed. China released about 38.19 tons PFOA/PFO into the atmosphere through industrial activities in 2019, 97 % of which originated from the production of fluoropolymers. PFOA/PFO showed aggregative emission along the eastern coastal zone, especially in the Yangtze River Delta. Cumulative PFOA/PFO emission from all provinces equaled to 0.28-0.47 million tons CO2e, of which Jiangsu and Zhejiang took the lead, while Shanghai's CO2-equivalent emissions intensity of PFOA/PFO in terms of area, population, gross domestic product (GDP), and industrial added value took the first in China. The available monitoring data on atmospheric concentration of PFOA in urban and rural China implied that its distribution pattern was similar to PFOA/PFO emissions, that is, the concentrations in the eastern regions with the highest degree of industrialization were significantly higher than that in the central and western regions, and the PFOA concentrations in urban China were higher than that in the rural, which proved that industrial use was an important source of PFOA pollution and would cause significant risks to the environment.
RESUMEN
As an important part of the water cycle, the hydrologic process and chemical compositions of groundwater have changed significantly due to the joint influence of climate change and human activities. Groundwater salinization becomes a serious threat to water security in coastal areas. In order to assess the relationships between surface water, groundwater and seawater in the coastal plain, we performed a synthesis study based on hydrochemical-isotopic data, hydro-dynamical records and environmental tracers. Deuterium and oxygen isotopes and water chemical indicators were used to identify pollution status, salt sources and migration processes. Radioactive isotopes and gaseous tracers were used to obtain reasonable groundwater age. With the help of multi-tracer approach, the surface-groundwater interaction, salinization of groundwater and nitrate pollution were identified in the Yang-Dai River plain, northern China. The estimated groundwater ages determined from chlorofluorocarbons (CFCs) and tritium (3H) ranges from 18 to 41 years in this area, suggesting a modern groundwater circulation. The spatial distribution of the groundwater age varies significantly due to horizontal hydrogeological heterogeneity. The total dissolved solids (TDS) content of the groundwater near the Well Field (average: 970 mg/L) was higher than the TDS values in samples derived from places located at an equivalent distance to the coastal line (average is 708 mg/L), which resulted from the vertical seawater intrusion through river channels and pollutant inputs from agriculture activities. The nitrate concentrations in groundwater were elevated up to 271 mg/L and increased with increasing groundwater age, which was another water environment problem that should be solved urgently but lacks sufficient attention for years. This study provides a conceptual model with a number of comparable hydrochemical information, which is significant for regional pollution control and water resources management.
