Insight study of rare earth elements in PM2.5 during five years in a Chinese inland city: Composition variations, sources, and exposure assessment.

The booming development of rare earth industry and the extensive utilization of its products accompanied by urban development have led to the accelerated accumulation of rare earth elements (REEs) as emerging pollutants in atmospheric environment. In this study, the variation of REEs in PM2.5 with urban (a non-mining city) transformation was investigated through five consecutive years of sample collection. The compositional variability and provenance contribution of REEs in PM2.5 were characterized, and the REEs exposure risks of children and adults via inhalation, ingestion and dermal absorption were also evaluated. The results showed an increase in the total REEs concentration from 46.46 ± 35.16 mg/kg (2017) to 81.22 ± 38.98 mg/kg (2021) over the five-year period, with Ce and La making the largest contribution. The actual increment of industrial and traffic emission source among the three pollution sources was 1.34 ng/m3. Coal combustion source displayed a downward trend. Ingestion was the main exposure pathway for REEs in PM2.5 for both children and adults. Ce contributed the most to the total intake of REEs in PM2.5 among the population, followed by La and Nd. The exposure risks of REEs in PM2.5 in the region were relatively low, but the trend of change was of great concern. It was strongly recommended to strengthen the concern about traffic-related non-exhaust emissions of particulate matter.

Decryption analysis of antimony pollution sources in PM2.5 through a multi-source isotope mixing model based on lead isotopes.

Antimony (Sb) in PM2.5 has attracted close attention as a new air pollutant due to its extensive use in daily life. The identification of antimony sources in PM2.5 by scientific methods is important to control its pollution. In this study, the Sb and other elements concentrations and Pb isotopic compositions in PM2.5 and possible pollution sources (soil, road dust, traffic emission, coal-fired fly ash, local factory emission dust and cement dust) were analyzed. The results showed that the Sb in the PM2.5 samples had seasonal change. The enrichment factors of Sb in PM2.5 samples were all above 100 in four seasons, which indicated anthropogenic pollution. The average value of potential ecological risk index was at extremely high-risk level greater than 320. Based on Pearson correlation coefficient and hierarchical cluster analysis results, the pollution sources of antimony and lead in PM2.5 samples were highly consistent which means that Pb isotopes might be a new and feasible tracer for Sb pollution in air. The sources analysis results based on Pb isotopes indicated that the proportion of Pb and Sb from coal-fired fly ash was the highest in winter (47.7%) and inclined to road dust in spring (34.5%), but it was mainly from traffic emissions in summer and autumn (34.2% and 32.8%). This study showed that Pb isotope tracing can be applied to predict the potential pollution sources, and it was also a feasible substitute for tracing Sb pollution in PM2.5.

Exceptional removal and immobilization of selenium species by bimetal-organic frameworks.

Binary metallic organic frameworks can always play excellent functions for pollutants removal. One binary MOFs, UiO-66(Fe/Zr)), was newly synthesized and applied to remove aquatic selenite (SeIV) and selenate (SeVI). The adsorption behaviors and mechanisms were investigated using batch experiments, spectroscopic analyses, and theoretical calculations (DFT). The characterization results showed that the material inherited the topological structure of UiO-66 and excellent thermal stability. The large specific surface area (467.52 m2/g) and uniform mesoporous structures of the synthesized MOFs resulted in fast adsorption efficiency and high adsorption capacity for selenium species. The adsorbent kept high adsorption efficiency in a wide pH range from 2 to 11 with good anti-interference ability. The maximum adsorption capacity for Se(IV) and Se(VI) reached as high as 196 mg/g at pH 3 and 258 mg/g at pH 5, respectively. The process was conformed to fit pseudo-second-order kinetics and Langmuir isotherm, and could be explained by the formation of Fe/Zr-O-Se bond on the material surface, which was interpreted by the results of XPS, FTIR and DFT calculation. The regeneration and TCLP experiments demonstrated that UiO-66(Fe/Zr) could be regenerated for five cycles without obvious decrease of efficiencies, and the leaching rate of the adsorbed Se(IV) and Se(VI) in the spent adsorbent were only 4.8% and 2.3%. More than 99% of original Se(IV) and Se(VI) in the lake and tap water samples (1.0 mg/L of Se) could be removed in 2.0 h.