Gongren Hu

With rapid urbanization and industrialization, pollution of rare earth elements (REEs) in air, soil, and water is increasing in urban areas. These critical high-tech elements are becoming more abundant in urban dust and other environmental settings. It is difficult to differentiate and quantify the sources of REE pollution, as natural and anthropogenic sources overlap. This work couples isotopic tracing techniques (Pb, Sr, and Nd isotopes) with receptor models (positive matrix factorization (PMF) and absolute principal component scores/multiple linear regression (APCS/MLR)) to obtain robust source apportionment of REEs in urban environments. Isotopic fingerprints, including Gd anomalies, have been shown to serve as powerful tracers for distinguishing vehicular emissions, industrial discharges, and soil erosion. Non-exhaust vehicular emissions, especially those from brake and tire wear, have been identified as the main sources of REE release into the environment. The combination of isotopic methods and receptor models enhances the accuracy of source apportionment and contributions, facilitating better environmental management. The review highlights the need for standardized isotope libraries and sophisticated modelling tools to characterize sources, thereby improving source apportionment and informing sustainable control strategies for urban pollution. Focusing on controlling industrial and vehicle emissions can be an effective strategy to reduce REE contamination levels and human exposure.

Atmospheric formaldehyde (HCHO) is a major component of oxygenated volatile organic compounds (OVOCs) and plays an important role in O₃ formation and atmospheric oxidation capacity. In this study, seasonal observations of gaseous pollutants (HCHO, O₃, peroxyacetyl nitrate (PAN), CO, NOx, and VOCs) and ambient conditions (J_HCHO, J_NO2, solar radiation, temperature, relative humidity, wind speed, and wind direction) were conducted in a coastal city in southeast China. The average HCHO concentrations were 2.54 ppbv, 3.38 ppbv, 2.53 ppbv, and 1.98 ppbv in spring, summer, autumn, and winter, respectively. Diurnal variations were high in the daytime and low in the nighttime, and the peak times varied in different seasons. The correlation between HCHO and O₃ was not significant in spring and winter, which is likely related to the effects of photochemical reactions and diffusion conditions. The contributions of background (23.0%), primary (47.6%), and secondary (29.4%) sources to HCHO were quantified using multiple linear regression (MLR) models, revealing that secondary formation was the most significant contributor in summer, whereas primary emissions were predominant in spring. These findings help to improve the understanding of the influence of atmospheric formaldehyde on photochemical pollution control in coastal cities.

Pollutants and pathogens in aquaculture systems may cause economic losses and threaten public health. Yet, the risks associated with microbiological contaminants and their relationship with environmental factors remain largely unknown. In this study, two typical eel farms in southeast China were chosen for investigation of water quality and microbial community in the treatment processes. It was found that flocculant addition can only effectively reduce total phosphorus (TP) in both farms. However, excessive total nitrogen (TN) was found (6.16 mg/L and 6.74 mg/L, respectively). NH₄⁺ (3.98 mg/L) was the main nitrogen pollutant in QR farm, while NO₃⁻ (3.81 mg/L) and NO₂⁻ (1.22 mg/L) were the main nitrogen pollutants in ZJ farm. The treatment processes could not effectively remove nitrogen pollution, and the abundance of nitrogen functional bacteria was low. NO₂⁻ was positively correlated with Verrucomicrobiota (p < 0.05). NH₄⁺ and TN were significantly negatively correlated with Nitrospirota and unclassified_f_Anaerolineaceae, respectively (p < 0.05). Some typical pathogens associated with aquaculture (e.g., Lactococcus) and human beings (e.g., Escherichia-Shigella,) were found in the systems. This study proposes suggestions for aquaculture tailwater by analyzing the shortcomings of the existing treatment processes. Meanwhile, it offers certain support for the prevention of pathogen risks in aquaculture systems.

Sulfate and nitrate are important components of atmospheric PM_2.5, which is the main contributor of haze. Therefore, studying the sources and formation mechanisms of atmospheric sulfate and nitrate is very important for the prevention and control of haze formation. Stable isotopes of sulfate and nitrate, including isotopic compositions of sulfur, oxygen, and nitrogen, can be comprehensively used to study the sources and formation pathways of sulfate and nitrate in PM_2.5, and to evaluate the contribution of each source and each formation pathway. This paper briefly reviews the determination methods for sulfur, oxygen and nitrogen isotopes in sulfate and nitrate, focuses on the application of the above isotopes in identifying the sources and formation pathways of sulfate and nitrate in atmospheric PM_2.5, and puts forward research prospects.

The source apportionment of fine particulate matters, especially PM_2.5, has drawn great attention worldwide. Since rare earth elements (REEs) and Nd isotopes can serve as source tracers, in this study, the characteristics and provenance implications of REEs and Nd isotopes in PM_2.5 of four seasons in Xiamen city, China, were investigated. The range of the ratios of ΣREE to PM_2.5 was 1.04 × 10⁻⁵ to 8.06 × 10⁻⁴, and the mean concentration of REEs in PM_2.5 were in the order of spring > autumn > winter > summer. According to the geoaccumulation index (I_geo), spring was the season in which anthropogenic sources had the greatest impact on the REEs in PM_2.5. The chondrite-normalized REE distribution patterns exhibited light rare earth elements (LREEs, including La, Ce, Pr, Nd, Pm, Sm and Eu) enrichment and a flat heavy rare earth elements (HREEs, including Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) pattern. Significant negative Eu anomalies and no significant Ce anomalies were observed in the PM_2.5. The results of La-Ce-Sm ternary plots indicated that the REEs in the PM_2.5 might be related to both natural and anthropogenic sources. Combined with the Nd isotope, the ¹⁴³Nd/¹⁴⁴Nd versus Ce/Ce* plot further illustrated that the REEs in the PM_2.5 seemed to mostly originate from multiple potential sources, in which vehicle exhaust emissions, coal burning and cement dust made a great contribution to REEs in PM_2.5.

The abundance and morphological characteristics of microplastics in the surface sediments of mangrove wetlands in the Jiulong River estuary were analyzed. The main sources of microplastics were also explored in detail. The results showed that the abundance of microplastics ranged from 640 to 1140 n·kg^-1 (dry sediment), with an average of 935 n·kg^-1, exhibiting a medium level compared with other domestic and abroad mangrove areas. The microscopic observation found that the microplastics were granular (39%), fragmented (31%), and fibrous (30%); the color was mainly transparent (55%); and the particle size was less than 1 mm (92%). As observed via Raman spectroscopy, the main polymer types of the microplastics were identified to be polyethylene, polyethylene terephthalate, and polypropylene, accounting for 57%, 34%, and 9%, respectively. The main sources of microplastics were the plastic waste from aquaculture nearby, urban and rural domestic or industrial wastewater in the basin, and the plastic waste transported here by the tide. Additionally, SEM-EDS results showed that the surface of the microplastics had the characteristics of depression, porosity, and tearing, and some heavy metal elements such as Pb, Cd, Hg, Cr, Fe, Mn, Zn, and Cu were attached to the microplastics. Microplastics may be transferred to the sediments as carriers of heavy metals, posing a potential threat to wetland ecological security.