Seasonal characteristics of chemical compositions and sources identification of PM2.5 in Zhuhai, China.

Fine particulate matter is associated with adverse health effects, but exactly which characteristics of PM2.5 are responsible for this is still widely debated. We evaluated seasonal dynamics of the composition and chemical characteristics of PM2.5 in Zhuhai, China. PM2.5 characteristics at five selected sites within Zhuhai city were analyzed. Sampling began on January 10, 2015, and was conducted for 1 year. The ambient mass concentration, carbon content (organic and elemental carbon, OC and EC), level of inorganic ions, and major chemical composition of PM2.5 were also determined. Average concentrations of PM2.5 were lower than the National Ambient Air Quality Standard (NAAQS) 24-h average of 65 µg/m3. The daily PM2.5 concentration in Zhuhai city exhibited clear seasonal dynamics, with higher daily PM2.5 concentrations in autumn and winter than in spring and summer. Carbon species (OC and EC) and water-soluble ions were the primary components of the PM2.5 fraction of particles. Apart from OC and EC, chemical species in PM2.5 were mainly composed of NH4+ and SO42-. There was a marked difference between the summer and winter periods: the concentrations of OC and EC in winter were roughly 3.4 and 4.0 times than those in summer, while NH4+, SO42-, NO3-, and Na+ were 3.2, 4.5, 28.0, and 5.7 times higher in winter than those in summer, respectively. The results of chemical analysis were consistent with three sources dominating PM2.5: coal combustion, biomass burning, and vehicle exhaust; road dust and construction; and from reaction of HCl and HNO3 with NH3 to form NH4Cl and NH4NO3. However, additional work is needed to improve the mass balance and to obtain the source profiles necessary to use these data for source apportionment.

Aquatic environmental changes and anthropogenic activities reflected by the sedimentary records of the Shima River, Southern China.

Reconstructing historical sedimentary records is essential for better understanding the effects of anthropogenic activities on river environments. We used lead-210 to date riverine sediment core from the Shima River in China. We obtained a sedimentary history of 34 years (1982-2015) for core S2, which had a length of 34 cm. The sedimentation rate of 0.304-2.04 cm y-1 was controlled by both flood events and anthropogenic activities. The conservative element content depth profiles remained relatively constant, suggestive of a relatively stable sediment provenance; therefore, the increase in the sedimentation rate over time was mainly the result of domestic and industrial wastewater effluent and the construction of a rubber dam at the middle and lower reach of the Shima River. From 1982 to 2015, the nutrient and trace metal depth profiles could be divided in three periods based on their trends. From 1982 to 1993, the vertical profiles of nutrients (organic carbon, total phosphorus, and total nitrogen) and three trace metals (nickel, zinc, and manganese) were relatively stable; however, the gradual decrease in copper and cadmium was likely associated with a reduction in agricultural chemical application. From 1993 to 2003, a population explosion and rapid industrialization were responsible for an increase in the input of pollutants into the Shima River, which was partly attenuated by water from the Dong River, leading to a gradual increase in nutrient and trace metal contents. Finally, from 2003 to 2015, the Shima River stopped being used as a source of water due to its deteriorating water quality. The relatively lower velocity of the water flow after the recovery of its flow direction and the reconstruction of the rubber dam in 2009 provided advantageous sedimentary conditions, promoting nutrient accumulation and significant trace metal enrichment.

Distribution characteristics and sources of trace metals in sediment cores from a trans-boundary watercourse: An example from the Shima River, Pearl River Delta.

Metal pollution in sediments from the Shima River, a typical transboundary watercourse in the Pearl River Delta area, was investigated. Sediment cores were collected at eight sites from the upper to the lower reaches crossing Shenzhen, Dongguan and Huizhou cities. Sediment physicochemical properties and the total concentrations of trace metals (V, Cr, Co, Ni, Cu, Zn, As, Cd and Pb) were determined. The results showed that riverine sediment was significantly polluted by Cr (content range: 13.8-469mgkg-1), Ni (14.1-257mgkg-1), Cu (10.8-630mgkg-1), Zn (50.2-1700mgkg-1) and Cd (0.172-2.26mgkg-1). The geoaccumulation indices (Igeo) of trace metals decreased in the order Cd>Zn>Ni>Cu>Co>Cr>Pb>As>V. The pollution load indices and potential ecological risk indices (RI) at the sampling sites were similar, with more severe pollution and greater risk presenting in the upper and middle reaches (S1-S6) compared with the lower reaches (S7 and S8). Cd contributed significantly (77.2-87.6%) to the RI. Source identification based on multivariate statistical techniques, including principal component analysis (PCA), correlation analysis (CA) and hierarchical cluster analysis (HACA), was performed to differentiate the origins of trace metals. PCA and CA yielded similar results, indicating that As and V originated from natural sources (e.g., parent materials) and that the other metals were related to anthropogenic activities. HACA based on the Igeo showed that Cd was associated mainly with fertilizers, and the origins of Cr, Ni, Cu and Zn were probably industrial effluents, whereas Co and Pb were related to traffic activities. HACA of sediment cores suggested that Dongguan and Shenzhen cities contribute large quantities of metals to the riverine sediment, whereas few metals were discharged from Huizhou City.