Characteristics, source apportionment and health risk assessment of heavy metals in urban road dust of the Pearl River Delta, South China.

To investigate the characteristics of heavy metals (As, Cd, Cr, Cu, Pb, Hg, Ni and Zn) in urban road dust from different cities and functional areas in the Pearl River Delta (PRD), South China, a total of 294 dust samples were analyzed. The contamination characteristics and health risk of heavy metals in the dust were assessed, their chemical speciation were distinguished, and their sources were identified by the correlations, cluster and principal component analysis (PCA). The mean concentrations of As (15.89 mg/kg), Cd (1.59 mg/kg), Cr (143.75 mg/kg), Cu (184.42 mg/kg), Pb (114.82 mg/kg), Hg (0.11 mg/kg), Ni (41.53 mg/kg) and Zn (645.94 mg/kg) in urban road dust were in high or moderate levels compare with other previous researches. In this case, the contamination of Cr, Cu, Ni and Zn in the industrial area (IA) and the contamination of Cd and Hg in the commercial area (CA) were significantly higher relative to other functional areas (P < 0.05), and the contamination of heavy metals in Foshan City was significantly higher than other cities (P < 0.01). The order of mobility of the heavy metals with higher concentration in urban road dust of the Pearl River Delta declined in the following order: Zn, Ni, Cu, Pb and Cr. Statistical analysis result showed the contaminated heavy metals in urban road dust were mainly contributed by industrial activities, traffic activities and building pollution. There were no significant carcinogenic and noncarcinogenic risks for adults, children however showed significant noncarcinogenic effect caused by As and Cr in partial points, albeit with low contamination level of the two metals. The ingestion was a principal pathway for heavy metals via urban road dust to exposure population. More protection measures should be considered to reduce children's exposure to the dust, especially in the CA and IA.

Effect of ablation behavior on the matrix effect in nanosecond laser ablation inductively coupled plasma mass spectrometry.

To investigate the effect of ablation behavior on the matrix effect, nanosecond laser ablation inductively coupled plasma mass spectrometry is used to analyze variations in element signal intensities of NIST 610 and GSE-1G standard samples with different laser fluence. Scanning electron microscopy and super depth-of-field microscopy are used to capture the morphology of the ablation crater and obtain depth information, respectively. A pump-probe shadowgraph is used to record the dynamic process of plasma plume evolution during sample ablation. Experimental results show that the proportion of refractory elements to volatile elements in the ablation materials with two different matrices increases with an increase in laser fluence. For the GSE-1G matrix, this range of increase is relatively small, and the signal loss of refractory elements occurs at a higher laser fluence. Combined with the morphology of the ablation crater and evolution of the plasma plume, this potential cause is related to the plasma shielding, which is beneficial to form and deposit large particles, resulting in the loss of refractory elements at high energy fluence.

Photoacoustically assisted material ejection from fused SiO2 following UV nanosecond laser ablation.

When an ultraviolet nanosecond laser focuses on the rear surface of a fused SiO2 sample through its front surface, two internal shock waves (SWs) generating from the rear surface propagate toward the front surface. These SWs are derived as the consequence of different physical processes giving rise to ablation particles. They will induce micro-ejection particles from the existing micro-crater sculpted by the laser at the front surface, if their intensities are higher than the yield strength of the material. Atomistic simulations reveal the formation mechanism of shock-induced ejection from the ablated defects. Photoacoustically assisted material ejection has been theoretically and experimentally verified.