Identification of inhalable rutile and polycyclic aromatic hydrocarbons (PAHs) nanoparticles in the atmospheric dust

Integrating multiple spheres to identify the provenance and risk of urban dust and potentially toxic elements: Case study from central Mexico

This study aims to improve the current method of studying potentially toxic elements (PTEs) in urban dust using direct chemical evidence (from dust, rock, and emission source samples) and robust geochemical methods. The provenance of urban dust was determined using rare earth elements (REEs) and geochemical diagrams (V-Ni-Th*10, TiO2 vs. Zr, and Zr/Ti vs. Nb/Y). The geogenic or anthropogenic source of PTEs was determined using the enrichment factor (EF) and compositional data analysis (CoDA), while a PTE's point emission source was identified using a 3.1*La-1.54*Ce-Zn diagram, mineralogy, and morphology analyses. The spatiotemporal distribution of PTEs was determined using a geographic information system, and their health risk (by inhalation) was estimated using a lung bioaccessibility test and particle size distribution. We collected urban dust (n = 38), rock (n = 4), and zinc concentrate (n = 2) samples and determined PTEs and REEs in a city of 1.25 million inhabitants in central Mexico. Results showed that urban dust derived from the San Miguelito Range. REEs, Sc, and Zr were geogenic, while Mn, Cu, Zn, As, and Pb were anthropogenic. Due to the presente of sphalerite particles, a zinc refinery was identified as the point emission source of Zn, As, and Pb. High concentrations of Zn (5000-20,008 mg/kg), As (120-284 mg/kg), and Pb (350-776 mg/kg) were found in urban dust near the zinc refinery. Additionally, particles of PM2.5 (66-84%), PM5.0 (13-27%), PM10 (3-8%), and PM20 (0-2%) and lung bioaccessibility of Sr (48.5-72.4%), Zn (9.6-28.4%), Cu (10.5-27.0%), Fe (4.5-8.6%), Mn (2.9-9.2%), Cr (38.3%) and Pb (30.6%) demonstrated a latent risk to human health. These approaches improve our understanding of the provenance of urban dust and its PTE emission sources in urban areas.

Coupling of redundancy analysis with geochemistry and mineralogy to assess the behavior of dust arsenic as a base of risk estimation in Dhaka, Bangladesh

Exposure to dust particles enriched with arsenic (As) is a significant health threat for populations living in Southeast Asian megacities. The mineralogical composition of dust particles is the key factor that controls the retention and release of As. This study investigated the degree of metal(oid)s pollution (As, Ca, Fe, K, Ga, Rb, Sr, Ti, V, Y, and Zr) in road dust of Dhaka city, Bangladesh. Enrichment factor and geoaccumulation index suggested that the road dust was heavily enriched with As, which triggers a comprehensive investigation of its controlling mechanisms and potential health risks by combining physicochemical and mineralogical information with multivariate analysis and a simulated probabilistic risk estimation model. Alkaline road dust (pH_1:5 ranges from 8.02 to 10.34) in Dhaka city was found to have significant enrichment of As. Dust alkalinity was possibly controlled by the presence of carbonate minerals, such as calcite. Quartz was identified as the dominant mineral phase followed by magnesium carbon arsenide (MgCAs₂). Carbonate mineral driven alkaline pH conditions in road dust would potentially trigger the release and mobilization of As to the environment. However, organic complexation can stabilize As on particle surfaces. Monte Carlo simulation-based health risk forecast suggested that the probability of As associated cancer risk has greatly exceeded the threshold value of 1E-4 for adults and children, and children are more vulnerable than adults. According to sensitivity analysis, the concentration of As and exposure duration (ED) posed the most significant impact (>58%) on risk estimation.

Release of Nanoparticles in the Environment and Catalytic Converters Ageing

A Three-Way Catalyst (TWC) contains a cordierite ceramic monolith coated with a layer of Al₂O₃, Ce_xZr_1−xO₂ and platinoids mixture. Under standard operation, the platinoid concentration decreases, exposing the remaining washcoat structure. After that particle release stage, the sintering process follows where the crystalline Ce_xZr_1−xO₂ solution is broken and begins to separate into ZrO₂ and CeO₂ phases. ZrO₂ is released to the environment as micro and nanoparticles, while a small amount of CeO₂ generates a new Al_xCe_1−xO₂ composite. The main effect of Ce capture is the growth in the size of the polycrystal structure from 86.13 ± 16.58 nm to 225.35 ± 69.51 nm. Moreover, a transformation of cordierite to mullite was identified by XRD analysis. Raman spectra showed that the oxygen vacancies (Vö) concentration decreased as Ce_xZr_1−xO₂ phases separation occurred_. The SEM-EDS revealed the incorporation of new spurious elements and microfractures favouring the detachment of the TWC support structure. The release of ultrafine particles is a consequence of catalytic devices overusing. The emission of refractory micro to nanocrystals to the atmosphere may represent an emerging public health issue underlining the importance of implementing strict worldwide regulations on regular TWCs replacement.

First X-ray Spectroscopic Observations of Atmospheric Titanium Species: Size Dependence and the Emission Source

Titanium dioxide (TiO2) in mineral dust is considered as one of the driving forces of photocatalytic reaction at the aerosol surface in the atmosphere. As a precursor of mineral dust, soil contains ilmenite (FeTiO3) and titanite (CaSiTiO5), which have lower photochemical reactivities than TiO2. However, Ti species other than TiO2 in aerosol particles are not well recognized due to the lack of observation in ambient samples. In this study, Ti species in size-fractionated aerosol samples collected in the Noto Peninsula, Japan, were determined by macroscopic and semi-microscopic X-ray absorption fine structure spectroscopy. Regardless of aerosol particle size, Ti species were primarily composed of rutile, anatase, ilmenite, and titanite. Semi-microscopic Ti speciation showed that Ti-poor spots associated with mineral dust were composed of a mixture of rutile, anatase, ilmenite, and titanite, and Ti-rich spots were primarily composed of TiO2 (rutile or anatase) derived from authigenic minerals or anthropogenic materials. Thus, the Ti species in aerosol particles, especially mineral dust, were not composed solely of TiO2 polymorphs. Therefore, the photochemical reactivities of Ti in aerosol particles may be overestimated when laboratory experiments or model studies employ TiO2 as the representative Ti species.

Concentrations of polycyclic aromatic hydrocarbons in street dust from bus stops in Qingyang city: Estimates of lifetime cancer risk and sources of exposure for daily commuters in Northwest China

Lifetime cancer risk and exposure of daily commuters to polycyclic aromatic hydrocarbons (PAHs) in cities of Northwest China were determined from a study of street dust samples obtained from bus stops in Qingyang city. The sum of 16 priority PAHs (Σ16 PAHs) concentrations in the dust samples ranged from 0.8 to 18.3 mg kg^-1 (mean 3.0 mg kg^-1) and the distribution of individual, carcinogenic, combustion specific, low (2-3 rings) and high molecular weight (4-6 rings) PAHs was determined. The benzo[a]pyrene toxic equivalents of Σ16 PAHs ranged from 0.01 to 12.2 mg kg^-1 (mean 0.8 mg kg^-1). Incremental lifetime cancer risk from exposure to PAHs in dust at bus stops in Qingyang city was estimated at 1.9 × 10^-6 for adults and 3.5 × 10^-6 for children (confidence limit ≥ 95%). Emission source analysis of PAHs in bus stop dust showed that they were mainly derived from residential coal, oil and biomass combustion, e.g. from boilers, traffic vehicles, and Kang heaters. Higher concentrations of PAHs were obtained at bus stops near transport hubs, commercial districts, and administrative institutions.