Heavy metal pollution and associated health risk assessment of urban dust in Riyadh, Saudi Arabia

Depending on their particle size and concentration, heavy metals in urban dust pose a health hazard to humans. This study investigated the total concentration, health risk, integrated pollution load index (IPI), and enrichment factor (EF) of various heavy metals in urban dust at different locations in Riyadh City. Surface dust samples were collected from 50 different residential yards in the north, south, west, east, and central corners of the city and analyzed for cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn). With respect to concentrations heavy metals were in the following order Zn > Cu > Mn > Cr > Ni > Pb > Cd. The EF trends exposed repeated anthropogenic activities were responsible for Mn, Cr, and Ni, while Pb, Zn, and Cu appeared to come from Earth’s crust. Since the heavy metal concentrations were lower than the threshold values, children and adults are exposed to lower health risk in investigated area. Also, there are no pollution of heavy metals in the dust with respect to IPI which is less than the critical limit (<1) with the exception of a sampling location in north side of the city with higher IPI showed unhealthy respiration conditions in particular areas. It was concluded that rapid industrialization and urbanization and their concentrations in dust may cause health problems in near future in north side as well as other sides of Riyadh City.

Leaf reflectance and functional traits as environmental indicators of urban dust deposition

Background How to quickly predict and evaluate urban dust deposition is the key to the control of urban atmospheric environment. Here, we focus on changes of plant reflectance and plant functional traits due to dust deposition, and develop a prediction model of dust deposition based on these traits. Results The results showed that (1) The average dust deposition per unit area of Ligustrum quihoui leaves was significantly different among urban environments (street (18.1001 g/m2), community (14.5597 g/m2) and park (9.7661 g/m2)). Among different urban environments, leaf reflectance curves tends to be consistent, but there were significant differences in leaf reflectance values (park (0.052–0.585) > community (0.028–0.477) > street (0.025–0.203)). (2) There were five major reflection peaks and five major absorption valleys. (3) The spectral reflectances before and after dust removal were significantly different (clean leaves > dust-stagnant leaves). 695 ~ 1400 nm was the sensitive range of spectral response. (4) Dust deposition has significant influence on slope and position of red edge. Red edge slope was park > community > street. After dust deposition, the red edge position has obviously “blue shift”. The moving distance of the red edge position increases with the increase of dust deposition. The forecast model of dust deposition amount established by simple ratio index (y = 2.517x + 0.381, R2 = 0.787, RMSE (root-mean-square error) = 0.187. In the model, y refers to dust retention, x refers to simple ratio index.) has an average accuracy of 99.98%. (5) With the increase of dust deposition, the specific leaf area and chlorophyll content index decreased gradually. The leaf dry matter content, leaf tissue density and leaf thickness increased gradually. Conclusion In the dust-polluted environment, L. quihoui generally presents a combination of characters with lower specific leaf area, chlorophyll content index, and higher leaf dry matter content, leaf tissue density and leaf thickness. Leaf reflectance spectroscopy and functional traits have been proved to be effective in evaluating the changes of urban dust deposition.

Determinación de metales pesados en material particulado atmosférico por espectroscopía de absorción atómica: validación

El análisis de Cr, Cd, Pb y Ni en material particulado (PM10) permite establecer los niveles de exposición y de cuantificación, empleando digestión ácida asistida por microondas y espectroscopía de absorción atómica. Se evaluaron los parámetros: linealidad, límite de detección y de cuantificación, precisión y veracidad. Se obtuvo comportamiento lineal (R2>0,995) entre 0,75-2,5 μgCd, 8,75-125 μgNi, 5-25 μgCr y 8,75-15 μgPb. También, se evidenció efecto matriz (α=0.05) en todos los metales estudiados. Los coeficientes de variación (0,9-12%) y los porcentajes de recuperación (66-126%) se encontraron dentro de los intervalos permitidos. El análisis del material de referencia (NIST 1649b Urban Dust) permitió determinar la veracidad de la metodología (71-102 % R). Por consiguiente, la metodología puede ser implementada para evaluar de manera confiable, el cumplimiento de la resolución 2254:2017 del Ministerio de Medio Ambiente y Desarrollo Sostenible. The analysis of Cr, Cd, Pb, and Ni in particulate matter (PM10) makes it possible to establish the levels of exposure and risk to the health of the population. This work presents the validation and implementation of analytical methodologies, using microwave-assisted acid digestion and atomic absorption spectroscopy. The parameters were evaluated: linearity, the limit of detection and quantification, precision, and veracity. Linear behavior (R2> 0.995) was obtained between 0.75-2.5 μg Cd, 8.75-125 μg Ni, 5-25 μg Cr and 8.75-15 μg Pb. Also, a matrix effect (α = 0.05) was evidenced in all the metals studied. The coefficients of variation (0.9-12%) and the recovery percentages (66-126%) were found within the allowed intervals. The analysis of the reference material (NIST 1649b Urban Dust) allowed to establish the veracity of the methodology (71-102 % R). Finally, the methodology can be implemented to reliably assess compliance with resolution 2254: 2017 of the Ministry of the Environment and Sustainable Development.

Post-deposition Weathering of Pb-rich Particles From a Pb-Zn Smelting and Refining Factory Under Semiarid Conditions

In this study, urban dust samples were collected at 1 km radius surrounding one of the largest Ag-Cd-Pb-Zn smelting and refining complex in the world (Met-Mex Peñoles), which is in operation in Torreón (North México) since 1901. Metal-rich particles in urban dust were analyzed for elemental composition, and Pb-rich particles were identified, characterized, and analyzed for mineral identification by using conventional techniques such as scanning electron microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and X-ray powder diffraction (XRD). Pb-rich particles showed a variety of sizes and morphologies and different contents of Pb and other elements. Pb-rich particles were related to the fugitive and non-controlled emissions from Met-Mex Peñoles. Galena occurs in individual and metal-rich agglomerate particles. The presence of secondary Pb minerals (e.g., Pb carbonates, Pb sulfate, and Pb oxides) evidenced the weathering in Pb-rich particles and metal-rich agglomerates. Secondary Pb minerals are incorporated in finer particles than original sulfide minerals, and they are also more concentrated in Pb and chemically more available than galena for the environment and humans. Physical-chemical transformations on the weathered Pb-rich particles are increasing the availability and toxicity of lead in the urban dust and the potential impacts on the environment and human health.

Overview and Seasonality of PM10 and PM2.5 in Guayaquil, Ecuador

The focus of this study is the assessment of total suspended particles (TSP) and particulate matter (PM) with various aerodynamic diameters in ambient air in Guayaquil, a city in Ecuador that features a tropical climate. The urban annual mean concentrations of TSP (Total Suspended Particles), and particle matter (PM) with various aerodynamic diameters such as: PM10, PM2.5 and PM1 are 31 ± 14 µg m−3, 21 ± 9 µg m−3, 7 ± 2 µg m−3 and 1 ± 1 µg m−3, respectively. Air mass studies reveal that the city receives a clean Southern Ocean breeze. Backward trajectory analysis show differences between wet and dry seasons. During the dry season, most winds come from the south and southwest, while air masses from the peri urban may contribute as pollutant sources during the wet season. Although mean values of PM10 and PM2.5 were below dangerous levels, our year-round continuous monitoring study reveals that maximum values often surpassed those permissible limits allowed by the Ecuadorian norms. A cluster analysis shows four main paths in which west and southwest clusters account for more than 93% of the pollution. Total vertical column of NO2 shows the pollution footprint is strongest during the dry season, as opposed to the wet season. A microscopic morphological characterization of ambient particles within the city during the wet and the dry season reveals coarse mode particles with irregular and rounded shapes. Particle analysis reveals that samples are composed of urban dust, anthropogenic and organic debris during the dry season while mainly urban dust during the wet season.

Susceptibility to Antibiotics and Reactive Oxygen Species in Escherichia coli: A Survey of Clinical and Environmental Isolates

Aims: Some bacterial responses to oxidative stress also diminish antibiotic susceptibility; also, some antibiotics do increase oxidative stress within bacterial cells. Linkage or cross-resistance to prooxidants and antibiotics could facilitate the selection of antibiotic resistance and/or virulence. We made this survey in order to detect this possible linkage in Escherichia coli isolates. Methodology: The susceptibility of 102 E. coli clinical (causative of urinary or gastrointestinal infections) and environmental (rural or urban dust) isolates towards paraquat, H2O2, and antibiotics was measured using disc assays. Catalase and superoxide-dismutase (SOD) activities were measured. Results: Susceptibility to prooxidants was similar across isolates of all four sources, but urinary and urban dust isolates were more resistant to antibiotics. H2O2 "resistant" organisms had more antibiotic resistance phenotypes, particularly towards sulfadiazine and tetracycline. Paraquat "resistance" seems associated to beta-lactam resistance; but paraquat "susceptibility" seems associated to resistance towards chloramphenicol, gentamicin, ciprofloxacin and nitrofurantoin. Prooxidant disc assays correlate to catalase and superoxide-dismutase activities. A weak relationship H2O2/antibiotic-resistance, but not superoxide/antibiotic-resistance, is suggested. Conclusion: Overall, antibiotics exerting their action through oxidative stress, do not seem to have resulted in the co-selection of oxidative stress resistance, or vice versa. However, a possible link between resistance to some antibiotics and to H2O2 might contribute to co-selection between these two chemical insults.