Heavy metal content estimation in the Mexico City Street dust: an inter-method comparison and Pb levels assessment during the last decade

Abstract

Elemental concentrations measured in 482 street dust samples from different urban and conurbated areas of Mexico City obtained using a portable energy-dispersive X-ray fluorescence spectrometer are reported. The data quality of eight different elements commonly used in pollution studies is evaluated, calculating the data precision and accuracy obtained with this handheld equipment. Precision for the various elements analyzed ranges between 1.2 and 15.9%, which can be considered as adequately precise for portable equipment. In the case of the accuracy, a maximum under-/overestimation of less than 20% was achieved. Pb and Zn correlation factors were 0.725 and 0.923, respectively. Similar mean Pb concentration values to those reported by ICP-OES were obtained. An average value of ~ 100 mg/kg for Pb concentration was estimated, which is significantly lower than the utmost permissible levels for residential/commercial usage. On the contrary, contamination factors calculated to identify the metal accumulation against those of the background values point from considerable to high contamination for 62 and 30% of the street dust samples analyzed, respectively. A comparison of the results recorded in Mexico City 10 years ago against those obtained suggests that no significant reduction in Pb concentration has occurred during this period despite the measures implemented to stop using leaded gasoline for three decades. Finally, the sample's low-amount requirements, simple nondestructive preparation procedure, and rapid elemental concentration determinations make portable XRF a promising geochemical determination technique for the fast and economic evaluation of contamination by heavy metals in large cities.

Higher heavy metal contamination indoors than outdoors during COVID-19 in Mexico City

“…There is a great concern due to Pb contamination worldwide and, in particular, in Mexican cities, since it is the metal with the highest concentrations in outdoor dust and represents an ecological and children’s health risk (Aguilera et al 2022 ). Pb concentrations in this study are lower than those found in a previous study in Mexico City (Morales et al 2020 ). In 2016 the average concentration of Pb was 122 mg/kg, while in 2020 (the sampling year for this study) the average concentration was 74.7 mg/kg.…”

“…This XRF equipment was the same one used to measure the concentrations of the metals in the present study. The average Zn in street dust from 2016 (sampling year in Morales et al 2020 ) to 2020 sampled for this research has increased by 13%, 495.5 and 569.4 mg/kg, respectively.…”

“…However, it is important to mention that the analytical concentration measurement technique (portable XRF) seems to yield higher Zn values than other techniques such as ICP-OES. In a previous study from Mexico City, carried out by Morales et al ( 2020 ), they compared the Zn concentrations measured with portable XRF and with ICP-OES and found an R 2 of 0.9 in the linear regression; however, the measured concentrations with portable XRF were almost double those obtained with ICP-OES. This XRF equipment was the same one used to measure the concentrations of the metals in the present study.…”

“…In 2018, this city was the fourth largest agglomeration in the world and the first in the American continent, behind Tokyo, Delhi, and Shanghai (SUN 2018 ). It has around 23 and a half million inhabitants, 40,000 small- and medium-sized industries, and 9.5 million vehicles (Morales et al 2020 ).…”