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.