33 Borderless Geoscience: Linking Baja and Southern California

We invite contributions from both geophysical and geological studies that integrate or reference observations from both sides of the U.S.–Mexico border. The purpose is to promote discussion regarding regional processes.

Friday, 24 April 2026
8:00 AM - 12:00 PM
LMH, Meeting Room

Source Identification of Potential Toxic Elements in Urban Dust and Soils Particles <20 µm in Tijuana Borderland, Baja California (México)

Paper number: 33-4
Program: Technical Sessions
Time: 9:05 AM – 9:25 AM

Authors

Abstract

Urban dust in border regions reflects the combined influence of vehicular traffic and industrial and metallurgical activities, which contribute to the emission of potentially toxic elements (PTEs). The Tijuana-Southern California borderland is physically linked through two major land ports of entry: 1) San Ysidro, dominated by private vehicle crossings and recognized as the busiest land border crossing in the Americas, and 2) Otay Mesa, where traffic is largely composed of heavy-duty cargo vehicles. At both sites, persistent congestion promotes the accumulation and resuspension of fine particles enriched in PTEs. This study evaluates the geochemical characteristics and sources of PTEs in <20 µm particles from the Tijuana borderland, based on elemental concentrations, contamination indices, particle size distribution, and SEM-EDS morphological and semi-quantitative analyses. Moderate to high contamination levels of Cr, Co, Ni, Cu, Zn, Mo, Cd, Ba, Sb, and Pb, as indicated by the geoaccumulation index, were identified at border sites and were primarily associated with anthropogenic emissions. In contrast, V and Mn exhibited low contamination levels with dominant geogenic contributions and low anthropogenic influence. Overall, samples collected at the ports of entry exhibited the highest levels of contamination within the urban setting, indicating a strong influence of traffic intensity on elemental enrichment. Particle size distribution results show that more than 85% of the analyzed particles are <5 µm, with 36–56% falling within the 1.5-2.5 µm range. This fine fraction is easily resuspended and capable of penetrating the deepest regions of the respiratory system. SEM-EDS analyses of <20 µm particles reveal abundant particles containing Pb, Ba, Cu, Sb, Zn, and Cr, particularly in samples collected at border crossings, with particle morphologies and elemental associations consistent with vehicular sources, including brake wear, tire and metallic abrasion, as well as urban paint. Health risk assessment results indicate a higher risk for children compared to adults in areas influenced by intense border traffic. Geochemical results indicate that metal-enriched particles preferentially accumulated at land ports of entry within the Tijuana-Southern California borderland, relative to the surrounding urban area of Tijuana.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410930

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