Is the Urban Form a Driver of Heavy Metal Pollution in Road Dust? Evidence from Mexico City

Anahi Aguilera,Dorian Bautista-Hernández,Rubén Cejudo,Francisco Bautista,Avto Goguitchaichvili

doi:10.3390/atmos12020266

Anahi Aguilera, Dorian Bautista-Hernández + Show 3 more

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https://doi.org/10.3390/atmos12020266

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Journal: Atmosphere	Publication Date: Feb 17, 2021
Citations: 13	License type: CC BY 4.0

Affiliation: Universidad Nacional Autónoma de México

Abstract

Environmental pollution is a negative externality of urbanization and is of great concern due to the fact that it poses serious problems to human health. Pollutants, such as heavy metals, have been found in urban road dust; however, it is unclear whether the urban form has a role in its accumulation, mainly in cases where there is no dominant unique source. We collected 482 samples of road dust, we determined the concentrations of five heavy metals (Cr, Cu, Pb, Zn, and Ni) using inductively coupled plasma optical emission spectrometry (ICP-OES), and then we derived the pollution load index (PLI). After estimating the mostly anthropogenic origin of these pollutants based on global levels of reference, there were two main aims of this study. Firstly, to analyze the spatial correlation of heavy metals, and secondly, to identify the main factors that influenced the heavy metal concentrations in the road dust of Mexico City. We did this by using a spatial autocorrelation indicator (Global Moran’s I) and applying ordinary least squares (OLS) and spatial regression models. The results indicated low levels of positive spatial autocorrelation for all heavy metals. Most variables failed to detect any relationship with heavy metals. The median strip area in the roads had a weak (significance level of 90%) but consistent positive relationship with Cr, Cu, Ni, Pb, and the PLI. The distance to the airport had a weak (significance level of 90%) and inverse relationship with Pb. Manufacturing units were associated with an increase in Cu (significance level of 95%), while the entropy index was associated with an increase in Ni (significance level of 95%).

Highlights

91.5% of the samples had a pollution load index (PLI) greater than 1. We propose that this is an important indication of the anthropogenic origin of the heavy metals found in the road dust from Mexico City
As it is very difficult to control aspects related to the deposition of dust in the points of sampling, we decided to work with the heavy metal concentrations instead of the total heavy metal contents as dependent variables
According to the global Moran’s I, there were low levels of positive spatial autocorrelation in all the heavy metals analyzed. We interpret this as an indication of the greater relevance of the local aspects over regional processes as determinants of the heavy metal content in urban road dust

Summary

Introduction

In Mexico, it is estimated that 80% of the population lives in urban areas [1]. The capital, Mexico City, along with its metropolitan area, concentrates around 17.5% of the country’s population and has over 40,000 industries and 4 million vehicles that consume more than 40 million liters of fossil fuels per day, releasing, as a result, thousands of tons of pollutants into the urban environment [2]. Research reported that road dust is a sink for polluting emissions, which are deposited on the surface of streets, sidewalks, and windows [6]. From a social point of view, aspects such as tax revenue and education level are associated with a decrease in urban pollution [9].

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