Evaluation of environmental pollution from the magnetic increase in urban dusts. A case study for the city of Mexicali, Mexico
Assessments of magnetic enhancement on urban dust samples collected on different surfaces, mostly paved and unpaved roads, were performed in order to evaluate the environmental contamination in Mexicali (medium-sized city on the Mexico-USA border). Rock and mineral magnetic techniques consisted of systematic measurements of mass-specific magnetic susceptibility and isothermal remanent magnetization at 0.7 T. Magnetic enhancement was estimated by comparing magnetic concentration for each sample relative to reference value obtained from the site with almost no human activity also known as conservation area in the suburb of town. Additional magnetic parameters as the S-200 ratio and Curie temperatures were used to identify predominant magnetic carriers. These experiments indicate that impure magnetic is the main mineral in most studied samples. Geostatistical analysis and interpolation techniques (experimental variogram and ordinary Kriging, respectively) were carried out in order to determine the spatial distribution of magnetic enhancement and relative levels of environmental contamination. High traffic roads with industrial areas as well as some land categories yielded unusually high level of contamination.