According to the World Health Organization six million people die each year from exposure to environmental pollution, there is no doubt the deadly risks of exposure to contaminants.
The diagnostics of contamination by heavy metals is not regularly performed because of high cost and substantial effort required. However, these heavy metals directly affect the health of the population. Since ash and flue gases prints a dark color in soils, the color itself may be a proxy indicator.
On the other hand, the view, based on shapes and colors, it is our first tool to obtain information, make assessments and make decisions. However, the information obtained visually carries a high level of subjectivity but, in recent years, devices have been developed which measure the color objectively and are not costly. Ash and flue gases give a dark colored to urban dust so that the color may be a proxy indicator. Urban dust is a mixture of soil with particles from pollution.
The aim of this work is to try to find a relationship between the color of urban dusts and the concentrations of heavy metals.
In total, 86 samples were analyzed of urban dusts from Ensenada, Baja California. Color was estimated with a colorimeter and specific color indexes were obtained. In addition, the heavy metals concentrations were determined by XRF and results were analyzed by statistical methods.
Figure 1. City of Ensenada Baja California, Mexico
The discriminant analysis forms four groups of samples considering color indexes. Multiple regressions of color indexes vs heavy metals by group were performed obtaining an IH with r2= 0.58 to 1, IR r2= 0.67 to 1; and IS r2= 0.31 to 1, all P values <0.09.
Figure 2. Note the difference in color of topsoil (1-2 cm)
The Kruskal-Wallis test showed statistically significant differences between the mean of each color group with Ni, Cu, Zn, Pb and Rb. Therefore, the color indices of urban dusts can be considered proxy indicators for its low cost, fastness and reliability.
Figure 3. Lead map in urban dust
Gray colored urban dust contains greater concentrations of Pb, Cu, Zn and Ni.
In this study, a methodology has been established in order to identify the pollution urban dust. The steps are:
- Analyze the color urban dust using the Munsell color chard
- Measure the color of urban dust and calculate the soil color indices
- Group the urban dust samples by Munsell colors and validate the groups by means of a discriminant analysis with color indices as independent variables
- Analyze the heavy metals in the urban dust
- Validate the formation the color groups with a discriminant analysis considering heavy metals as independent variables
- Carry out the multiple regressions between the color indices and the heavy metals
Now we have a new indicator of heavy metal pollution in urban dusts a good, nice and cheap indicator.
Cortés JL., F. Bautista, P Quintana, D. Aguilar y A. Goguichaichvili. 2015. The color of urban dust as an indicator of contamination by potentially toxic elements: the case of Ensenada, Baja California, Mexico. Revista Chapingo Serie Ciencias Forestales y del Ambiente, 21(3):255-266. http://www.chapingo.mx/revistas/forestales/contenido.php