HEAVY METALS POLLUTION OF URBAN-INDUSTRIAL SOIL AND ITS VEGETATION

Abstract

Pollution of soil by heavy metals is established by comparison against the defined value in the local regulations. In Mexico the NOM-147-SEMARNAT/SSA1-2004 defines the concentration criteria for As, Ba, Be, Cd, Cr VI, Hg, Ni, Ag, Pb, Se, Tl and V that must be achieved in order to consider that a contaminated soil has been remediated. The goals of this project were: 1) to evaluate the metals distribution and pollution level; and 2) the metals assimilation in the tissue of plants, of an urban-industrial site located north of Mexico City that had been exposed to pollution by heavy metals for more than five decades, as a result of uncontrolled process leaks; the infiltration had reached up to 15 m depth. Due to the site background, it was assumed that Ni, As and Cu were present in soil. Heavy metals were measured in both, the soil in site and the vegetation of the surrounding area. Soil samples taken between 3.2 and 5.0 m depth showed a Ni content up to 2010 ppm, while As was 4580 ppm and Cu was up to 29222 ppm. Heavy metals were also found in the leaves of trees of the surrounding area, confirming metals assimilation through their roots. Metal concentration in plant tissue (reported as ppm metal per biomass dry weight) was found up to 60 ppm Ni, 472 ppm Cu and 85.4 ppm As. These values are higher than the average metal concentration found for plants.

Key words: heavy metals, sampling, soils, vegetation.