Some aspects of the environmental exposure to chromium residues in Mexico

Research was conducted to determine the environmental effects of Cr residues from a chromite-ore processing plant (Cromatos de México) on the human population living in the surrounding area. The results of this study provided the first quantitative evidence of the transfer of Cr to the atmosphere, soil and subsequently to ground water. The atmospheric concentration of Cr ranged from 0.25 to 0.39 μg m^?3, seven times higher than the level found in the control area. Most of the well water samples (90%) had a higher Cr concentration than the threshold limit value for drinking water of 0.05 mg L^?1. The high Cr concentration in the environment may be responsible for the high concentration of this metal in urine (18.6 ng mL^?1) and hair (4.3 μg g^?1) found in the residents of this polluted area. These results were compared with those of people living in a Cr free zone through statistical analysis (Wilcoxon's signed-ranks test). A significant difference of p<0.01 was found between these two populations. In relation to the average concentrations in hair (1.4 μg g^?1) and urine (2.0 to 6.0 ng mL^?1) considered as normal for a non exposed population in the USA, 70 to 80% of the residents in the Mexican urban-industrial area registered higher values. The high Cr concentration in urine found in workers from the chromite-ore processing plant show the lack of an efficient pollution control system. Therefore the Cr levels found in urine and hair can be used as indicators of environmental exposure.