Health Risk Assessment of Zone 7 Contaminated with Benzene in the Environmental Liability Generated by the “March 18th Ex-Refinery” in Mexico City

Benzene is a constituent of oil regarded as a potential carcinogen, and therefore a dangerous compound. Its risk increases when spills occur, added to the effect of gravity and high mobility, it's infiltrated into the ground, reaching the phreatic area until dissolved, contaminating the water.The objective of this research was to evaluate the health risk of environmental liabilities caused by the contamination with benzene in the “Ex-refinery March 18” in Mexico City. For twenty years were carried out remediation work –which started since 2008– and today this space has been converted into a recreational park. This environmental liability is divided into seven zones for purposes of remediation, although in this case only was considered the 7 zone. It also, took into account only the concentration of this hydrocarbon (average, percentil 75 and 95) present in the soil. The results, –from a total of 642 samples from 122 soil profiles–, before the remediation –biospray with vapor extraction–, showed a health risk by depth between 1.2 to 7.2m, from 1.69E–07 to 1.2 1.25E–05m to 4.8m, which coincides with the phreatic level of aquitard, was the place where the highest level of health risk is present. After remediation, the measurements yielded 4.07E–07 to 1.2m and 3.85E–07 to 4.8m. These values indicate that the mass of benzene before decontamination exceeded the risk considered acceptable, 1.0E–06 at a depth of 4.8m; after that, reductions below the acceptable risk were achieved, which shows that the remnant hydrocarbon does not represent a health risk