Risk assessment and remediation proposals in an abandoned lead smelter complex in Chihuahua, Mexico

Lead has well-known deletereous effects, especially affecting women and children under 5 years old. Risk assessment of the residual lead intoxication risk is presented, 10 years after the closure of the one of the world's largest smelter complexes, to present the viable remediation alternatives for the encountered contamination. Seven years earlier, a risk assessment of the area was performed, in accordance with the Environmental Protection Agency (EPA) methodology, including stratification of the zone in function of the distance from the smelter. In each of the 3 defined strata, a random sample of mothers and their children between ages 1 and 5 was selected; capillary blood samples were taken, and these samples were analyzed through voltammetry (lead care) with strict quality control. In each of the sampled households, soil, paint, dust, and water samples were taken for later analysis through anodic voltammetry. Preschools from each stratum were selected as well, and in each of them capillary blood samples from children under age 6, as well as environmental samples corresponding to each school, were taken. Recently, an evaluation of stratum zero (the area of the facilities) and strategic points of the other strata was performed. The 2 groups of data were compared, and possible remediation alternatives were evaluated for the presentation of a proposal. In the initial evaluation, a total of 324 children were analyzed whose blood lead levels ranged from 3.0 to 59.0 μg/dL; they had a geometric mean of 11.45 μg/dL (SD, 8.72) and a percentage of 40% ≥ 10 μg/dL and 20% > 20 μg/dL. Lead concentrations showed an inverse relation to the distance from the smelter. The global lead mean in mothers was 5.22 μg/dL (SD, 3.36). The analyzed superficial soil samples show a range of 100 > 9000 mg/kg. The predictors of lead in children, through multiple linear regression, are related to exposure to soil. The recent evaluation shows concentrations from 509 mg/kg in strata I and II to over 15 000 mg/kg in stratum zero. The remediation of the site through phytostabilization was found to be an appropriate measure. This, together with a permanent educational program that includes hygienic and dietary recommendations, would result in the minimization of the associated risk, limiting the damage from exposure in children above all. It is estimated that soil is contributing to over 90% of the lead exposure, especially in small children, with values higher than those established by the EPA as requiring remediation measures. It is clear that there is residual contamination in the zone adjacent to the smelter, which must be remediated. To reduce the risk of exposure, it is recommended to perform a phytostabilization of the inhabited areas, together with educational activities and epidemiologic vigilance