Seasonal variation of atmospheric lead levels in three sites in Mexico City



Atmospheric lead concentrations associated to particles smaller than 10 µm were measured in Mexico City, to establish changes of levels of this pollutant in three sites (industrial, commercial and residential) for 1990-1991. Moreover, an attempt was made to establish a possible link between this airborne pollutant and blood lead levels reported in children and women living near the sampling sites. A marked gradient in atmospheric lead from North to South is observed with higher and more variable mean lead values in the northern site where industry is located. Lead concentrations and their corresponding variability gradually decrease (from about 1.2 to 0.5 µg m-3) toward the southern suburbs. Moreover, these values are significantly higher during the dry season than in the wet season when a marked washout effect is observed. However, the quarterly averages recorded during the sampling time do not exceed the international standard (1.5 µg m-3). Lead concentrations and corresponding PM10 values showed a significant correlation. This result shows that lead is associated to the fine fraction of airborne particles, with high proportion of them deposited in the respiratory tract. A substantial abatement in levels of atmospheric lead is observed in 1991 with respect to the previous year. This may be explained by the introduction of improved quality gasoline in the capital city. In spite of this measure more than 30 of the evaluated population in 1991 presented blood-lead levels > 10 µg dL-1.

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