Lead in Mexican Children: Pottery Use Slows Reductions in Blood

Abstract

Getting the lead out of Mexico City gasoline has contributed to a significant drop in the blood lead of local children, as it has elsewhere in the world, according to what is likely the first long-term study of such effects in a single group of people [EHP 112:1110–1115]. But the drop within children wasn’t nearly as large as the drop in the air might have suggested. Other lead sources such as ceramic pottery and local industry, combined with poor nutrition, likely are keeping blood lead concentrations elevated at levels 3–4 times higher than those found in U.S. children, concludes a team of researchers led by Lourdes Schnaas of the Mexican National Institute of Perinatology. The team began its study by recruiting 502 pregnant women attending the institute’s prenatal clinic in Mexico City. The researchers followed 321 healthy children born to these women between 1987 and 1992. Team members followed each child for 10 years, taking blood samples every six months. They also tracked airborne lead concentrations using government data. The study period coincided with government actions that led to sharp drops in lead in gasoline, with total elimination by September 1997. Those moves helped slash mean yearly airborne lead concentrations from 2.8 micrograms per cubic meter (μg/m3) in 1987 to 0.07 μg/m3 in 2002. The children’s mean blood lead dropped concurrently. In the group of children born earliest in the study (while most gasoline was still heavily leaded), 89% exceeded the present Mexican action limit for child blood lead of 10 μg per deciliter (dL) at age 2, whereas in the latest-born group only 26% exceeded the limit. For the 100 children with complete data, the peak average of 10.5 μg/dL at age 2 dropped to 4.9 μg/dL at age 10. The children without complete data had somewhat higher concentrations, but saw a parallel drop. Although significant, none of these drops were nearly as dramatic as the drop in airborne concentrations. The team speculates that poor nutrition—as indicated in other Mexico City studies showing low intake of key nutrients such as iron—may have contributed to higher blood lead in the children. Low intake of essential nutrients including iron, calcium, zinc, potassium, and copper has been shown in numerous studies to be associated with increased absorption of lead. The team found that children living in residential and mixed-use sectors of the metropolitan area had blood lead concentrations about 11% and 7% lower, respectively, than children in the more industrial northeastern area. In addition, socioeconomic differences showed a strong influence. Children in the lowest socioeconomic group had blood lead concentrations 32% higher than the highest group. The team also found that children in families that used lead-glazed ceramics had blood lead concentrations 18.5% higher than children in families that didn’t. One-third to one-half of the children’s families used lead-glazed pottery, depending on socioeconomic stratum, with the greatest use among poorer families. A strategy of educating parents about the tainted pottery during the course of this study did not help much; families still used the pottery on occasion, and children could use similar pottery at other family members’ homes. The problem of lead leaching from certain ceramic glazes has been recognized for more than a century, and in 1993 Mexican officials passed regulations cutting the lead content in pottery. But the businesses that make and sell such pottery are poorly monitored, and many are small family enterprises with no quality control. Today, lead-glazed pottery remains one of the greatest sources of lead exposure for Mexicans. Thus, conclude the researchers, eliminating tainted dishes and pots through better regulation of the ceramics industry is needed to further reduce lead body burden.