Wind blown lead-enriched dust appears to be the primary cause of lead poisoning in children living in cities, according to a new study conducted by researchers at Indiana University-Purdue University Indianapolis, Xavier University of Louisiana and SUNY ESF (Environmental Science and Forestry).
Until now, lead poisoning in children was believed to be caused primarily by what are called point sources, such as lead-based paint in homes.
Further, the researchers say they have developed a new method for predicting whether blood lead test results for a child taken on any date shows whether the child is at risk on an annual basis for exceeding safe blood lead concentrations established by the Environmental Protection Agency.
The researchers’ findings are in a paper published (available online) in Environmental Health Perspectives, a monthly journal of peer-reviewed research and news on the impact of the environment on human health (http://ehp.niehs.nih.gov/docs/2005/7759/abstract.html).
Lead poisoning is a hidden threat to many children living in urban environments, according to health experts. A neurotoxin, lead in the blood causes a variety of permanent health effects in children, including lowered IQ, Attention Deficit Hyperactivity Disorder (ADHD), and behavioral problems.
Environmental laws have significantly reduced new sources of lead to the environment, resulting in a significant decrease in lead poisoning of children in the U.S. as a whole. In cities, however, the percentages of children who are still lead poisoned sometimes exceed 20 percent, and are typically higher in lower income and minority populations, the researchers note.
According to the researchers, the top few inches of urban soil contains a potentially large reservoir of accumulated lead, the legacy of 100 years of lead use in cities. Recent studies indicate that this lead-enriched soil can be redistributed in dry and windy conditions, causing increased exposure to children living in areas where surface soils has high lead values, like transportation and population centers.
While some continued lead poisoning is due to point sources such as paint dust from poorly maintained homes, the researchers concluded that it appears that a significant additional source of lead contamination is from the soil.
“Because resuspension of lead from contaminated soil appears to be driving seasonal child blood lead fluctuations, concomitantly, it is suggested that lead contaminated soil in and of itself may be the primary driving mechanism of child blood lead poisoning in the urban environment,” the researchers state in the paper.
The fact that blood lead levels in children generally vary during the year, with higher levels in summer months and lower levels during the winter, had posed problems for health professionals who diagnose and treat lead poisoning in clinical situations.
Using health and environmental databases from three U.S. cities (Indianapolis, New Orleans and Syracuse), the research team, led by Mark Laidlaw in the Department of Geology at IUPUI, statistically examined monthly variations in children’s blood lead levels in comparison to climatic factors such as precipitation and soil moisture and air quality factors such as fine particulates in the air. These data were used to develop a predictive model for blood lead levels in these cities that is extremely accurate. In Indianapolis, for example, the climatic and air quality factors were able to predict 98 percent of the variation in monthly blood lead levels.
This result indicates the power of this technique for placing blood lead test results in context—for example, a result below the action threshold set by the EPA determined in the winter might exceed, in a predictable way, the safe level if that test had been administered in the summer. These results also speak to the mechanism of the seasonal variations, which had puzzled researchers —since much of the seasonal variation in blood lead results can be predicted by geological and meteorological factors.
A theory that outdoor play during the summer caused elevated blood lead levels is only part of a more complex story, according to the researchers.
In detail, the Environmental Health Perspectives study finds that seasonal trends in children’s blood lead levels seems to be controlled by exposure to lead-enriched dust originating from contaminated soils and suspended in the air when several weather related environmental conditions are present: temperature is high, soil moisture is low, and fine particulate is elevated. Under these combined weather conditions, lead-enriched dust disperses in the urban environment and is manifest by elevated lead dust loading. In this case, exposure is via increased dust loads in homes and on contact surfaces, with ingestion being the uptake mechanism. Although further work using detailed tracking of lead, possibly involving lead isotopic studies, may help to elucidate the connection between seasonality and blood lead values, these results indicate that the ability of geochemical and meteorological factors to predict blood lead supports the supposition that external loading and exposure drives much of the blood lead concentrations.