NEW STRATEGIES FOR REDUCING CHILDHOOD LEAD EXPOSURE FROM URBAN SOILS: MANAGING LOCALLY SOURCED CARBON WASTE STREAMS

From 2001-2010, less than 1% of the 1-to-5-year-old population in the U.S. was considered to have lead poisoning—a reduction hailed as a great public health achievement. Two recent developments, however, are prompting a radical reevaluation of childhood lead exposure and prevention: a new CDC lead poisoning benchmark and evidence of a new lead exposure pathway.

In 2012, the CDC adopted a new protocol for establishing elevated BLLs using the 97.5^th percentile BLL of U.S. children aged 1 to 5. This model yields a current U.S. reference value of 5 μg/dL, half of the former benchmark. Several demographic studies then examined this cohort of children newly considered to have elevated BLLs. Two key outcomes are that these children are no longer the “usual suspects,” and in some urban areas the number of children newly classifiable with elevated BLLs reaches 25%. The second major development involves urban lead exposure pathways. Recent studies from Zahran, Laidlaw, and Mielke demonstrate that resuspension of urban soils—not leaded paint, as previously thought—is the primary exposure pathway linked with elevated BLLs. Lead poisoning prevention now calls for locally sourced, low cost, low metal burden geomaterials that can be widely used as cover material to minimize the resuspension of urban soil.

To address this need we have geochemically fingerprinted a range of locally sourced compost waste streams from the metro Boston area, including municipal, loam mixes, commercial food, household food, and biosolids. We observed that each waste stream has a unique geochemical profile along with a range of metal inventories. We find that lead concentrations range from 95 ug/g in loam mixes to 241 ug/g in municipally sourced material, often exceeding EU benchmarks for total lead. Our primary finding, however, is that the bioaccessible lead as determined by the SBET gastric soluble fraction is less than 10% for all waste streams. This level is significantly lower than what has been observed for urban soils and is a fraction of the default values typically assumed for lead exposure models. We advocate for municipally managed composting facilities that, with proper source stream management and processing, could supply cost effective, locally sourced material to both cover lead contaminated soils and promote urban agriculture.