URBAN CARBON CYCLING: SOURCE STREAM ATTRIBUTION MODELING AND MINIMIZING LEAD EXPOSURE PATHWAYS

Manipulating the urban carbon cycle to create productive, affordable, lead safe compost can recycle urban carbon waste, provide growing media for sustainable urban agriculture, and minimize lead exposure pathways for urban children. This study examined the chemical and physical characteristics, trace element signatures, and bulk and bioaccessible lead of composts from various carbon streams. XRF spectroscopy was used to measure trace element concentrations. To characterize the variables associated with lead sorption and solubility, proxies for bulk compost matrix characteristics (loss on ignition, pH, and density) were measured. The EPA SBET method was used to measure compost lead bioaccessibility. Geochemical characterization of compost and Principal Components Analysis identified fingerprintable feedstocks (Municipal/Residential, Compost/Loam Mix, Commercial Food Sourced, Household Food Sourced, and Biosolid). Results showed that 48% of compost samples had bulk lead concentrations above the German 150 mg/g lead benchmark for compost. We observed a factor of six difference in average lead concentrations across source stream types with lead in municipally sourced compost averaging 234 mg/g (n=27). There is an order of magnitude difference in SBET soluble lead between the average municipally sourced compost (12.01 mg/L) and average commercially food sourced compost (1.15 mg/L). By combining bulk compost matrix characterization with lead inventory analysis, waste streams were ranked for geomobility potential. Carbon streams exhibited unique biogeochemical fingerprints that permit source stream attribution modeling. Low-level lead exposures in children contribute to downstream medical, economic and societal costs, making prevention critical. We advocate for municipal level repurposing of urban carbon waste streams as part of a primary prevention scheme to minimize urban lead exposure pathways.