Compostable materials constitute roughly half of waste generated globally, but only 5% of waste is actually processed through composting, suggesting that expanding compost programs may be an effective way to process waste. Compostable waste, if properly collected and processed, has value-added end use options including: residential and park landscaping, remediation of brownfield sites, and as growing media in urban agriculture (UA). Since 2001, our lab has partnered with The Food Project, a non-profit focused on youth leadership development through urban farming. From 2006 to 2022 we collected compost materials that were delivered to the farm from a variety of local sources and analyzed a suite of biogeochemical properties including lead (Pb) concentrations, organic carbon, and grain size distribution. Pb concentrations of Boston's municipal compost always exceeded the current City of San Francisco soil and compost purchase standard (80 mu g/g). In 2012 Boston's composting program was halted when it exceeded the 400 mu g/g Environmental Protection Agency's Pb in soil benchmark. Urban Pb is geomobile and must be managed to minimize resuspension and transport of fines whose Pb concentration is often elevated compared to bulk compost. Consequently, urban farmers have to source lower Pb compost from suburban suppliers at significantly greater cost. Over a 15 year period and through several city vendor contracts, Pb concentrations in municipal compost remain at levels that warrant continued surveillance and risk assessment. Locally sourced compost is the life blood of urban agriculture (UA). It is used to fill raised beds, added as a soil amendment to increase carbon contents, and helps manage soil moisture. In the greater Boston area, consistent access to compost low in fugitive lead (Pb) and rich in nutrients is limited. Starting in 2006, our lab began collecting compost delivered to The Food Project, a non-profit urban farm in Dorchester, MA. The Pb concentrations consistently exceeded California's compost benchmark of 80 mu g/g and in 2012, Boston's composting program was halted because it exceeded the Environmental Protection Agency Pb in soil benchmark of 400 mu g/g. We demonstrate that geochemical fingerprinting management of feedstocks can yield consistent, quality compost. This supports the growing urban farming movement. Rather than treating organic urban waste streams as a problem to manage solely around cost control, design collection and processing approaches must minimize all fugitive contaminants so that these carbon sources can support UA, increase food sovereignty, and promote environmental justice. Municipal composting represents an opportunity to transform waste and create media that critically support Urban Agriculture (UA) Resuspended legacy Pb from urban soils contaminates urban compost through commonly sourced feedstocks, resulting in elevated Pb levels Pb in compost can reach levels of public health concern requiring geochemically informed, health protective benchmarks for compost Pb
