The legacy of urbanization: historical land use and its impact on current health hazards at a community garden in Charlestown, Massachusetts
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INTRODUCTION: The Charlestown Sprouts Community Garden, one of Bostonʼs largest community gardens, comprises 105 plots--all producing food--located in the historic neighborhood of Charlestown. It serves mainly minority and recent immigrant member households who rely on the land as a source of fresh produce. To ensure the safety of food production at the garden, the coordinators sought assistance from the Department of Environmental Health at the Boston University School of Public Health (BUSPH) to: 1. conduct a historical survey identifying past land uses, 2. characterize potential contaminant exposures to gardeners, and 3. furnish health-protective recommendations to minimize gardener hazard exposures. In the process of meeting these aims, broader dimensions of food production in the urban environment emerged from the literature: soil safety for urban agriculture, environmental justice, food security, determining “safe” levels of contaminants in urban soil, and the expansive policy implications that these issues engendered. For the work presented in this thesis project, the scope of interrelated topics were refined and lended contextual structure for a semi-quantitative characterization of human health risk from potential soil lead (Pb) exposures. This was accomplished by employing probabilistic modeling with the USEPA's Integrated Exposure Uptake Biokinetic Model for Lead in Children (IEUBK) (2010). Under specified assumptions of multimedia Pb exposures, the model predicts a theoretical young childʼs probability of his or her lead blood concentrationʼs (PbB) exceeding a PbB cutoff. For this analysis, the recently promulgated CDC reference value of 5 μg/dL was used as a cutoff in addition to the model default of 10 μg/dL. The IEUBK was also employed to approximate a range of soil Pb concentrations that could be considered “acceptable,” based on a health-protective approach; that is, to estimate a soil Pb concentration that would not significantly contribute to the exceedance of PbB > 5 μg/dL as a result of exposures to lead in soil. In this evaluation, an acceptable soil Pb concentration is defined as a mean soil Pb concentration that is determined by consideration of minimizing human health risk and maximizing practicability of the means to achieve the soil criterion—a level that could be reasonably achieved and be safe for urban agriculture. METHODS: Research for the historical survey included, but was not limited to, consulting historical fire insurance maps, archived municipal and county records, environmental databases, geographic information systems (GIS), and gathering accounts from local community members, historical societies, and multiple Boston city agencies to build a historical narrative about the garden land and the adjacent properties. For the IEUBK model runs, multimedia exposure parameter values from Boston environmental data (air, water, and soil) were used as inputs for the IEUBK modeling runs in the absence of suitable site-specific data. Comparison runs were executed with soil Pb concentration data from compost sourced from the City of Boston Department of Public Works Leaf and Yard Waste composting program and from Boston-area private compost facilities. RESULTS AND CONCLUSIONS: The garden was established at a site with a varied history of land uses from rail yard, to salt plant, to unknown activities. Community-member accounts, corroborated by photointerpretation data, suggest that the site was possibly an dumping grounds in the 1970ʼs-80ʼs. Based on the findings of the survey, it is likely that a number of potential contaminants exist at the garden, including lead, arsenic and/or polyaromatic hydrocarbons (PAHs). Based on visual inspection, point-source contamination of the soil is likely to be occurring at the garden, stemming from the treated rail ties that compose a majority of the garden plot constructions and of the plots inspected, the timbers appeared to be CCA-treated wood. The accumulation of site-specific knowledge gained through historical research, (GIS), and anecdotal evidence aided in determining what historical hazards were likely to pose a current risk to gardeners through gardening activities. The IEUBK model predicted a geometric mean blood value of 2.73 μg/dL with an associated risk of a young childʼs PbB exceeding 5 ug/dL as 9.9% using default parameter values. In comparison, to achieve a goal of less than 5% risk, the IEUBK modeling indicated that soil Pb would have to be less than 153 mg/kg. Under the guidance of BUSPH faculty, the findings and consequent recommendations, differing in remediation technique and resource-intensiveness, were summarized in a document for the garden steering committeeʼs development of imminent renovation plans.