EVAULATING COMPOST SOURCE AND MANAGEMENT PRACTICES IN THE CONTEXT OF REDUCING LEAD EXPOSURE TO URBAN GARDENERS

Amending soil with compost to increase soil productivity is a long established best practice. In the urban agricultural context compost amending can provide the added advantage of reducing soil lead concentrations so that the benefits of food security and community building can be achieved without increasing the risk of lead exposure. Based on availability and pricing pressures municipally derived compost is often the first choice source for not-for-profit organizations advocating for sustainable urban agriculture. However, spatial and temporal variations in lead concentrations in City of Boston compost has led some organizations to seek alternative sources for compost used in this urban setting. In our study we evaluate a range of feedstocks (food and yard waste, municipal solid waste, and biosolids) as constituents of compost sourced from municipal, commercial, and backyard sources.

XRF Spectroscopy was used to determine bulk trace element concentrations and EPA-SBET protocol was used to evaluate lead bioaccessibility. To determine lead mobility potentials as a function of varying compost matrix we also measured soil pH and organic matter. Locally sourced commercial compost (n=8) contained 78± (31.6) ug/g Pb on average, while municipal solid waste compost had an average lead concentration of 235 ± (71.1) ug/g (n=21). Results also show that bulk [Pb] is not a good predictor of bioaccessibility. In 2010, municipal solid waste compost contained [Pb] of 264 ug/g with a 1.5% bioaccessibility, while the same source in 2011 contained [Pb] of 420 ug/g and 0.7% bioaccessibility. The goal of this study is to merge geochemical characterization with practitioner level assessment to provide recommendations on compost sources that generate high yield, are cost effective, and prevent lead exposure.