Soil assessment for urban agriculture: a Vancouver case study

With the expansion of urban agriculture in many North American cities, there is a current need to evaluate the soil and urban environment to assess potential risks of metal contamination in urban grown food. In this study, a university farm, a community garden, and a brownfield located in Vancouver, BC were characterized with respect to soil metal concentrations, atmospheric deposition of metals, and bioaccumulation of metals in Poa pratensis. Wet and dry deposition were collected over five months. Aqua regia and HCl extractions were used to evaluate total and labile metal fractions of Zn, Pb, Ni, Mn, and Cu. Highest soil metal concentrations, atmospheric deposition flux, and bioaccumulation in Poa were found at the community garden, followed by the brownfield site, and the University of British Columbia Farm. Concentrations of Ni and Mn seem to be associated with soil parent material, while Zn, Pb, and Cu were indicators of industrial activity. Concentrations of metals in atmospheric deposition were not an immediate concern but their potential accumulation in the soil requires attention. The framework developed by the case study identified three factors meaningful for assessing metal contamination on an urban agriculture site: site history, atmospheric deposition trends, and parent material.