The viability of biofuel production on urban marginal land: An analysis of metal contaminants and energy balance for Pittsburgh's Sunflower Gardens

• Low-input sunflower production is possible on urban vacant lots in Pittsburgh.
• Urban marginal soil is subject to the risk of low Fe, Pb and As contamination.
• Sunflowers from urban land are safe biofuel feedstock due to limited metal uptake.
• Urban biofuel system can produce net energy under constraints of plot and method.

After three years’ monitoring of the concentration of Al, Fe, Zn, Ni, Pb, As, Cd, Cr and Se in soil, Fe, Pb and As in Pittsburgh's vacant lots were found sometimes to exceed the residential maximum soil contaminant concentrations set by the Pennsylvania Department of Environmental Protection. Heavy metal uptake by sunflowers was insignificant at the soil metal concentrations observed in Pittsburgh, indicating that sunflowers produced on marginal urban land could be a safe biofuel feedstock. However, there was a risk that sunflowers grown on more contaminated spoils could be unsafe. Calculations of the energy balance of the total biofuel production system suggested that lots in Pittsburgh of over 0.2 ha would be able to produce an energy gain, particularly if community volunteers were involved in the process. Using marginal urban land for biofuel production can be a worthwhile strategy to replace costly traditional vacant lot management methods.