This study involved a comparative experimental characterization of trace metals and relative toxicity evaluation of particulates emitted by a medium-duty transportation diesel engine using diesel and 20% (v/v)Jatropha biodiesel blend (B20). The engine was operated at 1800 rpm and particulate samples were collected on a filter paper at five loads (0%, 25%, 50%, 75% and 100% rated load) at steady state using a partial flow dilution tunnel, for both diesel and B20. Samples were then analyzed for trace metals, particulate morphology, total organic carbon and benzene soluble organic fraction (BSOF), which is a marker of toxicity. Concentrations of crust elements (Al, Ca, Fe and Mg) in the particulates were relatively higher than that of anthropogenic elements (Cd, Cr, Cu, and Zn) for both test fuels. B20 emitted relatively lower trace metal concentrations in particulates compared to baseline mineral diesel and these concentrations decreased with increasing engine load. Concentrations of gaseous emissions namely CO and THC in biodiesel exhaust were relatively lower than mineral diesel however NOx was relatively higher. Scanning electron microscopy of the particulate samples collected on the filter papers was done along with EDAX analysis for comparison. (C) 2016 Elsevier Ltd. All rights reserved.