This invention discloses a stabilized biosolids composition and a method for the stabilization of biosolids. It entails the use of a chemically and biologically reactive material, in the form of ultrafine iron particles. The nanometer-sized iron particles are capable of degrading odorous organosulfur compounds, transforming persistent and toxic organic pollutants such as PCBs and chlorinated pesticides, inhibiting the growth of pathogens by increasing pH and maintaining the increased pH of the stabilized biosolids, immobilizing toxic metal ions such as mercury and lead, and improving the overall quality of biosolids for land application and plant growth.