The efficiencies of different grain sizes (< 63, 63-93, 93-106 and 106-125 μm ) of mined rock phosphate (RP), in addition to the vital role of different phosphate sources ( < 63 μm rock phosphate, processed and biogenic ) as an effective remedial technology (based on solubility, percentage of metal/metalloid impurities and availability of impurity metal/metalloids) were assessed in contaminated urban soil. The results demonstrate that the application of RP substrate with smaller grain size (< 63) was significantly more effective than larger grain size for Cu, Co, Cd and Pb immobilization. Depending on phosphate solubility, the reduction of metals availability were highest in biogenic and processed phosphates than mined rock phosphate, while the lower dissolution of rock phosphate may be advantageous for long term maintenance. [ABSTRACT FROM AUTHOR]