BACKGROUND: Urban surface sediments,the source and aggregation of various pollutants in the urban environment,have become an important part of urban environmental pollution. It is of significance in urban environment monitoring to study the physicochemical and mineralogical characteristics of urban surface sediments.OBJECTIVES: To investigate the particle size distribution,heavy metals distribution mineral compositions and topographic characteristics of surface sediments in Chengdu City.METHODS: 40 surface sediment samples were collected from different areas in Chengdu City. Physicochemical and mineralogical characteristics of urban surface sediments were studied by the comprehensive analysis and mutual verification of various technical means and disciplines,such as laser particle size analyzer,inductively coupled plasma-mass spectrometry, inductively coupled plasma-optical emission spectrometry, scanning electron microscopy with EDS and X-ray diffraction.RESULTS: There was a high consistency between the mass distribution and volume distribution of surface sediment particles,which were dominated by the medium-fine particles. Particle size less than 0. 3 mm accounted for more than 70% of the total weight and total volume of surface sediment particles,whereas particle size less than0. 125 mm accounted for about 40%. The contents of heavy metals such as Cu,Pb,Zn,As,Hg,Cr,Cd and Ni in surface sediments increased with the decreasing particle size of sediments,which were mainly distributed in particle with size less than 0. 125 mm. The distribution of heavy metals varied with direction and ring roads. The rock-forming elements such as Si,Ca,K,Na were abundant in different particle size sediments. Surface sediments mainly contained minerals such as quartz,feldspar and calcite,and they had similar content in different particle size sediments. The fine-grained minerals exhibited colloidal behavior and easily adsorbed various heavy metals.CONCLUSIONS: Particle size distribution and mineral composition characteristics of urban surface sediments are the internal factors affecting the distribution of heavy metals content in sediments,and human activities are the key factors controlling the degree of heavy metal pollution in surface sediments.