『Abstract
This paper examines the surface sediments collected from Dongping Lake in China for speciation and distribution of toxic heavy metals (Cu, Pb, Ni, Cd) in different grain size fractions, and for the factors that need to be considered in potential hazard of metals to the environment. Four grain size fractions (＜63, 63-78, 78-163 and 163-280μm), divided in wet condition, and bulk samples less than 280μm in diameter were analyzed for their distribution, density and appearance. A three-stage extraction procedure following the BCR protocol was used to chemically fractionate metals into “acid soluble”, “reducible”, “oxidizable” and “residual” fractions. Correlation analysis was used to analyze the datasets. The results showed that ＜63μm grain size part constitutes the major proportion of the sediments, but its density is the smallest among the four grain size fractions. In general, the metal content curve against grain size presents “S” distribution, and the highest concentrations do not exist in ＜63μm grain size. Appearance observation indicates that the adsorbed substance increases gradually along with the decreasing grain size. The dominant speciation of elements and the extent of pollution are responsible for the metal distribution in different grain size sediments. While studying bioavailability and mobilization of metals, it is advisable to take metal speciation, grain size distribution and density into consideration.

Keywords: Grain size; Sediments; Heavy metal; Speciation; Fractionation; Dongping Lake; TEM』

Introduction
Materials and methods
Study area
Sampling and size fractionation
Chemical classification for heavy metals
Analytical method
Quality assurance
Results and discussion
Grain size distribution and density
The exterior characteristics of different grain size sediments
The variation regulation of heavy metal contents along with grain size
Correlation analysis of total metal concentrations to metal speciation
Conclusions
References