Partitioning Pattern of Metals Onto Sediment Particles in Shallow Lakes : An Exponential Decrease with Particle Size and its Environmental Implications

Sediment particle size is an important indicator to explain spatial variability of metal concentration during transport of sediments and distribution of metal pollution. However, the partitioning pattern of metals sediment particles and its underlying mechanisms have not been revealed. Here, we propose the equation cx=c0+cmexp(-kdx), in which the metal concentration (cx) of sediment particles decreases exponentially with increase in particle size (x). This equation effectively classified the affecting factors of metal concentration into metal pollution and particle size with environment implications. In this equation, c0 is a constant based on the background concentration, cm represents the maximum metal concentration of the finest particles reflecting metal pollution degree, and kd is a constant describing the decrease rate with particle size (x). This partitioning pattern is achieved from a set of individual sediment samples, which were separated into size-grouped particles ranging from 1 μm to 50 μm and were analysed to determine the concentrations of iron (Fe) oxides, aluminium (Al) oxides, arsenic (As), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd). The adsorption isotherms of the metals on sediments, with Cu and Pb as representatives, explaining the underlying mechanisms of this proposed exponential partitioning pattern. The partitioning amount is proportional to the sorption affinity of particles, which is a comprehensive parameter dependent on the amount of metal adsorbents including organic matter, Fe and Al (hydr)oxides contained in particles