Aggregate stability

cadmium distribution and transformation in bulk samples

and particle size fractions were studied of brown soil through freeze-thaw cycle method. The freezing conditions were implemented under -10

-20 and -30 ℃

respectively

and the thawing condition was implemented under 10 ℃. Soil aggregate particle size

soil mean mass diameter

grain size fraction cadmium loading

and the cadmium transformations in bulk soil and particle size fractions were measured. The results showed that both the fraction of particles ＞2 mm and soil mean mass diameter increased significantly when soil experiencing freeze-thaw cycles

and the formerranged 38.4%～54.6%.Cadmium mainly accumulated in particles ＞2 mm

and it contributed 51.2%～57.2% of cadmium to the contents in bulk soil. The exchangeable fraction of cadmium and the organically bound fraction of cadmium significantly decreased (P＜0.05)

and the Fe and Mn oxide bound fraction of cadmium and the residual fraction of cadmium increased significantly (P＜0.05) in bulk soil and particle size fractions for the soil experiencing freeze-thaw cycles. The results suggest that the bioavailability of cadmium decrease in soil experiencing freeze-thaw cycles.