Abstract: We used laboratory simulation methods  to investigate the effects of freeze thaw (FT) and microplastics on transformation of arsenic (As) speciation in  soil. The results show that under the condition of not adding microplastics,  FT leads to an increase in the proportions of organic-bound As and weakly crystalline iron oxide-bound As (3.67% and 4.17%),  while the proportion of manganese oxide-bound As and extremely difficult to  crystallize iron oxide-bound As decreases (0.28% and 5.33%). Adding polyethylene (MP-PE) under FT can reduce the proportion of organic-bound As (0.96%), increase th proportion of manganese oxide-bound As,  sulfide-bound As,  and crystalline iron oxide-bound As(1.55%,  0.60%,  and 2.05%). Adding butylene adipate-co-terephthalate (MP-PBAT) under FT can reduce the proportion of water-soluble As and crystalline iron oxide-bound As (1.33% and 2.65%),  and increase the proportion of  manganese oxide-bound As and extremely difficult to  crystallize iron oxide-bound As (1.11% and 3.82%). Under the condition of not adding microplastics, FT significantly increases the bounding strength coefficient IR between As and soil by 1.85%, but  adding MP-PBAT under FT, IR significantly decreases by 6.27%. The IR value is positively correlated with water-soluble As,  organic-bound As,  and manganese oxide-bound As, and  negatively correlated with the effect of the crystalline iron oxide-bound As. The research results  provide theoretical  basis for revealing  the environmental behavior of As in contaminated soils and evaluating the  ecological risks of As, and provide important  reference value   for the treatment and risk management of As-contaminated soil.

Key words: arsenic,  , freeze thaw,  , microplastics,  , paddy soil,  , morphological transformation