Optimized HPLC-ICPMS Method for Arsenic Speciation in Paddy Soils: Application to Water Management in Can Tho, Vietnam

Arsenic (As) contamination in paddy soils threatens food safety. This study optimized and validated an HPLC-ICPMS method for As III /As V speciation, which involved extraction with 1 M H 3 PO 4 and 0.5 M ascorbic acid, gradient elution on a Hamilton PRP-X100 column using (NH 4 ) 2 HPO 4 /water mobile phases, and achieved good linearity, low detection limits, and precision. The method was applied to evaluate the effects of water management strategies of rice cultivation (i.e., Continuous Flooding - CF, Alternate Wetting and Drying - AWD, Dry - D) on As speciation in paddy soils located in Can Tho, Vietnam. Total extractable As was highest under D and lowest under CF conditions. CF significantly increased the As III proportion (45.7% of total extractable As), while D favored As V (87.5%); AWD resulted in a mixed speciation profile, with proportions of both AsIII and AsV falling between the other two watering approaches. These results demonstrate that water management profoundly influences As speciation. AWD emerges as a promising strategy to reduce As mobilization compared to CF, contributing to safer rice production, and the developed method is robust for environmental monitoring.