Effect of water management, arsenic and phosphorus levels on rice in a high-arsenic soil-water system: II. Arsenic uptake.

Rice consumption is one of the major pathways for As intake in populations that depend on a rice diet in several countries of South and South-east Asia. Pot experiments were undertaken to investigate the effects of water management (WM), arsenic (As) contaminated soil-water and Phosphorus (P) rates on As uptake in rice plants. There were 18 treatments comprising of three each of As rates (0, 20 and 40 mg kg(-1) soil) and P rates (0, 12.5 and 25 mg kg(-1) soil) and two WM (aerobic and anaerobic) strategies on winter (boro var. BRRI dhan 29) and monsoon (aman var. BRRI dhan 32) rice at the Wheat Research Center (WRC), Nashipur, Dinajpur, Bangladesh. Arsenic concentrations in rice grain and straw increased significantly (P ≤ 0.01) with the increasing As rates in the soil. Arsenic availability in soil pore-water solution was less (58%) under aerobic WM (redox potential-Eh=+135 to +138 mV; pH-6.50 at 24.3 °C) as compared to anaerobic WM (flooded: Eh=-41 to -76 mV; pH-6.43 at 23 °C). The highest total grain As content 2.23 ± 0.12 mg kg(-1) and 0.623 ± 0.006 mg kg(-1) was found in T(6) (P(12.5)As(40)-anaerobic) and T(9) (P(25)As(40)-anaerobic) in BRRI dhan 29 and BRRI dhan 32, respectively, which was significantly higher (41-45%) than in the same As and P treatments for pots under aerobic WM. The As content in rice straw (up to 24.7 ± 0.49 ppm in BRRI dhan 29, 17.3 ± 0.49 mg kg(-1) in BRRI dhan 32 with the highest As level) suggested that As can more easily be translocated to the shoots under anaerobic conditions than aerobic condition. BRRI dhan 29 was more sensitive to As than BRRI dhan 32. Under aerobic WM, P soil amendments reduced As uptake by rice plants. The study demonstrated that aerobic water management along with optimum P amendment and selection of arsenic inefficient rice varieties are appropriate options that can be applied to minimize As accumulation in rice which can reduce effects on human and cattle health risk as well as soil contamination.