ABSTRACT
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.
Subject(s)
Arsenic/metabolism , Oryza/metabolism , Soil Pollutants/metabolism , Water Pollutants, Chemical/metabolism , Agriculture/methods , Animals , Arsenic/analysis , Bangladesh , Cattle , Conservation of Natural Resources , Environmental Monitoring , Floods , Food Contamination/analysis , Food Contamination/statistics & numerical data , Humans , Oryza/growth & development , Phosphorus/metabolism , Phosphorus/pharmacology , Risk Assessment , Seasons , Soil/chemistry , Soil Pollutants/analysis , Water Pollutants, Chemical/analysisABSTRACT
The total arsenic content of 150 paddy rice samples collected from Barisal, Comilla, Dinajpur, Kaunia, and Rajshahi districts, and from the BRRI experimental station at Rajshahi city in the boro and aman seasons of 2000 was determined by hydride generation-inductively coupled plasma emission spectroscopy (ICP). Arsenic concentrations varied from 10 to 420 microg/kg at 14% moisture content. Rice yields and grain arsenic concentrations were 1.5 times higher in the boro (winter) than the summer (monsoon) season, consistent with the much greater use of groundwater for irrigation in the boro season. Mean values for the boro and aman season rices were 183 and 117 microg/kg, respectively. The variation in arsenic concentrations in rice was only partially consistent with the pattern of arsenic concentrations in drinking water tube wells. There was no evidence from yield or panicle sterility data of arsenic toxicity to rice. Processing of rice (parboiling and milling) reduced arsenic concentrations in rice by an average of 19% in 21 samples collected from households. Human exposure to arsenic through rice would be equivalent to half of that in water containing 50 microg/kg for 14% of the paddy rice samples at rice and water intake levels of 400 g and 4 L/cap/day, respectively.
