M. Asaduzzaman Khan
Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.,
Jacqueline L. Stroud
Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.,
Yong-Guan Zhu
Institute of Urban Environment, Chinese Academy of Science, Xiamen, 361021, China
Steve P. Mcgrath
Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.,
Fang-Jie Zhao*
Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, U.K.,
Arsenic, Bioavailability, Rice, Bangladesh, Paddy soils
Risk Management in Agriculture
Pot Experiment. Fourteen soils were used in this study, including 10 Bangladeshi paddy soils (labeled B1-B10) that have been contaminated with As to various degrees by irrigation with groundwater,two paddy soils from China (C1, C2) impacted by mining orgeogenic As contamination, and two upland arable soils from the UK (U1, U2) that have elevated As concentrations due to geogenic reasons. The 10 Bangladeshi soils were collected from different areas near the inlet of irrigation water from STW, B1 from Noakhali district, B2 and B3 from Naraynganj, and B4-B10 from Faridpur district (Ganges Floodplain). Selected soil properties, such as pH; texture; organic C%;CaCO3; total N; available P (Olsen P), phosphate-extractable As; and total Fe, Mn, As concentrations (by aquaregiadigestion), were determined following standard methods of soil analysis. The experiment was conducted inside a glasshouse (day/night temperatures 28/25°C, light period16 h per day with natural sunlight supplemented with sodium vapor lamps to maintain light intensity of>350μmol m-2s-1). A total of 42 pots (three pots per soil) were arranged randomly. A subsample of 500 g of soil (air-dried,<8 mm)was placed in each pot and deionized water was added to maintain a 2-3 cm layer of standing water. Basal fertilizers(120 mg N kg-1 as NH4NO3, 30mg Pkg-1 as K2HPO4, 75.5 mg Kkg-1 as KCl, and 25 mg of S kg-1 as MgSO4) were added to the soil and mixed thoroughly. Soils were maintained under flooded conditions for 30 days before transplanting of four pre germinated rice seedlings (Oryza sativaL. cv. Shatabdi) in each pot. A soil pore water sampling device (Rhizon MOM10 cm length, 2.5 mm OD, Rhizosphere Research Products, Wageningen, The Netherlands) was buried diagonally in them idle of the soil of each pot for collecting soil solution.Further doses of fertilizers (172 mg of N, 15 mg of P, and 75mg of K) were added into each pot at the rice tillering and stem extension stages. The plants were thinned to two perpot 25 days after transplanting (DAT). One plant each was harvested at stem extension (45 DAT) and at maturity (160DAT). Plants were rinsed with deionized water and dried at65°C for 48 h. At maturity, grains were separated from straw and filled and unfilled grains counted. The weights of grain and straw were recorded after drying; grains were then separated into brown rice and husk. Soil pore water samples were collected at 15 and 145 DAT. Chemical Analyses.Soil solution was diluted with 0.1 MNa2 EDTA at 9:1 ratio to prevent Fe precipitation and preserve As speciation, filtered through a sterilized 0.2μm membrane filter, and immediately analyzed for As speciation using HPLC-ICP-MS (Agilent LC1100 series and Agilent ICP-MS7500ce, Agilent Technologies, Santa Clara, CA), as described previously (15). Soil solution pH and Eh were determined immediately after collection by using pH and Eh electrodes.The concentrations of Si and ferrous Fe in soil solutions were determined by colorimetric methods (31, 32). A part of the soil solution was acidified with 5% HNO3 and analyzed for major and trace elements by using ICP-AES (Perkin-ElmerOptima 3300 DV, Norwalk, CT). Phosphate-extractable As was extracted from soil using 0.05 M ammonium phosphate solution (NH4H2PO4) and centrifuged at 2200g(33). The soils were digested with a mixture of hydrochloric and nitric acid(3:1) for total As determination. Ground shoot, straw, husk,and grain samples were digested with high purity HNO3/HClO4 (87/13 v/v). As concentrations in the digest solutions were determined by ICP-MS (Agilent 7500ce) operating in the reaction cell mode with helium gas. A certified reference material (NIST 1568a rice flour) and blanks were included for quality assurance. Repeated analysis of NIST 1568a (certified value 0.29(0.03 mg As kg-1) gave a satisfactory recovery of 0.29 (0.02 mg As kg-1. For As speciation in brown rice, 0.2 g of powdered samples was weighed into a microwave vessel. Samples were extracted with 1% HNO3in a microwave digester as described by Sunet al. Arsenic speciation was performed using HPLC-ICP-MS. The extraction method resulted in some oxidation of arsenite to arsenate; therefore, only the sum of inorganic As was presented, together with methylated As species. NIST 1568a rice flour and blanks were included for quality assurance. The As speciation results obtained for NIST 1568arice flour were in good agreement with those reported previously. Statistical Analyses.Analysis of variance was performed to assess the differences between soils. Relationships between soil and plant variables were investigated by regression analysis. Where appropriate, data were log-transformed prior to statistical analysis. The software Genstat (version 12; VSN International Ltd., Hemel Hempstead, UK) was used.
Environ. Sci. Technol. 2010, 44, 8515–8521
Journal