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26A study was conducted to investigate the accumulation and distribution of arsenic in 27 different fractions of rice grain (Oryza sativa L.) collected from arsenic affected area of 28Bangladesh. The agricultural soil of study area has become highly contaminated with 29 arsenic due to the excessive use of arsenic-rich underground water (0.070±0.006 mg l -1 , 30 n=6) for irrigation. Arsenic content in tissues of rice plant and in fractions of rice grain of 31 two widely cultivated rice varieties, namely BRRI dhan28 and BRRI hybrid dhan1, were 32 determined. Regardless of rice varieties, arsenic content was about 28 and 75 folds higher 33 in root than that of shoot and raw rice grain, respectively. In fractions of parboiled and 34 non-parboiled rice grain of both varieties, the order of arsenic concentrations was; rice hull 35 > bran-polish > brown rice > raw rice > polish rice. Arsenic content was higher in non-36 parboiled rice grain than that of parboiled rice.

The seasonal variations of arsenic species in lake water were studied in the mesotrophic northern and eutrophic southern basins of Lake Biwa in Japan. Within the euphotic zone, arsenite [As(III)] increased in spring and fall, and dimethylarsinic acid [DMAA(V)] became the dominant form in summer. Measurable concentrations of monomethylarsonic acid [MMAA(V)] and trivalent methylarsenic species [monomethylarsonous acid, MMAA(III), and dimethylarsinous acid, DMAA(III)] also appeared, although they were always minor fractions. The total arsenic concentration in the euphotic zones remained constant in the northern basin throughout the year. However, it was increased by 2−4 times in the southern basin in summer. The enhancement was caused by the increase of As(V), which was accompanied by the increase of iron, manganese, and phosphorus. The concentration of methylarsenicals per chlorophyll a was lower in the southern basin. These results indicate that the variations of arsenic species in lake water largely depend on biological processes, such as the metabolism of phytoplankton, decomposition of organic matter by bacteria, and microbial reduction of iron and manganese oxides in sediments. Moreover, they show that eutrophication affects the concentration and speciation of arsenic in the lake water.