【正文】 hange and reverse osmosis (Naidu and Bhattacharya, 2006). In addition, lowcost remediation methods, such as autoattenuation and the use of geological material as natural sorbents for As (. laterite, bauxsols, natural red earth or Ferich oxisols) have emerged as possible alternatives for the removal of As from groundwater in the developing world (Gen?Fuhrman et al., 2004, 2005。 Jones et al., 2000). This has led researchers to conclude that these microorganisms play an important role in As cycling in the subsurface (Ahmann et al., 1997。 arsA and arsB act as the As(III) efflux pumps。 Smith et al., 1998). In addition, during manufacturing of Ascontaining pesticides and herbicides, release of waste and Asladen liquids near the manufacturing areas may contaminate soil and water bodies (Mahimairaja et al., 2005). There are several “hot spots” around the world where soils have very high concentrations of As caused by natural geochemical enrichment and longlasting ore mining and processing. For example, in Poland, mine spoils, slag dumps and tailings, that remained in the areas of As manufacturing and industrial processes, also contain extremely high concentrations of As (Karczewskam et al., 2004, 2005). There is a widespread concern regarding bioavailability of As in the terrestrial environment in industrialized regions of the world. The majority of incidences of soil As pollution could be traced back to a period prior to extensive statutory controls over As emissions (Meharg et al., 1994). For example, England was one of the cradles of the industrial revolution in the 19th century that has left behind an extensive legacy of Ascontaminated sites. As part of the Land Ocean Interaction Study (LOIS) the As concentrations in the rivers of northeastern England reveal As enrichment within the urban and industrially affected rivers (Neal and Robson, 2000。 KabataPendias and Pendias, 2001). Although many minerals contain As pounds, the anthropogenic contribution to the environment in the past accounted for 82,000 metric tons/year worldwide (Nriagu and Pacyna, 1988). Inorganic As pounds such as calcium arsenate, lead arsenate, sodium arsenate and many others were used by farmers as insecticides pesticides for debarking trees, in cattle and sheep dips to control ticks, fleas, lice and also in aquatic weed control. Water soluble preparatives, such as chromated copper arsenate (CCA) and other Asbased chemicals used as wood preservatives during the past have lead to widespread metal contamination in soils around the wood preservation facilities (Bhattacharya et al., 2002c). However, the use of inorganic As pounds in agriculture has gradually disappeared since the 1960s due to greater understanding of As toxicity and awareness regarding food safety and environmental contamination (Vaughan, 1993。 Pacyna and Pacyna, 2001). Elevated concentrations of As in soils occur only locally, but in areas of former industrial areas it may cause environmental concern (Nriagu, 1994。 Juillot et al., 1999。 Naidu et al., 2006). Crop quality and the effect of As on crop quality and yield is being a major worldwide concern, particularly for rice which forms the staple for many SouthAsian countries where groundwater is widely used for irrigation (Meharg and Rahman, 2003). In a recent study it was reported that irrigation has increased in Bangladesh since 1970, while since 1980, the area under groundwater irrigation for the cultivation of Boro rice has increased by almost an order of magnitude (Harvey et al., 2005). Based on available information on the distribution of As concentration in groundwater (BGS and DPHE, 2001) and the area under shallow tubewell irrigation (BADC, 2005), Saha (2006)n estimated that approximately 1000 metric tons of As is cycled with irrigation water during the dry season of each year. Rice yield has been reported to decrease by 10% at a concentration of 25 mg/kg As in soil (Xiong et al., 1987). A greenhouse study by Abedin et al. (2002) revealed reduced yield of a local variety of rice (BR11) irrigated with water having As concentrations in the range of to 8 mg/L. The accumulation of As in rice field soils and its introduction into the food chain through uptake by the rice plant is of major concern (Duxbury et al., 2003).. Anthropogenic arsenicLarge quantities of As are released into the environment through industrial activities, which can be dispersed widely and as such play an important role in the contamination of soils, waters, and air (Nriagu,1989。 Al Rmalli et al., 2005。 Mandal et al., 2001). In general, MMAIII is more toxic than As(III) and As(V) ( et al., 2000, 2001).. AgricultureThe adverse effects of As in groundwater used for irrigation water on crops and aquatic ecosystems is also of major concern. In addition to potential human health impacts caused by ingestion of food containing As, thep otential for reduced crop yield due to its buildup in the soil is an active area of research. The fate of As in agricultural soils is often less well studied pared to groundwater, and in general has been studied in the context of As uptake by different plants (Huq et al., 2001, 2006。 HopenhaynRich et al., 1996). Recent studies have found monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII) in trace quantities in human urine (Aposhian et al., 2000。 Mandal et al., 2003). Studies of As speciation in the urine of exposed humans indicate that the metabolites prise 10–15% inorganic As (iAs) and monomethylarsonic acid (MMAV) and a major proportion (60–80%) of dimethylarsenic acid (DMAV) (Tam et al., 1979。 Buchet et al., 1981。Kapaj et al., 2006). Arsenic is perhaps the only human carcinogen for which there is adequate evidence ofcarcinogenic risk by both inhalation and ingestion (Centeno et al., 2002。 van Geen et al., 2005。 Khandaker, 2004。 Bhattacharya et al., 2006b。 BarragnerBigot, 2004。 Smedley et al., 2002。 Vuki et al., 2007this volume), a small island in Western Pacific