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1、 外文文獻(xiàn)：　 Arsenic in the environment: Biology and Chemistry Abstract： Arsenic (As) distribution and toxicology in the environment is a serious issue, with millions of individuals worldwide being affected by As toxicosis. Sources of As contamination are both natural and anthropogenic and the scale

2、 of contamination ranges from local to regional.There are many areas of research that are being actively pursued to address the As contamination problem. These include new methods of screening for As in the field, determining the epidemiology of As in humans, and identifying the risk of As uptake in

3、 agriculture.Remediation of As-affected water supplies is important and research includes assessing natural remediation potential as well as phytoremediation. Another area of active research is on the microbially mediated biogeochemical interactions of As in the environment. In 2005, a conference w

4、as convened to bring together scientists involved in many of the different areas of As research. In this paper, we present a synthesis of the As issues in the light of long-standing research and with regards to the new findings presented at this conference. This contribution provides a backdrop to t

5、he issues raised at the conference together with an overview of contemporary and historical issues of As contamination and health impacts.Crown Copyright . 2007 Published by Elsevier B.V. All rights reserved. 1. Introduction 1.1. Location and scale of problem Arsenic (As) has been detected in gro

6、undwater in several countries of the world, with concentration levels exceeding the WHO drinking water guideline value of 10 μg/L (WHO, 2001) as well as the national regulatory standards (e.g. 50 μg/L in India and Bangladesh, Ahmedet al., 2004; Mukherjee et al., 2006). Arsenic in groundwater is ofte

7、n associated with geologic sources, but in some locations anthropogenic inputs can be extremely important. Ingestion of geogenic As from groundwater sources is manifested as chronic health disorders in most of the affected regions of the world (BGS & DPHE, 2001; Bhattacharya et al.,2002a,b; Smedley

8、and Kinniburgh, 2002; Welch and Stollenwerk, 2003; Bundschuh et al., 2005; Naidu et al., 2006). In Asia, the impact of As toxicity is particularly alarming. For example, in the Bengal Basin of Bangladesh and West Bengal, India (Bhattacharya et al., 1997, 2002a,b, 2004, 2006a; Mukherjee and Bhattacha

9、rya, 2001), As in groundwater has emerged as the largest environmental health disaster putting at least 100 million people at risk of cancer and other As-related diseases. Recent studies indicate the occurrence of geogenic As in the Central Gangetic Plains of Uttar Pradesh, Bihar, Jharkhand and the

10、Brahmaputra valley in Assam, and several regions of Madhya Pradesh and Chattisgarh, India (Chakraborti et al., 2004; Mukherjee et al., 2006). During the past few years, As has also been detected in groundwaters of the sedimentary aquifers of the Terai Belt in Southern Nepal (Bhattacharya et al., 200

11、3; Tandukar et al., 2006), Pakistan (Nickson et al., 2005), the Red River Delta and Mekong Basin of Vietnam and Cambodia (Berg et al., 2001, 2007), raising severe constraints on its use as a drinking water resource. However, few reports are available on the epidemiology and prevalence of Asrelated d

12、iseases in these areas. Arsenic is also reported in groundwaters of Australia (Smith, 2005; OShea, 2006; Smith et al., 2003, 2006), where the concentrations levels are well above the drinking water standard of 7 μg/L recommended by the National Health and Medical Research Council and the Natural Res

13、ource Management Ministerial Council of Australia (NHMRC/NRMMC, 2004). In addition, As from anthropogenic sources is also reported in groundwaters of Guam (ATSDR, 2002; Vuki et al., 2007-this volume), a small island in Western Pacific Ocean. Arsenic is also found in widely scattered geographical are

14、as in the United States and Canada as well as in many other countries of Latin America such as Mexico, Argentina, Bolivia, Brazil andNicaragua,where the sources of As are geogenic as well as anthropogenic sources (Matschullat, 2000; Nordstrom, 2002; Smedley et al., 2002; 2005; Barragner-Bigot, 2004;

15、 Bundschuh et al., 2005; Bhattacharya et al., 2006b; Nriagu et al., 2007). 1.2. Field screening for arsenic Following the discovery of As in the Bengal Basin, there is now an urgent need to address the public health implications due to exposure from drinking water sources. In order to do this and

16、initiate appropriate mitigation measures, there is an urgent need to identify the As-contaminated tubewells (TW) that supply most of this drinking water (Chowdhury and Jakariya, 1999). This involves screening of water in millions of TW, and raising community awareness about the health problems relat

17、ed to chronic As exposure from drinking water. An overall risk assessment including a component of mitigation for As contamination should be based on accurate determination of As levels in TW water using economically viable methods for As screening. Field test kits offer a more practical tool than l

18、aboratory measurements within the time frame and financial resources available for screening and assessment of the As-contaminated wells as well as their monitoring. Simple, low-cost methods for As determination, such as the field test kits have proved to be most suitable for performing the TW scree

19、ning quickly. Several commercial field test kits are available for determination of As in TW water (Rahman et al., 2002; Khandaker, 2004; Deshpande and Pande, 2005; van Geen et al., 2005; Steinmaus et al., 2006). Field kits provide semiquantitative results and the reliability of several field kits a

20、re questioned because of poor accuracy (Rahman et al., 2002). Thus, there is a need for further evaluation of the screening results by the field kit, prior to its recommendation for wide scale use in Bangladesh and elsewhere in the world. 1.3. Epidemiology Ingestion of groundwater with elevated As

21、 concentrations and the associated human health effects are prevalent in several regions across the world. Arsenic toxicity and chronic arsenicosis is of an alarming magnitude particularly in South Asia and is a major environmental health disaster (Chakraborti et al., 2004; Kapaj et al., 2006). Ars

22、enic is perhaps the only human carcinogen for which there is adequate evidence ofcarcinogenic risk by both inhalation and ingestion (Centeno et al., 2002; Chen and Ahsan, 2004). Most ofthe ingested As is rapidly excreted via the kidney within a few days (Tam et al., 1979; Buchet et al., 1981; Vahter

23、, 1994). However, high levels of As are retained for longer periods of time in the bone, skin, hair, and nails of exposed humans (Karagas et al., 2000; Mandal et al., 2003). Studies of As speciation in the urine of exposed humans indicate that the metabolites comprise 10–15% inorganic As (iAs) and m

24、onomethylarsonic acid (MMAV) and a major proportion (60–80%) of dimethylarsenic acid (DMAV) (Tam et al., 1979; Vahter et al., 1995; Hopenhayn-Rich et al., 1996). Recent studies have found monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII) in trace quantities in human urine (Aposhian

25、 et al., 2000; Del Razo et al., 2001; Mandal et al., 2001). In general, MMAIII is more toxic than As(III) and As(V) (viz.Petrick et al., 2000, 2001). 1.4. Agriculture The adverse effects of As in groundwater used for irrigation water on crops and aquatic ecosystems is also of major concern. In add

26、ition to potential human health impacts caused by ingestion of food containing As, thep otential for reduced crop yield due to its build-up in the soil is an active area of research. The fate of As in agricultural soils is often less well studied compared to groundwater, and in general has been stud

27、ied in the context of As uptake by different plants (Huq et al., 2001, 2006; Das et al., 2004; Al Rmalli et al., 2005; Correll et al., 2006; Naidu et al., 2006). Crop quality and the effect of As on crop quality and yield is becoming a major worldwide concern, particularly for rice which forms the s

28、taple for many South-Asian 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 incre

29、ased 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 cycl

30、ed 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 (BR-11) irrigated with water havin

31、g As concentrations in the range of 0.2 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). 1.5. Anthropogenic arsenic Large quantities of As are released into the environment th

32、rough industrial activities, which can be dispersed widely and as such play an important role in the contamination of soils, waters, and air (Nriagu, 1989; Jacks and Bhattacharya, 1998; Juillot et al., 1999; Matschullat, 2000; Pacyna and Pacyna, 2001). Elevated concentrations of As in soils occur o

33、nly locally, but in areas of former industrial areas it may cause environmental concern (Nriagu, 1994; Smith et al., 1998; Kabata-Pendias and Pendias, 2001). Although many minerals contain As compounds, the anthropogenic contribution to the environment in the past accounted for 82,000 metric tons/ye

34、ar worldwide (Nriagu and Pacyna, 1988). Inorganic As compounds 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

35、soluble preparatives, such as chromated copper arsenate (CCA) and other As-based 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 compounds

36、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; Sanok et al., 1995; Smith et al., 1998). In addition, during manufacturing of As-containing pesticides and herbicid

37、es, release of waste and As-laden 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 long-lasting ore mining

38、 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

39、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

40、 in the 19th century that has left behind an extensive legacy of As-contaminated 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; Neal a

41、nd Davies, 2003). The study revealed that the concentration of dissolved As in the rural areas averaged between 0.6 and 0.9 mg/L, while for the rivers influenced by industrial discharges the average between 3.2 and 5.6 mg/L, while suspended particulate As is much lower (average 0.1 to 0.2 mg/L for t

42、he rural and 0.2 to 0.8 mg/L for the industrial rivers). However, for the industrialized rivers dissolved As concentrations can be as high as 25.6 mg/L. The possible mobilization of As in the soils, and subsequent leaching into ground or surface water or entry into the human food chain, should alwa

43、ys be considered as a serious hazard. Detailed investigations are therefore necessary to estimate the total concentrations of As in soils in such areas, its chemical fractionation, and potential solubility to evaluate the potential risks from As mobilization. 1.6. Microbial transformations of arsen

44、ic Mobilization of As in natural ecosystems is predominantly driven by microbially mediated biogeochemical interactions. Microbial reduction of As(V) to the more toxic and mobile As(III) species occurs via detoxification (Cervantes et al., 1994) or respiration processes (Ahmann et al., 1994). The g

45、enes that encode the proteins involved in As resistance are either plasmid or chromosomally borne, and have been best studied in Escherichia coli. Plasmid R773 comprises of five genes arsRDABC organized in an operon (Chen et al., 1986). The arsC gene encodes the As(V)-reductase; arsA and arsB act as

46、 the As(III) efflux pumps; arsR and arsD regulate the ars operon. Only a handful of microorganisms capable of respiring As(V) have been isolated (Oremland and Stolz, 2003). The As(V)- reductase genes (arrA and arrB) involved in As(V) reduction have been identified in a number of bacteria, and they s

47、hare high sequence identities (Santini and Stolz, 2004). The As(V)-respiring microorganisms can use different electron donors (e.g. acetate, hydrogen), and range from mesophiles to extremophiles (Oremland and Stolz, 2003). These laboratory studies indicate that microbial processes involved in As(V)

48、reduction and mobilization is many times faster than inorganic chemical transformations (Ahmann et al., 1997; Jones et al., 2000). This has led researchers to conclude that these microorganisms play an important role in As cycling in the sub-surface (Ahmann et al., 1997; Jones et al., 2000; Islam et

49、 al., 2004). 1.7. Remediation Several technologies are currently available for As removal, ranging from simple and effective coagulation– flocculation, to sophisticated technologies such as ion exchange and reverse osmosis (Naidu and Bhattacharya, 2006). In addition, low-cost remediation methods,

50、such as auto-attenuation and the use of geological material as natural sorbents for As (e.g. laterite, bauxsols, natural red earth or Fe-rich oxisols) have emerged as possible alternatives for the removal of As from groundwater in the developing world (Gen?Fuhrman et al., 2004, 2005; Naidu and Bhatt

51、acharya, 2006; Vithanage et al., 2006), but there is a pressing need to develop these methods further and in a cost-effective way. The concept of phytoremediation of As-contaminated sites was proposed over twenty years ago (Chaney, 1983). Phytoremediation has an advantage over conventional remediati

52、on of As-contaminated soils that include burial and chemical stabilization, which may pose long-term health threats due to leakage or chemical instability (Allen, 2001; Fostner and Haase, 1998). Thus phytoremediation has the potential to become an environmentally friendly and low-cost alternative re

53、mediation technique. It is well documented that some tropical and sub-tropical plant species can tolerate and uptake various inorganic and organic forms of As (Meharg and Hartley-Whitaker, 2002). Mesquite is am plant that grows well in humid and desert environments that has been shown to absorb Cr(V

54、I) and other metals such as Pb (Aldrich et al., 2004). X-ray absorption spectroscopic (XAS) studies revealed that mesquite can bioreduce Cr(VI) to the less toxic Cr(III) (Aldrich et al., 2003). However, a significant gap of information exists on the ability of desert plant species to uptake As or ot

55、her toxic elements. 1.8. Current research Research on As is currently very active and includes assessment of interactions at scales ranging from molecular bonding to sub-continental, As speciation in inorganic and organic materials through a wide variety of chemical and spectroscopic approaches, a

56、nd an emerging understanding of the role of microbes and other biota in As cycling. A recent review on health impacts of As resulted in drinking water standards of 10 μg/L or even lower in some countries (Kapaj et al., 2006). These lowered standards are projected to greatly increase water supply cos

57、ts in many regions. The increased pressure on society to protect human health and the ecosystem has stimulated research using a wide multitude of approaches and techniques (Naidu et al., 2006; Bhattacharya et al., 2007). Considering the seriousness of this global As problem, a two-day symposium was

58、organized to facilitate a thorough discussion on a broad range of inter-disciplinary issues that are related to the research on As in the environment. These include understanding the natural and anthropogenic processes which accelerate or control human exposure to As and different aspects of remedia

59、tion. The outline of the symposium and the subsequent publications are described below. 2. Theme of the Special Symposium The Special Symposium (SYP-4) “Arsenic in the Environment: Biology and Chemistry” was organized as part of the 8th International Conference on Biogeochemistry of Trace Elements

60、 (ICOBTE) in Adelaide, Australia during April 2005. This Special Symposium attracted a wide range of contributions from a large number of multidisciplinary As researchers, that covered major themes, such as: 1) sources and characterization of As in groundwater environment; 2) processes that control

61、mobility and speciation of As in soil, water and biota; 3) prediction of the fate of As in natural environments in response to geochemical, hydrologic, and biologic changes; 4) analytical techniques and speciation studies; 5) remediation and management of As-contaminated soils and groundwater; and 6

62、) impact of As on agriculture and water supply management. The articles included in this special issue address many of these issues and pave the way through recent findings on the environmental behaviour of As in terms of its occurrence, sources, health impacts, and remediation. Besides understandin

63、g the fundamental processes of As mobilization, the articles discuss a wide variety of chemical and spectroscopic approaches, and increased understanding of the importance of microbes and other biota in As cycling. Although much has been learned about As in the environment the ability to predict the

64、 impact of intentional and unintentional changes to hydrologic and geochemical regimes often remains elusive. Key research contributions from several international teams of scientists working on As in the environment, groundwater in the Bengal Delta Plain and elsewhere in the world were presented

65、and discussed during the symposium and are amalgamated in this Special Issue of The Science of the Total Environment. 3. Layout and summary of the articles This special issue comprises 14 articles and 1 short communication, grouped into four sections. 1) Arsenic in the groundwater environment; 2)

66、arsenic in agricultural soils and mining environment; 3) biogeochemistry of As and toxicity, and 4) remediation of Ascontaminated soils and sediments. 3.1. Arsenic in the groundwater environment This section has five articles. The first two contributions deal with the specific issues related to the occurrence of geogenic As in the alluvial aquifers of Bangladesh. The first paper (von Brmssen et al., 2007-this volume) targets low-arsenic aquifers in areas with high concentrations of geogenic