Arsenic contamination in inland open water ecosystems and risk of arsenic ..... high phosphorous (P) and low iron (Fe) concentrations in irrigation water.
(An overview of research highlights)
Editors K. Bhattacharyya S. Bhattacharyya
Directorate of Research Bidhan Chandra Krishi Viswavisyalaya Kalyani, Nadia, West Bengal
Arsenic contamination through food-chain: Source, impact and management (An overview of research highlights)
Editors
K. Bhattacharyya S. Bhattacharyya
Directorate of Research Bidhan Chandra Krishi Viswavisyalaya Kalyani, Nadia, West Bengal 2016
Arsenic contamination through food-chain: Source, impact and management (An overview of research highlights in India and abroad) Bidhan Chandra Krishi Viswavidyalaya All rights reserved. No part of the publication may be reproduced or transmitted in any form or by any means without permission.
Published by
Directorate of Research Bidhan Chandra Krishi Viswavidyalaya Kalyani, Nadia, West Bengal
With financial assistance from: Indian Council of Agricultural research (ICAR) through Agri-Consortia Research Project entitled “Groundwater contamination due to geogenic factors and industrial effluents and its impact on food chain.”
The contents of this publication are at sole responsibility of the authors and do not necessarily represent the official views of ICAR or BCKV.
Cover page illustration Kallol Bhattacharyya
Designed and Printed by Bishnupriya Printers Kalyani- 741 235, West Bengal
from editors’ desk……. The contamination of arsenic, globally, perpetuates through anthropogenic and geogenic routes, of which problems are more grave, unprecedented and insurmountable when the causes are geogenic. The arsenic contamination in groundwater of Bengal basin (West Bengal and Bangladesh) is widespread where nearly 75 million people are exposed to arsenic in some way or other. First spot of arsenicosis patient (by Dr. K. C. Saha) in West Bengal and trail of arsenic contamination through drinking water was made in early 80’s. It took 20 years to look into the possibilities of arsenic contamination through contaminated irrigation water and food chain when emphasized by the research group at Bidhan Chandra Krishi Viswavidyalaya (BCKV) led by Professor Saroj Kr. Sanyal in late 90’s. Subsequently, a consortium was formed with agricultural scientists vis-à-vis reputed physicians, veterinarians, environment specialists, microbiologists etc to understand the multifaceted nature of the problem. Since then, BCKV never quit the leadership of the research related to arsenic contamination through food chain and possible mitigation options. In such, some meaningful research collaborations were also developed under the leadership of BCKV, some of which are still continuing. During its journey, we sensed that paucity of an appropriate book is a major inadequacy in making the policy makers understand the total gamut of the problem and its feasible solutions. We’ve made a modest attempt to put on record the findings of such research initiatives in the backdrop of peer reviewed global references in the form of a research digest. We would like to put on record our appreciation for the untiring efforts rendered by all the authors and co-authors that ultimately made this edition possible. We’ll feel privileged if this edition sensitizes environmental research, in its true prudence, through updating and fine tuning research strategies. We will be grateful for any observation and suggestions which would help in bringing out an improved version of this effort.
Kallol Bhattacharyya Somnath Bhattacharyya
Content Sl
Subject
Pages
1.
Prologue
S. K. Sanyal
1-4
2.
Origin, geochemical occurrence & chemistry of arsenic in soil & groundwater
5-12
S. K. Sanyal 3.
Arsenic polluted soils and management strategies
13-21
K. Bhattacharyya 4.
Arsenic contamination in food crops, the species level toxicity and the dietary risks
22-29
K. Bhattacharyya 5.
Soil microorganisms – role in arsenic detoxification
30-36
S. C. Kole, T. Biswas and A. Majumdar 6.
Uploading of arsenic in plants and related stresses
37-43
S. Bhattacharyya and S. Mondal 7.
Breeding for low-accumulating rice genotypes: status and prospects
44-50
S. Bhattacharyya 8.
Arsenic contamination in inland open water ecosystems and risk of arsenic exposure through fish and other aquatic biota
51-57
A. N. Chowdhury and Srikanta Samanta 9.
Arsenic contamination in livestock, its impact and plausible management
58-62
A. K. Bera, T. Rana and D. Bhattacharya 10.
Advanced analytical techniques and methodologies
63-69
K. Bhattacharyya 11.
Recent developments in electrochemical sensors for arsenic detection
70-77
Amit Bansiwal, Shrabanti Mukherjee and Payal Dhawale 12.
13.
clinical
78-84
D. N. Guhamazumdar K. Bhattacharyya and S. Bhattacharyya
85-87
Arsenic contamination and human manifestation and therapeutic measures Epilogue
sufferings:
Prologue Saroj Kr. Sanyal Arsenic (As), a toxic trace element, is of great environmental concern due to its presence in soil, water, plant, animal and human continuum. Its high toxicity and increased appearance in the biosphere has triggered public and political concern. Out of 20 countries (covering Argentina, Chile, Finland, Hungary, Mexico, Nepal, Taiwan, Bangladesh, India and others) in different parts of the world where groundwater arsenic contamination and human suffering therefrom have been reported so far, the magnitude is considered to be the highest in Bangladesh, followed by West Bengal, India (Sanyal et al., 2015). The scale of the problem is grave and unprecedented, exposing millions of people in the Bengal delta basin to risk. The widespread arsenic contamination in groundwater in different parts of West Bengal, located primarily in five districts adjoining the river Bhagirathi, as well as the contiguous districts in Bangladesh, is of great concern. Even beyond the Bengal delta basin, the widespread arsenic contamination in groundwater above the permissible limit (50 μgl-1; WHO, 2001; see below) has also been detected in several places in the country (Table 1, Figure 1), for instance at Chandigarh (1976), Nepal (2001), Bihar (2002), Uttar Pradesh (2003), Jharkhand (2003-2004) (Sanyal and Dhillon, 2005) and Punjab (2006-2007). Guideline Value of Maximum Arsenic Concentration
As mentioned briefly earlier, the World Health Organization (WHO)recommended provisional guideline value of total arsenic (As) concentration in drinking water is 10 µg As. L-1 since 1993 (WHO, 1993), mainly because lower levels preferred for protection of human health are not reliably measurable on a large scale. However, the National Standard for maximum acceptable concentration (MAC) of arsenic in drinking water is 50 µg As. L-1 in several countries including India and Bangladesh, based on an earlier WHO (1971) advice. The proposed new standard value of 5 µg As. L-1 is under consideration (WHO, 2001). This is due mainly to the fact that inorganic arsenic compounds are classified in Group 1 (carcinogenic to humans) on the basis of adequate evidence for carcinogenicity in humans and limited evidence for carcinogenicity in animals (IARC, 1987). Adequate data on the carcinogenicity of organic arsenic have not been generated. The joint FAO/WHO Expert Committee on Food Additives (JECFA) set a provisional maximum tolerable daily intake (PMTDI) of inorganic arsenic as 0.002 mg As. kg-1 of body weight for humans in 1983 and confirmed a provisional tolerable weekly intake (PTWI) as 0.015 mg As. kg-1 of body weight in 1988 (FAO/WHO, 1989). Such guideline values for soil, plant and animal systems are not available. 1
Table-1. Groundwater arsenic contamination in Indian Subcontinent West Bengal- 12 Districts, 111 blocks (Maldah, Murshidabad, Nadia, North 24Parganas, South 24-Parganas, Kolkata, Howrah, Hooghly, Bardhaman, North Dinajpur, South Dinajpur, Coochbehar); Groundwater arsenic range: 50-3700 µgl-1 http:// www.soesju.org./arsenic/wb.htm Assam- 18 Districts, 72 blocks; In 5 Districts (Barpeta, Dhemaji, Dhubgiri, Darrang and Golaghat), Groundwater arsenic range: 100-200 µg L-1; In 4 Districts (Jorhat, Lakhimpur, Nalbari and Nagaon) Groundwater arsenic range: 228-657 µgl-1 Singh, A. K. (2007). Curr. Sci. 92 (11):1506-1515. Bihar- 12 Districts, 32 blocks (Bhagalpur, Khagaria, Munger, Begusarai, Lakhisarai, Samastipur, Patna, Baishali, Saran, Bhojpur, Buxar and Katihar), Groundwater arsenic range: >50 µgl-1 Acharya, S. K. et al. (2004). Environ. Health. Pers. 112 (1): 19-20 Jharkhand- 1 District (Sahibgunj). Groundwater arsenic range: >50 µgl-1 http:// www.soesju.org./arsenic/wb.htm Uttar Pradesh- 21 Districts (Ballia, Lakhimpur, Kheri, Baharaich, Chandauli, Gazipur, Gorakhpur, Basti, Siddharthnagar, Balarampur, Sant Kabir Nagar, Unnao, Bareilly, Moradabad, Rae Bareli, Mirzapur, Bijnore, Meerut, SantRavidas Nagar, Shahjahanpur and Gonda). Groundwater arsenic range: >50 µgl-1 http://www.nerve.in/news:253500133730 Madhya Pradesh- 1 District (Rajnandgaon). Groundwater arsenic range: 52-88 µgl-1 Press Trust of India, September 4, 1999. Manipur- 1 District (Thoubal). Groundwater arsenic range: 798-986 µgl-1 Singh, A. K. (2007). Curr. Sci. 92 (11):1506-1515. Tripura- 3 Districts (North Tripura, Dhalai and West Tripura). Groundwater arsenic range: 65-444 µgL-1 Singh, A. K. (2007). Curr. Sci. 92 (11):1506-1515. Nagaland- 2 Districts (Mokokchung and Mon). Groundwater arsenic range: >50 µgl-1 Singh, A. K. (2007). Curr. Sci. 92 (11):1506-1515.
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Figure-1. Global, Indian and West Bengal profiles of groundwater arsenic contamination (Sanyal, 2005) Health Implications of Arsenic Poisoning
Arsenic is a widely occurring toxic metal in natural ecosystems. As small as 0.1 g of arsenic trioxide can prove lethal to humans (Jarup, 1992). Early symptoms of arsenic poisoning include skin disorders, weakness, languor, anorexia, nausea and vomiting with diarrhoea or constipation. With the progress of poisoning the symptoms attain more characteristic features, which include acute diarrhoea, edema (especially of the eyelids and ankles), skin pigmentation, arsenical melanosis and hyperkeratosis, enlargement of liver, respiratory diseases and skin cancer. In severe cases, gangrene in the limbs and malignant neoplasm are also observed (Sanyal et al., 2012). “Bell Ville Disease” (typical arsenic induced cutaneous manifestations among the people of Bell Ville) in Argentina, “Black Foot Disease” in Taiwan and “Kai Dam” disease in Thailand are well established as health disorders due to arsenic poisoning (Sanyal et al., 2012). As a matter of fact, the hair, nail, skin-scale and urine samples of a large number of people residing in the affected belt of West Bengal (India) and Bangladesh, have been analyzed by several workers. Many of these samples had arsenic loading more than the corresponding permissible toxic levels.
3
References FAO/WHO. (1989). Joint FAO/WHO Expert Committee on Food Additives. Toxicological evaluation of certain food additives and contaminants. Cambridge Univ. Press. IARC (1987). International Agency for Research on Cancer. Overall evaluations of carcinogenicity; an updating of IARC Monographs vols. 1-42. Sanyal, S. K. and Dhillon, K. S. (2005). Arsenic and selenium dynamics in watersoil plant system: a threat to environmental quality. In: Proc. Intern. Conf. Soil, Water and Environmental Quality-Issues and Strategies, Indian Soc. Soil Sci., New Delhi. pp. 239-263. Sanyal, S. K., Gupta, S. K., Kukal, S. S. and Jeevan Rao, K. (2015). Soil degradation, pollution and amelioration. In: State of Indian Agriculture-Soil (H. Pathak, S. K. Sanyal and P. N. Takkar, Eds.), National Academy of Agricultural Sciences, New Delhi, pp. 234-266. Sanyal, S. K., Jeevan Rao, K. and Sadana, U. S. (2012). Toxic elements and other pollutants- A threat to nutritional quality. In: Soil Science in the Service of Nation (Goswami, N.N. et al., Eds.), Indian Soc. Soil Sci., New Delhi: 266291. Sanyal, S. K. (2005) Arsenic contamination in agriculture: A threat to water-soilcrop-animal-human continuum. Presidential Address, Section of Agriculture & Forestry Sciences, 92nd Session of the Indian Science Congress Association (ISCA), Ahmedabad, January 3-7, 2005; Indian Science Congress Association Kolkata. WHO (1971). International standards for drinking water, Third edition. WHO (1993). Guidelines for Drinking-Water Quality, Second edition, Volume-1. WHO (2001). http://www.who.int/inf-fs/en/fact210.html
4
Origin, geochemical occurrence and chemistry of arsenic in soil & groundwater Saroj Kr. Sanyal Origin
Two major hypotheses, both of geogenic origin, have been proposed to account for such widespread arsenic contamination in the groundwater in parts of West Bengal and Bangladesh confined within the delta bound by the rivers Bhagirathi and Ganga-Padma. Of these two hypotheses, namely the arsenopyrite oxidation hypothesis and the ferric oxyhydroxide reduction hypothesis, the latter is more consistent with the experimental observations reported for the aquifer sediments and water of the Bengal delta basin (Sanyal et al., 2012). According to this hypothesis, an anoxic condition of the aquifer causes arsenic mobilization from arsenic-bearing sediments into the groundwater aquifer. The maintenance of such anoxic condition is proposed to be facilitated by the widespread practice of wetland paddy cultivation in the affected belt. Natural Abundance
Dissolved arsenic concentrations in natural waters (except groundwater) are generally low, except in areas characterized by geothermal water and/or mining activities. The sedimentary rocks generally have higher arsenic content (Table-1) than do igneous and metamorphic rocks, while suspended and bottom sediments in most aquatic systems contain more arsenic (Table-1) than most natural waters (Table-2). The capacity to retain arsenic is primarily governed by the sediment grain-size and the presence of surface coating composed of clays, clay-sized iron and manganese oxides and organic matter. Arsenic held by solid phases within the sediments, especially iron oxides, organic matter and sulphides may constitute the primary arsenic sources in groundwater under conditions conducive to arsenic release from these solid phases (Sanyal et al., 2015). These include abiotic reactions (oxidation/reduction, ion exchange, chemical transformations) and biotic reactions (microbial methylation). Table-1. Arsenic in rocks and some other materials Rocks/minerals
Arsenic (mg kg-1)
Rocks/minerals
Arsenic (mg kg-1)
Igneous rock
Igneous rock
Ultrabasic Peridotite, Dunite, Serpentine
Basic Basalt (extrusive)
0.18-113
Gabbro (intrusive)
0.06-28
0.3-15.8
5
Intermediate Latite, Andesite, Trachyte (extrusive) Diorite, Granodiorite, Syenite (intrusive)
Acidic 0.5 - 5.8
Rhyolite (extrusive)
0.09 - 13.4 Granite (intrusive)
Metamorphic rocks
Quartzite Slate/Phyllite Schist/Gneiss
2.2 - 7.6 0.5 - 143 0.0 - 185
Coal Crustal Average
Sedimentary rocks
Sedimentary rocks
Marine
Non-marine
Shale/Claystone (nearshore) Shale/Claystone (offshore) Carbonates Phosphorites Sandstone
4.0 – 25 Shales 3.0 - 490 Claystone 0.1 - 20.1 0.4 - 188 0.6 - 9.0
Up to 2000 2.0
3.0-12 3.0-10
Source: Sanyal (2005) Table-2. Arsenic concentrations in water other than groundwater (μgl-1) Arsenic concentration (μgl-1)
Source
Rainwater and snow
organo-arsine compounds > arsenites (As3+ form) and oxides (As3+ form) > arsenates (As5+ form) > arsonium metals (+1) > native arsenic metal (0) (Sanyal et al., 2012; Sanyal et al., 2015).
The arsenites are much more soluble, mobile, and toxic than arsenates in aquatic and soil environments. The organic forms, namely dimethyl arsinic acid (DMA) or cacodylic acid, which on reduction (e.g., in anoxic soil conditions) forms di- and trimethyl arsines, are also present in soil. Another organic form present in groundwater and soil is monomethylarsonic acid (MMA). At pH 6-8, and in an aerobic oxidized environment (redox potential, Eh= 0.2-0.5V), arsenic acid species and arsenate oxyanions, that is, Hn AsVO4 (3-n)- ions, with n= 1, 2), (pentavalent arsenic forms) occur in considerable proportions in most aquatic systems, whereas under mildly reducing conditions (such as one encountered in flooded paddy soils with Eh= 0 - 0.1V), the arsenous acid, H3AsIIIO3, and arsenite oxyanion species (arsenic in trivalent form) are the predominant species. Furthermore, As (III) is more prevalent in soils of neutral pH range (and in most groundwater), as in the soils of the affected belt of West Bengal, India and Bangladesh, than otherwise thought, and hence is of concern. This is primarily because As (III) exists as a neutral, uncharged molecule, namely arsenous acid, H3AsIIIO30 (pKa= 9.2), at the pH of the neutral soils and most natural groundwater as one would expect based on the Henderson’s equation (Sanyal et al., 2015), and is thus less amenable to retention by the charged mineral surfaces in soils and sediments. There have been both direct and indirect evidence to suggest that arsenic (and selenium) is held in soils and sediments by oxides (e.g., of Fe, Al, Mn) through the formation of inner-sphere complexes via ligandexchange mechanism. This is illustrated below by the following scheme of reactions. M–OH + H2O ⇌ M–OH2+ + OH-… (2.1) M–OH2+ + H2AsVO4-⇌M-OH2+……H2AsVO4-⇌ M–AsVO4 + H2O ….(2.2) However, the non-specific adsorption (through electrostatic mechanism) of As also occurs at pH values below the point of zero-charge (PZC) for a given adsorbent (Sanyal et al., 2012). As shown above, the said ligand exchange tends to increase the negative charge of the soil colloidal fraction, for instance, of iron oxides, and thus push the point of zero-charge (PZC) of the arsenic laden soil to lower pH. Indeed, this was shown to be the case with concomitant increase in the negative magnitude of the variablesurface charge and the surface potential of the corresponding soil colloidal 8
fraction (Sanyal et al., 2015). However, the non-specific adsorption (through electrostatic mechanism) of arsenic also occurs at pH values below the point of zero charge (PZC) for a given adsorbent. It ought to be emphasized that groundwater or soil solution, which is subject to affluxes and influxes, as well as circulation and also to man-made perturbations of groundwater due to its withdrawal, cannot be expected to remain in thermodynamic equilibrium, it being very much of an open system (thermodynamically speaking). Thus, more often than not, the ratio of concentrations of arsenic species, namely the ratio, [(As III)/ (AsV)], in field soils does not quite agree with the ones computed from the observed redox potential (Eh) and the application of the Nernst’s equation (at 250C) to the equilibrium redox reaction, namely AsVO43- + 2H++2e = AsIIIO33- + H2O 0
3-
…..(2.3) 3-
Eh= E h– 0.0295 log [(AsO3 )]/ (AsO4 )] – 0.059 pH
..…(2.4)
Where the (Eh) terms refer to the equilibrium concentrations of the respective ionic species in dilute soil solution, and E0h is the standard redox (reduction) potential of the AsVO43- / AsIIIO33- redox couple at 250C. It is evident from the above equation that the proportion of AsIII, and hence soluble arsenic level in soil, should increase substantially with diminishing Eh and increasing pH. Furthermore, at a high pH, the OH- ion concentration would increase, causing displacement of As III and AsV species from their binding sites through competitive ligand exchange reactions. The dependence of arsenic sorption on pH of the sorption medium is governed largely by the nature of the soil colloidal fraction. A fall of arsenate adsorption was noted with increasing pH, but only at lower arsenate concentrations, which got reversed at a higher arsenate equilibrium concentration. This trend was explained in terms of the varying electrostatic potential of the variable-charge soil colloidal surfaces with pH, solubility product principles, and buffering action of the arsenic salt used (Majumder and Sanyal, 2003). Arsenic loading in soils of West Bengal
Some of the research studies, conducted at the selected affected areas, revealed that the total and Olsen extractable (i.e., 0.5M NaHCO3, pH 8.5 – extractable arsenic which constitutes the soil arsenic pool amenable to plant uptake) arsenic varied from 8.4 to 24.3 mg/kg and from 2.90 to 15.8 mg/kg, respectively (Sanyal et al., 2015), in the given affected soils of West Bengal. The soil arsenic contents of these areas were generally higher than those reported for the soils of several other countries like Argentina, China, Italy, Mexico, France, Australia, etc. (Sanyal et al., 2012). Inorganic soil arsenic fractions from the affected soils were also fractionated into different soil 9
arsenic pools, namely water soluble As (Ws – As), arsenic associated with Al compounds in soil, the so-called aluminium-bound As (Al-As), iron-bound As (Fe–As) and calcium-bound As (Ca–As), by following the sequential extraction methodology. The findings suggested that these inorganic soil As pools fell in the order: Ws-As < Al-As < Ca-As < Fe-As. In particular, the Fe-As fraction contributed 45% to 74.7% towards the total soil arsenic sequential sum (Sanyal et al., 2015). Interaction of arsenic with organics in soil system
As mentioned earlier, soil acts as an effective sink of arsenic present in the contaminated groundwater used for irrigating the crops. The soil organic fractions including humic acid (HA) and fulvic acid (FA) behave as effective accumulators of toxic heavy metals by forming the metal-humate complexes (chelates) with different degrees of stability (Datta et al., 2001; Mukhopadhyay and Sanyal, 2004; Sinha and Bhattacharyya, 2011; Ghosh et al., 2012; Sanyal et al., 2012; Sanyal et al., 2015). Besides, soil clays, Al oxides, Fe oxides, especially the amorphous Fe and Al oxides in soil also influence the As retention by soils, soil minerals and sediments. The above mentioned organo-arsenic complexes were quite stable, even in the presence of competing oxyanions such as phosphate and nitrate (Sanyal et al., 2015). Further, the moderating influence of the organic fractions from FYM, vermicompost, municipal sludge, mustard cake, and surface soil of West Bengal was assessed in terms of the stability of the corresponding arsenohumic/fulvic complexes formed in organic manure treated contaminated soils (Sinha and Bhattacharyya, 2011; Ghosh et al., 2012). Sinha et al. (2011) reported that the organic manures added as soil amendment significantly reduced the accumulation (concentration) of arsenic in sesame seed to the maximum extent of 65.5% (vermicompost), 50% (phosphocompost), 42% (mustard cake) and 40% (FYM), compared with the control counterpart. The risk associated with dietary exposure to arsenic-contaminated sesame oil reached a value of 15.55% of provisional tolerable weekly intake for arsenic at the maximum accumulation of arsenic in sesame oil. Thus, improving the soil organic matter stock in the tropical soils of the As-affected belt, relatively poor in native organic matter, by adopting the appropriate management practices (such as recycling of crop residues, incorporation of the appropriate organic manure, etc.) will facilitate As retention in the affected soils. Interaction of arsenic with phosphorus
Phosphorus (P) is one of the essential major plant nutrients for plant growth. Because As and P are both placed in Group Vb of the Periodic Table, the interaction of As and P in soil-plant system is an important issue in respect of arsenic mobilization. Indeed the indications are that these 10
oxyanions would not be adsorbed independently in mixtures, but rather would tend to compete for some portion of the same type of adsorption sites (Sanyal et al., 2012). Several workers showed that the presence of phosphate caused a reduction in arsenate adsorption, and that the reduction was much greater for the competitive effects of arsenate on phosphate adsorption by soil minerals, although a large variation in the degree of competition between these two oxyanions has also been reported (Mukhopadhyay et al., 2002; Sanyal et al., 2015). References Acharya, S. K. (1997). Arsenic in groundwater-Geological overview. Consultation on Arsenic in Drinking water and Resulting Arsenic Toxicity in India and Bangladesh. World Health Organization, New Delhi, India, 29 April to 01 May, 1997. Datta, A., Sanyal, S. K. and Saha, S. (2001). A study on natural and synthetic humic acids and their complexing ability towards cadmium. Pl. Soil 225: 115-125. Ghosh, K., Das, I., Das, D. K. and Sanyal, S. K. (2012). Evaluation of humic and fulvic acid extracts of compost, oilcake and soils on complex formation with arsenic. Soil Res. CSIRO Pub. 50: 239–248. GuhaMazumdar, D. N., Haque, R., Ghosh, N., De, B. K., Santra, A., Chakraborti, D. and Smith, A. H. (1998). Arsenic levels in drinking water and the prevalence of skin lesions in West Bengal, India. Interl. J. Epidemiology. 27: 871-877. GuhaMazumder, D. N., Deb, D., Biswas, A., Saha, C., Nandy, A., Das, A., Ghose, A., Bhattacharyya, K. and Mazumdar, K. K. (2014). Dietary arsenic exposure with low level of arsenic in drinking water and biomarker: A study in West Bengal. J. Environ. Sci. Health, Part A. 49: 555–564. GuhaMazumder, D. N., Deb, D., Biswas, A., Saha, C., Nandy, A., Ganguly, B., Ghose, A., Bhattacharyya, K. and Mazumdar, K. K. (2013). Evaluation of dietary arsenic exposure and its biomarkers: A case study of West Bengal, India. J. Environ. Sci. Health, Part A. 48: 896-904. Jarup, L. (1992). Dose-response relation for occupational exposure to arsenic and cadmium. National institute for occupational health, Sweden. Majumdar, K. and Sanyal, S. K. (2003) pH-Dependent arsenic sorption in an Alfisol and an Entisols of West Bengal. Agropedology. 13: 25-29. Mukhopadhyay, D. and Sanyal, S. K. (2004). Complexation and release isotherm of arsenic in arsenic-humic/fulvic equilibrium study. Aust. J. Soil Res. 42: 815 -824.
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Mukhopadhyay, D., Mani, P. K. and Sanyal, S. K. (2002). Effect of phosphorus, arsenic and farmyard manure on arsenic availability in some soils of West Bengal. J. Indian Soc. Soil Sci. 50: 56-61. Sanyal, S. K., Gupta, S. K., Kukal, S. S. and Rao, J. K. (2015). Soil degradation, pollution and amelioration. In: State of Indian Agriculture-Soil (H. Pathak, S. K. Sanyal and P. N. Takkar, Eds.), National Academy of Agricultural Sciences, New Delhi, pp. 234-266. Sanyal, S. K., Rao, J. K. and Sadana, Upkar S. (2012). Toxic elements and other pollutants- A threat to nutritional quality. In: Soil Science in the Service of Nation (Goswami, N. N. et al., Eds.). Indian Soc. Soil Sci., New Delhi: 266-291. Sanyal, S. K. (2005). Arsenic contamination in agriculture: A threat to water-soilcrop-animal-human continuum. Presidential Address, Section of Agriculture & Forestry Sciences, 92nd Session of the Indian Science Congress Association (ISCA), Ahmedabad, January 3-7, 2005; Indian Science Congress Association, Kolkata. Sinha, B. and Bhattacharyya, K. (2011). Retention and release isotherm of arsenic in arsenic–humic/fulvic equilibrium study. Biol. Fertil. Soils 47: 815–822. Sinha, B., Bhattacharyya, K., Giri, P. K. and Sarkar, S. (2011). Arsenic contamination in sesame and possible mitigation through organic interventions in the lower Gangetic Plain of West Bengal, India. J. Sci. Food Agric 91: 2762–2767.
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Arsenic polluted soils and management strategies Kallol Bhattacharyya Debates surrounding arsenic accumulation in soils are contentious and pivot around questions of uptake, extent, and the chemical and biophysical mechanisms involved. A survey of paddy soils throughout Bangladesh (Meharg and Rahman, 2003) for instance, showed elevated As levels in soil were highly correlated with elevated As content in irrigation water and long term tube well use. Similarly, Alam and Sattar (2000), Das et al. (2008) and Sarkar et al. (2012) all found a direct correlation between irrigating with arsenic-contaminated water and elevated soil arsenic levels. Some studies also demonstrate the strong residual effect of soil arsenic contamination on subsequent crops (Abedin et al., 2002; Huq et al., 2007; Khan et al., 2010). Factors which have been shown to influence arsenic retention in soil and soil water include: soil texture (Duxbury and Panaullah, 2007); relatively high phosphorous (P) and low iron (Fe) concentrations in irrigation water (Duxbury and Panaullah, 2007); distance from the irrigation inlet (Hossain, 2005; Duxbury and Panaullah, 2007; Stroud et al., 2011); field to field water distribution method (Duxbury and Panaullah, 2007); and arsenic leaching out during monsoon flooding (Pal et al., 2009; Roberts et al., 2011). Taken together, these studies suggest that there are considerable differences in soil properties at regional, local, and even within tube well areas that affect arsenic accumulation and availability (Brammer and Ravenscroft, 2009). Arsenic fractions in soil
Arsenic is present in soils or sediments in various forms with varying degree of bioavailability, toxicity and mobility. In order to assess arsenic toxicity and impact, a good understanding of the chemical forms of the element is required (Shiowatana et al., 2001). The use of sequential extraction technique for fractionation of metals in solid materials and evaluation of their potential effects has been widely used and well recognized (Tessier et al., 1979). The As fractionation studies, in general, revealed that the As affected soils were endowed with internally held arsenic followed by Fe and Al chemisorbed arsenic, Ca associated arsenic and freely exchangeable arsenic (McLaren et al., 1998; Shiowatana et al., 2001; Das et al., 2011). The fractions of arsenic varied mainly due to the mineralogical make-up of the soils, surface area, pH, total and Olsen extractable As, amorphous iron and, to a smaller extent, calcium and magnesium content of these soils (McLaren et al., 1998; Welch et al., 1988; Ghosh et al., 2002; Masue et al., 2007; Das et al., 2011). 13
Arsenic species in soils
The topic of elemental speciation is now a well-established area of research. Studying the chemical forms of elements helps elucidate the mobility, biological availability distribution, and toxicity of the chemical element (Gupta et al., 2012; Ure and Davidson, 2002). The greatest arsenic (As) toxicity is attributed to inorganic arsenic (i-As), a non-threshold class-1 human carcinogen (IARC, 2004). In arsenic-contaminated soils, simultaneous reactions of arsenic, such as adsorption/desorption, precipitation, and oxidation/reduction, might occur on mineral surfaces, which influences the arsenic solid-state speciation in the soil environment (Kim and Batchelor, 2009). The predominant inorganic As species in the oxic layer of soils is arsenate which has a similar chemical behavior to phosphate with limited presence of arsenite (Sadee et al., 2016). As(V) is the predominant form that exists in soils, in which the pH + pe > 10; in contrast, As(III) is the dominant form found in soils, in which the pH + pe is less than 6 (Sadiq, 1997). Under aerobic conditions, sulfides are easily oxidized, and as a consequence arsenic is released into the environment (Adriano, 2001); when soil pH is between 3 and 13, the major species found are H2AsO4- and HAsO42− (Smedley and Kinninburgh, 2002). In reducing environments, arsenic is found as arsenite, the predominant species of which is H3AsO3. Arsenite is more mobile and more toxic than is arsenate. Highly reducing conditions can cause As co-precipitation with iron-sulfurs, such as arsenopyrite, or the formation of arsenic sulfides (AsS, As2 S3). During the oxidation of pyrite, Fe is oxidized from valence II to III, and arsenic is oxidized to arsenate. In contrast, under reducing conditions, Fe and Mn oxides are dissolved, releasing arsenate that is rapidly reduced to arsenite (Gräfe and Sparks, 2006). Organic amendment and arsenic mitigation
A large number of studies explore the mitigation potential of soil amendments such as the application of inorganic fertilizer or organic manure which can immobilize, adsorb, bind or co-precipitate arsenic in situ. The overwhelming majority of studies found that fertilization (irrespective of type) reduces available arsenic in soils. Das et al. (2008) and Mukhopadhyay and Sanyal (2002) found that the arsenic content in soil markedly decreased, especially with farmyard manure application. Organic amendments such as composts and manures which contain a high amount of humified organic matter can decrease the bioavailability of heavy metals through adsorption and by forming stable complexes with humic substances (Sinha and Bhattacharyya, 2012). In soil and organic manures, humic substances often represent a high fraction of dissolved organic matter due to their recalcitrance, and they have 14
functional moieties with a variety of properties (Stevenson 1994). The chelation of cations can influence the presence of free metal ions and regulate their availability and mobility in soils and aquatic environments following the formation of metal–humate complexes (chelates) with different degrees of stability (Sanyal 2001; Sinha and Bhattacharya 2011). Ghosh et al. (2012) observed that HA/FA extracted from compost was found to be the better in scavenging arsenate in its matrices and more specifically Sinha and Bhattacharyya (2011) observed higher stability of As-HA/FA complexes with vericompost rather than FYM or oil cakes. Similar observations were also recorded by Giri et al. (2011), Pati and Mukhopadhyaya (2009) in summer rice soil environment in West Bengal. Phytoremediation
Phytoremediation is considered an economical and environmentally friendly method of exploiting plants to extract contaminants from soil (Padmavathiamma and Li, 2007; Prasad, 2003). At present, there are totally more than 400 species of hyperaccumulator plants for As, Cd, Mn, Ni, Zn etc. have been found. Phytoextraction, an environmental friendly low-input technology, has the potential to remediate metal contaminated soils (Purakayastha et al., 2008). In this context, arsenic hyperaccumulator Pteris vittata L. has a great potential to be used for phytoremediation of arseniccontaminated soils (Komar et al., 1998; Ma et al., 2001; Gonzaga et al. 2008). It accumulates as much as, 23000 mg kg−1 arsenic in the fronds when growing in a soil spiked with 1500 mg kg-1 As (Ma et al., 2001). In a successful phytoremediation process the most prerequisite is to make available the contaminant (arsenic) to the rhizosphere of the phytoremediating plants. As arsenic interacts with soil matrix in a complex way making it less available to the phytoextracting plant therefore, proper soil and nutrient management strategies should be evolved to enhance the availability of arsenic to the phytoremediating plants. P fertilization and successive growing cycles of P. vittata could be important strategies for successful phytoextraction of arsenic from a contaminated soil (Mandal et al., 2012). Wan et al. (2016) worked out the total cost of phytoremediation which was lower than those of most technologies reported in literature. The benefits of phytoremediation are expected to offset the project costs in less than seven years. Iron derivatives and arsenic mitigation
Iron oxyhydroxides strongly sorb oxyanions of arsenic, phosphorus, selenium, molybdenum and others (Roy et al., 1986). Removal of dissolved arsenic from wastewater using ferric iron compounds is a proven treatment technology (USEPA, 2002). The use of Fe-based soil amendments to reduce arsenic mobility and toxicity has been extensively reported in the literature 15
(Komarek et al., 2013; Miretzky and Cirelli (2010); Kumpiene et al., 2008). Sources of Fe have included agricultural or industrial grade chemical compounds (e.g., ferrous sulfate, ferric chloride), natural Fe oxide minerals and industrial waste by-products (e.g., fly ash, water treatment sludges, ore process in muds, Fe shot). Goals of soil treatment techniques have included reduction of As mobility (leaching), reduced uptake in crops, and reduced oral bioavailability to humans and ecological receptors (Cutler et al., 2014). The enhanced iron (Fe2+) in the soil solution due to application of FeSO4, may be responsible for reducing extractable As through sorption/coprecipitation as insoluble Fe-As complexes (Al-Abed et al., 2007; Giri et al., 2011). The possible effects of the application of Fe materials include: coprecipitation around neutral pH when the ratio of Fe to As increases, and suppression of the release of soluble arsenite by the adsorption of arsenate by Fe (Matsumoto et al., 2015). Zinc derivatives and arsenic mitigation
The arsenic toxicity may be reduced by applying sulfates of Zn to the soil (Brady, 1974), although Nielsen et al. (1980) reported that the interaction between arsenic and zinc apparently was noncompetitive. Significant reduction in available arsenic content of rice soils of West Bengal were observed when amended with ZnSO4 (Garai et al., 2000; Bandyopadhyay et al., 2002; Das et al., 2005; Giri et al., 2011). Such decrease in its concentration might be due to the suppressing effect of Zn that results in precipitation/fixation of arsenic as Zn-arsenate, which makes it unavailable to plants (Craw and Chappell, 2000), zinc-mediated As adsorption on magnetite were also noted by Yang et al. (2010). Phosphorus and arsenic mitigation
Arsenic and phosphorus exist in the same periodic family and have similar chemical and physical properties as well as similar electron configuration. Phosphate has long been reported to suppress plant uptake of arsenate (Woolson et al., 1973; Tu and Ma, 2003). In arsenate spiked hydroponic solutions, addition of sufficient phosphate alleviated arsenate toxicity and improves plant growth. Plant arsenate uptake rate is reduced by 75% at 0.5 m phosphate (Meharg and Macnair, 1991). In soil, however, the influence of phosphate on arsenate phytotoxity varies. This is because of the soil properties that affect the availability of phosphate and arsenate (Tu and Ma, 2003). Effect of P application on arsenic availability and uptake is rather complex and contrasting findings were obtained. Woolson (1975) concluded that low levels of phosphorus added to an arsenic toxic soil will displace arsenic from soil particles to increase the toxicity to plants, but larger applications of phosphorus will compete at the root surface and decrease toxicity. 16
Tu and Ma (2003) observed that soluble arsenate was significantly increased only by higher phosphate application as compared to the low phosphate levels. Application of phosphate fertilizer to arsenic contaminated soils has resulted in displacement of arsenic in the soil and redistribution of arsenic to lower depths in the soil profile (Woolson et al., 1973; Fitz and Wenzel, 2002; Cao et al., 2003). Since the adsorption of As by soil solids is similar to that of Pi, competitive adsorption between Pi and As (both AsIII and AsV) may occur when Pi is applied to an As-enriched soil, and this may result in an increase of As release into soil solutions. Heikens (2006) reported that both ions (As(III) and PO43-) compete for sorption sites on FeOOH depending upon the balance between competition for sorption sites and competition for plant uptake. In general, the addition of P-fertilizer resulted in increasing concentrations of soluble total As, arsenate and arsenite. It was obvious that pH played an important role in controlling the effects of the addition of Pfertilizers on As chemistry; addition of P fertilizers to soils will also affect As chemistry by decreasing the pH value of the soil. Addition of P resulted in higher soluble concentrations of both P and As; however, soluble As increased up to an application rate of 600 mg P kg−1 soil and remained constant thereafter (Signes-Pastor et al., 2007). In the solution culture system, P addition competed for As absorption by plant roots thereby decreasing its uptake. In the soil system, P addition facilitated the desorption and bioavailability of As. However, the net effect of P on As phytoavailability in soils depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots (Bolan et al., 2013). Effect of P fertilization in arsenic contaminated soils came up with interesting and contrasting findings. For the soils with high retention capacity of Pi, the Pi additions did not result in any obvious change in As concentration of the soil solution while the Pi concentration in the soil solution increased. For the soils with low retention capacity of Pi, the application of Pi largely increased both the As and Pi concentrations in the soil solutions, which could be attributed to competitive adsorption by solids and the As toxicity was aggravated when As concentration in soil solution was increased with high Pi application (Lee et al., 2016). EDTA, Silicates and arsenic mitigation
The chelating agent, EDTA nutrient complexes have been widely used as fertilizers in arid soils because of their high solubility (Luo et al., 2005) and stability in soil (Wang et al., 2010). Moreover, this chelating agent is widely used for enhancing the phytoextraction of heavy metals from contaminated soils (Hovsepyan and Greipsson, 2005; Park et al., 2008). 17
Arsenic (As) is thought to be slightly affected by EDTA applications to soil (Vaxevanidou et al., 2008). However, the results obtained by Rahman et al. (2008), Abbas and Abdelhafez (2013) revealed that the application of EDTA to the growth media could increase the availability and uptake of As(III) and As(V) by the aquatic floating duckweed plants. The application of EDTA amendments to As contaminated soil is still a matter of confliction concerning its effect on As availability in soil, its uptake and concurrent toxicities on the grown plants. Combining the action of the iron reducing microorganism D. palmitatis with the chelating strength of EDTA was observed to remove soil As up to 90% whereas only 35% was obtained when pure chemical treatment was applied (Vaxevanidou et al., 2008). It was reported that the application of silicate (Giri et al., 2011; Seyfferth and Fendorf, 2012) decreased the absorption of As by paddy field rice. Li et al., (2009) reported that Si fertilization decreased the total As concentration in straw and grain by 78% and 16%, respectively, and that it specifically decreased the uptake of arsenite. One of the primary factors is thought to be a competition between As (III) and Si because of their chemical similarities; that is the uptake of arsenite and methylated As into shoots is mediated by Si uptake mechanisms. Although, Matsumoto et al. (2015) did not find silicate application to have a significant effect on the concentration of As in both grain and straw, although the content of available silicate in the soil was significantly increased. References Abbas Md., H. H. and Abdelhafez, A. A. (2013). Role of EDTA in arsenic mobilization and its uptake by maize grown on an As-polluted soil. Chemosphere. 90: 588–594. Abedin, M. J., Cotyter-Howells, J. and Meharg, A. A. (2002). Arsenic uptake and accumulation in rice (Oryza sativa L.) irrigated with contaminated water. Plant Soi. 240: 311–319. Alam, M. B., Sattar, M. A. (2000). Assessment of arsenic contamination in soils and waters in some areas of Bangladesh. Water Sci. Technol. 42: 185–193. Bolan, N., Mahimairaja, S., Kunhikrishnan, A. and Choppala, G. (2013). Phosphorus-arsenic interactions in variable-charge soils in relation to arsenic mobility and bioavailability. Sci. Tot. Env. 463-464:1154-1162. Brammer, H. and Ravenscroft, P. (2009). Arsenic in groundwater: a threat to sustainable agriculture in South and South-east Asia. Environ. Int. 35: 647– 654.
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Cao, X., Ma, L. Q. and Shiralipour, A. (2003). Effects of compost and phosphate amendments on arsenic mobility in soils and arsenic uptake by the hyperaccumulator Pteris vittata L. Environ Pollut. 126: 157–167. Das, D. K., Sur, P. and Das, K. (2008). Mobilization of arsenic in soils and in rice (Oryza sativa L.) plant affected by organic matter and zinc application in irrigation water contaminated with arsenic. Plant Soil Environ. 54 (1): 30–37. Duxbury, J. M. and Panaullah, G. (2007). Remediation of Arsenic for Agriculture Sustainability, Food Security and Health in Bangladesh. Working Paper. Food and Agriculture Organization (FAO), Rome. Fitz, W. J. and Wenzel, W. W. (2002). Arsenic transformations in the soilrhizophere-plant system: fundamentals and potential application to phytoremediation. J Biotechnol. 99: 259–278. Ghosh, K., Das, I., Das, D. K and Sanyal, S. K. (2012). Evaluation of humic and fulvic acid extracts of compost, oilcake, and soils on complex formation with arsenic. Soil Res., CSIRO Publishing. 50: 239–48. Giri, P. K., Bhattacharyya, K., Sinha, B. and Roy, N. R. (2011). Mitigation options of arsenic uptake by rice plant in arsenic endemic area. ORYZA 48 (2): 127131. Gräfe, M, and Sparks, D. L. (2006). Solid phase speciation of arsenic. In: Naidu R et al (eds) Managing arsenic in the environment. From soils to human health. CSIRO Pub, Collingwood, Australia, pp 75–92. Hossain, M. F. (2005). Arsenic contamination in Bangladesh: an overview. Agriculture Ecosyst. Environ. 113 (1–4): 1–16. Hovsepyan, A. and Greipsson, S. (2005). EDTA-enhanced phytoremediation of lead contaminated soil by corn. J. Plant Nutr. 28: 2037–2048. Huq, S. M., Abdullah, M. B. and Joardar, J. C. (2007). Bioremediation of arsenic toxicity by algae in rice culture. Land Contam. Reclam. 15 (3), 327–333. Khan, A. M., Rafiqul, I., Panaullah, G. M. (2010). Accumulation of arsenic in soil and rice under wetland condition in Bangladesh. Plant Soil. 333 (1–2): 263– 274. Lee, C. H., Wu, C. H., Syu, C. H., Jiang, P. Y., Huang, C. C. and Lee, D. Y. (2016). Effects of phosphorous application on arsenic toxicity to and uptake by rice seedlings in As-contaminated paddy soils. Geoderma. 270: 60–67. Li, R. Y., Stroud, J. L., Ma, J. F., McGrath, S. P. and Zhao, F. J. (2009). Mitigation of arsenic accumulation in rice with water management and silicon fertilization. Environ. Sci. Technol. 43: 3778–3783. Luo, C., Shen, Z., and Li, X., (2005). Enhanced phytoextraction of Cu, Pb, Zn and Cd with EDTA and EDDS. Chemosphere. 59: 1–11.
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Meharg, A. A. and Macnair, M. R. (1991). Uptake, accumulation and translocation of arsenate in arsenate-tolerant and non-tolerant Holcus lanatus L. New Phytol. 117: 225-231. Meharg, A. A., Rahman, M. M. (2003). Arsenic contamination of Bangladesh paddy field soils: implications for rice contribution to arsenic consumption. Environ. Sci. Tech. 37 (2): 229–234. Mukhopadhyay, D. and Sanyal, S. K. (2002). Effect of phosphate, arsenic and farmyard manure on the changes of the extractable arsenic in some soils of West Bengal and reflection thereof on crop uptake. In: Proc. Natl. Seminar on Developments in Soil Science. Ind. Soc. Soil Sci., Nagpur, December 28– 31, 2000. Pal, A., Chowdhury, U. K. and Mondal, D. (2009). Arsenic burden from cooked rice in the populations of arsenic affected and non affected areas and Kolkata City in West Bengal, India. Environ. Sci. Technol. 43 (9): 3349–3355. Park, J. Y., Kim, K. W., Kim, J. Y., Lee, B. T., Lee, J. S. and Bae, B. H. (2008). Enhanced phytoremediation by echinochloafrumentacea using PSM and EDTA in an arsenic contaminated soil. In: Pisutha-Arnond, V. (Ed.), The International Symposia on Geoscience Resources and Environments of Asian Terranes, 4th IGCP 516, and 5th APSEG. Bangkok, Thailand, pp. 487–488. Pati, R. and Mukhopadhyay, D. (2009). Effects of organics influencing the arsenic transport in soil-plant systems. Ind. J. Agric. Sci. 79 (12): 996-999. Rahman, M. A., Hasegawa, H., Ueda, K., Maki, T. and Rahman, M. M. (2008). Influence of EDTA and chemical species on arsenic accumulation in Spirodelapolyrhiza L. (duckweed). Ecotoxicol. Environ. Safe. 70: 311–318. Roberts, L. C., Huq, S. J., Voegelin, A. (2011). Arsenic dynamics in pore water of an intermittently irrigated paddy field in Bangladesh. Environ. Sci. Technol. 245: 971–976. Sarkar, S., Basu, B., Kundu, C. K. (2012). Deficit irrigation: an option to mitigate arsenic load of rice grain in West Bengal, India. Agric. Ecosyst. Environ. 146 (1): 147–152. Seyfferth, A. L. and Fendorf, S. (2012). Silicate mineral impacts on the uptake and storage of arsenic and plant nutrients in rice (Oryza sativa L.). Environ. Sci. Technol. 46: 13176–13183. Shiowatana, J., McLaren, R. G., Chanmekha, N. and Samphao, A. (2001). Fractionation of arsenic in soil by a continuous-flow sequential extraction method. J. Environ. Qual. 30: 1940–1949. Signes-Pastor, A., Burló, F., Mitra, K. and Carbonell-Barrachina, A. A. (2007). Arsenic biogeochemistry as affected by phosphorus fertilizer addition, redox potential and pH in a West Bengal (India) soil. Geoderma. 137: 504–510.
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Sinha, B. and Bhattacharya, K. (2011). Retention and release isotherm in arsenic humic/fulvic equilibrium study. Biology and Fertility of Soils. 47: 815–822. Sinha, B. and Bhattacharyya, K. (2012). Role of organics in reducing arsenic loading in soil-plant system under rice. In the lower Gangetic plain of West Bengal. Journal of Crop and Weed. 8 (1): 79-83. Smedley P. L. and Kinninburgh D. G. (2002). A review of the source, behavior and distribution of arsenic in natural waters. Appl Geochem. 17: 517–568. Stroud, J. L., Norton, G. J., Islam, M. R. (2011). The dynamics of arsenic in four paddy fields in the Bengal delta. Environ. Pollut. 159 (4): 947–953. Tessier, A., Campbell, P. G. C. and Bisson, M. (1979). Sequential extraction procedures for the speciation of particulate trace metals. Anal. Chem. 51: 844–851. Tu, C., and Ma, L. Q. (2003). Interactive effects of pH, arsenic and phosphorus on uptake of As and P and growth of the arsenic hyperaccumulator Pteris vittata L. under hydroponic conditions. Environ. Exp. Bot. 50: 243-251. Vaxevanidou, K., Papassiopi, N. and Paspaliaris, I. (2008). Removal of heavy metals and arsenic from contaminated soils using bioremediation and chelant extraction techniques. Chemosphere. 70: 1329–1337. Wang, J., Wang, X., Li, G., Guo, P. and Luo, Z. (2010). Degradation of EDTA in aqueous solution by using ozonolysis and ozonolysis combined with sonolysis. J. Hazard. Mater. 176: 333–338. Woolson, E. A., Axley, J. H. and Kearney, P. C. (1973). The chemistry and phytotoxicity of arsenic in soils: II. Effects of time and phosphorus. Soil Sci. Soc. Am. Proc. 37: 254 – 259.
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Arsenic contamination in food crops, the species level toxicity and dietary risks Kallol Bhattacharyya The countries with the highest daily intake of total arsenic (t-As) are Spain and Japan followed by India and France. The world's two most significant cases of As contamination where the population suffers the most are located in Asia, particularly in Bangladesh and West Bengal in India (Rahaman et al., 2003). At this point, it is interesting to distinguish among different situations. The first is represented by Spain (but could also be represented by Japan), where seafood is the main source of As in the diet. The second is represented by Chile, where drinking water is the main source although vegetables also contribute to the daily intake. The third example is West Bengal (India) and Bangladesh, where cooked rice plays an important role together with drinking water. In general, As from seafood is organic (oAs) while As from drinking water and vegetables is inorganic (i-As) (Rahaman et al., 2003; Mondal et al., 2008; Diaz et al., 2004; Urieta et al., 1996; Cortes et al., 2016; Diaz et al., 2016) Although As is potentially toxic to humans, animals, and plants, its actual toxicity varies widely with its oxidation state. Inorganic species are generally more toxic than organic species, and arsenite (AsIII) is 60 times more toxic than arsenate (AsV), which is 70 times more toxic than methylated species, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) (WHO 1981). The methylated species are consequently considered to be moderately toxic, whereas arsenobetaine (AsB) and arsenocholine (AsC) are considered to be nontoxic (Kumaresan and Riyazuddin, 2001). Recent studies suggest that methylation is not fully a detoxication process. Lin et al. (1999) found that MMAIII is more than 100 times more potent than inorganic AsIII as an in vitro inhibitor of thioredoxin reductase. Thus, formation of MMAIII appears to be indicative of toxification of both inorganic AsIII and inorganic AsV. Vega et al. (2001) reported the toxicity order of arsenicals as iAsIII > monomethylarsine oxide (MMAOIII) > DMAIII > DMAV > MMAV > iAsV. In nine districts of West Bengal (South 24-Parganas, North 24Parganas, Howrah, Hooghly, Nadia, Bardhaman, Murshidabad, Malda, and South Calcutta), groundwater has an arsenic concentration above 0.05 mg L1 . Approximately 42.7 million people live in these 9 districts who are exposed and at risk pf dietary arsenic toxicity because the maximum permissible limit of As established by the World Health Organization in 2006 is 0.01 mgl-1 (Roychowdhury et al., 2002). There is strong evidence of elevated As levels in rice grain and vegetables in regions of West Bengal and 22
Bangladesh, where fields have been irrigated with As-contaminated water. Signes et al. (2008) reported that the most popular types of commercial rice from West Bengal (paddy, atab, and boiled) have As concentrations as high as 55013 μgkg-1, 33914 μgkg-1, and 50752 μgkg-1, respectively. Farid et al. (2003) reported As contents in different vegetables irrigated with Ascontaminated water: amaranth, 572 μgkg-1; Indian spinach, 189 μgkg-1; chilli, 112 μgkg-1 and potatoes, 103 μgkg-1. Table-1. Total arsenic recoveries from crop edibles From affected villages of 24 Pgs (N) Total arsenic (μgkg-1) (Mean ± SE)
Samples
Vegetables
From affected villages of Nadia Crop edibles
Total arsenic (mgkg-1)
Rice
0.10-0.59
Carrot
121±02
Potato
0.05-1.05
Radish
167±05
Wheat
0.45-1.08
Onion
55±05
Mustard
1.37-1.60
Tomato
56±4
Sesame
0.31-1.02
Brinjal
53±11
Brinjal
1.50-2.55
Potato
80±07
Pointed gourd
1.20-3.65
Cabbage
2.50-5.60
Cereals Paddy rice
496±17
Chilli
1.05-3.80
Atap rice
271±20
Banana
1.20-4.80
Boiled rice
469±06
Papaya
1.80-5.60
Signes-Pastor et al. (2008)
ICAR (2011), WHO-BCKV (2008)
These high As contents in rice and vegetables are indicators of the level of As contamination in the environment. In order to assess the risk posed by As in the diet, however, As speciation must be ascertained because methylated organic As (o-As; monomethyl arsenic acid, MA; dimethyl arsenic acid, DMA) is much less toxic than inorganic As (i-As: arsenate and arsenite) (Signes et al., 2008), which has been classified by the International Agency for Research on Cancer (IARC) as carcinogenic to humans (Diaz et al., 2004). 23
Table-2. Arsenic species recoveries from crops Kasimpur Village Nadia West Bengal Vegetables (dw) Carrot
Arsenic species (μg kg-1) Inorganic arsenic Organic arsenic Arsenite Arsenate MA DMA
Total As
90±7
nd
22±11
nd
112±10
Radish
94±12
nd
60±7
nd
154±11
Tomato
54±5
nd
n.d
nd
54±5
Onion
56±6
nd
n.d
nd
56±6
Cauliflower
60±9
nd
n.d
nd
60±9
Brinjal
48±2
nd
n.d
nd
48±2
34±7
nd
81±5
Potatoes 47±2 nd Cereals (dw) Paddy rice 243±10 nd Boiled rice 380±11 nd dw- Dry weight, nd- not detected.
nd nd
242±12 488±11 91±9 471±10 Signes-Pastor et al. (2008)
Rice is considered a principal dietary component, particularly in the Asian countries, where per person daily rice consumption may be up to 0.5 kg (dry weight). (Zavala and Duxbury, 2008). In West Bengal and Bangladesh, rice consumption provides an average of 72.8% of the daily caloric intake per capita. (Mondal and Polya, 2008). As rice is cultivated in As-contaminated soils under anaerobic conditions, the As concentration in rice is high compared with other crops and regions (Abedin et al., 2002; Meharg 2004). In rice, As is mostly present in inorganic and methylated forms, (Williams et al., 2005) but their distribution varies genetically (Norton et al., 2009). Therefore, rice is considered as one of the potential routes of dietary As exposure in many parts of the world (Chatterjee et al., 2011). Meharg et al. (2008) studied As speciation in brown and white rice samples obtained from Bangladesh, United States, and China. Total As concentration in all rice samples ranged from 0.28 to 0.61 mgkg-1, with the brown rice from Bangladesh having the highest As concentration. As speciation detected main species DMA and iAs which represented between 39 and 57% of the t-As. Signes-Pastor et al. (2008) also recovered major species of arsenite and DMA from paddy rice and boiled rice, while from vegetables mostly arsenite is recovered (Table-2). Arsenic species recovered from autumn rice straw and grain are principally As-V and As-III. It is interesting to note that As-III accounted for the major As species recovered from grains of transplanted autumn paddy while As-V predominates As 24
recoveries from rice straw (Sinha and Bhattacharyya, 2014). As species recovered from summer rice grain and straw are principally As(III) and As(V) with a small amount of DMA and almost non-detectable MMA and AsB. The per cent recoveries of organic arsenic were observed to be higher in (summer) rice straw as compared to grain (Sinha and Bhattacharyya, 2015). Biswas et al. (2012) found that arsenic species in raw rice (summer) cultivated in Nadia (West Bengal) came up in the proportions of 76% arsenate, 11% arsenite, and 12% DMA, with no trace of AsB and MMA. Other studies in the same area samples also reported the presence of 91%, 74%, 80%, and 95% inorganic As in raw rice of the households (Rahman et al., 2003b; Mondal and Polya 2008; Signes-Pastor et al., 2008; Halder et al., 2013) Arsenic accumulation was also reported in day-to-day-used vegetables grown on contaminated soils and/or from plants irrigated with contaminated water (Meharg and Rahman, 2003; Biswas et al., 2012). A study with from common vegetables from Nadia district (West Bengal, India) showed significant tAs recoveries (0.114–0.910 mgkg-1) showing highest arsenic values in spinach 0.910 mg/kg (Biswas et al., 2012). Arsenic species recoveries from market vegetable samples of Nadia (west Bengal, India) showed AsV to be the predominant species followed by AsIII
