Impact of irrigating with arsenic contaminated water on farmers’ incomes in west bengal

IMPACT OF IRRIGATING WITH ARSENIC CONTAMINATED WATER ON FARMERS’ INCOMES IN WEST BENGAL Madhavi Marwah Malhotra* Abstract With high arsenic contamination of groundwater in West Bengal m

IMPACT OF IRRIGATING WITH ARSENIC CONTAMINATED WATER ON

FARMERS’ INCOMES IN WEST BENGAL Madhavi Marwah Malhotra*

Abstract

With high arsenic contamination of groundwater in West Bengal much beyond permissible limits

for irrigation water, and institutional measures aimed at enhancing groundwater pumping to

meet the growing food requirements in the country, the long-run sustainability of agricultural

production and farmers’ livelihoods in arsenic affected areas are under threat This study

undertakes a comparison of the net incomes of farmers earned from crop production between

arsenic affected and non- arsenic affected areas’ agricultural situation To analyse the

differences in the agricultural situation in detail, the non-parametric Mann-Whitney U test for

comparing two samples is used In conclusion, the study finds evidence that farmers using

arsenic contaminated water for irrigation for over two decades in West Bengal are now facing

triple impoverishment on account of having to adopt a less profitable cropping pattern, lower

yield of crops and higher input costs per unit of cultivated land area

Key words: arsenic, agriculture, groundwater

Introduction

Much of Eastern India, underlain with alluvial aquifers receiving plentiful rainfall for recharge, is not posed with a challenge as far as volume of groundwater availability is concerned Particularly, for the state of West Bengal, the stage of groundwater development1(SGD) was about 42 percent in 2013, as compared to Punjab and Haryana with SGD close to 140 percent and 120 percent, respectively (CGWB, 2013) However, there are serious issues on account of groundwater quality deterioration due to contamination with several dangerous chemicals such as arsenic and fluoride

Arsenic is well-known to be a carcinogen (cancer-causing substance) While cancer takes a longer time (more than 5 to 10 years) to develop, the most common clinical manifestations of arsenic poisoning are skin lesions Skin abnormalities caused by arsenic ingestion include hyper-pigmentation and keratosis Hyper-pigmentation leads to discoloured spots, dark brown spots and darkening of limbs, whereas keratosis shows up as thickening of palm and feet soles (Mazumder et al, 2010) The extent of arsenic impact on human health is related to the nutritional status of a person, such that the effects are more prominent for those who are malnourished and have low immunity (Das, Roy and Chakrabarti, 2016)

The arsenic-led groundwater crisis has burdened the lives of the affected populations, particularly the rural poor who use wells and tube-wells for sourcing drinking, domestic as well as irrigation water, in such a way that it has physical, economic and social impacts While physical impacts include weakness and other illnesses, the economic impacts due to added medical treatment, costs and       

1 Stage of groundwater development = (Annual groundwater draft for all uses / Net groundwater availability) * 100

* Madhavi Marwah Malhotra is a PhD scholar at the Centre for Economic Studies and Policy, Institute for Social and Economic Change, Bengaluru This paper is part of her ongoing PhD research She is grateful to the guidance received from her PhD supervisor, Prof Krishna Raj and doctoral committee members: Prof R S Deshpande, Prof

S Madheswaran and Dr A V Manjunatha Madhavi is also thankful to the two anonymous reviewers for their constructive suggestions on the paper The usual disclaimers apply

social impacts such as social exclusion, polygamy, threat of divorce and dowry demands, have further worsened their situation (Das, Roy and Chakrabarti, 2016) Wage loss due to arsenic poisoning in rural populations worsens the households’ economic condition (Indu, Krishnan and Shah, 2007) The causal relation between learning outcomes of secondary school children and drinking arsenic-contaminated water has also been established (Asadullah and Chaudhury, 2011)

Additional economic impacts of arsenic contaminated groundwater arise on account ofits use for irrigation purposes Several crops and crop varieties have been scientifically tested and proven to be susceptible to arsenic loading in irrigation water and soil in different quantities Crop vulnerabilities are known to be in the form of reduced yield, lower grain weight and uptake of arsenic in the crop, resulting in its entry into the food chain

In India, the state of West Bengal is severely affected with the groundwater aquifer in 11 out

of 23 districts (104 blocks) having reported arsenic levels much higher than the permissible limit for drinking water set by World Health Organisation at 0.01 mg per litre and even the less restrictive limit set by the Bureau of Indian Standards at 0.05 mg per litre These districts are Malda, Murshidabad, Nadia, North 24-Parganas, South 24-Parganas, Howrah, Hooghly and Bardhaman It can be observed that arsenic presence (orange and red area) is concentrated in the region to the east of the Ganges (see Figure 1)

While there are many competing explanations on the occurrence of arsenic in groundwater aquifers of the Indo-Gangetic Plain region, it is well established that arsenic is present in the underground rock formations and gets mixed with the groundwater

There are two types of rocks in this region – deep Pleistocene and Holocene depositions – where arsenic presence is known It gets mixed with groundwater due to processes like oxidations of different chemical compounds, pumping of groundwater from the aquifer, etc

Figure 1: Arsenic map of West Bengal

Source: Public Health Engineering Department, Government of West Bengal (2014)

This paper examines the impacts of arsenic-contaminated water irrigated on famers’ incomes through a field survey in four blocks in West Bengal characteristically differentiated in terms of the groundwater situation The study is relevant in the light of institutional developments aimed at increasing the use of groundwater for irrigation Based on the descriptive analysis of primary data supplemented with econometric analysis including Mann-Whitney U test for comparison of means of selected variables between arsenic and non-arsenic areas, we observe a negative influence of using arsenic contaminated irrigation water on farmers’ incomes Findings from the study are used in deducing policy suggestions for groundwater management in arsenic affected areas

Statement of the Problem

Arsenic contamination in groundwater is widespread and found to be much above the permissible/threshold limits for drinking (0.01 mg per litre by World Health Organization) and irrigation purpose (0.05 mg per litre by Food and Agriculture Organization) in the state of West Bengal Given the adverse impacts of using arsenic concentrated water on human health and agriculture, policies and programmes towards increasing groundwater extraction for agriculture in this region can have serious implications on the sustainability of agriculture as West Bengal is the largest rice producing state in India

Since the states which were once known as the ‘Food Bowl of India’ are unable to fulfil the food requirements of the growing population, the government has moved towards the eastern states to bring about a second Green Revolution in India (Government of India, 2015)

In this regard, the ‘Bringing Green Revolution to Eastern India’ scheme was launched in 2011 under the Rashtriya Krishi Vikas Yojana, covering the eastern States of Assam, Bihar, Chhattisgarh, Jharkhand, eastern Uttar Pradesh, Odisha and West Bengal Under this scheme, “100 percent assistance

is provided for construction activities (INR 30,000/ dug well/ bore well and INR 12000/shallow tube well)” (BGREI scheme guidelines) In addition, a 50 percent subsidy on cost of pumpsets, up to INR 10,000 has also been provided (ibid.)

Moreover, the state government of West Bengal is itself motivated to encourage groundwater extraction for irrigation purposes, to ensure agriculture sector growth To achieve this goal, two important initiatives have been taken in 2011 with the relevant government department committing to provide access to pumping facilities at reduced setup costs Specifically, in February 2011, the West Bengal State Electricity Distribution Company Limited (WBSEDCL) passed a policy resolution stating that

it would provide new electricity connections to farmers against a payment of a fixed fee amounting between Rs 1,000 and Rs 30,000 per connection, depending on the connected load This meant a reduction in expenses for farmers who would no longer bear the full cost of wires, poles and transformers, as required earlier (Mukherji, Shah and Banerjee, 2012).In addition, the Water Resources Investigation and Development Directorate (WRIDD) in Bengal, vide a memo dated November 9, 2011, changed a provision of the aforementioned Act As per this amendment, farmers located in “safe” groundwater blocks and owning pumps of less than 5 horsepower (HP) and tube wells with discharge of less than 30 cubic metres per hour would no longer need a permit from the State Water Investigation Department (SWID) to apply for electricity connection from WBSEDCL With this new amendment, farmers other than those in the semi-critical and critical blocks (53 semi-critical and 1 critical as of 2011;

76 semi-critical and 1 critical as of 2013) would be outside the purview of the Act, making it easier to put in an application for electricity connection in safe groundwater blocks (Mukherji, Shah and Banerjee, 2012; CGWB, 2013) As per the CGWB assessment, groundwater extraction for irrigation in West Bengal has increased from 9.72 billion cubic metres (bcm) to 10.84 bcm between 2011 and 2013

The point to be noted here is that the blocks in ‘safe’ category are assessed only with respect

to the depth of water level by the Central Ground Water Board (CGWB) It has no bearing on the quality aspect of groundwater, which means that the policies do not restrict groundwater extraction in ‘safe’

but arsenic contaminated blocks Table 1 below shows groundwater extraction for irrigation in arsenic

affected blocks of West Bengal over the years from 2009 to 2013

Table 1: Groundwater Extraction for Irrigation (bcm) in Arsenic Contaminated Districts of WB

With respect to linkages between the level of arsenic content in groundwater and groundwater

extraction, Ghosh and Singh (2009) report that arsenic gets mobilized into the aquifer with continuous

groundwater pumping The concentration of arsenic, however, is known to be higher in the shallow

aquifers of the Bengal Delta Plain The deep, confined aquifers are relatively free from arsenic, whereas

the shallow unconfined waters are the contaminated ones (Government of West Bengal, 2005)

Study Objective

Pitt, Rosenzweig and Hassan (2012) studied the impact of arsenic ingestion on incomes of rural

households in Bangladesh using household expenditure data and found evidence of lower labour

productivity due to the health impacts of arsenic intake They further estimated its impact on women’s

productivity in doing household work Similarly, men, who are the primary wage earners, had a lower

labour productivity and therefore had lower than usual working and earning capacity due to the intake

of arsenic The consumption of purchased goods and production of household goods were found to be

significantly lower for households which use arsenic contaminated tubewell water for drinking and

cooking purposes

Impacts in terms of decline in crop productivity and deteriorating soil fertility are likely to

increase the cultivation costs and squeeze the profit margins for the already impoverished

agriculture-based population However, to the best of the authors’ knowledge, there is no study to have estimated

the loss of farmers incomes on account of lower crop yields and higher cultivation costs other than

labour To fill this gap in literature, the study aims to estimate the monetary impact on farmers’ incomes

of irrigating with arsenic-contaminated water

The study has its limitations in the sense that it considers the impacts only in terms of realised

costs of cultivating crops The impact on family labour productivity and costs due to additional hired

labour thereof is complex and therefore a statistical significance test is carried out to compare all

variables of interest across the arsenic and non-arsenic sample areas Gross returns to a farmer from

production include only the returns from selling the main crop output and not those received on account

of by-products Further, it fails to attribute the income losses to different factors causing a yield decline

or low selling price, i.e how much is on account of arsenic and how much is due to other factors

Review of Literature

™ Occurrence and mobilization of arsenic in groundwater

Developments in natural sciences have been engaged in understanding the occurrence and mobilisation

of arsenic in groundwater Primarily, arsenic occurs in two forms: trivalent and pentavalent states, i.e Arsenite As(III) and arsenate As(V) respectively The toxicity of various forms of arsenic strongly depends on their oxidative states and chemical structures The inorganic forms of arsenic present in soil, when taken up and transported through the food chain, turn out to be toxic, affecting various life forms Among the two oxidation states As(III) and As(V), As(V) is less toxic and mostly present in immobile mineral forms, whereas the As(III) form is more toxic and gets mobilized into water and enters living cells (Shrivastava et al 2015)

Ravenscroft et al (2009) have described four geochemical mechanisms of natural arsenic pollution: reductive dissolution, alkali desorption, sulphide oxidation and geothermal activity, of which the first is the most relevant in the South Asian context Reductive dissolution occurs when arsenic adsorbed2 to iron oxyhydroxides in sediments gets mixed with groundwater because of microbial degradation of organic matter which reduces ferric iron to the soluble ferrous form The presence of arsenic is in the relatively un-withered alluvial sediments derived from igneous and metamorphic rocks

in the Himalayas and related young mountain chains (Brammer and Ravenscroft, 2009) Similar results were reported by Nickson et al (2000) and UNICEF (2008) who find reductive dissolution of iron oxyhydroxides present in sediments as the source of arsenic release into groundwater in the Ganges Plain area of West Bengal and Bangladesh

In another study, Smedley and Kinniburgh (2002) found that high-arsenic groundwater was not related to areas of high arsenic concentration in the source rock Two key factors were identified: first, there should be very specific biogeochemical triggers to mobilize arsenic from the solid phase to groundwater, and second, the mobilized arsenic should have sufficient time to accumulate and not be flushed away, that is, it should be retained in the aquifer In other words, arsenic released from the source should be quick, relative to the rate of groundwater flushing There are a number of processes for the mobilization of arsenic in groundwater namely, (i) mineral dissolution, (ii) desorption of arsenic under alkaline and oxidizing conditions, (iii) desorption and dissolution of arsenic under reducing conditions, (iv) reduction of oxide mineral surface area, and (v) reduction in bond strength between arsenic and holt mineral surface (Smedley and Kinniburgh, 2002)

Oxidation of sulphide minerals (pyrite-FeS

2) is another hypothesis which has been conceived as the cause of groundwater arsenic contaminationin West Bengal According to this hypothesis, arsenic is released from the sulfide minerals (arseno-pyrite) in the shallow aquifer due to oxidation (Mandal et al, 1998) The lowering of the water table owing to over- exploitation of groundwater for irrigation is the cause of the release of arsenic Some investigators explained that excessive use of water for irrigation and use of fertilizers have caused the mobilization of phosphate from fertilizers down below the shallow aquifers, which have resulted in the mobilization of arsenicdue to anion exchange onto the reactive mineral surfaces Sikdar and Chakraborty (2008) asserted that the combined processes of recharge of       

2 Adsorption: the adhesion in an extremely thin layer of molecules (as of gases, solutes or liquids) to the surfaces of solid bodies or liquids with which they are in contact (Merriam Webster dictionary)

groundwater from rainfall, sediment water interaction, groundwater flow, infiltration of irrigation return water (which is arsenic rich due to the use of arsenic-bearing pesticides, wood preservatives, etc and the pumping of arsenic-rich groundwater for agriculture purpose), oxidation of natural or anthropogenic organic matter and the reductive dissolution of ferric iron and manganese oxides, are the key factors in the evolution of groundwater arsenic contamination in the area It seems that there are a number of hypotheses, which have their own discrepancies and limitations to explain the physical processes

Shrivastava et al (2015) report that arsenic mobilization in the Bengal Basin can happen due

to the discharge of arsenic into alluvial sediments by the oxidation of arsenic-containing pyrite, and displacement of anions of arsenic present in aquifer sedimentary minerals by phosphate anions used

in fertilizers which are applied on the soil surface, and discharge of arsenic in anoxic conditions by the reduction of iron oxyhydroxide during sediment burial

Specifically, for India, Ghosh and Singh (2009) report that the release of arsenic, by the

natural processes in groundwater, has been recognized, from the Holocene sediments comprising sand, silt and clay in parts of the Bengal Delta Plains (BDP), West Bengal and in the Gangetic plains of Bihar Several isolated geological sources of arsenichave been recognized, viz Gondwana coal seams in Rajmahal basin, Bihar mica-belt, pyrite-bearing shale from the Proterozoic Vindhyan range, Son valley gold belt and Darjeeling Himalayas belt The contaminated aquifers are of Quaternary age and comprise micaceous sand, silt and clay derived from the Himalayas and the basement complexes of eastern India These are sharply bound by the River Bhagirathi-Hooghly in the west, the rivers Ganges and Padma in the north, the flood plain of the River Meghna and the River Yamuna in the northeast (Ghosh and Singh, 2009)

Another important finding in the literature is the high degree of spatial variation in arsenic levels over a few metres of the same aquifer as well as lateral variation in the same well at different depths (The World Bank, n.a.) This means that generalization with a few sample tests lacks credibility and rather a more wide scale individual testing of all wells is needed to ascertain the extent of contamination

Furthermore, the linkage between groundwater pumping and arsenic mobilization, although not well established, has been brought under discussion In this context, it is suggested that groundwater development should be undertaken cautiously after thorough laboratory tests and assessment of potential threats of contamination in unexploited areas or of worsening arsenic levels in already exploited regions (UNICEF, 2008)

™ Agronomic impacts of irrigating with arsenic contaminated water

While arsenic is well-known to be extremely harmful to human health through both external exposure to the skin as well as consumption of arsenic-contaminated water, another branch of literature deals with understanding the impacts of using the same for irrigation purposes

Since the last decade or so, research on irrigation with arsenic-rich water has received much attention, primarily due to the increasing dependence on groundwater as a major source of irrigation and its role as a critical input in producing food for the burgeoning population In South Asia,

Bangladesh is the worst affected by arsenic contamination in terms of both population at risk as well as areal extent, followed by India

Here, we explore the existing literature to understand the following relevant issues: What are the impacts on crops of irrigating with water contaminated with arsenic? Within each impact, what are the heterogeneities across different crops and crop varieties? What are the impact mechanisms? What

are the possible impacts on other agricultural inputs like soil and labour?

There are three main impacts on crops identified from the literature These are: Crop uptake of arsenic and impact on crop yield We also find a negative impact on tangible agricultural inputs like soil The following three sub-sections discuss each of these impacts and the related heterogeneities

Arsenic uptake by crops

Several studies have confirmed the uptake of arsenic by different crops when irrigated with arsenic-rich water and grown in arsenic accumulated soil However, the amount and type of arsenic found in crops tends to differ, depending on several other factors including crop type, crop variety, soil type and so on Therefore, it is safe to say that the relationship between the arsenic level in irrigation water and soil, and the amount of arsenic uptake in crops, is extremely complex

A majority of the arsenic affected areas in India and Bangladesh have a rice-based cropping pattern with three rice seasons in a year and studies show differences in arsenic uptake of rice grown during different parts of the year Analysis of rice samples of both winter and summerseasons of year

2000 from four selected villages in Bangladesh, representative of different agricultural and soil conditions as well as different rice varieties, was undertaken by Duxbury et al (2003) The study revealed arsenic content in summer rice (108 to 331 mg/kg) was higher than that grown in winter season (72 to 170 mg/kg) and mean arsenic level in summer rice was 1.5 times more as compared to winter rice (at 5 percent level of significance) Similarly, a statistically significant difference was found in grain arsenic content of winter and summer rice samples collected from the same districts, such that arsenic level in summer rice was 1.3 times higher than winter rice (Williams et al 2006) The primary reason for such a result is that summer rice is entirely dependent on irrigation, which is largely groundwater based and so there is much more arsenic addition during this time of cultivation The arsenic uptake by winter rice is a residual impact of arsenic-rich irrigation during summer cultivation Winter rice is majorly rainfed but the arsenic accumulation in soil during summer cultivation causes the arsenic uptake during this season

Another important factor in paddy cultivation is the soil condition – aerobic or anaerobic In the aerated soils, arsenic presence is in arsenate (AsV) form, which is mostly unavailable for crop uptake as arsenate gets adsorbed by iron hydroxides In anaerobic soils like flooded paddy cultivated lands, arsenic is readily available to crops since it is present in its reduced form, i.e arsenite (AsIII) (Brammer and Ravenscroft 2009; Xu et al 2008)

Arsenic accumulation in crops is also determined by the longevity of groundwater irrigation in the affected regions This can be explained by the long-term arsenic buildup in the soil due to continuous irrigation with the contaminated water In a Bangladesh study, Williams et al (2006) analyzed 330 winter and summer rice samples, 94 vegetables, 50 pulses and spices samples for arsenic

and reported the highest arsenic rice grain levels in the samples from south-west districts These districts are characterized by high arsenic water concentrations, extensive use of shallow tube wells for

rice cultivation and a much longer history of groundwater irrigation

Not all crops take up equivalent amounts of arsenic In a China-based study, comparing arsenic accumulation in wheat and rapeseed, it was found that wheat accumulates more arsenic than rapeseed (Liu et al 2012) While both wheat and rapeseed were found suitable for cultivation given soil arsenic content of 0 to 60 mg/kg, rapeseed is preferable beyond 80 mg/kg A more general finding is that plants belonging Cruciferae type such as mustard, rapeseed etc have high tolerance to arsenic (Liu

et al 2012; Chaturvedi 2006; Zhong et al 2011)

Williams et al (2006) report substantial differences in the arsenic levels between and within different types of vegetables, the mean maximum arsenic concentration being higher in the root and tuberous vegetables than the fruit vegetables, and lowest in leafy vegetables Similar findings were reported from West Bengal in the report of the Inter-Ministerial Group (IMG) on Arsenic Mitigation (2015) They state higher arsenic accumulation in potato, brinjal, arum, amaranth, radish, ladies finger, and cauliflower, and relatively low levels of arsenic accumulation in beans, green chilli, tomato, bitter gourd, lemon and turmeric The major oil seeds and pulses have been found to contain a high arsenic content Moreover, the high yielding rice varieties have more arsenic accumulation than the local varieties (IMG on Arsenic Mitigation, 2015)

Furthermore, even within crops, different parts of the plant take up different arsenic quantities

In rice crop, the arsenic accumulation in ascending order of plant parts follows the order: economic produce, leaf, stem, root (Das et al, 2013) For rice in particular, the accumulation followed the order: root, straw, husk, grain with highest arsenic accumulation in the root and lowest in grain (Abedin et al, 2002)

Although the present study does not look into human health or food chain implications of arsenic contamination, understanding these dynamics within arsenic uptake by crops would prove to be useful in developing holistic adaptation strategies which address both human health and economic impacts including productivity in terms of cropping pattern in affected areas

Arsenic impact on crop yields

Theoretically, Heikens (2006) explains the process and trajectory of arsenic accumulation in soil and the resultant impact on crop yields due to continuous irrigation with arsenic contaminated water (see Figure 2)

Figure 2: Arsenic Accumulation in Soil and Impact on Crop Yields

As arsenic from irrigation water accumulates in the soil, crop concentrations of arsenic also tend to increase beyond a point, depending on bioavailability, uptake and transport However, after a certain level of soil arsenic content, the plant growth becomes severely inhibited and arsenic concentration in the plants are then no longer relevant, as shown by the dotted line Crop yields may not be severely affected until a threshold level, beyond which yields will fall sharply (Heikens, 2006)

A substantial number of scientific research studies point towards crop yield reduction due to continuous irrigation with arsenic concentrated water Khan et al (2010) for instance found that arsenic addition in either irrigation water or as soil-applied arsenic resulted in yield reductions from 21 to 74 percent in summer rice and 8 to 80 percent in winter rice, the latter indicating the strong residual effect

of arsenic on subsequent crops

Hossain (2005) also found yield reductions of more than 40 and 60 percent for two popular rice varieties (BRRI Dhan-28 and Iratom-24), when 20 mg/kg of arsenic was added to soils, compared

to the control In a controlled pot experiment study, Abedin et al (2002) found that contaminated irrigation water accounted for 26, 38, 56 and 65 percent rice yield reduction by the addition of 1, 2, 4 and 8 mg arsenic respectively for BR-11 variety

arsenate-Moreover, the number of rice grains (filled spikelets) also decreased significantly (at 1 percent level of significance) to 120, 106, 77 and 61 with 1, 2, 4 and 8 mg arsenic treatment, respectively as compared to 160 in the control group Abedin et al (2002) also observed a decline in the weight of rice grain with arsenic addition such that the highest thousand grain weight (i.e., mass of 1,000 grains) of 19.8 grams was found in the control case which decreased to 18.3 grams in the highest arsenate treatment case Azad et al (2012), Panaullah et al, (2009), Huq et al (2006) and Pigna et al (2009) all present similar findings

In another study by Das et al (2013), the number of active seedlings per pot was unaffected until 15 mg/kg of arsenic addition in soil, but was reduced significantly beyond this level in the case of summer paddy The study found that filled and matured grains per panicle were reduced substantially after 10 mg/kg of soil arsenic as compared to the control pot, the decline being65.2 percent with 60 mg/kg of soil arsenic As far as yield was considered, the decline was as high as 80.8 percent in the case of 60 mg/kg arsenic content in soil (Das et al, 2013)

Yields of sixteen potato varieties were tested for arsenic accumulation in Bangladesh, which revealed that there was a negative influence of arsenic on potato yield in different degrees (Haque et al 2015) The impact was as high as 66 percent reduction in ‘Jam Alu’ variety with 50 mg/kg arsenic addition in soil (ibid.)

Wheat and mustard seem to be less sensitive than potato to arsenic contaminated soils, which possibly explains the cropping pattern across the sample blocks In a study in China, Liu et al (2012) found that there was no impact of arsenic until 60 mg/kg of arsenic concentration in soil and yield reduction was observed only beyond 80 mg/kg of arsenic For mustard, there is no conclusive evidence indicating adverse impact on its yield

The point at which arsenic accumulation in soil reaches a ‘toxic level’ or ‘upper limit’ is not clear and varies with crop and crop variety Das et al (2008) for instance, show that only arsenic levels exceeding10 mg/kg arsenic in soils affect plant productivity and growth Meharg and Rahman (2003)

confirm these findings, citing similar adverse crop impacts when soil arsenic levels exceed 10 mg/kg Some other studies suggest that the upper toxic limit is higher In short, there is no single level of soil arsenic that is toxic to crops, and different tolerance levels between crops and crop cultivators need to

be taken into account in all studies which measure arsenic toxicity to crops and changes in yields (Brammer and Ravenscroft, 2009)

Particularly, in rice plant, Das et al (2013) find that chlorophyll content was reduced significantly beyond 25 mg/kg of arsenic addition in soil because of change in the shape of the chloroplast This is responsible for lowering of rice yield in the presence of arsenic Further, the study revealed that the leaf tip of the rice plant turned red; there was a lateral expansion of the leaf blade after 25 days of sowing which eventually led to yellowing of the leaves

Arsenic accumulation in soil

Arsenic in soil could be in inorganic or organic form Inorganic forms of arsenic are more prevalent than the organic forms The inorganic components are often in mineral form, whereas the organic form is mostly present in living organisms due to arsenic consumption (Shrivastava et al (2015)

The bioavailability of arsenic in soil is strongly affected by the chemical and physical properties

of the soil along with mineral composition, clay content, organic matter, texture, pH and Eh, exchange capability, content of oxides and hydroxides of aluminum, manganese and so on

cation-Fine-grained soils limit the quality of all arsenic species as compared to coarse-grained soils However, if the iron and aluminum hydroxides content in soil is low, arsenic tends to be more mobile Moreover, in the presence of less-soluble mineral parts and ionic forms which strongly adsorb to soil particles or co-precipitate with various minerals, the bioavailability of arsenic in the soil reduces Aging and sequestration are other factors which influence arsenic accumulation in soils

Clayey soil contains more iron hydroxide as compared to sandy soil, and hence clayey soils bind greater amount of arsenic In anaerobic condition under microbial activity or reductive conditions, arsenic held by iron oxyhydroxides is freely released In aerobic conditions, iron oxyhydroxides become insoluble and therefore are unable to release much arsenic

The behaviour of arsenic is not like that of other metal contaminants Arsenic is very soluble in neutral to alkaline pH (6.6-7.8) whereas most other heavy metals require acidic conditions for getting dissolved However, arsenic can also be moderately soluble in acidic conditions This makes its chemistry more complex than that of other contaminants

As(III) and As(V) get adsorbed onto the surface of Fe(OH)3, but the adsorption of As(V) is much higher than As(III) In general, highly oxic soils sorb more As(V) than soils containing small amounts of oxic minerals Iron, aluminum and calcium are very important factors in affecting the arsenic fixation in soil Moreover, the sorptive capacity of a soil for an ion is a function of its surface area and therefore, its clay content which is why arsenic is more soluble in sandy soils vis-à-vis fine-textured soils (Shrivastava et al 2015)

Land and soil degradation on account of prolonged usage of arsenic concentrated water for irrigation is a debatable topic, with one group of researchers documenting a positive causal relationship

between arsenic affected groundwater irrigation and higher arsenic content in soil whereas another set

of studies show significant variations between the arsenic levels in irrigation water and soil

Examining the paddy cultivated areas throughout Bangladesh, Meharg and Rahman (2003) observed higher arsenic levels in soils where arsenic content in groundwater used for irrigation was high and where there was a longer duration of tubewell irrigation Similar findings were reported by Norra et

al (2005), Roychowdhury et al (2005)), Das et al (2008) and Sarkar et al (2012)

Hossain (2005) observed topsoil arsenic content ranging between 61 mg/kg in the field which was nearest to the well and 11 mg/kg at the site at the far side of the command area, at Faridpur site (Bangladesh) with a history of 20 years of well irrigation A similar finding was reported by Dittmar et al (2007) which found consistent decline in arsenic concentration in soil from field inlet site (23 mg/kg) to the far end of the field (11.3 mg/kg) Brammer and Ravenscroft (2009) explain that such differences within command areas and within fields would increase over time

The level of arsenic in irrigation water and soil water are usually different Heikens (2006) states that arsenic content was more in irrigation water than soil water in non-flooded condition due tosorption of iron hydroxides On the other hand, the situation was the reverse in the flooding conditions as arsenic concentration in soil water exceeded that in the irrigation water After analysing the complex relationship between arsenic and other chemicals often present in soil such as phosphate, iron, etc., Heikens (2006) concludes that the arsenic concentration in irrigation water and arsenic in soil also depend on the soil chemical portfolio

The other branch of literature suggests no direct relationship between high arsenic levels in groundwater used for irrigation and elevated soil arsenic concentration The study identifies certain factors which influence the extent of arsenic accumulation and retention in the soil Heikens (2006) and Duxbury et al (2009) explain how soil texture plays an important role in the given context, with clayey soils having a higher capacity to bind arsenic than sandy soils The phosphorous and iron content in the irrigation water are other determinants of the arsenic retention in soil when irrigated with arsenic-rich water (Duxbury et al 2007) Moreover, there is likely to be some amount of arsenic leaching out during the monsoon season which in turn can reduce arsenic levels in the soil (Pal et al 2009; Dittmar et al 2007)

These studies thereby suggest at least some degree of soil degradation on account of irrigation with contaminated water Heikens (2006) reports that groundwater extraction for irrigation from the shallow aquifer leads to an addition of 1 million kg of arsenic per annum to the arable soil in Bangladesh Due to the accumulation of arsenic in the soil on account of continuous irrigation with arsenic-rich groundwater, Heikens (2006) anticipates deterioration in soil quality and decline in crop yields Therefore, what is interesting to explore are the impacts of this arsenic accumulation in soil in terms of agricultural productivity and finding out that threshold level at which such impacts occur

Sampling frame

The sampling technique used for the study is purposive three stage random sampling Since there is no established relationship between groundwater depletion and the level of arsenic contamination, we identified four blocks by segregating blocks based on variation in groundwater quantity and quality

parameters Quantity depletion of groundwater is based on the assessment of long-term changes in the pre and post-monsoon water level below the ground, and groundwater quality dimensionis confined to the extent of arsenic contamination

Table 2: Criteria for Selection of Blocks

High arsenic level in groundwater No arsenic in groundwater

In other words, the blocks chosenare such that:

(I) 1 block with highest average arsenic contamination among the groundwater depleted blocks; (II) 1 block with highest average arsenic contamination among the non-groundwater depleted blocks; (III) 1 block with high groundwater depletion but no arsenic contamination; and

(IV) 1 control block with neither depletion nor arsenic contamination

The groundwater depletion and non-depletion categorisation of blocks is based on the classification by the Central Ground Water Board (CGWB) into ‘over-exploited’, ‘critical’, ‘semi-critical’ and ‘safe’ The latest available assessment of blocks is from the year 2013 As per the latest CGWB assessment in 2013, out of 231 blocks in the state, 76 blocks were ‘semi-critical’ and 1 block was

Yes/No No/Yes Semi-critical

Yes Yes Critical

Yes Yes Over-exploited

Source: Groundwater Estimation Committee 1997 report, CGWB

The data on arsenic level in groundwater is available from the Public Health Engineering Department (PHED), Government of West Bengal which regularly monitors this parameter by testing samples from specified drinking water wells and tube wells across the state PHED publishes well-wise data on arsenic levels above the permissible limit of 0.05 mg/l in drinking water wells across the state with details on location of the well The latest arsenic level data is available for the year 2015-16 and therefore we compute block-wise average arsenic levels for 2015-16 for all blocks in the state

However, the depth of the well from which the water sample is collected is not known Hence the methodology assumes that the depth of the well does not alter the arsenic level in groundwater and

level of arsenic in (deeper) drinking water wells is a good proxy for the level of arsenic in (shallow)

wells and tube wells used for irrigation

A sample of 55 to 60 households from each block, covering two villages in each block, were

surveyed using an interview schedule, such that the total sample size was 230 households for the

agricultural year 2016-17 The villages and sample households in each village were selected through a

random sampling procedure

(I) Groundwater depletion and high arsenic contamination – Raninagar-II block

Out of the 77 blocks (semi-critical and critical blocks) facing groundwater depletion, 26 blocks

also face arsenic contamination of groundwater Assuming similar depletion level among the blocks as

all are classified as ‘semi-critical’, we choose the block with the highest average arsenic level in

2015-16 The top three blocks ranked from high to low average arsenic level in 2015-16 are shown in table 3

Raninagar-II in Murshidabad district is the selected block It consists of 30 villages

Table 4: Top Three Blocks with Highest Average Arsenic Level Among Semi-Critical Category 3

observations Average arsenic level (mg/l)

Murshidabad Raninagar-II Semi-critical 953 0.235

Murshidabad Domkal Semi-critical 1,241 0.154

Murshidabad Raninagar-I Semi-critical 986 0.153

Source: PHED and CGWB

(II) High arsenic contamination but no groundwater depletion

Out of 177 blocks in ‘safe’ category, 46 blocks are contaminated with arsenic in groundwater The top

three blocks ranked from high to low average arsenic level in 2015-16 among non- groundwater

depleted blocks are shown in table 4 Basirhat-I in North 24-Parganas district is the chosen block This

block consists of 59 villages

Table 5: Top Three Blocks with Highest Average Arsenic Level Among ‘Safe’ Category 4

observations Average arsenic level (mg/l)

North 24-Parganas Basirhat-I Safe 867 0.201

Source: PHED and CGWB

3 Sagardighi block in Murshidabad district had the highest arsenic level on average among all semi-critical blocks

But the number of data points / wells from which arsenic level is reported, was one Assuming this block to be an

outlier, it has been left out

4 Sandeshkhali-I block, in North 24-Parganas, with data from one well shows the highest arsenic level in 2015-16

among all the ‘safe’ blocks and can therefore be considered as an outlier

(III) No arsenic contamination but groundwater depleted

As per CGWB (2013) assessment of changes in groundwater depth (metres below ground level), there

is only one block in the state of West Bengal which has been categorised as ‘critical’ Being categorised

as ‘critical’ in terms of groundwater exploitation implies that there is significant long-term decline in either pre-monsoon or post-monsoon water level (refer to Table 3) There is no arsenic contamination

by far in this block and therefore it would be the most appropriate block in the no arsenic and high depletion category Goghat-II in Hooghly district is, therefore, the chosen block It consists of 110 villages

(IV) No groundwater depletion and no arsenic contamination

The control category block was selected randomly from non-arsenic ‘safe’ blocks in the same

agro-climatic zone as the treatment blocks and the villages within are selected randomly from those with dependence on groundwater for irrigation Ausgram-I in Bardhaman district was the selected block

Profile of Sample Villages and Households Table 6: General Profile of Sample Villages (as of 2011)

Category Arsenic, depleted Arsenic, non- depleted Non-arsenic, depleted Non-arsenic, non- depleted

Village Rakhaldaspur Godhanpara Sankchura Panitar Satberia Agai Alefnagar Warishpur

Gram

Panchayat Malibari-I Raninagar-I Sankchura Bagundi Itinda Panitar Kamarpukur Bengai Ausgram Ausgram Population - 14,173 2548 13,947 1378 2090 2278 2223 Households - 3352 596 3177 290 448 593 579

SC / ST - 0.8% 11.2% 42.5% 61.7% 55% 40% 39% Literacy - 59.2% 69.8% 74.2% 77.8% 75.1% 71.7% 69.4% Source: Census of India 2011, Ministry of Home Affairs, Government of India

Almost all villages have high proportion of SC/ ST population, comprising over 40 percent of total population except in Godhanpara and Sankchura The literacy rate across the villages is fairly reasonable ranging from 60 percent to 78 percent

Table 7: Season-wise Size of Operational Landholding (in hectares) in the Sample Blocks

Arsenic, depleted non-depleted Arsenic, Non-arsenic, depleted non-depleted Non-arsenic,