The arsenic
contamination in rice

 

Arsenic
(As) is a heavy metal that is well-known as a poison and a carcinogen. Its
average concentration in the soil ranges from 5 to 6 mg/kg which is generally
related to rock type and industrial activity.

Arsenic
contamination of paddy soils is widespread and elevated arsenic levels in rice
grains is now a hot issue in many parts of the world. Martha Rose Shulman wrote
in the New York Times (15 April 2013) that “it is clear that the levels of
inorganic arsenic in rice and rice products are high, and that we and
especially children, babies and pregnant women should limit our intake of rice
and rice products.”

 

According to Bogdan and
Schenk (2012) in their recent study published in the highly respected Journal
of Plant Nutrition and Soil Science (Wiley-VCH Verlag GmbH), flooded rice may
contain high arsenic concentration compared to other grain crops. In fact,
aside from arsenic-contaminated drinking water, rice is the largest food
dietary source of inorganic arsenic. This is because the reducing environment
in flooded rice fields causes the dissolution of arsenic and thus increases its
availability to the rice plant. Meharg (2004) added that under paddy field
conditions, inorganic arsenic introduced into the soil is inter-converted
between the reduced inorganic species arsenite (the dominant type) and the
oxidized species arsenate. Moreover, arsenite is taken up into the root by the
highly efficient Si pathway and arsenate can be taken up via the phosphate
transport system.

According to Bogdan and
Schenk (2012) in their recent study published in the highly respected Journal
of Plant Nutrition and Soil Science (Wiley-VCH Verlag GmbH), flooded rice may
contain high arsenic concentration compared to other grain crops. In fact,
aside from arsenic-contaminated drinking water, rice is the largest food
dietary source of inorganic arsenic. This is because the reducing environment
in flooded rice fields causes the dissolution of arsenic and thus increases its
availability to the rice plant. Meharg (2004) added that under paddy field
conditions, inorganic arsenic introduced into the soil is inter-converted
between the reduced inorganic species arsenite (the dominant type) and the
oxidized species arsenate. Moreover, arsenite is taken up into the root by the
highly efficient Si pathway and arsenate can be taken up via the phosphate
transport system.

 

Arsenic Contamination in Rice, Wheat,
Pulses,

and Vegetables: A Study in an Arsenic
Affected

Area of West Bengal, India

 

              Arsenic is one of the major
global environmental pollutants because of its highly toxic and carcinogenic properties.
The intake of arsenic by humans occurs through contaminated water and food. The
epidemiological studies show that the chronic arsenic poisoning can cause
serious health effects including cancers,melanosis (hyper-pigmentation or dark
spots and hypopigmentation or white spots) hyperkeratosis
(skinhardening),
restrictive lung disease, peripheral vascular disease (black foot disease),
gangrene, diabetes mellitus, hypertension, and ischemic heart disease (Guha-Mazumder
et al. 2000; Morales et al. 2000; Srivastava et al. 2001;Rahman2002).

             Arsenic seems to be a cancer
promoter rather than a cancer initiator (Lee-Feldstein 1986). The World Health Organization
(WHO) ranked this calamity as “the largest poisoning of a population in history”(Smithet
al. 2000). The presence of arsenic in groundwater has been reported in many
countries, like Argentina, Bangladesh, Chile, China, India, Japan, Mexico,
Mongolia, Nepal, Poland, Taiwan, Vietnam, and USA (Chowdhury et al. 2000;Smithetal.,2000;Anawaretal.2002;
Mitra et al. 2002;Pandeyetal.2002).

           Although the groundwater
contamination by arsenic is already considered as a serious global environmental
problem, it is not the only source for intake of arsenic in the human body.
Crops and vegetables grown on the arsenic-contaminated soils can also be a
source of arsenic for human beings (Williams et al. 2005), and itis especially
detrimental in the areas where drinking water arsenic concentration is more
than 0.05 mg l-1 (WHO 2001). US Food and Drug Administration, on the basis of
the total diet study, reported that food contributed 93% of the total intake of
arsenic (Adams et al. 1994). Studies on the impact of the arsenic-contaminated groundwater
irrigation on crops has attracted attention only during the last couple of
years (Roychowdhury et al. 2002; Duxbury et al. 2003; Ghosh et al. 2004; Samal 2005;
Norra et al. 2005; Huang et al. 2006; Rahman et al. 2007; Dahal et al. 2008;
Bhattacharya et al. 2009).

            Groundwater is the
major source of irrigation in the study area. For the past 15–20 years, higher
exploitation of groundwater has been done for the extensive cultivation of
rice, pulses, and vegetables to ensure food security. Thus, the potential of
arsenic contamination is increasing day by day in the groundwater of the study
area and enhancing the human health risk from arsenic toxicity via
water–soil–plant system. Results from the present investigation reinforced the
severity of arsenic toxicity of the irrigation water and soil in West Bengal,
India, and their influence in contaminating rice, pulses, and vegetables,
commonly consumed by the people living in and around the study area. Also, a
significant amount of the crops and vegetables are transported to the various
markets of West Bengal. Thus, probable indirect arsenic toxicity in the people
living in the non-arsenic-contaminated areas is also a concern. Other than a few
samples of potato, all the studied samples of rice, pulses, and vegetables
showed arsenic content below the food hygiene concentration limit of 1.0 mg
kg-1.

            Thus, the study does not indicate
an immediate danger, but the uptake of arsenic by agricultural plants should be
monitored periodically as there is high possibility of increase of arsenic in
the crops in near future, if the common trend of using arsenic contaminated
groundwater for irrigation continues. Proper watershed managements by minimizing
the excessive withdrawal of groundwater and by using available sources of
surface water (river, pond, etc.) for irrigation are to be done in an urgent
basis. In addition, crops requiring high irrigation should be replaced by the
crops requiring low irrigation in the arsenic-prone areas.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These works document the
enrichment of arsenic in soil and a limited uptake by different plants, including
rice, cereals, and vegetables. The reported arsenic concentrations in
agricultural plants varied from 0.007 to about 7.50 mg kg -1 (Mandal and Suzuki
2002; Roychowdhury et al. 2002; Liao et al. 2005; Dahal et al. 2008). Mandal
and Suzuki (2002), on their study on arsenic around the world, reported that the
arsenic concentration in plants varied from less than 0.01 to about 5.0 mg kg -1.
Roychowdhury et al. (2002), studying arsenic affected areas of Murshidabad, West
Bengal, India, found that the accumulation of arsenic in various food
composites (potato skin, leaves of vegetables, rice, wheat, cumin, turmeric
powder, and cereals) ranged between <0.0004 and 0.693 mg kg-1. Abedin et al. (2002) and Meharg and Rahman (2003) have reported about the rice samples with arsenic accumulation much above the WHO recommended permissible level of 1.0 mg kg-1. From their study in Bangladesh, Das et al. (2004) reported that the concentrations of arsenic in vegetables like Kachu sak (Colocasia antiquorum), potato (Solanum tuberosum), and Kalmi sak (Ipomea reptans) exceeded the food safety limits of 1.0 mg kg-1 (Abedin et al. 2002). Insimilar studies on the agricultural plants of China and Nepal, Huang et al. (2006) and Dahal et al. (2008 ) havefound that the arsenic accumulated in the range 0.003–0.116 and <0.01–0.55 mg kg-1 dry weight, respectively. In Haringhata block of our study area, arsenic accumulation (milligrams per kilogram) by rice (0.156–0.194) and crops (0.084–0.330) has been previously reported by Samal (2005). Not only uptake of arsenic but uptake of other metals by plants has also been studied by some researchers. Uptake of the metals As, Cd, Cu, Pb, and Zn in rice and pulses were reported by Alam et al. (2002). In a similar study, significantly lower amount of uptake and translocation of five toxic metals (Cd, Cr, Pb, As, and Hg) in the rice grain compared with the uptake in the rice straw and root parts have been reportedbyLiuetal.(2007). The arsenic concentration was further found to vary between different parts of the plants. Higher amount of arsenic was reported to accumulate in the root of the rice plant as compared with other parts (Norra et al. 2005;Rahmanetal.2007; Bhattacharya et al. 2009). People in West Bengal, India, have been reported to be suffering from groundwater arsenic toxicity for long (Chowdhury et al. 2000,2001). Over 50 million people living in the Ganga-Meghna-Bramhaputra plain are at the risk through severe arsenic toxicity (Chakraborty et al. 2004; Pal et al. 2007). Nine out of total 19 districts of West Bengal have groundwater arsenic contamination (Nickson et al. 2000; Chakraborty et al. 2002). Among the contaminated districts, the severely affected Nadia district deserves special mention in terms of level of arsenic contamination and area coverage (Samal 2005;Bhattacharyaetal.2009). In rural West Bengal, farmers are generally not aware of the Food and Agricultural Organization (FAO) guideline value of arsenic in irrigation water (0.10 mg l-1; FAO 1985), and as the irrigation system in these areas is mostly dependent on groundwater, there is a high possibility of transfer of arsenic from contaminated irrigation water and soil to crops. Thus, the objectives of the present study were to find the distribution of arsenic in irrigation water, soil, and crops and to assess the influence of arsenic-contaminated irrigation water and soil on rice, pulses, and vegetables cultivated in the arsenic affected five blocks of Nadia district, West Bengal. This study would help to evaluate the severity of human health risk from arsenic toxicity through water–soil–plant system.