NATURAL ARSENIC IN GROUNDWATER: OCCURRENCE, REMEDIATION AND MANAGEMENT - CHAPTER 11 pot

Natural Arsenic in Groundwater: Occurrence, Remediation and Management – Bundschuh, Bhattacharya and Chandrasekharam eds © 2005, Taylor & Francis Group, London, ISBN 04 1536 700 X Arseni

Section 2: Environmental health assessment-arsenic in the food chain

Natural Arsenic in Groundwater: Occurrence, Remediation and Management –

Bundschuh, Bhattacharya and Chandrasekharam (eds)

© 2005, Taylor & Francis Group, London, ISBN 04 1536 700 X

Arsenic in groundwater and contamination of the food chain:

Bangladesh scenario

S.M Imamul Huq

Department of Soil, Water & Environment, University of Dhaka, Dhaka, Bangladesh

Ravi Naidu

Centre for Environmental Risk Assessment and Remediation (CERAR), University of South Australia, Mawson Lake Campus, Adelaide, Australia

ABSTRACT: Ingestion of arsenic (As) contaminated groundwater is the major cause of As poi-soning in Bangladesh However, poipoi-soning among the population is not consistent with the level

of water intake Moreover, there is also a spatial variation of the manifestation of arsenicosis in the country This has raised the question about the role of the food habit, nature and amount of food intake in the As dilemma Even if an As-safe drinking water supply is ensured yet, the same As contaminated groundwater will continue to be the main source of irrigation for about 40% of the net cultivable area as more than 60% of irrigation water comes from groundwater This leaves a risk of soil accumulation of the toxic element and eventual exposure of the food chain to As con-tamination through plant uptake and animal consumption Water (hand tube wells and irrigation pumps), soil and vegetables/crop samples collected from as many as 150 different locations cover-ing 15 districts of the country have revealed that the average background concentration of

As in Bangladesh is much below 10 mg/kg soil However, in some areas where soils receive As-contaminated groundwater irrigation, the concentration has been found to be as high as 80 mg/kg soil The soil As varies both spatially and vertically The soil formation and the aquifer characters control the spatial variation, while the vertical distribution is controlled by the clay contents The maximum As concentration in irrigation water was found to be 0.55 mg/L; irrigating a rice field with this water when the requirement is 1000 mm of water, it has been calculated that the As load will come to 5 kg As/ha/yr Many crops receiving As contaminated water as irrigation have been found to accumulate As at levels that exceed the maximum allowable daily limit (MADL) of 0.2 mg

per kg dry weight (dw) Some vegetables crops like Arum (Colocassia antiquorum), Kalmi (Ipomea

aquatica ), Amaranthus (Amaranthus spp.) etc were found to be As accumulators The transfer

fac-tor for As has been found to exceed the value of 0.1 in a number of plants indicating their affinity towards this element In Arum, the concentration of As have been found to be as high as more than

150 mg/kg dw Rice and wheat receiving As-contaminated irrigation water have been found to sequester the toxic metalloid into roots and stems However, the quantities of rice consumed per person per day with the content of As in the grain may in many instances, surpass the MADL

1 INTRODUCTION

Contamination of groundwater by arsenic (As) in the deltaic region, particularly in the Gangetic Alluvium of Bangladesh has become one of the world’s most important natural calamities In many areas of the country, water containing more than 0.05 mg/L As, a limit value set for drinking water has been reported (DPHE-BGS 1999) Efforts are being directed towards ensuring safe drinking water either through mitigation technique or through finding alternative sources Even if an As-safe drinking water supply is ensured the same groundwater will continue to be used for irrigation

purpose, leaving a risk of soil accumulation of this toxic element and eventual exposure to the food chain through plant uptake and animal consumption Between 30 to 40% of net cultivable land is under irrigation and more than 60% of this irrigation is met from groundwater

Studies in the last few years have focused on ingestion of As through intake of groundwater containing As The observation that As poisoning among the population is not consistent with the level of water intake has raised question on potential pathways of As ingestion In a preliminary

study from a village of Laksimpur, Huq et al (2001) observed that certain vegetables growing on

soil supposed to be affected by As contamination, accumulated substantial amount of As in them This observation prompted the authors to undertake further study to see the loading of arsenic in soils from irrigation water and subsequently to different crops growing on those soils

2 MATERIALS AND METHODS

For the study, information on As contamination in Bangladesh was obtained from secondary sources (DCH 1997, DPHE/BGS 1999) On the basis of the information, some areas were identified as con-trol (where groundwater As contamination was not reported), less affected, moderately affected, severely affected (according to the incidence of As patients) Thus water, soil, and vegetables/crop samples were collected from 143 locations, covering 13 districts of Bangladesh (Huq & Naidu 2003) Water samples from hand tube-wells or irrigation pumps were collected Soon after collection of water samples 2–3 drops of concentrated HCl was added to the vials containing water and transported to the laboratory for further analysis

Surface (0–15 cm) and subsurface (15–30 cm) soil samples were collected in replicate from locations covering the alluvial flood plains of Ganges, Teesta and Meghna-Brahmaputra rivers as well as from the Pleistocene terraces (Huq et al 2003) Arsenic poisoning was reported from all these areas except the Pleistocene terraces, which was taken as control for comparison In order to monitor the As load on soils from water, samples were collected from regions subjected to hand tube-well, shallow tube-well, and surface water irrigation Random grid sampling was adopted and from each site the number of samples collected ranged from 25 to 40 per acre After collec-tion, samples were air dried, ground and screened to pass through 0.5 mm sieve and stored in plas-tic vials and set for further analysis Replicate samples of consumable parts of the vegetables/crops commonly grown in the sampling area were collected

All plant samples were dusted free of adhering soil particles, washed with deionized water and 0.05 M HCl and then washed with deionized water 3 times to ensure dislodging of adhering dust particles Samples were then dried in oven at 60 5°C for 48 h, ground, screened to pass through 0.2 mm sieve, stored in plastic vials, and kept for further analysis The As in soil was extracted by digesting with aqua regia while As in plant samples was extracted with HNO3digestion (Portman & Riley 1964) Arsenic in water, soil extract, and plant extract was estimated by HG-AAS technique and certified reference materials were used to ensure QA/QC

3 RESULTS AND DISCUSSION

The As concentration in water used for irrigation was found to vary between 0.14 to 0.55 mg/L

So, for a Boro rice requiring 1000 mm of irrigation water per season, the load of As comes to between 1.36 to 5.5 kg/ha/yr Similarly, with winter wheat requiring 150 mm of irrigation water per season, the load of As is estimated to be between 0.12 to 0.82 kg/ha/yr The results on soil As indicated that the collected soils were not contaminated with As, and contained less than 10 mg/kg

As Expressed in terms of kg per hectare; the values did not exceed 20 kg/ha (Fig 1) Moreover, the As concentration was higher in the surface layer than the sub-surface layer with a few excep-tions in soils collected from Meghna Alluvium On the other hand, soils from arsenic

here that soils belonging to the Gangetic Alluvium contained higher amount of As than the soils belonging to the Teesta Floodplain Usually in soils contaminated through anthropogenic activity the arsenic contents may rise up to 50 mg/kg In the present study, although the source of As is geogenic (Nickson 1998) yet, in some cases the values were equal to that of anthropogenic activ-ity This is an indication of As accumulation in the soil due to irrigation

Results on As contents of the analyzed vegetables/crops showed that some of the vegetables/crops accumulated As in the plant tissues (Table 1) It is also apparently clear that plants of the same type growing on uncontaminated soil had much less As content in their tissues

For rice and wheat, most of the As taken up by the plants were sequestered in the roots and

leafy vegetables, particularly arum (Colocassia antiquorum) appeared to be an As accumulator.

This was true for all the areas studied (Fig 3), indicating that As from groundwater was entering into the food chain through soil to crops transfer

The levels of As in plants seldom exceed 1 mg/kg (Markert 1992) In the present study, quite a few plant samples had values much higher than this level Farago & Mehra (1992) have considered that when the plant/soil ratios for any particular element are 0.1, then the plant can be considered

as excluding the element from its tissues In our case, many plants have shown this phenomenon while some like arum and a number of leafy vegetables had shown the reverse phenomenon indicating

0 5 10

15

20

Pleistocene Alluvium soil

Alluvium soil Gangetic Alluvium soil

0-15 cm 15-30 cm

Figure 1 Arsenic content in different soils of Bangladesh.

Table 1 Arsenic content (mg/kg dw) in common plants from uncontaminated and

contaminated areas of Bangladesh.

Uncontaminated Contaminated

Green papaya (Carica papaya) 0.46 2.22

Arum (Colocassia antiquorum) 0.39 153.2

Indian spinach (Brasilia alba) 0.15 1.00

Bitter gourd (Momordicum charantia) 1.56 2.12

Aubergine (Solanum melongena) 0.23 2.3

their affinity to As accumulation (Table 2) It was observed that arum (Colocassia antiquorum)

showed very high accumulation of As when grown with As contaminated water This plant grows

in wet areas As a result it is all the time taking up As from groundwater Moreover, this plant is consumed very widely in the rural areas of Bangladesh It is a good source of vitamin A, C and Fe Every parts of the plant such as leaves, stems, rhizomes, and creepers are edible and are con-sumed For this reason, this plant was thoroughly analyzed The average As content in arum plants collected from different areas of Bangladesh is presented in Table 3

The maximum allowable daily level of As in foodstuff is taken as 0.22 mg per day (OEHHA 2003) On the basis of this level, calculations were made on the possibility of exceeding this MADL for the various plants analyzed For example, a person who daily consumes 100 g of arum that contains 2.2 mg/kg of As would have a MADL from arum alone However, when the concentration

0

20

40

60

80

Average Maximum Minimum

Figure 2 Arsenic content in different parts of rice plant.

Plant of Gangtetic Alluvium soil Plant of Meghna Alluvium soil Plant of Teesta Alluvium soil Plant of Pleistocene terrace soil

10

9

8

7

6

5

4

3

2

1

0

Arum Brinjal

Amaranthus

Gourd Onion Papaya

Indian spinach

Radish

Figure 3 Arsenic content in different crops collected from soils of various origin.

is as high as 22 mg/kg, only 10 g would give the MADL Similarly, 440 g of rice with 0.5 mg/kg would also represent the MADL Such inputs are comparable to drinking 4.4 L of water with 0.05 mg/L

On the basis of the As content in rice, the amount of average daily consumption, the extent of

As contamination in the area, the incidence of arsenicosis patients and the number of population

at risk to exposure of arsenic ingestion, the dietary load estimation, i.e., the possibility of the per cent of population risking the exposure to excess of MADL, has been calculated for Jessore (rep-resenting Gangetic Alluvium) and Rangpur (rep(rep-resenting Teesta Alluvium) areas In Jessore area, 32% of the people are above the MADL, while in Rangpur area the value is only 2% (Huq et al 2001) This again substantiates the fact that the groundwater in the Gangetic alluvial plain is more contaminated than the other parts of Bangladesh

Cooked food from the households of arsenic affected people were collected and analyzed Arsenic contaminated water has been used to cook these foods The foods contained various amount of As in them (Table 4) It is interesting to note that As could not be detected in cooked lentil soup, locally called “Dal” and in eggs The cooked rice contained different amounts of As; the differences could be due either to the variety of rice and also due to variation in the As content

in the cooking water It can be seen that in many of the cooked foods the values are well above the

Table 2 Arsenic transfer factors in different plants of Bangladesh.

Arsenic transfer Name of Arsenic transfer

Table 3 Arsenic content in arum collected from different locations of Bangladesh.

As content (mg/kg dw)

MADL of 0.22 mg/kg This is a matter of concern and it is an indication that As ingestion in human beings is affected not only through water but also through foodstuffs The food habit and the nutritional status of a person thus could be related to the manifestation of arsenicosis This, however, is also related to the biomethylation activity of the individual (Alauddin et al 2002) The above information indicates that there are other pathways of As ingestion in human body besides drinking water, and that is through food chain Crops receiving As contaminated irrigation water take up this toxic element and accumulate it in different degrees depending on the species and variety as well as on the type of soils on which these plants are growing

However, the portion of this As that goes directly to the different metabolic pathways and causes the problem of arsenicosis needs to be assessed The bioavailability of this arsenic in the different food materials also needs to be assessed In a preliminary study by the authors with swine feeding trials, it has been observed that 27% of the total amount of As in silverbeet and 82% of As in rice were bioavailable

ACKNOWLEDGEMENTS

The present work is a part of a joint research financed by Australian Center for International Agricultural Research (ACIAR) and the Ministry of Education, Government of Bangladesh

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