Risk of arsenic contamination in groundwater: response from Chakraborti et al.

We would like to reply to Acharyya and Shah's comments on our paper (Chakraborti et al. 2003) First, Acharyya and Shah should better document their statements. For example, in their discussion of the relationship of iron oxyhydroxide to arsenic, they state that

   Reduction of FeOOH is common and intense in
   the Bengal Basin as shown by a maximum level of
   dissolved Fe concentration ([less than or equal to] 9-36 mg/L)
   (Acharyya et al. 1999; British Geological Survey
   1999; Nickson et al. 1998).

In none of these articles, including Acharyya et al. (1999), did we find mention of dissolved Fe in the Bengal Basin at the value of 9-36 mg/L.

In fact, in Nickson et al.'s (1998) report on the distribution of dissolved Fe ([less than or equal to] 29 mg/L) in 46 wells in Bangladesh, their Figure 1 showed that the distribution of Fe in 46 samples was between close to 0 and 29 mg/L, and most of the samples were from 1 to 10 mg/L. Also, in the British Geological Survey's (1999) report on the frequency distribution of the total dissolved Fe concentration in a regional survey of wells, the distribution was determined for 1,534 wells. Of these, 23% of samples contained < 0.3 mg/L Fe, 17% contained 0.3-1.0 mg/L, 11% contained 1.0-2.0 mg/L, 38% contained 2.0-5.0 mg/L, and 10% contained > 5.0 mg/L. Thus, we found that the available data do not support the value of 9-36 mg/L of dissolved Fe in the Bengal Basin.

In their letter, Acharyya and Shah stated that "The concentration of dissolved Fe in groundwater is generally low (< 1 mg/L) in the Ganga Alluvial Plain (Acharyya et al. 2000)." However, Acharyya et al. (2000) actually stated that

   The dissolved iron in groundwater in the Ganges
   basin in [Uttar Pradesh] and Bihar states in India
   is reported to have trace concentrations of
   1.0 mg/L compared with values up to 36 mg/L in
   the south of West Bengal (Acharyya and others
   1999) and 30 mg/L in Bangladesh (Nickson and
   others 1998).

Further, Acharyya et al. (1999) stated that "the groundwater of Uttar Pradesh and Bihar has trace concentrations of iron (0 to 0.7 [mg/L])...." We have some reservations about the zero Fe concentration in 0-0.7 mg/L, and we also find an inconsistency between the "trace concentration of 1 mg/L" (Acharyya et al. 1999) and "< 1.0 mg/L" (Acharyya et al. 1999). However, it would have been helpful if Acharyya et al. (1999, 2000) had provided information about the sources of the data, how many samples were analyzed, and who analyzed them.

Without providing experimental evidence or citing other sources for data, Acharyya et al. (2000) reported that floodplains of the Jamuna and Old Brahmaputra Rivers in the Bengal Basin were free of arsenic, whereas the British Geological Survey (1999) and Chowdhury et al. (1999) established that hand tube-well water in floodplains of the Jamuna and Old Brahmaputra Rivers is contaminated with arsenic.

In their letter, Acharyya and Shah stated that "pyrite or arsenopyrite is absent or very rare in aquifer sediments from the Bengal Basin (Acharyya et al. 1999, 2000)." However, Acharyya et al. (1999) did not cite any reference of their own work or provide an analysis of bore-hole sediments to prove the absence of pyrite or arsenopyrite. Does citing these two published articles (Acharyya et al. 1999, 2000) that do not include experimental evidence prove Acharyya and Shah's comment? They seem to think so.

It is extremely interesting that in an earlier article, Achyrra (1997) stated,

   Excessive withdrawal of groundwater, [e]specially
   [in] summer when recharge is low, might lead to
   induced oxidation of aquifer material by
   increased access of atmospheric oxygen. Under
   such conditions the arsenopyrite/pyrite grains
   now known to be present in the aquifer material
   would be decomposed and arsenic will be
   released into the groundwater.

This is exactly what we reported earlier (Das et al. 1996).

In their letter, Acharyya and Shah comment that

   Chakraborti et al. (2003) misquoted our previous
   work (Acharyya et al 2000) when they stated that
   the source is confined to the "Chotonagpur [and]
   Rajmahal Highlands."

In the statement to which they refer, we (Chakraborti et al. 2003) cited both Acharyya et al. (2000) and Saha et al. (1997).

Acharyya et al. (2000) stated that

   The environment is not sufficiently reducing in
   Ganges floodplains upstream of Rajmahal to
   mobilize iron and arsenic in groundwater.

They also stared that a possible source of arsenic contamination in the Ganges basin is the Gondwana coal seams in the Rajmahal Basin, which contain up to 200 ppm arsenic. On the basis of these statements, it appears that we have not misquoted Acharyya et al. (2000).

We have been studying Bihar for the last 14 months and Uttar Pradesh for the last 5 months. This work in progress will prove that the Semria area is not an isolated case and that dissolved iron in the Ganga Alluvial Plain is not "generally low (< 1 mg/L)," as stated by Acharyya and Shah.

The authors declare they have no competing financial interests.

REFERENCES

Acharyya SK. 1997. Arsenic in groundwater--geological overview. Presented at Consultation of Arsenic in Drinking Water and Resulting Arsenic Toxicity in India and Bangladesh, 29 April-1 May 999, New Delhi, India.

Acharyya SK, Chakraborty P, Lahiri S, Raymahashay BC, Guha S, Bhowmik A. 1999. Arsenic poisoning in the Ganges delta. Nature 401:545.

Acharyya SK, Lahiri S, Raymahashay BC, Bhowmik A. 2000. Arsenic toxicity of groundwater in parts of the Bengal basin in India and Bangladesh: the role of Quarternary stratigraphy and Holocene sea-level fluctuation. Environ Geology 39:1127-1137.

British Geological Survey 1999. Groundwater Studies for Arsenic Contamination in Bangladesh. Main Report. London:UK British Geological Survey, Mott MacDonald Ltd., UK.

Chakraborti D, Mukherjee SC, Pati S, Sengupta MK, Rahman MM, Chowdhury UK, et al. 2003, Arsenic groundwater contamination in Middle Ganga Plain, Bihar, India: a future danger. Environ Health Perspect 111:1194-1201.

Chowdhury UK, Biswas BK, Dhar RK, Samanta G, Mandal BK, Chowdhury TR, et al. 1999. Groundwater arsenic contamination and sufferings of people in Bangladesh. In: Arsenic Exposure and Health Effects (Chappell WB, Abernathy CO, Calderon RL, eds). Amsterdam:Elsevier, 165-182.

Das D, Samanta B, Mandal BK, Chowdhury RT, Chanda CR, Chowdhury PP, et al. 1996. Arsenic in groundwater in six districts of West Bengal, India. Environ Geochem Health 18:5-15.

Nickson R, McArthur J, Burgess W, Ahmed KM, Ravenscroft P, Rahman M. 1998. Arsenic poisoning in Bangladesh groundwater [Letter]. Nature 395:338.

Saha AK, Chakraborti C, De S. 1997, Studies of genesis of arsenic in groundwater in parts of West Bengal. Indian Soc Earth Sci 24:1-5.

Dipankar Chakraborti

Sad Ahamed

Mohammad Mahmudur Rahman

Mrinal Kumar Sengupta

Dilip Lodh

Bhaskar Das

Mohammad Amir Hossain

School of Environmental Studies

Jadavpur University

Kolkata, India

E-mail: [e-mail]

Subhash Chandra Mukherjee

Medical College

Kolkata, India

Shymapada Pati

Niloy Kanti Das

S.S.K.M. Hospital

Kolkata, India