Dear Dr. Imam/Dr. Acharyya:

In some of our articles, we used data collected by Dr. Chakraborti and his team.
I find that their data is unbiased and reliable. If their data was not reliable
then we would not use their data in our articles.

I respectfully request you to review the following paragraphs (from our article
"Arsenic Crisis: A challenge for scientiests to find the origin of arsenic that
caused the poisoning disaster in Bangladesh", published in The Bangladesh
Observer, November, NFB, 2000). These paragraphs are an analysis of sediment
and groundwater parameters used by Ross Nickson and others in support of the
"Oxyhydroxide Reduction Hypothesis".

[Ross Nickson et.al wrote the following articles based on the data collected
from 46 wells:

1. Arsenic Poisoning of Bangladesh Groundwater, NATURE,395,338,1998

2. Mechanism of arsenic poisoning of groundwater in Bangladesh and West Bengal,
APPLIED GEOCHEMISTRY., 15, 403-413, 2000). ]

Here are the paragraphs from our article:

"RELIABILITY OF SEDIMENT DATA

The chemical parameters obtained from samples collected at ten different depth
between 1.8 m to 9.1 m below ground level from only two borings in Gopalgonj.
There is no report of sediment samples from any other part of the country. They
did not collect sediment samples within the screening interval of 46 wells
except for two wells in Gopalgonj. There is no mention in their report of the
depth to water (Please see Table-1 & 2 of 1999 report). In a delta like
Bangladesh lithofacies and thickness change vertically and laterally. A few
samples from Gopalgonj can not be considered a representative sample for the
whole area of Bangladesh. Nickson et.al mentioned the possibility of the
oxidation of arsenic pyrites during the lowering of the water table by pumping
but believed the adsorption of the arsenic by iron hydroxides would prevent
contamination of the groundwater by this mechanism. We do not accept this
evaluation and do believe that oxidation of arsenopyrite minerals has a real
potential for the cause. Apparently the contamination began after the mid
seventies and was caused by the lowering of water table. The lowering of the
water table produced chemical reactions that released arsenic that contaminated
the groundwater when reducing conditions returned when the water table rose to
it's normal level during the wet season. Since then arsenic contaminants have
migrated cross gradient and down gradient along with the groundwater flow
direction in the Bengal delta. Increased irrigation required because of reduced
flow of the rivers on which dams were built resulted in the use of arsenic
contaminated groundwater which intern contaminated the soil.. Nickson et.al in
their study did not present any evidence that supports the presence of arsenic
contaminants in sediments as well as in groundwater in Bangladesh prior to 1975.
Their statements about the presence of arsenic poisoning in Bengal delta for
thousands of years is speculation and is not supported by historical medical
evidences presented in the articles(When did the groundwater arsenic poisoning
in Bangladesh begin? Groundwater arsenic poisoning and a solution to the arsenic
disaster in Bangladesh; Oxyhydroxide Reduction and Agrochemical hypotheses: Myth
or reality?).

RELIABILITY OF GROUNDWATER CHEMICAL PARAMETERS

Nickson et.al collected water samples in May and June of 1997 once from each of
46 wells. In a 1998 publication they attributed the cause of arsenic
mobilization in groundwater to oxyhydroxide hypothesis and justified it on the
correlation between Fe, As and HCO3. In 1999 they presented chemical parameters
obtained from the same 46 wells. No further samples were included from areas of
high, low or arsenic free areas of Bangladesh. Their data can not be considered
a representative sample for all of Bangladesh aquifer systems. However, the data
from the 46 wells obtained once in May and June of 1997 from this very small
area shows variations from one well to another. Another group of scientists
sampled 320 wells and they found that the shallow wells are highly contaminated
and the deep wells are contaminant free. According to recent article entitled
"Arsenic Poisoning in the Ganges delta", published in Nature on 7 October, 1999
an opposite view to that of Nickson and Mc Arthur et.al. is presented.
Chowdhury, T.R. et.al.'s stated: "we disagree with Nickson et al.'s claim that
arsenic concentrations in shallow (oxic) wells are mostly below 50 ug per liter.
In our samples from Bangladesh (n=9,465), 59% of the 7,800 samples taken at
known depth and containing arsenic it over arsenic 50 ug per liter ug per liter
were collected from depths of less than 30 m, and 67% of the 167 samples with
arsenic concentrations above 1,000 ug per liter were collected from wells
between 11 and 15.8 m deep. In the Lakshmipur district of Bangladesh, three of
the shallowest tube wells (depths of 6.4 to 9.7 m) contained arsenic
concentrations of over 1,000 ug per liter . The shallowest tubewell in
Bangladesh is 6.4 m, and at that depth in the village of Chandipur, at the
Ramganj police station, we found an arsenic concentration of 1,354 ug per liter.
In the Noakhali district, we found arsenic at 2,700 lLg per liter at a depth of
9.7 m. As shown in Fig.1, many of the shallowest wells contain more than 50 ug
per liter r of arsenic. In West Bengal, (n=55,000), we found arsenic above 50 ug
per liter in 28% of wells that were less than 34 m deep. Furthermore, 37 of 38
samples with more than 1000 ug per liter of arsenic were collected from depths
shallower than 34 m. Nickson et.al., reported that the arsenic concentration
increases with depth in wells at Manikgoanj, Faridpur and Tungipara, apparently
on the basis of only a small number of samples. From studies of 320 tubewells in
this areas, we find that arsenic concentration increases with depth for depths
of less than 22m and decreases at depth of over 22m(Fig.1), and we have observed
a similar trend in West Bengal. The British Geological Survey has recently
reported that deep tubewells are free of arsenic in Bangladesh."

According to our analysis it appears that the sediment and groundwater chemical
parameters that Ross Nickson collected and analyzed are unreliable and
incorrect. If their data are unreliable, then what is the basis of
"Oxyhydroxide Reduction Theory? In the West Bengal and Bangladesh arsenic
poisoned patients were first discovered in 1983 and 1994 respectively. This
medical data clearly indicates that the groundwater arsenic poisoning in
Bangladesh and West Bengal of India is a recent environmental episode.

Dr. Acharyya and Dr. Imam, I do not doubt either your or Dr.Chakraborti's
findings. Dr. Chakraborti has followed good scientific procedures for
confirming his analytical data which was verified by the USGS and many other
laboratories. I believe the absence of pyrite or arsenic rich pyrite minerals
in your samples may be due to the following reasons:

1. If samples are collected from highly oxidized zones, and if arsenic rich
pyrite particles are present in that zone, then the finer particles will oxidize
very rapidly because of their high surface area of reaction. In that case one
may not find pyrite particles in the oxidized zone.

2. In the Bengal Delta the change of lithofacies is a common phenomenon.
Therefore one may or may not find arsenic-rich pyrite even at such a very close
distance as well as vertical intervals.

3. Besides arsenic rich pyrite, there may be other arsenic bearing minerals
present in the sediments.


However, the available data suggests that oxidation is the major cause for the
mobilization of arsenic into the groundwater of Bangladesh and West Bengal of
India. I personally believe a systematic discussion on the age, source,
mechanism of arsenic poisoning and the solution to the problem needs to be
conducted. In our next post we will try to give you more information about the
oxidation mechanism and some evidence that supports the mechanism.

Sincerely,

Meer Husain