Oxyhydroxide Reduction and Agrochemical Hypotheses: Myth or Reality?
Meer Husain, Environmental Geologist, Kansas Department of Health and
Environment, Kansas, USA.
The article "Arsenic Crisis: The Real Story" was printed in "The Independent" on May 26, 2000. It caught my attention because Mr. Ross Nickson and Mr. Zabed Hossain tried to refute the validity of the pyrite oxidation hypothesis as the cause of groundwater arsenic poisoning in Bangladesh, in their article. I am one of the strongest proponents of the pyrite oxidation hypothesis. I have examined all available theories for the cause of groundwater arsenic poisoning in Bangladesh. I have also examined the "oxyhydroxide reduction hypothesis" proposed by Nickson et.al and accepted by BGS as the main cause for the mobilization of arsenic into the groundwater. In my research, I found that the data used by Nickson et.al. in their study is negligible and appears to be unrepresentative and therefore unreliable. I also examined the "pyrite oxidation hypothesis" that is based on available data. We have written two articles related to the pyrite oxidation process in the context of groundwater arsenic poisoning in Bangladesh. The articles are: Groundwater Arsenic Poisoning and a Solution to the Arsenic Poisoning in Bangladesh. and Increased Drawdown and Recharge and their Relationship to the Groundwater Arsenic Problem in Bangladesh. These two articles describe the age of the poisoning, sources and causes of the poisoning, and the relationship of the oxidation process with the extraction of groundwater and diversion of surface water from rivers such as the Ganges, Tista, and other common rivers of Bangladesh and India.
Ross Nickson & Zabed Hossain in their article stated that "Groundwater Fiction: The arsenic in tubewell water is due to over-use of groundwater for irrigation. Lowering of the water table has drawn oxygen into the ground, which has oxidized pyrite, leading to release of arsenic. Fact: This is commonly referred to as the oxidation hypothesis' and is a popular misconception in Bangladesh. After extensive study, the British Geological Survey stated that there is no scientific evidence to support this hypothesis." We are not aware of the extensive study that the British Geological Survey conducted, which refutes the pyrite oxidation hypothesis as the cause of groundwater arsenic poisoning in Bangladesh. If Ross Nickson and Zabed Hossain's statement is true and the BGS study is adequate enough to refute the pyrite oxidation process, then obviously both studies would be correct. In rebuttal, I request that Nickson and Hossain share the BGS study they cited, with the people of Bangladesh as well as the scientific community.
Ross Nickson and Zabed Hossain further stated that "Dams and Barrages Fiction: The dams and barrages on the rivers entering Bangladesh have created the arsenic problem. Less water entering Bangladesh has led to lowering of the water table, this has drawn oxygen into the ground, which has oxidized pyrite, leading to release of arsenic. Fact: Variations in the ground water level have an influence on the arsenic problem, but they are not the cause." I do not know which study Ross Nickson and Zabed Hossain conducted to verify the above statement. In our articles, we clearly explained the oxidation process and its relationship with the dams and barrages. I would request that Ross Nickson and Zabed Hossain clarify their statement and share their explanation with the scientific community.
According to Nickson, et al. in refuting our articles, they stated that "Fiction: Dams and barrages have been built on the rivers entering Bangladesh in the last 30 years so these must be the cause of the arsenic problem. Fact: Use of groundwater for drinking started at the same time as use of groundwater for irrigation and the construction of dams. This is why the arsenic crisis has become apparent in the same period, not because they are responsible for it." In our article, Groundwater Arsenic Poisoning and a Solution to the Arsenic Disaster in Bangladesh, we clearly discussed the age of the arsenic poisoning in Bangladesh. The Farakka barrage was built on the Ganges river and was commissioned in 1975. Millions of tube wells were installed between the mid sixties and seventies before the commission of the Farakka barrage. During these ten years, million of infants, children, and adults drank water from the same tube wells. During that time in Bangladesh no arsenic related diseases were known. If any arsenic related diseases were developed at that time, doctors would have diagnosed the diseases as eczema or any other skin disorder because of their lack of knowledge and experience, regarding arsenic related diseases. By prescribing the wrong medication and treatments, they could not cure the deadly arsenic related diseases at that time. If the arsenic poisoning was present in Bangladesh prior to 1975 before the construction of Farakka and other dams on the common rivers of Bangladesh and India, we would have seen the people of Bangladesh suffering from arsenic diseases prior to 1975. We know from Dr. Shaha's survey in the West Bengal that the lag time for the appearance of arsenic disease is two to five years. People of Bangladesh and West Bengal have similar physical conditions, their food habits and intake of water are similar. If groundwater arsenic poisoning was present in Bangladesh prior to 1975, then millions of tube well water users between 1965 and 1975 would have certainly been poisoned by arsenic. Ten years is an adequate time for the appearance arsenic diseases on the people of Bangladesh. If knowledgeable, experienced, and dedicated professionals survey arsenic poisoned patients in the community, they will find none of the people were poisoned prior to 1975. In fact Mr. Fariduddin, a professional health engineer of DPHE, in his article In Quest of Safe Water for Rural Bangladesh, stated: "Groundwater of Bangladesh contain arsenic was known to the community only in 1994. The patients with arsenic pollution were initially detected in the bordering area of Bangladesh with primary initiative of Dhaka Community Hospital and NIPSOM. Increasing numbers of patients have been identified through limited field survey with the assistance of UNDP and Ministry of Health. The Department of Public Health Engineering also initiated water sampling program through 4 zonal laboratories with assistance of WHO / UNICEF/ DFID since 1994."
In our article, "When Did the Groundwater Arsenic Poisoning in Bangladesh Begin?", we clearly stated that there is no difference between dug well and tubewell water. Both types of wells are located in unconfined aquifers. If both wells are located in the similar geological, hydrogeological, and geochemical conditions, and at the same depth, both will reveal similar types of arsenic concentrations. I strongly disagree with the investigators who found that dug well water is contaminant free and the tubewell water is highly contaminated under similar geological, hydrogeological, and geochemical conditions. I believe that their statements are not based on reliable data. Recently in Dhaka 3rd International Conference, a group of scientists with the Dhaka Community Hospital (DCH) presented an article entitled "Are Dug Wells a Good Option for the Community?". In their article they stated, "If the community can protect dug wells from out side contamination by following WHO guidelines, which are possible without extra cost, then dug wells may be a good option in some areas of Bangladesh for safe water as the water of a large number of the tube wells is arsenic contaminated." I am interested in the credentials of these scientists and respectfully ask them whether or not they have sufficient geological, hydrogeological, and geochemical knowledge, as well as experience in groundwater sampling. If they are not geologists, I ask them if their sampling procedures were supervised by an experienced and knowledgeable groundwater geologist. I would also like to know whether their samples were analyzed by a reputed laboratory. If they do not have the required knowledge and experience, then their data can not be considered reliable and representative. As a result, their interpretations can not be credible. The groundwater arsenic poisoning in Bangladesh is a geological problem. Therefore, any soil and groundwater samples
related to geological, hydrogeological, and geochemical studies must be collected by geologists or by other experienced technicians/scientists under the supervision of experienced geologists. The data must also be interpreted by experienced groundwater geologists.
Dr. Dipankar Chakraborti, an analytical chemist and a dedicated worker has been working on the arsenic problem in West Bengal and Bangladesh for a long time. He made a comment on our article "When did the Groundwater Arsenic Poisoning in Bangladesh Begin?" He stated that "A) In your article you have written "If conditions were the same after the tube well were drilled as when the hand dug wells were used then the hand-dug well water would have been poisoned by arsenic in the same geologically contaminatedareas where poisoning occurs today. If groundwater arsenic contamination had been present for thousands of years, as suggested by the UK report, then both shallow hand-dug well and tube wells would extract arsenic contaminated water and would have impacted water users with arsenic poisoning before 1975." Please note, in our more than 100 dugwells water for arsenic analyses from arsenic affected area of West Bengal and Bangladesh we have not found arsenic above 50 :g/l in any one of them."
Dr. Chakraborti provided valuable information about the presence of arsenic contamination in hand dug wells. Although his analyses did not show arsenic
concentration above 50 ppb, his data confirms that arsenic is present in the dug well water. The concentration may not be above the Bangladesh limit, but it may be above the WHO limit. I have serious questions concerning Dr. Chakraborti's hand dug well data. Did Dr. Chakraborti collect representative samples from the dug wells? Did he collect samples from both hand dug wells and tube wells at the same sampling event? The geological, hydrological, and geochemical conditions/concepts do not support either Dr.Chakraborti's or the British Geological Survey's findings on dug wells. My experience with groundwater sampling as an Environmental Geologist indicates that if representative groundwater samples are collected from similar geological, hydrogeological, and geochemical environments as in hand
dug wells and tube wells in the same sampling period, then both hand dug wells and tube wells will reveal similar types of contamination. From Dr.Chakraborti's findings it is evident that arsenic is present in dug well water today. If arsenic contamination had been present for thousands of years in the sediments and groundwater in Bangladesh as suggested by DPHE/DFID/BGS/Mott MacDonald investigators, then arsenic would have been present in dug wells for thousands of years too. There is no difference between hand dug wells and tube wells when large amounts of water is abstracted and consumed within a short period of time. Hand dug well water is collected by a balti/kalshi/bucket with a rope, where as tube well water is collected by hand pump or electric pump. The source of water for both hand dug well and tube well is groundwater. Both wells are sitting in an unconfined aquifer. In hand dug wells, water comes in contact with air, oxidizes, and precipitates arsenic, thus decreasing the level of concentration in comparison to the tube well water, because groundwater is directly abstracted from tube wells. Prior to the 1960's, about 250-300 gallons of water would have been abstracted from a single hand dug well, and about 25 to 40 people would have consumed that water three times a day; in the morning, at noon, and in the evening. The agitation and limited contact of water with oxygen occurring in hand dug wells are not sufficient enough to completely precipitate arsenic. If groundwater arsenic contamination had been present for thousands of years, as suggested by the DPHE/DFID/BGS/Mott Mac Donald report, then both shallow hand dug wells and tube wells would extract arsenic contaminated water. As a result water users would have been impacted with arsenic poisoning prior to 1975. If the DPHE/DFID/BGS/Mott MacDonald investigator's statement on the age of arsenic poisoning was true, then prior to 1965 the people of Bangladesh, who had been drinking hand dug well water for thousands of years would have certainly been poisoned by arsenic, and today we would see people who had been suffering from arsenic diseases for generations before 1965. If proper tests are conducted on hand dug wells, we will see
that high levels of arsenic concentration are present in the dug well water in areas where other investigators found tube wells highly contaminated and hand dug wells uncontaminated in similar geological, hydro-geological, and geochemical conditions. The time between extraction and consumption of water from hand dug wells (three times daily) is not adequate enough to precipitate the arsenic. In other words, the dug well water is not safe to drink. It may be safe for a few people, but it will not be safe for a large population over time. Recently, Harvard professor Dr. Richard Wilson, who is trying to alleviate the arsenic problem, attended the 3rd international conference in Dhaka, Bangladesh. After his return to the USA, Dr. Wilson and I discussed the possibility of using hand dug well water as an alternative safe water source in arsenic affected areas of Bangladesh. I believe that before using the hand dug wells, the Bangladesh Government must conduct detailed testing on the dug wells using knowledgeable and experienced professionals.
In 1998, Nickson et. al., proposed the oxyhydroxide reduction hypothesis for the cause (mobilization) of arsenic poisoning in Bangladesh. This theory became well known when it was published in "Nature" and "Applied Geochemistry" journals as well as being accepted by the British Geological Survey and Mott MacDonald's investigators as the main cause for the mobilization of arsenic into groundwater. In 1998 Nickson et.al., stated "Arsenic has been reported to derive from the oxidation of arsenic-rich pyrite in the aquifer sediments as atmospheric oxygen invades the aquifer in response to a lowering of the water level by abstraction4,5. This explanation is not consistent with the following observations3, made on 46 wells, typical of those in Bangladesh, that were sampled during May and June, 1997: in oxic (shallow) wells, arsenic concentrations are mostly below 50 ug1-1; in anoxic waters, arsenic concentrations (= 260 ug 1-1) correlate with concentrations of dissolved iron (= 29 mg l-1) and bicarbonate ( Fig.1a); arsenic concentrations increase with depth in wells at Manikganj, Faridpur, and Tungipara. These observations suggest that arsenic is released when arseniferous iron-oxyhydroxides are reduced in anoxic groundwater6, a process that solubilises iron, and its absorbed load, and increases bicarbonate concentrations. Sedimentary iron oxyhydroxides are known to scavenge arsenic7 and, in aquifer sediments, concentrations of diagenetically-available iron (< 3.7%) and arsenic (< 26 PPM) correlate well3 (Fig.1b)." In 1999, another article written by R.T.Nickson, J.M. McArthur, P. Ravenscroft, W.G. Burgess, and K.M. Ahmed entitled "Mechanism of Arsenic release to groundwater, Bangladesh and West Bengal" was published in "Applied Geochemistry" 15(2000) 403-413, 1999. The article was written based on additional chemical parameters obtained from the same 46 wells in 1997.
On the other hand, another group of scientists using data from 320 wells revealed reverse results to those of Nickson at el. Their data showed that shallow wells are highly contaminated and the deep wells are contaminant free. The article Arsenic Poisoning in the Ganges Delta was written by Chowdhury, et,al. and published in "Nature" on October 7, 1999. The authors in the article stated "we disagree with Nickson et al.'s claim that arsenic concentrations in shallow (oxic) wells are mostly below 50 ug per litre. In our samples from Bangladesh (n=9,465), 59% of the 7,800 samples taken at known depth and containing arsenic at over arsenic 50 ug per litre were collected from depths of less than 30 m, and 67% of the 167 samples with arsenic concentrations above 1,000 ug per litre were collected from wells between 11 and 15.8 m deep." Chowdhury et.al. further stated that "Nickson et.al. reported that the arsenic concentration increases with depth in wells at Manikgonj, Faridpur and Tungipara, apparently on the basis of only a small number of samples. From studies of 320 tube wells in these areas, we find that arsenic concentration increases with depth for depths of less than 22m and decreases at depths 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".
From the above statements, it is clearly evident that Nickson's data group is very small in comparison to Chowdhury's et.al data and appears to be unreliable. A sample may present false positive or false negative results either from improper sampling or from improper analysis or from both sources. Mr. Nickson is the principal author of the oxyhydroxide hypothesis. He was directly involved in sediment and groundwater sampling and analysis. If Nickson's data is wrong, then their oxyhydroxide reduction theory is also incorrect as the mechanism under which arsenic mobilizes into groundwater in Bangladesh. The oxyhydroxide reduction theory is not a new theory. This theory may work in Ohio and other parts of the world, but geologists must examine the theory with factual data. They have to be sure that it functions in the context of Bangladesh geological, hydrological, hydrogeological and geochemical frameworks.
Recently, Dr. Jamal Anwar, a researcher at Berlin University in Germany, claimed that the indiscriminate use of agrochemicals and fertilizers is causing the groundwater arsenic poisoning in Bangladesh. On October 6 of 1999, a BBC science correspondent, Helen Sewell reported that the researchers with the Geological Survey of India(GSI) also proposed that the use of phosphate fertilizers is causing arsenic poisoning in Bangladesh. The GSI researchers produced no factual data to support their claim. Logically, massive amounts of very high arsenic
contaminated agrochemicals and fertilizers would have to be used to be responsible for the scale of groundwater arsenic poisoning observed in Bangladesh and West Bengal. I ask Dr. Anwar to support his scientific findings with tangible scientific evidence.
Geologists, scientists, and environmentaly concerned people must analyze that prior to 1975 under natural conditions, Bangladesh had never faced an environmental crisis of the present magnitude. The groundwater arsenic poisoning in Bangladesh is a recent environmental episode and it began after 1975. This is the largest man-made disaster in the history of human civilization. The crisis appears to be directly related to the Farakka, Tista, and about 28 others dams/barrages that India constructed on the common rivers of Bangladesh and India after 1975. Scientists must realize that the arsenic crisis in Bangladesh is a life and death problem of a nation. This crisis can not be solved based on inadequate and unreliable data, or irrelevant as well as speculative theories. This is a very critical geological, hydrological, hydrogeological, and geochemical related problem associated with recent human activities i.e., over use of groundwater and the diversion of surface water from the rivers.
As strong proponents of the "Pyrite Oxidation Hypothesis", myself and Dr.
Bridge have used available data and our working experience as scientists, as the basis for our published hypotheses. We are aware of what types of data need to be collected to verify the validity of the "Pyrite Oxidation", Oxy-hydroxide Reduction", and "Agrochemical" hypotheses. The arsenic crisis in Bangladesh was discovered about six years ago. It is unfortunate that about 90 million people are drinking arsenic-contaminated water on a daily basis. Scientists and policy makers of Bangladesh must take immediate steps, using sound scientific methods, and reproducible techniques to find the real source(s) and cause(s) of the groundwater arsenic contamination, and establish safe, cost effective, and long-lasting solutions to the arsenic disaster in Bangladesh.