Letters

 
Published: Friday 15 August 2003

All about arsenic

This is in response to the cover story 'The Dark Zone', (Down To Earth, Vol 11 No 22, April 15, 2003). I compliment you for the incisive write-up on arsenic and fluoride pollution in groundwater in India. However, Down To Earth readers are misinformed about several aspects of arsenic pollution.

It is reported that "arsenopyrite has been primarily identified as the main source of arsenic pollution in Bangladesh". Arsenopyrite-bearing layers in the alluvial aquifer get oxidised due to draw down of the water table induced by heavy irrigation related pumping, and thereby releasing arsenic into the groundwater. But these theories are far from the truth. In 1999, we reported in the journal Nature and in the September 2000 edition of Environmental Geology, that pyrite, arsenopyrite or any other arsenic-bearing mineral are absent or rare in affected aquifers of West Bengal.

Pyrite occurs rarely within woody fragments or carbonaceous sediments, which are formed biogenically and under reducing condition. And if arsenic is present then it is sorbed within such pyrite. This pyrite (which is not arsenopyrite) thus acts as 'sink' and not the 'source' of arsenic.

Our studies confirm that arsenic occurs adsorbed on dispersed phases of iron-oxide, which is usually present as coatings over sediment grains, organic matter and also in magnetite (magnetic oxide of iron), biotite grains. The Himalayas is a major, but not the exclusive source for arsenic. Based on our studies we infer that it is not the source but the release of arsenic from rocks to sediments and then to the groundwater, which is more important.

P Bhattacharya and R Nickson reported in the Water Resource Development in 1997 and in Nature in 1998 that the release of arsenic to the groundwater in Bangladesh and West Bengal is not by oxidation of pyrite. According to them it was by the reduction and dissolution of iron-oxide coatings with the release of sorbed load of arsenic to the groundwater.

The groundwater in the arsenic affected belt of West Bengal and Bangladesh is bi-carbonate and iron-rich, but poor in sulphate. This corroborates their reducing nature and contending pyrite oxidation hypothesis. Is it necessary to know whether oxidation of reduction process is responsible for the release of arsenic into the groundwater? Yes. It is, as only then science-driven and logical remedial actions can be planned instead of adhoc actions.

The dug-wells (which are conventional wells built with modifications keeping in mind that only the shallow layer of water is utilised) are free from arsenic contamination. Had there been a pyrite-oxidation process, then these would have been the most polluted. Because of the oxygenated nature of arsenic, dissolved ferrous iron is oxidised and as the ferric iron is insoluble, it precipitates at the bottom, thus removing arsenic. Hence, dug-wells are a cheaper alternate source for arsenic-free water, provided the well is kept free of pathogen. Oxidising agents such as potassium permanganate or bleaching powder can be added in dug-wells regularly to keep them free of pathogens.

We reported in the Environmental Geology in 2000, that arsenic contamination in West Bengal and Bangladesh is caused due to sedimentation below the rising sea level during the Holocene period. During the Pleistocene ice age, sediments in the Bengal Basin were exposed to erosion and oxidation. Groundwater in them was well drained due to steeper hydraulic gradients. These sediments though old are free from arsenic contamination. A rapid rise in sea level during 10,000 to 7,500 years before the present resulted in Deltaic organic rich sedimentation. Arsenic from the source area was preferentially captured in these fine-grained organic rich sediments and released later to the groundwater by a reduction process. Due to poor hydraulic gradient released ar.

"Unfounded allegations"

In the article 'A terrible accident', (Down To Earth, Vol 12, No 3, June 30, 2003), Sarita Bahl outlines the controversy raised by a British journalist about the earlier version of the oral polio vaccine that was tested in the former Belgian Congo. The journalist alleges that the scientists contaminated the vaccine with a chimpanzee virus that mutated to the human immunodeficiency virus (hiv), that causes Acquired Immunodeficiency Syndrome (aids).

The article mentions that supporters of the polio vaccine hypothesis were not invited to a Royal Society meeting in 2000. It also quotes the claims made by an Australian, Julian Cribb that the scientists tried to suppress the polio vaccine hypothesis.

This is pure balderdash. The meeting was called specifically to consider the polio vaccine theory. The British journalist, Cribb and three other scientists supportive of the hypothesis were given the privilege of addressing the Royal Society. That the outcome of the meeting was the rejection of the poliovirus hypothesis was not a result of suppression, but rather in view of the evidence. Bahl has contributed unwittingly to unfounded allegations regarding the vaccination.

STANLEY A PLOTKIN
Stanley.Plotkin@aventis.com...

Productive waste

The editorial 'Waste, by any other name...' (Down To Earth, Vol 12, No 2, June 15, 2003) is thought provoking and timely. In the past, to dispose off human excreta, people in India had adopted dry disposal systems. Every village used to have a certain area earmarked for this purpose. The soil was transported to the fields and used as a fertiliser, thus making it an ecofriendly system.

In the 20th century, we switched over to the wet disposal system, which is a water-intensive and highly expensive method. It involves building of sewer lines and establishment of Sewage Treatment Plants (stps). Unfortunately, a country like India cannot meet the water requirements for such a system. Therefore, we are unable to handle our sewage properly. If you study stps today in metros, hardly any significant quantity of sewage is treated. Either the established stps are not functioning properly, or are inactive. No wonder, the Ganga Action Plan could not clean the river water because of the failure of the stp technology. Wet disposal systems and stp technologies are developed in temperate regions, where low environmental temperatures make biodegradation a slow process, while in the tropical countries there is no such problem.

In such a scenario, the only way out is to:

Consider human excreta as a resource rather than a waste

Dispose off excreta after separating urine

As urine contains urea, which is a natural fertiliser, technology to extract urea from urine should be practised

Excreta should be used to produce gobar gas

These steps will not only solve sewage disposal and contamination problems, it will also save freshwater resources and be a source of income. Finally, our attitude towards waste should change. Hope someone in the planning commission is reading this.

M S KODARKAR
kodarkar_mohan@yahoo.com

The editorial 'Waste, by any other name...' and the cover story 'By hook, crook or vision' (June 15, 2003) establishes that waste is the by-product of an inefficient process that ignores the principle of optimum utilisation of inputs.

We should concentrate on ecotechnologies for conversion of waste into value-added products. Take for instance hemicellulose -- a component of black liquor -- which when hydrolysed (by adding hydrogen molecules) becomes a new biochemical, xylan. If further processed, it can produce natural sweeteners like xylitol that is sweeter than sugar, but low in calories. Lignin, yet another component of black liquor, if extracted before the production of cellulose can be used as a clean fuel and natural glue. In the case of bagasse, the fibre in the waste could be recovered in the form of organic cement additives and can be used as a strengthener during the manufacture of cement boards.

There are many other methods of converting waste into valuable resources. On an average, we use less than five per cent of the agro-forestry outputs and discard about 95 per cent of it. If we adopt an economic system that uses this discarded 95 per cent, we would be able to satisfy as much as 20 times more material needs without expecting nature to produce more.

JAYDEV JANA
Salt lake, Kolkata...

Democratic view

The editorial on 'Ordering a new world', (Down To Earth, Vol 11, No 24, May 15, 2003) made me literally shudder to think of the possible consequences of a future framed under a "shared sovereignty". I would argue strongly that even though "the global problem-solving mechanisms are not working adequately", the core of a sovereign democracy is to allow its citizens to decide their political fate through indigenous struggles. Democracy can never be fostered through the gun.

Nine out of every 10 dictator or authoritarian leader in the world was supported by the us. While this worked well for them earlier, now they want to re-inaugurate the 19th century idea of the "white-man's burden", claiming that the coloured people must be liberated from the groaning weight of their corrupt leaders.

The "new world managers" should realise that the ideological charge of this burden has considerably withered. The civil society of "old Europe" if not its leaders, with exception of the British, know this truth better than perhaps many others.

SHISHIR K JHA
shishir_jha@hotmail.com...

Stop axing

The Delhi Metro Rail Corporation's (dmrc) proposal to cut down 200 trees lining Panchkuian road and Barakhambha road is very distressing. DMRC's activities in Civil Lines in north Delhi have already been disastrous.

Though I contacted the "so-called" tree helpline, run by the Delhi government, I was told that since the felling was being undertaken by another department, the agency could do nothing to stop it. Unlike Sham Nath Marg in Indraprastha College in north Delhi, where an entire avenue of trees vanished virtually overnight, Barakhambha road is surely wide enough to accommodate the DMRC's activities.

But instead of trees, if there were houses, wouldn't every effort have been made to tunnel under the buildings rather than cut trees. The only difference is that if you cut trees, then you compromise on your own health. It is not enough for the DMRC to just plant a few saplings (like it claims to have done in Civil Lines) as it's almost ludicrous to compare saplings with trees which are over 80 years old. Even as we beat our breasts about worldwide ecological responsibility, a substantial hole is being carved out of our own lungs perhaps forever. I request the media to highlight this issue.

SHYAMA HALDAR
shyama@ekno.com...

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