Chris Casteel | NewsOK.com |Shared as an education material
ready to gain unsuspected entrance to our bodies from the food we eat,
the water we drink and the air we breathe” Karl Vogel, 1928.
The Effect of Diet
The regulatory limits on arsenic exposure were set primarily to be sure that these acute toxic effects were avoided. The first regulatory limit of which the webmasters are aware was set as a result of a public inquiry (subsequent to arsenic being found in beer) of six members chaired by the physicist William Thompson, first Lord Kelvin, in 1903. They recommended that sake of liquids with more than 100 grains of arsenious oxide per gallon (which works out at about 90 ppb of arsenic or 0.09 ug/l) This was reduced two fold over the next century and until recently the limit set by Bangladesh, the United Kingdom, and the United States was 50 parts per billion (ppb). But the discovery that there are adverse effects of continuous chronic exposure led WHO to lower their recommendation to 10 parts per billion (10 ppb). The European Union (EU) plans to enforce a standard of 10 ppb by 2003. After a long travail , on October 31st 2001, the administrator of US EPA confirmed a new standard for drinking water of 10 ppb to be enforced by 2006. In Australia there does not seem to be a specific regulatory level but there are work rules for those working around mine tailings sites.
The US EPA has recently come out with an extensive review of mechanisms of action of Dimethyl Arsenic (DMA) and its possible mechanisms of action. They cannot rule out a linear dose response at the lowest doses. It is effectively impossible to reduce the content of arsenic in drinking water to a risk level of one in a million lifetime risk calculated with a linear dose-response relationship, a risk level and a calculational procedure frequently used by the U.S. EPA. The present 10 ppb standard is perhaps the first in which the U.S EPA explicitly compared costs and benefits and used a value of $6.1 million per calculated life saved. References to the extensive US national discussion are available on the “countries” page and in particular the section on travail.
Arsenic contamination has become a problem in many parts of the world. At first as a result of leaching from mine tailings in Australia, Canada, Japan, Mexico, Thailand, United Kingdom, and the United States, but now also from the arsenic in natural acquifers now or recently used for water supply in Argentina, Bangladesh, Cambodia, Chile , China, Ghana, Hungary, Inner Mongolia, Mexico, Nepal, New Zealand, Philippines, Taiwan, the United States and Vietnam. Arsenic was also widely used as a pesticide. 20,000 tons a year was imported into the USA, and perhaps double that amount was used, to spray on crops in the USA alone. No attention was paid to the ultimate fate of the chemical,and in consequence arsenic now appears in foodstuffs . (Papers describing data in some of these countries are listed by country in the list of useful references. ) It is important to distinguish the problems in Bangladesh, West Bengal and, to a lesser extent, Inner Mongolia, Chile, Nepal and Vietnam, from the problems that have been found so far in the rest of the world. These situations have in common that they are an alluvial plain where arsenic has been brought down from the surrounding hills for millenia. It seems that no one has looked carefully at similar geological situations such as the Mekong delta or the Irrawaddy delta. In most of the world exposures above 50 parts per billion (50 ppb) are rare, and once observed, can easily be avoided. But the sheer scale of the problems in Bangladesh dwarfs the imagination. The catastrophe is much worse than the well known catastrophe of the Chernobyl nuclear power plant accident, the Bhopal isothiocyanate leak or the Kuwait oil fires. For 90% of the Bangladeshi communities, pure water is still a long time away.
The World Bank made a study for SE Asia in the beginning of the 21st century which is available on the web:
Volume I: Policy Report Full Report (1,038kb pdf)
Paper 2: An Overview of Current Operational Responses to the Arsenic Issue in South and East Asia (413kb)
Paper 3: Arsenic Mitigation Technologies in South and East Asia (345kb)
The situation in Bangladesh has received a lot of attention because it is the most important. The new Bangladeshi government has made the solution of the problem a priority as stated clearly by Prime Minister Begum Khaleda Zia as she opened the special WHO workshop in Dhaka on January 14th -16th 2002. Feroze Ahmed, presented an excellent review of the situation at that time. Particpants made recommendations to the government of Bangladesh (GoB). Another (2002) review from the NGO forum is copied here from the NAISU website in pdf. Professor Chakriborti of Kolkata (Calcutta), a tireless and enthusiastic worker in the field regularly issues his reports on the Bangladesh situation, has a year 2001 report on Bangladesh which we have also captured in a local file.
Why Does Arsenic Get into the Water?
This is the subject of a whole issue of the journal Applied Geochemistry:
Bhattacharya, P., A. H. Welch, K. M. Ahmed, G. Jacks and R. Naidu (Eds.)
Arsenic is plentiful in the ground. Yet it does not awlays appear in the water supply. Scholars at the Cambridge University Department of Geography have identified the following mechanisms for arsenic entering the water which vary between locations. Alkali-desorption, Geothermal, Reductive dissolution and Sulphide oxidation. lthough the worst arsenic catastrophe is in Bangladesh, where 35 million people are exposed to levels above the US EPA standard, the amount of arsenic in the soil is less than in many other areas, including areas such as Massachussets, USA, where it does not, nonetheless, appear in unsafe quantities in ground water. In most of these areas, such as the delta of the Ganges and Irrawaddy, and the bend of the Yellow river, arsenic has come down from the mountains over millenia, attached itself to iron, forming iron pyrites, and been deposited. Professor McArthur of UC London argues: “It becomes increasingly clear that severe arsenic pollution of ground water in most alluvial aquifers worldwide is driven by the microbially-mediated metabolism of organic matter, with FeOOH acting as the source of oxygen: the oxide is reduced during the process and its sorbed arsenic is released to ground water. Despite the widespread acceptance of this mechanism, much about it remains obscure.” One issue is whether the reduction takes place at the surface before the water filters down to the aquifer in the monsoon (as suggested by group (a) below) or whether it is reduced in the aquifer itself.
Papers describing this mechanism include:
(a) Two papers were presented by Charles Harvey et al.:
“Arsenic. Its Biogeochemistry and Transport in Groundwater,” in “Biogeochemical Cycles of the Elements”
“Subsurface geochemistry and arsenic mobility in Bangladesh”
“Response to Technical Comment on “Arsenic Mobility and Groundwater Extraction in Bangladesh”
and a brief report in Science. Most recently they suggest that reduction occurs in arsenic ponds before water enters the aquifer.
(b) The group at Columbia University have also presented a papers on the same topic of which the most recent is:
“Redox control of arsenic mobilization in Bangladesh groundwater“, Zheng et al., Applied Geochemistry, 19(2), 163-260, Feb 2004, 201-214.
(c) Professor McArthur and colleagues at UCL in London have several reports available on their webpage of which the following may be downloaded:
“Arsenic in groundwater: testing pollution mechanisms for sedimentary aquifers in Bangladesh”
Their most recent paper disagrees with the hypothesis of group (a) that the reduction occurs in ponds.
An older idea was that water was being drained from the aquifer, allowing oxidation. A recent paper describing arsenic contamination in Perth, Australia – shows that there is one location, in Perth where pyrite oxidation clearly WAS the source of the As (although there is evidence that anerobic release from Fe oxyhydroxides is also taking place deeper in the aquifer). But the ideas that pyrite oxidation is the problem in Bangladesh whether caused by recent rapid pumping that allowed for oxidation and release of arsenic, or by the man-made change in river flow, such as the barrage across the Ganges are now considered to be untenable.
In the Americas, from Alaska in the north, through Crater Lake in Oregon, Mono Lake and Searles lake in California, volcanic lakes in Niceragua and Costa Rica, and on to the Andes, lie a chain of volanic activity that brings arsenic to the surface. This mecahnism of sulfate reduction in the arsenic-rich soda lakes (Mono Lake and Searles lake) of is being studied in detail by Dr Oremland and his group at the US Geological Survey in Menlo Park. They attrbute the mechanism to bacteria, but of course different bacteria from those responsible for the reduction of iron pyrites in SE Asia and Bangladesh. Presumably this is the same mechanism as is responsible for the arsenic pollution in the mountains of Argentine and Chile where so much epidemiological studies have been made.
Possible Solutions to the Problems
The first and most obvious necessity is to measure the arsenic levels in any ground water that is intended for human use. The next step is to purify the water or, better still, provide an alternate supply of pure water. The way in which this is done varies from country to country. In SE ASIA, and Bangladesh in particular, two facets of a solution seem to be agreed.
(1) There is no one solution for all places and communities. It is vital to involve the local community in the decision and even more important in the follow up and maintenance.
(2) The solution in any community and location must based upon the best possible scientific understanding. The webmaster has attempted to summarize the possibilities in the remediation page. Please add and correct. It is very important to share data and experiences as set out in declarations from seven arsenic conferences in Dhaka held by Dhaka Community Hospital.