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Summary of the acute and chronic effects
of arsenic
and the extent of the world arsenic catastrophe
A brief historical
survey is in preparation here
Acute effects
Arsenic has been used since 3000 BC (Partington, 1935). In the
United Kingdom, for
example, it was used to extract iron from iron ore. It has long been
known that arsenic is acutely toxic. Anyone who drinks arsenic in water
at 60 parts per million (ppm) will soon die. There are several
toxicological summary references for acute effects available on the web
such as
SCORECARD,
ASTDR,
USEPA and
LSUMC.
Beneficial effects
Arsenic has been used for many years for medicinal purposes. It
used to be used as a cure for diseases such as syphilis and has been shown
to assist in curing some leukemias. It was taken as a medicine in
Fowler’s Solution for well over a century.
That arsenic at low levels is safe seemed to be reinforced by animal
studies that seemed to show that arsenic is beneficial (to animals) at low
doses. Indeed, the fact that laboratory animals could not be persuaded to
develop cancer misled toxicologists throughout the world and greatly
contributed to the present catastrophe. Others have written about
other possible
beneficial effects at very low levels. It is
important to note that the beneficial effects are for different medical
outcomes (end points) than either the acute or chronic adverse effects and
that both beneficial and adverse effects can be observed simultaneously
(as is well known for alcohol ingestion). Another detailed article about
beneficial uses of arsenic can be found
here . Mineral
hot springs in the
USA still advertise
arsenic pools and their users, including this webmaster, are convinced
that the effects are beneficial! (But arsenic penetrates the skin only
slowly)
Chronic
adverse effects
Chronic effects of prolonged low level exposure
have recently showed up. Among various summaries we link to an
information site run by
ASTDR.
Skin pigmentation,
keratoses and skin cancers were found by Tseng
in Taiwan in 1966 among people who drank from arsenic contaminated wells (but
no effect was seen below about 150 parts per billion (ppb), which
might therefore be a biological threshold) and a very high incidence of
lung, bladder and other cancers was found in Taiwan by Dr Chien-Jen Chen
in 1986 and by
Dr
Allan Smith and collaborators in Chile in
1993.
These convinced WHO to recommend lowering the regulatory level from 50
ppb to 10 ppb for arsenic in water.
It appears that there are no data on humans to contest the idea that
prolonged exposure to low doses is dangerous. Although arsenic was
used medicinally in “Fowler’s Solution” (1% arsenite), prolonged use had
led to these chronic skin effects. This was observed as early as 1888 by
Hutchinson. A follow up of a
number of English patients treated with Fowler’s Solution has been
reported by Dr Susan Evans in published literature, in a report at the
February 1998 conference in Dhaka and in a
presidential address by Susan Evans to the
Liverpool Medical Institute, which is available for download in PDF
format. This shows that the use of “Fowler’s solution” (which is
primarily medicinal arsenic) in the
UK is
probably responsible for 5 bladder cancer cases among the patients
among whom only 1.6 were expected from natural causes. The arsenic dose
was equivalent to an average lifetime dose that would come from drinking
water with about 25 ppb of arsenic therein.
After several years of low level arsenic exposure, various skin lesions
appear. These are manifested by hyperpigmentation (dark spots),
hypopigmentation (white spots) and keratoses of the hands and feet. After
a dozen or so years skin cancers are expected.
Twenty or thirty years after exposure to 500 ppb of arsenic, internal
cancers (lung, kidney, liver and bladder) appear among 10% of all exposed.
Moreover, the dose-response relationship for these internal cancers is
consistent with being linear with no threshold. Photographs of a number
of victims of this poisoning are available both from
Bangladesh and from
Inner Mongolia.
Although the most dramatic effect was the observation of internal
cancers in Tawian, the most extensive epidemiological studies have come
from the work in
Chile, in
which Dr Allan Smith of UC Berkeley has been heavily involved. They find
the extraordinarily surprizing result that
ingested arsenic in
Chile has produced
lung cancer at a rate greater than that of a heavy cigarette smoker!
Recently, the group identified an effect of arsenic exposure to chldren -
who have developing lungs -. Children exposed to arsenic have
ten times the normal lung
cancer incidence.
The Effect of diet
An important issue for coping with arsenic exposure is the effect of diet.
A general issue can be stated: there is frequently more than one cause of
a cancer or a lesion. For example lung cancer can be caused by cigarette
smoking or asbestos or both together, in a synergistic way such that the
risks multiply (rather than add) when both are present.
In the
USA it has been
found that people who have a good diet of fresh fruit and vegetables (5
servings per day) have half the risk of many cancers, including lung
cancers caused by cigarettes, as those without a good diet. By
analogy, one might expect that the lung cancer risk from arsenic will be
less among those with a good diet.
Anecdotal indications from Bangladesh suggests that a good diet reduces
skin lesions, and the
effect is seen in West Bengal,
but the effect is small and the authors recommend that effort is better
spent on obtaining pure water. Nonetheless epidemiological studies to
confirm this are highly desirable. Khaliquzzaman and Khan have
calculated the “Arsenic Exposure of
Bangladesh
Population through Food Chain” using known amounts in food, in an
unpublished
World Bank report. The amount is less than from
drinking water but not much less.
There are several specific chemicals that have been suggested that
would either (i) help to prevent arsenic lesions by rapid removal of
arsenic from the body or (ii) help to cure arsenic lesions. Encouragement
of methylation of the arsenic probably accelerates methylation, but the
methylation has been suggested as a cause of internal cancers. The
specific chemical that has come to the mind of many health experts is
selenium. It
was noted in the 1930s that effects of excess selenium can be counteracted
by adding arsenic to the diet because As and Se combine. Does the
inverse take place? It
is reported that areas with high incidence of arsenical lesions have low
selenium in the water. Some victims have low selenium levels.
Does adding selenium to the diet really help, either to prevent the
lesions from forming (likely), or to treat them afterwards (less likely)?
We have, with help from others, compiled a list of
references
and a
recent paper
on the subject.
Professor Zuberi
of
Rajshashi
University has
suggested methionine to reduce the arsenic lesions. Dr. OGB
Nambiar
has suggested that ferrous sulphate, after conversion to sulfide by
bacteria in the colon, absorbs arsenic and assists safe excretion. The
evidence for these remains indirect, and there may be (as suggested above)
competing adverse effects. Only good epidemiology can tell and this is
under way in several places.
Regulatory limits for continuous exposure.
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.
The worldwide scope of the catastrophe
.
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 has recently completed a study for SE Asia which is
available on the web:
Arsenic Contamination of Groundwater in South
and East Asian Countries
Volume I:
Policy Report
Full Report
(1,038kb
pdf)
Volume II: Technical Report
Full Report
(2,879kb
pdf)
Paper 1: Arsenic Occurrence
in Groundwater in South and East Asia—Scale, Causes, and Mitigation
(715kb)
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)
Paper 4: The Economics of
Arsenic Mitigation
(335kb)
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. You are invited to comment upon the
recommendations to the government of
Bangladesh
from the participants of that workshop.
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. Another recent draft summary
of the
Bangladesh situation
has been circulated for comment by
WATERAID
The best review of the situation in
Bangladesh is in the
paper by Feroze Ahmed,
presented to the International Workshop on Arsenic on January 14-16 2002
in
Dhaka. A recent (2002) review from the
NGO forum is copied here from the NAISU website in
pdf
or
html
.
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 in Groundwater of
Sedimentary Aquifers.
Applied Geochemistry, 19(2), 163-260, February 2004
The table of contents, with links to
abstracts and full text,
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. although 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 sugegsted 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.:
“On the Spatial Variability of Arsenic Contamination in the Groundwater
of Bangladesh; A Geochemical and Hydrological
Analysis of Arsenic Mobilization at a Field Site in Bangladesh” and a
brief
report in Science
(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. Applied Geochemistry, 19(2), 163-260, February 2004,
201-214. Y. Zheng, M. Stute, A. van Geen, I. Gavrieli, R. Dhar, H. J.
Simpson, P. Schlosser and K. M. Ahmed.
(c) Professor McArthur and colleagues at UCL in London have several
reports available of which the following may be downloaded -
Arsenic in groundwater: testing pollution mechanisms for sedimentary
aquifers in Bangladesh, Their most recent
paper is: “Natural organic matter in sedimentary basins and its relation
to arsenic in anoxic ground water: the example of West Bengal and its
worldwide implications,” by J.M. McArthur and others is available at
http://www.es.ucl.ac.uk/research/lag/as/ This
shows that the arsenic pollution in West Bengal appears to be related
spatially to the distribution of organic matter in the aquifer. The
authors also argue that tectonics influence arsenic pollution, and that
peaky vertical profiles of arsenic pollution in ground water, seen widely
across the Bengal Basin, show that abstraction of water, for domestic use
and irrigation, is purging the shallow aquifer of arsenic pollution.” If
so that is good news indeed.
In June of 2005, a collaborative study between the Department of
Geological and Environmental Sciences, Parsons Laboratory at M.I.T, the
Consortium for Advanced Radiation Sources and Department of Geophysical
Sciences at the University of Chicago has established that As may be
released at the near-surface and is then leached to greater depths. Among
other things, they establish the existence of a consistent input of
Arsenic via sediment deposition. Further details can be obtained at the
SOS-Arsenic website
.
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.
Social Issues
Western experts from developed countries often
regard the arsenic pollution problem as a technical problem to be solved
by purely technical means. But that is naive. There are tremendous
social issues which control the ability of anyone to help. One set of
papers discussing these has been
put on
the APSU website and is also
copied on this site.
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 four arsenic conferences in
Dhaka held by
Dhaka
Community
Hospital. Also
please comment upon the
recommendations of the conference organized by
WHO but sponsored by the Bangladesh Government in January 2002.
“It is
an uncanny thought that this lurking poison (arsenic) is everywhere about
us, 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.
Contact
us
Please tell us what is missing from this website,
and send any useful material you know about to us at
wilson5@fas.harvard.edu
. If you wish to be informed of any updates, please send an e-mail and
say: “Please keep me informed!”
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