Linking epidemiology to arsenic mitigation in Bangladesh
Dr Tony Fletcher
Environmental Epidemiology Unit, London School of Hygiene and
Tropical Medicine, Keppel St London WC1 7ET, UK
There is sufficient evidence to warrant immediate and large scale implementation
of mitigation strategies: evidence from both the many measurements indicating
hazardous levels of arsenic in drinking water, and the substantial numbers
of victims of arsenicosis (especially skin lesions) identified in some
communities in Bangladesh. It is important too that these efforts are prioritised
to alleviate the problem where it is, or could become, most severe, and
this aspect is rather uncertain.
Epidemiological approaches have much to offer in making the alleviation
of arsenic related disease in Bangladesh most effective, and I shall identify
some of the relevant contributions. By "epidemiology" I refer
to disciplines involved in understanding the causation of disease (which
usually comprises many interacting factors), quantifying the spread of
disease and evaluating both prevention and treatment. These would all appear
to be relevant in addressing the arsenic problem. It is by its nature multi-disciplinary
involving among others, collaborations between specialists with skills
in clinical medicine, biology, exposure assessment, laboratory analysis,
nutritional science, statistics and social science.
Epidemiological methods can be used to evaluate the effectiveness of
each approach to mitigation by conducting surveys of exposure, uptake,
health status and awareness, before and after the mitigation intervention.
The future success of the mitigation strategy will benefit from identifying
the most effective approaches. Careful design and quality control is necessary
to ensure that these comparisons are credible. The numbers who need to
be surveyed, depend on how many different circumstances are being assessed,
with due allowance for sufficient numbers of samples or examinations in
Epidemiological methods will allow a quantitative assessment of how
risk is related to arsenic uptake as well as other factors, such as other
water contaminants, nutritional intake, and general health status. This
information, combined with nation-wide mapping of the patterns of arsenic
contamination will assist in prioritising the mitigation programme. It
will also allow the first good estimate of the extent of current illness
attributable to arsenic. This is not just of academic interest as there
is uncertainty about what level of arsenic may be judged as "safe"
or if not safe, then in some sense "acceptable".
Characterising the dose response relationship will be an important practical
goal of the epidemiology. For this careful diagnosis and detailed characterisation
of patterns of water consumption, analysis of arsenic in the water, measurements
of arsenic in the body, and other factors, especially nutritional, will
all be required. Sufficient numbers of individuals with different exposure
will need to included to achieve some precision at the different exposure
levels, including the lower ones where the corresponding risk is lower.
Epidemiological methods can be used to predict and measure the medium
to long term impact of exposure to date, particularly in for the incidence
of cancers. Health impact estimation (using the results of studies in other
countries) will also allow the quantification of the long term impact if
exposure were allowed to continue. Establishment of a surveillance system,
for example in the framework of rural primary care schemes, should allow
improved prognosis arising from earlier diagnosis among the exposed population.
Follow-up of the population through careful surveillance and follow-up
of a population of known past exposure, will also provide a measure of
true incidence to compare with predicted estimates.
Helping to answer some urgent questions
There is no need to delay mitigation pending epidemiological research,
but the evolving mitigation programme should benefit from answers to the
- What is the magnitude of the health impacts?
- What are the future impacts?
- Is the mitigation successful? What are the determinants of successful
- What level of exposure is hazardous?
- Which clinical treatments work best?
To address these we need:
- In-depth baseline surveys of health status -
Providing prevalence of disease by range and severity of condition:
Skin lesions, psychosocial effects, cardiovascular problems, diabetes,
- Repeat surveys of health status -
To test impact of mitigation and impact of treatment, including any
problems in changes of water supply. Will need short term and long term
- In-depth baseline surveys of exposure and uptake -
Providing data on patterns of exposure in relation to pattern of well
contamination and consumption of contaminated food.
- Repeat surveys of exposure and uptake -
Essential for demonstrating effectiveness of mitigation.
- Dose-response analyses -
Linking the data on exposure to data on health status, the quantitative
relationship between arsenic exposure and ill-health can be described.
Essential to distinguish importance of water and food - Linked to national
water surveys, the total health impact may be estimated. Depending on the
shape of the relationship, it may be possible to identify a no-effect level
- Taking into account age, sex, nutritional status etc, we can identify
groups at higher risk.
- Socio-epidemiological surveys -
Epidemiology involves not just studying disease. Interviews and group
discussions will be needed to check on the population awareness, stigma
and long term sustainability of the mitigation, for example:
- Does the population appreciate the risks of both arsenic contaminated
and dirty water?
- Are they aware of the precautionary options?
- Can they still afford access to clean water?
- Are patients with arsenicosis still subject to stigma?
This will give insight into different characteristics of the mitigation
which may be more or less successful.
- Assessment of treatments -
For skin lesions, treatments (creams, dietary supplements) need to be
given but also assessed by clinical trials.
- Prediction and assessment of long term impacts -
From the detailed population exposure profile, long term effects such
as cancer can be predicted but extrapolations are uncertain. A follow up
study, following a sample of exposed villages to identify future cases
of cancer is recommended.