Water at the Heart of Science
9
Unhealthy
Water
The primary cause of diseases
in the world is water, which can contain a variety of contaminants of natural, agricultural,
mining or industrial origin. Nearly 150 major rivers are considered to be polluted, particularly
in developing countries.
Numerous contaminants
Diagnosis and treatment
Water provides a favourable
environment for the
development of viruses,
parasites, bacteria and insects
that carry diseases. Stagnant
water is a breeding ground for
infection, especially in warm
regions. Agricultural fertilisers
and pesticides pollute
waterways, while mining and
industrial activities contribute
to an alarming increase
in heavy metals in certain
rivers and aquifers. So-called
“emerging” contaminants
such as residues of medicinal
products or nanoparticles are
also found.
Researchers are developing
methods to analyse and tools
to detect these pollutants.
Progress in measuring
techniques has made it possible
today to identify “emerging”
contaminants or traces thereof.
Computer models simulate the
processes by which pollutants
are transferred to ground and
surface water. Researchers
are also studying their impact
on ecosystems and people’s
health. Finally, they are
looking at water treatment
processes suited to each type
of contaminant.
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1 2 million tonnes of waste are
thrown into rivers each day, without
any form of treatment.
2 1.4 million children die every year
from diarrhoeal diseases that might
have been prevented if they had
access to safe drinking water and
sanitation.
3 Intensification of human activities
over the past century has led to the
increased pollution of waterways.
Lead and arsenic contamination
caused by mine drainage in the Oruro
region in Bolivia.
4 Nitrates used as fertiliser greatly
pollute most of the freshwater in
North America, Europe and Asia.
Discarded in the sea, they intensify
the development of green algae.
5 All factors considered and on an
average global scale, half of all
freshwater species have become
extinct since 1970. The European eel
is in critical danger of extinction, due
inter alia to pesticides that diminish
its capacity to reproduce.
6 Water is a breeding ground for
numerous disease vectors such as
malaria and dengue fever. This
picture shows tiger mosquito larvae,
which is vector of Chikungunya fever.
7 Collecting sediment samples from
Lake Uru Uru in Bolivia. Tests are
done to detect traces of industrial
metals dissolved in the water.
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Water at the Heart of Science
10
Trapping
Arsenic
The arsenic-contaminated
aquifer of Mekong
is causing serious public health problems for village populations
in Cambodia and Vietnam. Researchers are looking for ways to purify the water.
The aquifer is polluted partly
by farming pesticides, but
above all by a natural process:
the dissolution of a mineral
contained in upstream rocks,
namely arsenic-rich pyrite
(iron sulphide with traces of
arsenic).
If left untreated, arsenic-rich
drinking water generates
serious health problems. The
presence of arsenic, which
was recently detected in this
region, causes skin lesions that
can lead to death.
Financed by the Francophone University
Agency (AUF) and coordinated by the Institute
of Technology of Cambodia in Phnom-Penh,
this research is carried out jointly with the
Technological University of Ho Chi Minh
(Vietnam) and a team from CIRAD (France,
Unité de service «Analyse des eaux, sols et
végétaux»).
Researchers have developed
a purification system to make
the water drinkable. It uses
ordinary materials: a layer of
crumbled bricks dispersed in
the water of the system, a bed
of nails to increase the iron
content of the water which
helps to capture the arsenic,
and a sand filter with grains of
increasing size to retain the
arsenic-iron mixture.
The equipment is easy to use,
simple to maintain, low in cost,
and provides efficiently in the
needs of a household or a small
village.
1 Agriculture is a significant source of
contamination.
2 Arsenic is present in the
groundwater of the aquifer at levels
of 40 to 1,200 µg/l, whereas the
maximum rate recommended for
human consumption by the World
Health Organisation is around 10 µg/l.
3 A test to measure the arsenic ratio
in water.
1
Mekong
5 The purification system efficiently
reduces the initial arsenic content to
an acceptable level recommended by
the WHO.
6 Researchers are now wondering
whether the arsenic could also be
transmitted to the food chain. They
are planning to study irrigation water
and the arsenic concentration in
planted crops.
4 About ten of these purification
systems can provide the inhabitants
of a village with safe drinking water.
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Water at the Heart of Science
11