Environmental risks in resource-poor settings:
the case of salination and climate change
Aneire E. Khan
Paolo Vineis
A neglected consequence of climate change is the
increasing salinity level in coastal areas, due to several
mechanisms including sea level rise.
Salinity in drinking water can reach extremely high levels
like in coastal Bangladesh, and potentially millions of
people are exposed to a substantial risk of high blood
pressure.
The setting and the problem
•
Bangladesh is vulnerable to natural
hazards and the future effects of
climate change.
–
Deltaic plains of the Ganges,
Brahmaputra Meghna rivers
–
Suffer from acute climate events –
floods, droughts, cyclones
–
Long-term environmental
degradation → salination & soil
degradation, river erosion
–
Effects likely to be exacerbated by
climate change & sea-level rise
Simplified causal diagram of salinity & health
Shrimp farming
Poor land
management
Runoff
Rainfall,
Monsoon
River flow
Snowmelt
Sea-level
rise
CLIMATE CHANGE
Estuarine
intrusion
Saltwater
intrusion
[shallow
groundwater]
Surface water
salinity
[downstream]
[river]
Pond water
[consumption]
Health
effects
Prevalence of hypertensive disorders in women attending antenatal
check-ups in Dacope and other areas [May – July 2007] (Khan et al.,
Lancet 2008)
16
14
12
10
preeclampsia
eclampsia
hypertension
8
6
4
2
0
Dacope
Terokhada
Matwail
Prevalence rates of hypertension (with or without proteinuria)
among pregnant patients aged 13-45, recorded between July 2008
and March 2010 in Upazilla Health Complex, Dacope, Bangladesh.
Month
No. of cases
Total no. of pregnancies
Prevalence (95 % C.I.)
May – Sept
Oct - April
20
70
393
576
5.09 (2.91 – 7.26)
12.2 (9.48 – 14.8)
Total
90
969
9.28 (7.46 – 11.1)
Prevalence odds ratio (95% CI): 2.39 (1.43 – 3.99)
Khan et al, Environmental Health Perspectives, 2011
Geographic distribution of sodium levels in water
Average sodium levels in drinking water in the different areas
included in the study (1,006 healthy pregnant women at week 20 of
pregnancy)(Khan et al, submitted)
Mean Water Sodium by water source
24-hr urinary sodium (mmol/d) by water source
Testing the hypothesis: case-control study
Logistic regression of disease outcome (pre-eclampsia,
eclampsia and/or gestational hypertension) with water sodium
levels
Water sodium mg/L
Cases (n=202)
Controls
(n=1006)
Min – 300
43 (21.3)
1.00
2.73 (1.70 – 4.40)
3.36 (2.07 – 5.60)
3.65 (2.30 – 5.80)
4.35 (2.61 – 6.94)
5.21 (3.25 – 8.33)
5.40 (3.28 – 8.92)
97 (17.5)
900.01 - max
59 (29.2)
1.00
106 (19.2)
600.01 – 900
55 (27.2)
OR Adjusted by age,
parity, SES
277 (50.1)
300.01 – 600
45 (22.3)
Crude Odds Ratio
(OR)
73 (13.2)
A large share of the population in coastal Bangladesh may be
consuming levels of up to 16g/day of salt in the dry season from
only 2L of natural drinking water.
Based on the INTERSALT model, the changes introduced by water
salinity would lead a large proportion of the population to develop
pre-hypertension (systolic BP between 120 and 139mmHg or
diastolic BP between 80 and 89mmHg) and hypertension
(SBP>140mmHg or DBP>90mmHg), depending on the baseline
levels.
The larger picture
634 million people live in coastal areas within 30 feet (9.1m) of sea
level. About two-thirds of the World’s cities with over 5 million
people are located in these low-lying coastal areas.
The IPCC predicts that sea level will further increase in the next
decades. This will make the problem of salinity in drinking water
becoming a major health issue in most coastal areas, particularly
in low-income countries.
Relative vulnerability of coastal deltas by number of people potentially
displaced by trends to year 2050. (Extreme= >1 million; High= 1 million
to 50,000; Medium=50,000 to 5000. (Ericson et al 2006)
Perspectives
For better description and prediction - including in
other areas of the world - remote sensing can be used
Satellite images capture the density of “yellow matter”
(CDOM) in estuaries and ponds. Yellow matter is an
indirect and reliable estimate of salinity
(in collaboration with D Bowers, Bangor University)
A satellite image of Bangladesh. Much of the country is a vast river
delta for the Ganges, Brahmaputra and Meghna Rivers. Directly in the
middle of the image, just at the edge of the world’s largest mangrove
forests – the Sundarbans (dark green ), shrimp farming has taken over
from rice farming.
Photo from http://www.spiegel.de/fotostrecke/fotostrecke-21321-2.html
Relationship between surface salinity and CDOM in the Clyde Sea.
(Binding et al 2003)
Relationships between surface salinity and yellow substance
(g440) for each of the three Clyde Sea surveys at different time
points. (Binding et al 2003)
Summary of studies that have used satellite images for salinity modelling in estuarine areas,
using CDOM as a proxy
Sensor
Spatial
resolution
R2
Value
Difference
Between
Observed and
Predicted
Salinity (ppt)
Observed
Salinity Range
(ppt)
Reference
Sofala
Bank,
Mozambi
que
SeaWifs
1.1km
0.76
±1.5
24-35
Siddorn et al 2001 (122)
Clyde
Sea,
Scotland
SeaWifs
1.1km
0.93
+1.1
16-34
Binding et al 2003
East
China
Sea
SeaWifs
1.1km
0.86
±1.0
26-34
Y.H.Ahn et al 2008 (123)
Columbia
River
Plume,
USA
MODIS
250m
0.92
Single value
unavailable as
authors used 2
different models at
2 different dates***
0-30
Palacios et al 2009 (124)
Mandovi*
and Zuari
Estuary
Ocean
Colour
Monitor
360m
0.76
Correlation,
R2=0.75
31-34
Menon et al 2010 (125)
Location
Estimates of the overall impact on a world scale – in estuarine
areas - can be made after validation of satellite data.
We are now conducting a study in Bangladesh that combines
hydrology (Adrian Butler, Mohammad Hoque, Imperial
College), sodium measurements in 500 women (Aneire Khan,
ICL) and satellite data (Pauline Scheelbeek, Yu-Jeat Chong,
ICL; David Bowers, Bangor University)
Funded by the Grantham Institute, Imperial College, and
Leverhulme Trust (grant to PV, 2011)
Thank you!