Arsenic Pollution of
Groundwater in Lahore,
Pakistan
Karen Hudson-Edwards
Kausar J. Cheema, Moneeza .R. Abbas, M.Atiq ur Raman
Lahore College for Women University, Pakistan
Thanks to…
• Mark Maslin
• Sarah Bell
• Tony Osborn
Currently > 50% of the global population lives in urban areas,
& this is projected to increase considerably by 2050
www.wateraid.org
Therefore, the quality of urban
environments is a matter of global concern
who.int/water_sanitation_health
Millenium Development Goal: to halve, by 2015, the
number of people without access to adequate-quality
drinking water and basic sanitation
Arsenic Pollution of Groundwater in
SE Asia
www.rgs.org
Problems with Excess As Intake
phys4.harvard.edu
Lahore, Pakistan
www.opf.org.pk/home/photos/53.jpg
www.historycentral.com/nationbynation/
Pakistan/Map.gif
Irrigation & Agriculture
pakistanhousing.pk
lahorenama.files.wordpress.com/
2009/01/canal.jpg
Extensive lowering of water
table in Lahore over past
decades due to agricultural
and industrial use
Mechanisms of Arsenic Pollution
of Groundwater
IRON OXIDE REDUCTION
Arsenic-bearing Iron Oxide + Organic
Matter + Carbonic Acid

Arsenic + Iron + Alkalinity
PYRITE OXIDATION
Arsenic-bearing pyrite (iron sulphide) +
Oxygen + Water

Arsenic + Iron + Sulphate + Acidity
EVAPORATIVE CONCENTRATION
Arsenic level in Selected Union
Councils of Lahore along the river Ravi
N
W
E
S
Cantt.
Area
2
0
2
4
6
8 Kilometers
Road.shp
River.shp
Rail.shp
Canals.shp
River_objects.shp
Arsenic Level ppb
Administrative boundary
0 - 10
11 - 50
51 - 100
101 - 1000
1001 - 4870
U_c.shp
Arsenic
As (ug/L)
1
10
100
1000
10000
0
Depth (m)
50
100
150
200
250
300
Allama Iqbal
Aziz Bhatti
Data Gunj Baksh
Gulberg
Nishtar
Ravi
Samanabad
Shalimar
Wahga
50 ug/L
10 ug/L
5 of 52 wells (10%) contain < 10 ug/L As,
39 of 52 wells (75%) contain < 50 ug/L As
No relation between As and well depth
Wells contain very low amounts of Cu, Pb, Ni, Cr
Major Element
Chemistry
400
10:1
Two groups defined on
Na:Cl ratios:
4:1
200
3:1
100
1:1 to 4:1 – largely salt
weathering
1:1
0
0
25
50
75
100
125
Cl (mg/L)
4:1 to 15:1 – silicate and
salt weathering, + ion
exchange
18
15
Si (mg/L)
Na (mg/L)
15:1
300
12
9
6
Most saline
sample
3
0
0
25
50
75
Cl (mg/L)
100
125
Some saline
samples have high
As, suggesting
some evaporative
control, but there
are also moderate
Cl samples with
low As
125
Cl (mg/L)
100
75
50
Controls on
Arsenic?
25
0
1
10
100
1000
10000
No clear
relationship
between As and
Cl or As and Si
As (ug/L)
18
Weak increasing trend for
As < 50 ug/L, suggesting
some(?) silicate weathering
control?
Si (mg/L)
15
12
9
6
3
0
1
10
100
As (ug/L)
1000
10000
No clear relationship between Arsenic & Fluoride
Arsenic level in Selected Union
Councils of Lahore along the river Ravi
Fluoride level in Selected Union
Councils of Lahore along the river Ravi
N
N
W
E
W
E
S
S
Cantt.
Area
0
2
4
6
8 Kilometers
Road.shp
River.shp
Rail.shp
Canals.shp
River_objects.shp
Arsenic Level ppb
Administrative boundary
0 - 10
11 - 50
51 - 100
101 - 1000
1001 - 4870
U_c.shp
2
0
2
4
6
8 Kilometers
Fluorides.shp
Road.shp
River.shp
Rail.shp
Canals.shp
River_objects.shp
Flouride Level ppm
Adminstrative Boundary
0 - 1.5
1.6 - 2.5
2.6 - 3.6
U_c.shp
10000
As (ug/L)
2
Cantt.
Area
1000
100
10
1
0
1
2
3
F (mg/L)
4
5
As (ug/L)
10000
High As
with high
NO3
1000
100
Redox Sequence
O2/H2O
10

1
0
50
100
150
200
250
NO3/N2
NO3 (mg/L)
As (ug / L)
10000
1000

100
10
1
0
50
100
150
200
Redox
Controls
> 50 ug/L wells show
increasing Mn and Fe
with increasing As: This
and low DO% suggests
some As-bearing hydrous
Fe-Mn oxide reduction
Mn4+/Mn2+
BUT there are wells
with high Mn and Fe
and low As

Most wells contaminated
with NO3: this does not
appear to suppress
hydrous Fe-Mn oxide
reduction: mixing of two
sources?
250
Mn (ug/L)
As (ug/L)
10000
1000
100
Fe3+/Fe2+
10
1
0
100
200
300
Fe (ug/L)
400
500
600
Controls on Arsenic – SO4
West Bengal
1400
Lahore
1200
As ppb
1000
800
5000
600
400
4000
0
0
5
10
15
20
25
30
35
SO4 ppm
Lack of As-SO4
relationship suggests
pyrite weathering not
responsible for As
As (ug/L)
200
3000
2000
1000
0
0
50
100
150
200
SO4 (mg/L)
As-bearing pyrite framboid:
Removal of As and SO4
through sulphide precipitation
Similar pattern suggests similar
processes may be occurring.
250
Arsenic Summary (1)
• 25% of 52 Lahore wells have As > 50 ug/L
• As does not relate to:
– Depth
– Silicate/salt weathering (?except at low
concentrations)
– Contamination with industrial chemicals (Cu, Pb,
Cr, etc.)
Arsenic Summary (2)
• As may relate to:
– Evaporative concentration
– Hydrous As-bearing Fe-Mn oxide reduction
– Removal by sulphide precipitation
– ?Nitrate contamination? (but may reflect mixing
of two sources of water)
Overall Summary
• As groundwater contamination in
Lahore appears to be related to natural
rather than anthropogenic causes, but
there are mixed signals and more work
is needed
• Urban groundwater chemistry is very
complicated
Gaps in Data / Knowledge
• Data on industry, agriculture, sewage
disposal, etc.
• Chemical and biological influences on
contaminant behaviour
• Influence of contaminants on human health
• Water management and remeciation policies
and methods