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Arsenic Pollution ofGroundwater in Lahore,
Pakistan
Karen Hudson-Edwards
Kausar J. Cheema, Moneeza .R. Abbas, M.Atiq ur Raman
Lahore College for Women University, Pakistan
Therefore, the quality of urbanenvironments is a matter of global concern
Currently > 50% of the global population lives in urban areas,& this is projected to increase considerably by 2050
www.wateraid.org
Millenium Development Goal: to halve, by 2015, thenumber of people without access to adequate-quality
drinking water and basic sanitation
who.int/water_sanitation_health
Lahore, Pakistan
www.opf.org.pk/home/photos/53.jpg
www.historycentral.com/nationbynation/Pakistan/Map.gif
Irrigation & Agriculture
lahorenama.files.wordpress.com/2009/01/canal.jpg
pakistanhousing.pk
Extensive lowering of watertable in Lahore over pastdecades due to agriculturaland industrial use
Mechanisms of Arsenic Pollutionof Groundwater
IRON OXIDE REDUCTIONArsenic-bearing Iron Oxide + Organic
Matter + Carbonic Acid
Arsenic + Iron + Alkalinity
PYRITE OXIDATIONArsenic-bearing pyrite (iron sulphide) +
Oxygen + Water
Arsenic + Iron + Sulphate + Acidity
EVAPORATIVE CONCENTRATION
N
EW
S
Arsenic level in Selected UnionCouncils of Lahore along the river Ravi
U_c.shp
Arsenic Level ppbAdministrative boundary0 - 1011 - 5051 - 100101 - 10001001 - 4870
River_objects.shpCanals.shpRail.shpRiver.shpRoad.shp
Cantt.Area
2 0 2 4 6 8 Kilometers
Arsenic
5 of 52 wells (10%) contain < 10 ug/L As,39 of 52 wells (75%) contain < 50 ug/L AsNo relation between As and well depthWells contain very low amounts of Cu, Pb, Ni, Cr
0
50
100
150
200
250
300
1 10 100 1000 10000
As (ug/L)
De
pth
(m)
Allama Iqbal Aziz Bhatti Data Gunj Baksh Gulberg
Nishtar Ravi Samanabad Shalimar
Wahga 50 ug/L 10 ug/L
0
100
200
300
400
0 25 50 75 100 125
Cl (mg/L)
Na
(mg/ L
)
1:1
4:1
15:1 10:1
3:1
0
3
6
9
12
15
18
0 25 50 75 100 125
Cl (mg/L)
Si(m
g/ L
)
Major ElementChemistry
Two groups defined onNa:Cl ratios:
1:1 to 4:1 – largely saltweathering
4:1 to 15:1 – silicate andsalt weathering, + ionexchange
Most salinesample
Controls onArsenic?
0
3
6
9
12
15
18
1 10 100 1000 10000
As (ug/L)
Si(m
g/ L
)
0
25
50
75
100
125
1 10 100 1000 10000
As (ug/L)
Cl(m
g/ L
)
No clearrelationshipbetween As andCl or As and Si
Some salinesamples have high
As, suggestingsome evaporativecontrol, but thereare also moderateCl samples with
low As
Weak increasing trend forAs < 50 ug/L, suggestingsome(?) silicate weatheringcontrol?
N
EW
S
Fluoride level in Selected UnionCouncils of Lahore along the river Ravi
U_c.shp
Flouride Level ppmAdminstrative Boundary0 - 1.51.6 - 2.52.6 - 3.6
River_objects.shpCanals.shpRail.shpRiver.shpRoad.shpFluorides.shp
Cantt.Area
2 0 2 4 6 8 Kilometers
N
EW
S
Arsenic level in Selected UnionCouncils of Lahore along the river Ravi
U_c.shp
Arsenic Level ppbAdministrative boundary0 - 1011 - 5051 - 100101 - 10001001 - 4870
River_objects.shpCanals.shpRail.shpRiver.shpRoad.shp
Cantt.Area
2 0 2 4 6 8 Kilometers
No clear relationship between Arsenic & Fluoride
1
10
100
1000
10000
0 1 2 3 4 5
F (mg/L)
As
(ug
/ L)
1
10
100
1000
10000
0 50 100 150 200 250
NO3 (mg/L)
As
(ug
/L)
1
10
100
1000
10000
0 50 100 150 200 250
Mn (ug/L)
As
(ug
/ L)
1
10
100
1000
10000
0 100 200 300 400 500 600
Fe (ug/L)
As
(ug
/L)
O2/H2O
NO3/N2
Redox Sequence
Mn4+/Mn2+
Fe3+/Fe2+
> 50 ug/L wells showincreasing Mn and Fe
with increasing As: Thisand low DO% suggests
some As-bearing hydrousFe-Mn oxide reduction
Most wells contaminatedwith NO3: this does not
appear to suppresshydrous Fe-Mn oxide
reduction: mixing of twosources?
High Aswith highNO3
RedoxControls
BUT there are wellswith high Mn and Fe
and low As
Controls on Arsenic – SO4West Bengal
As-bearing pyrite framboid:Removal of As and SO4
through sulphide precipitation
Lahore
Similar pattern suggests similarprocesses may be occurring.
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30 35
SO4 ppm
As
pp
b
0
1000
2000
3000
4000
5000
0 50 100 150 200 250
SO4 (mg/L)
As
(ug
/L)
Lack of As-SO4
relationship suggestspyrite weathering not
responsible for As
Arsenic Summary (1)
• 25% of 52 Lahore wells have As > 50 ug/L
• As does not relate to:
– Depth
– Silicate/salt weathering (?except at lowconcentrations)
– 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 mixingof two sources of water)
Overall Summary
• As groundwater contamination inLahore appears to be related to naturalrather than anthropogenic causes, butthere are mixed signals and more workis needed
• Urban groundwater chemistry is verycomplicated
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