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

Thanks to…

• Mark Maslin

• Sarah Bell

• Tony Osborn

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

Arsenic Pollution of Groundwater inSE 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

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

Gaps in Data / Knowledge

• Data on industry, agriculture, sewagedisposal, etc.

• Chemical and biological influences oncontaminant behaviour

• Influence of contaminants on human health

• Water management and remeciation policiesand methods