lead lability in alluvial soils of the river trent catchment, u.k. m. izquierdo, a.m. tye, s.r....

Lead lability in alluvial soils of the river Trent catchment, U.K.M. Izquierdo, A.M. Tye, S.R. Chenery

British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

Lead lability in alluvial soils of the river Trent catchment, U.K.M. Izquierdo, A.M. Tye, S.R. Chenery

British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

SOURCE APPORTIONMENT

27 sampling sites

paired topsoils (0-15cm)

and subsoils (35-50cm)

+ extraction of pore waters

Pb= 40-1280 mg/kg

Extensive Pb mining since pre-Roman times

Pb-rich sediments still pulse into the Trent tributaries

Floodplains downstream the Orefield are a primary Pb repository

ACKNOLEDGEMENTS

Pb IN TRENT ALLUVIAL SOILS

Overbank sediments in the river Trent

floodplains act as a focus for deposition

and short- to long-term storage of Pb

Pb can be released back into the drainage

network through bank erosion

Potential for increased Pb uptake to grazing

livestock, terrestrial and aquatic

ecosystems

AIMS & METHODOLOGY

Pb SOURCES IN THE TRENT CATCMENT

2. Coal

Coal mining

Coal combustion emissions

3. ‘BHT’ Pb

Diffuse source

Petrol-derived

1. Pennine Ore

Examine the sources, lability and

solubility of Pb in alluvial soils from

the River Trent and River Dove

Pb source apportionment

Pb Isotope dilution

2.350

2.370

2.390

2.410

2.430

2.450

2.470

2.490

1.070 1.090 1.110 1.130 1.150 1.170 1.190

208 P

b/20

7 Pb

206Pb/207Pb

coal

Pennine ore (galena)UK petrol lead

pore water surfacetopsoil

pore water subsoilsubsoilLondon aerosols

labile poolroad dustsewage

BHT (petrol) Pb

UK coalPennine Pb ore

Km d

owst

ream 0

50

100

150

200

2500 20 40 60 80 100

Lability %E

2 3 4 5 6 7pH

8

pH% E

206Pb/207Pb1.100 1.200

Pennine ore Pb dominant BUTBHT (petrol) Pb contribution=0-

50% despite withdrawal in 2000

BHT Pb in subsoilspost depositional vertical

migration of Pb from traffic related sources

Pb LABILITY-10

0

10

20

30

40

50

-10 10 30 50

% petrol Pb

topsoil

su

bsoil

Current UK regulations on metal contamination are based on the total

concentration in soil no indication of the chemically reactive or labile

fraction of a given element in a soil system

ISOTOPE DILUTION TECHNIQUES (E-value) allow the determination of

the reactive pool of metal in soils i.e. pool of metal in equilibrium with soil

pore water

L labile: soluble+adsorbed+solubilised in pore waterN fixed Pb: occluded, inert, inaccessible

NN

LN

L

N

LL

LL L

NN

LN

L

N

LL

LL L

spike 204Pb

E-VALUE Isotopically exchangeable fraction:

geochemically active – bioavailable for uptake

LABILE Pb=9-56% over the total pool

No differences in Pb lability with depth

No Pb >fixation with depth

evidence of continuous

bank recycling

No differences in Pb

contents with depth

No source control on lability

Strong pH control on %E

1.120

1.130

1.140

1.150

1.160

1.170

1.180

1.190

1.120 1.130 1.140 1.150 1.160 1.170 1.180 1.190

LABILE POOLNONLABILEPORE WATER

This work has been funded by a Marie Curie Fellowship (Project no. 254983) to M.Izquierdo

206Pb/207Pb

208 P

b/20

7 Pb

Pb isotopic ratios in total, labile and pore water pools

Enrichment of ‘BHT’ Pb in the bioavailable poolspossible causes

BHT Pb still being deposited (dry/wet deposition + present/recent dissolution of poorly soluble traffic related Pb-bearing species

BHT Pb bound to sub-micron FeO colloids in soil pore waters

M.Izquierdo, A.M.Tye, S.R.Chenery Sci Total Environ 433 (2012) 110-122