Explaining Low Bioavailability Explaining Low Bioavailability of Metals in Contaminated of Metals in Contaminated

Urban SoilsUrban Soils

Sauvé S, Ge Y, Murray P, Hendershot WSauvé S, Ge Y, Murray P, Hendershot W

Département de chimie, Université de Montréal

Department of Natural Resource Sciences, Macdonald Campus of McGill University

© Sauvé 2001

Explaining…Explaining…

Soil chemistry

• pH

• partitioning

• chemical speciation

Bioavailability

• plant metal uptake

• soil fauna

• soil microbial process

© Sauvé 2001

4 5 6 7 8 9Soil pH

0

5

10

15

20

0.0

0.1

0.2

0.3

0.4

0.5 Proportio

n p

er B

ar

4 5 6 7 8 9Soil pH

0

10

20

30

40

50

60

0.00.10.20.30.40.50.60.70.8 Pro

portio

n p

er B

ar

Soil pH RangesSoil pH Ranges3045 US Agricultural soils

Mean pH=6.3

70 Montreal Urban soils

Mean pH=7.7

Holmgren et al. 1993. J. Environ. Qual. 22:335-348.

Ge et al. 2000. Environ. Pollut. 107:137-144 and Sauvé et al. 1998. Environ. Pollut. 98:149-155.

10th centile = 5.0

90th centile = 7.9

© Sauvé 2001

PartitioningPartitioning

TotalOM-Bound

Free Metal

Cl Complexes

SO4 Complexes

© Sauvé 2001

Solid/liquid PartitioningSolid/liquid Partitioning

• Assumes a unique and constant ratio between solution and solid phases:

• Total metal is in mg/kg dry soil and dissolved metal is in mg/L, hence Kd are usually reported as L/kg

• Sensitive to determination method, solid:liquid ratio, extracting solution, time of extraction and filtration

MetalDissolved

MetalTotalKd

© Sauvé 2001

Dependence of KDependence of Kdd on pH on pH

For a compilation of literature Kd’s, 29 to 58 % of the variability depends on soil solution pH.

Soil Solution pH

2 4 6 8 10

Soil Solution pH

2 4 6 8 10

Soil Solution pH

2 4 6 8 10

Soil Solution pH

2 4 6 8 10

Soil Solution pH

2 4 6 8 10

Kd(L

kg

-1)

10-1100101102103104105106107

Cd Cu Ni

Pb

Zn

Sauvé S. Hendershot W., Allen H.E. 2000. «Solid-Solution Partitioning of Metals in Contaminated Soils: Dependence on pH, Total Metal and Organic Matter  ». Environ. Sci. Technol. 34:1125-1131 .

© Sauvé 2001

Solution SpeciationSolution Speciation

3 4 5 6 7 8 9pH

2

4

6

8

10

12

p(ac

tivity

)

3 4 5 6 7 8 9pH

2

4

6

8

10

12

p(ac

tivity

)Cu=250 mg kg-1

Cu2+

CuOH+

Cu(OH)20

CuCO30

CuSO40

CuNO3+

CuCl+CuTotal

© Sauvé 2001

PartitioningPartitioning

1.E-10

1.E-8

1.E-6

1.E-4

1.E-2

1.E+0

1.E+2

1.E+4

7.41 7.21 6.99 4.73 3.91

Soil Solution pH

Co

nta

min

atio

n (

mg

Cu

/kg

dry

so

il)

Total Dissolved Free

Sauvé S. 2001. The Role of Chemical Speciation in Bioavailability. In: Naidu R., Gupta V.V.S.R., Kookana R.S., Rogers S., Adriano D. (Eds.), Bioavailability, Toxicity and Risk Relationships in Ecosystems. (in press).

MineralMineral Solubility Solubility EquilibriaEquilibria

3 4 5 6 7 8 9pH

0

2

4

6

8

10

12

p (a

ctiv

ity)

CdOH2

CdCO 3

CdSO4·2Cd(OH)2

Cd3(PO4)2

3 5 7 9

0

4

8

123 5 7 9

0

4

8

123 4 5 6 7 8 9

pH

0

2

4

6

8

10

12

Cu(OH) 2

CuO

Cu4(OH)6SO4

CuCO 3

Cu3(PO4)2·H2O

3 5 7 9

0

4

8

123 5 7 9

0

4

8

123 4 5 6 7 8 9

pH

0

2

4

6

8

10

12

Pb2(CO)2(OH)2

PbOPb(OH)2

PbSO4PbHPO4

Pb5(PO4)3OH

Pb5(PO4)3Cl

3 5 7 9

0

4

8

123 5 7 9

0

4

8

12

Sauvé S. 2001. «The Role of Chemical Speciation in Bioavailability » In: Naidu R., Gupta V.V.S.R., Kookana R.S., Rogers S., Adriano D. (Eds.),

Bioavailability, Toxicity and Risk Relationships in Ecosystems. (in press).

© Sauvé 2001

Chicory uptake of CdChicory uptake of Cd

0 5 10 15 20Soil Total Cd (mg/kg)

01020304050607080

Leaf

Cd

(mg /

k g)

0 5 10 15 200

1020304050607080

Ge Y, Murray P, Sauvé S, Hendershot W. Low metal bioavailability in a contaminated urban site. Submitted to Environmental Toxicology and Chemistry.

© Sauvé 2001

Linking plant uptake and soil Linking plant uptake and soil metalsmetals

Dandelion, bladder campion, chicory with Cd, Cu, Ni, Pb and Zn (n=20 to 40)

Bladder campion (leaf) Cd, Ni, Pb and Zn were significant, but not Cu.

Dandelion, Cd and Zn (leaves and roots) were significantly related to total metals

For chicory, only Pb in the roots had any significant relationship with total soil Pb

© Sauvé 2001

Dandelion field dataDandelion field data

Marr K, Fyles H, Hendershot W. 1999. Trace metals in Montreal urban soils and the leaves of Taraxacum officinale. Canadian Journal of Soil Science 79:385-387.

© Sauvé 2001

Soil RespirationSoil Respiration

Dumestre A, Sauvé S, McBride M, Baveye P, Berthelin J. 1999. Copper speciation and microbial activity in long-term contaminated soils. Archives of Environmental Contamination and Toxicology:36:124-131.

BioavailabilityBioavailability

No consistent predictor of plant metal uptake

In the field, wild chicory was absent from the most contaminated sites

Soil respiration (in a glucose amendment assay) is unaffected by metals

Nitrification potential significantly inhibited by higher Cu, Ni, Pb and Zn levels Ge Y, Murray P, Sauvé S, Hendershot W. Low metal bioavailability in a

contaminated urban site. Soumis à Environmental Toxicology and Chemistry.

© Sauvé 2001

EarthwormsEarthworms

10 100 1000 10000

Soil Cu (mg·kg-1)

0

20

40

60

80

100

Tiss

ue M

e ta l

(mg ·

k g-1

)

R2=0.674***

N=11

10 100 1000 10000

Soil Pb (mg·kg-1)

0

10

20

30

40

R2=0.714***

N=11

Soil Zn (mg·kg-1)

0

200

400

600

800

R2=0.329*

N=11

Kennette D, Sauvé S, Hendershot W, Tomlin A. 2001. Uptake of trace metals by the earthworm Lumbricus terrestris L. in urban contaminated soils. Applied Soil Ecology (sous presse).

© Sauvé 2001

Soil FaunaSoil Fauna

Little or no toxicological effects on earthworms, albeit some accumulation of metals is observed

No effects observed on species occurrence or distribution of soil invertebrates

Could represent a risk for trophic transfer to worm-eating birds or rodents

© Sauvé 2001

ConcernsConcerns

Wild chicory is absent from the most contaminated areas of the site and this suggests a potential for reduced species diversity

The sensitivity of soil microbes responsible for nitrification also suggests that nutrient cycling is affected, with some potential effects on species distribution

© Sauvé 2001

Concerns at mid- to long-Concerns at mid- to long-termterm

No drastic effects, but nevertheless some problems with a decreased sustainability of the ecosystem on some sites

Present, future and potential land uses have to be considered