Contaminant Metals in Boston Harbor:Processes Influencing long-term fate

Bill MartinLinda KalnejaisMike Bothner

Study Site:Hingham Bay2000 - 2008

Ag, Pb, and Cu:1980 - 2002

8

6

4

2

20001995199019851980

Year

140

120

100

80

6.0

5.0

4.0

Cu

Ag

Pb

Al

Fe

Boston HarborStation 8

25

20

15

10

5

0

12080

Cu (ppm)

25

20

15

10

5

0

108642

Ag (ppm)

25

20

15

10

5

0

16012080

Pb (ppm)

Concentration vs. depth : 2002

Surface Sediments: Concentration vs. time

Cu, Ag, and Pb

All are associated with organic matter : Cu > Ag, Pb

All form stable complexes and sparingly soluble solid phases with S(-II)

All coprecipitate with / sorb to Fe oxides : Pb > Ag, Cu

Depth Distributions of Sedimentary ProcessesHingham Bay Site

(not to scale)

Data Treatment:Averaged and smoothed profiles

25

20

15

10

5

0

200150100500

Fe (µM)

HB July 02

25

20

15

10

5

0

0.80.60.40.20.0

Ag (nM)

HB July 02

25

20

15

10

5

0

Depth (cm)

3002001000Fe

2+ (µM)

January

25

20

15

10

5

0

Depth (cm)

10008006004002000

H2S (µM)

January July Sept./Oct

Fe and S cyclingWinter

25

20

15

10

5

0

Depth (cm)

10008006004002000

H2S (µM)

January July Sept./Oct

25

20

15

10

5

0

Depth (cm)

3002001000Fe

2+ (µM)

January July

Fe and S cyclingSummer

25

20

15

10

5

0

Depth (cm)

10008006004002000

H2S (µM)

January July Sept./Oct

25

20

15

10

5

0

Depth (cm)

3002001000

Fe (µM)

January July Sept./Oct.

Fe and S cyclingLate Summer / Early Fall

Trace Metal Cycling: Cu - Winter

25

20

15

10

5

0

3002001000Fe

2+ (µM)

January

25

20

15

10

5

0

50403020100

Cu (nM)

Trace Metal Cycling: Cu - Summer

25

20

15

10

5

0

3002001000Fe

2+ (µM)

January July

25

20

15

10

5

0

50403020100

Cu (nM)

January July

Trace Metal Cycling: Cu - Late summer

25

20

15

10

5

0

3002001000

Fe (µM)

January July Sept./Oct. 25

20

15

10

5

0

50403020100

Cu (nM)

Compare: Cu and Ag

25

20

15

10

5

0

50403020100

Cu (nM)

25

20

15

10

5

0

0.80.60.40.20.0

Ag (nM)

January July Sept./Oct.

Compare: Cu and Pb

25

20

15

10

5

0

12840

Pb (nM)

JanuaryJuly Sept./Oct.25

20

15

10

5

0

50403020100

Cu (nM)

The sedimentary environment

Sediment Resuspension:Experimental Setup

Sediment Resuspension:Mass resuspended vs. bottom stress

Solid Phase Metals

Dissolved metals

Longer-term releasefrom resuspended particles

Incubations: Filled : particle incubations Open: filtered controls

Bottom stress at theHingham Bay Site

80

60

40

20

0

Frequency (events/year)

0.400.350.300.250.200.150.10

Shear stress (N/m2)

Including Sediment-Seawater exchange in the budget for Cu in Boston Harbor

4000

3000

2000

1000

0

Input to harbor (kg/yr)

TributariesAtmosphereGroundwaterAirportCSO

StormwaterErosion - fastErosion - slowDiffusion

Sum: dissolvedSolid phase

Cu

Conclusions

Remobilization of contaminant metals, deposited earlier, may be asignificant source of metals to Boston Harbor.

Ongoing work: Complete analyses and interpretation of Boston Harbor and Mass Bay experiments. To date: Kalnejais (2005) - PhD Thesis (and presentations at AGU, ASLO, GSA) Oates (2008) MS Thesis Morford et al. (2007) Kalnejais et al. (2007) Martin and Kalnejais (2007)

Future work:

Update and extend contaminant metal budgets for Boston Harbor

Determine distributions of particulate metals in Mass. Bay - especially after important resuspension events