(Jeremiason et al., 1994) David Reckhow CEE 577 #36 1 Homologs - - PowerPoint PPT Presentation

Lecture #36 Toxics: PCBs in the Great Lakes

(Jeremiason et al., 1994)

David Reckhow CEE 577 #36 1

Updated: 17 April 2013

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What are the PCBs

 Biphenyl  2,2’ - Dichlorobiphenyl  2,3’ - Dichlorobiphenyl

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Cl Cl

4 2 3 4’ 5’ 6’ 2 3 5 6 1 1’

Cl Cl

Homologs (11) Isomers (1-46) Congeners (209)

History

 1930: Monsanto is major US producer  1970: Monsanto decides to sell PCBs only for

closed use

 1975: NY State warns public about salmon and

bass in Hudson

 1979: PCB manufacture banned in US  1982: NY State begins dredging “hot spots”  1990: all PCB-containing equipment must be

removed from US public buildings

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Arochlor Mixtures

 Arochlor 12xx (xx=% chlorine)

 1221: 50% Cl1, 35% Cl2  1232: 26% Cl1, 29% Cl2, 24% Cl3  1242: 13% Cl2, 45% Cl3, 31% Cl4  1248: 49% Cl4, 27% Cl5  1254: 15% Cl4, 53% Cl5, 26% Cl6  1260: 12% Cl5, 42% Cl6, 38% Cl7  1262: no data  1268: no data

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PCBs in the Lake Superior

 Reference: “PCBs in Lake Superior, 1978-1992: Decrease in Water

Concentrations Reflect Loss by Volatilization,” by Jeremiason, Hornbuckle and Eisenreich, Environmental Science and Technology, 28:903 (1994)

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• St. Mary’s

River

Empirical Models

 Data tell us that about 26,500 kg has been lost from

the water column between 1980 and 1992

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( )

PCB PCB e

• t

= ∑

∑

− 25 0 20 25 .

( )

PCB PCB e

• t

= ∑

∑

− 82 0 22 82 .

Loss rate and Kow’s

• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

4.5 5 5.5 6 6.5 7 7.5 Log Kow k (/yr) k (yr-1) k-regr.

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Areal Sediment Burden (mass)

 Estimated at 4900 kg in 1986

 using data from sediment cores  relatively small compared to total lost from water column (26,500

kg from ‘80 to ‘92)

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PCB PCB z

areal i i s i

= −

∑ ∑

( ) 1 φ ρ

PCB conc. (ng/g-dry sediment) in depth increment “i” Porosity of increment “i” Thickness of depth increment “i”

Inputs

 Riverine

 Known Q  Estimate c from analysis of pristine rain

 Other

 estimates from industrial, municipal, (urban) runoff

and storm sewer flows gives a combined total of about 40 kg/yr

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( )

W Qc x L yr ng L kg yr = = = 54 10 2 110

13

. / / /

Inputs (cont.)

 Direct Atmospheric deposition

 wet deposition  dry deposition

 calculated for 4 seasons, then averaged

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F PCB P SA ng L cm x m kg yr

wet T rain

= = =

∑

,

( ) / ( )8. / 2 76 21 10 125

10 2

Surface Area precipitation F PCB V SA f kg yr

dry T air d d

= =

∑

,

( ) / φ 32

Dry particle deposition velocity (0.2 cm/s) Fraction of year when it is not precipitating (0.9) Fraction of PCBs associated with particles

Outputs

 Outflow

 St. Mary’s River

 Burial (net loss to sedimentation)

 estimated at 110 kg/yr from sediment cores

collected in 1986 and 1990

 Net Volatilization

 true volatilization minus gas absorption  assumed to account for missing flux

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W x L yr ng L kg yr

• utflow =

= 71 10 084 60

13

. / ( . / ) /

Reactions

 NONE!

 “evidence does not exist to support PCB degradation in

Lake Superior or any other oligotrophic, aerobic system exhibiting low ambient concentrations”

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PCB Mass Balance in Lake Superior, 1986

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Rivers ~110 kg/yr

Atmosphere ~200 kg Atmospheric Deposition Wet 125 kg/yr Dry 32 kg/yr Net Volatilization ~1900 kg/yr

Outflow ~60 kg/yr

Sediment ~4900 kg Particle Settling ~3000 kg/yr Recycling ~2890 kg/yr Water Column ~10,100 kg Burial ~110 kg/yr Other discharges ~40 kg/yr

Congener-specific sedimentation

 Calculation of first-order net sedimentation rate

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k W INV f RR

sed sed w p

=      

Recycling ratio = downward flux (from sed trap) divided by the accumulation in the sediment Mass sedimentation rate (mg/cm2/yr) Inventory (or areal TSS) Fraction particulate

Sedimentation vs overall loss rate

• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

4.5 5 5.5 6 6.5 7 7.5 Log Kow k (/yr) k (yr-1) ksed (yr-1) k-regr.

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Two Film Volatilization Model

 Jeremiason’s equation

 Same as Chapra’s

 Where:

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k v H f

v v d

=

1 1

k K h f

vol

• l

w

=

w a

• l

k H k RT K 1 1 + =

Estimating 2-film parameters

 The gas film coefficient  The liquid film coefficient

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k u

a H O ,

. .

2

0 2 0 3

10

= +

k k D D

a PCB a H O PCB air H O air , , , , .

=        

2 2

0 61

k k Sc Sc

w PCB w CO PCB CO , , .

=        

−

2 2

0 5

k u

w CO , .

.

2

0 45 10

1 64

=

Schmidt Number

Kinetic viscosity: molecular diffusivity

Volatilization vs overall loss rate

• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

4.5 5 5.5 6 6.5 7 7.5 Log Kow k (/yr) k (yr-1) kvol (yr-1) k-regr. kvol-regr.

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 To next lecture

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