(Jeremiason et al., 1994)

Transcription

1 Updated: 17 April 2013 Print version Lecture #36 Toxics: PCBs in the Great Laes (Jeremiason et al., 1994) David Rechow CEE 577 #36 1

2 What are the PCBs Biphenyl Homologs (11) Isomers (1-46) Congeners (209) 5 6 2,2 - Dichlorobiphenyl 6 5 Cl 2,3 - Dichlorobiphenyl Cl Cl Cl David Rechow CEE 577 #36 2

3 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 David Rechow CEE 577 #36 3

4 Arochlor Mixtures Arochlor 12xx (xx=% chlorine) 1221: 50% Cl 1, 35% Cl : 26% Cl 1, 29% Cl 2, 24% Cl : 13% Cl 2, 45% Cl 3, 31% Cl : 49% Cl 4, 27% Cl : 15% Cl 4, 53% Cl 5, 26% Cl : 12% Cl 5, 42% Cl 6, 38% Cl : no data 1268: no data David Rechow CEE 577 #36 4

5 PCBs in the Lae Superior Reference: PCBs in Lae Superior, : Decrease in Water Concentrations Reflect Loss by Volatilization, by Jeremiason, Hornbucle and Eisenreich, Environmental Science and Technology, 28:903 (1994) St. Mary s River David Rechow CEE 577 #36 5

6 Empirical Models ( ) 25 PCB = PCB e o ( ) 82 PCB = PCB e o 0. 20t 0. 22t Data tell us that about 26,500 g has been lost from the water column between 1980 and 1992 David Rechow CEE 577 #36 6

7 David Rechow CEE 577 #36 7 Loss rate and K ow s -0.6 Log Kow (/yr) (yr-1) -regr.

8 Areal Sediment Burden (mass) Estimated at 4900 g in 1986 using data from sediment cores relatively small compared to total lost from water column (26,500 g from 80 to 92) PCB = PCB ( 1 φ ) ρ z areal i i s i PCB conc. (ng/g-dry sediment) in depth increment i Porosity of increment i Thicness of depth increment i David Rechow CEE 577 #36 8

9 Inputs W = Qc Riverine 13 = 5. 4x10 L / yr 2ng / L Known Q = 110g / yr 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 g/yr David Rechow CEE 577 #36 9

10 Inputs (cont.) Direct Atmospheric deposition wet deposition precipitation Surface Area dry deposition Fwet = PCBT, rain P( SA) = 2ng / L( 76cm)8. 21x10 m = 125g / yr calculated for 4 seasons, then averaged 10 2 Dry particle deposition velocity (0.2 cm/s) F = PCB, V φ( SA) f = 32g / yr dry T air d d Fraction of year when it is not precipitating (0.9) Fraction of PCBs associated with particles David Rechow CEE 577 #36 10

11 Outputs Outflow St. Mary s River 13 Woutflow = 7. 1x10 L / yr( 084. ng / L) = 60g / yr Burial (net loss to sedimentation) estimated at 110 g/yr from sediment cores collected in 1986 and 1990 Net Volatilization true volatilization minus gas absorption assumed to account for missing flux David Rechow CEE 577 #36 11

12 Reactions NONE! evidence does not exist to support PCB degradation in Lae Superior or any other oligotrophic, aerobic system exhibiting low ambient concentrations David Rechow CEE 577 #36 12

13 PCB Mass Balance in Lae Superior, 1986 Atmospheric Deposition Wet 125 g/yr Dry 32 g/yr Atmosphere ~200 g Net Volatilization ~1900 g/yr Other discharges ~40 g/yr Rivers ~110 g/yr Particle Settling ~3000 g/yr Outflow ~60 g/yr Water Column ~10,100 g Sediment ~4900 g Recycling ~2890 g/yr Burial ~110 g/yr David Rechow CEE 577 #36 13

14 Congener-specific sedimentation Calculation of first-order net sedimentation rate Mass sedimentation rate (mg/cm 2 /yr) sed Wsed INV f w = RR p Inventory (or areal TSS) Fraction particulate Recycling ratio = downward flux (from sed trap) divided by the accumulation in the sediment David Rechow CEE 577 #36 14

15 David Rechow CEE 577 #36 15 Sedimentation vs overall loss rate -0.6 Log Kow (/yr) (yr-1) sed (yr-1) -regr.

16 Two Film Volatilization Model Jeremiason s equation vol = K h ol f w Same as Chapra s v = vv H f 1 d1 Where: 1 K ol = RT H a + 1 w David Rechow CEE 577 #36 16

17 Estimating 2-film parameters The gas film coefficient = 0. 2u , 2 10 a H O The liquid film coefficient = a, PCB a, H O 2 D D PCB, air H O, air w, CO. = 0. 45u 2 10 Kinetic viscosity: molecular diffusivity 1 64 = w, PCB w, CO 2 Sc Sc PCB CO Schmidt Number David Rechow CEE 577 #36 17

18 David Rechow CEE 577 #36 18 Volatilization vs overall loss rate Log Kow (/yr) (yr-1) vol (yr-1) -regr. vol-regr.

19 To next lecture David Rechow CEE 577 #36 19