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Superfund and Mining Megasites: Lessons from the Coeur d’alene River Basin
Appendix D
Procedures Used in Model Comparisons
Similar to the Agency for Toxic Substances and Disease Registry (ATSDR) Health Consultation (ATSDR 2000), data from the Field Sampling Plan Addendum (FSPA06) conducted in support of the remedial investigation (RI) (URS Greiner and CH2M Hill 2001) were used in this analysis. For the present study, however, the number of homes was slightly different for two reasons: (1) data for two houses originally tabulated in the RI were not used in the ATSDR comparison—these were added for the committee comparisons. (2) The ATSDR analysis used geometric mean house-dust values for seven houses where those data were not originally collected. In the present comparison, those houses were dropped from consideration, and the results are based solely on residences where both soil and house dust measurements were available. The data set used in these calculations (referred to below as the 75 homes’ data) is presented in Table D-1 of this appendix.
THE ONTARIO MINISTRY OF ENVIRONMENT AND ENERGY BIOKINETIC SLOPE FACTOR MODEL
The Ontario Ministry of Environment and Energy (OMOEE) has established an intake of 3.7 micrograms (μg) lead per kilograms (kg) of body weight/day as the level of intake for which more than 95% of children will have blood lead values less than 10 μg per deciliter (dL). This intake of concern (IOC) is divided by 2 to provide a safety factor; the resulting IOC is 1.85 μg of lead/kg of body weight/day. For the model comparisons, lead
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Superfund and Mining Megasites: Lessons from the Coeur d’alene River Basin
TABLE D-1 FSPA06 Data Used in Calculations
House
Arithmetic Mean of Yard Soil, 0-1 in. (mg/kg)
Geometric Mean of Community Soil (mg/kg)
Vacuum Bag Dust
House
Arithmetic Mean of Yard Soil, 0-1 in. (mg/kg)
Geometric Mean of Community Soil (mg/kg)
Vacuum Bag Dust
1
663
419
606
38
278
419
427
2
804
419
480
39
1,423
568
1,020
3
174
419
764
40
364
352
341
4
448
419
173
41
766
628
682
5
4,796
110
3,140
42
769
419
23
6
1,189
419
1,000
43
688
368
1,820
7
1,610
628
1,620
44
16,026
771
6,150
8
1,080
419
978
45
718
568
2,430
9
870
419
528
46
503
419
769
10
259
419
390
47
500
568
387
11
623
257
525
48
3,054
568
2,730
12
239
257
422
49
843
568
619
13
979
419
154
50
852
771
3,300
14
290
257
389
51
56
368
626
15
665
257
765
52
319
419
504
16
342
419
332
53
256
419
492
17
760
419
1,260
54
3,026
419
621
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Superfund and Mining Megasites: Lessons from the Coeur d’alene River Basin
18
3,491
352
604
55
787
419
1,550
19
5,566
628
1,960
56
735
257
315
20
794
419
1,200
57
544
368
504
21
1,014
568
1,660
58
642
568
384
22
276
352
680
59
353
368
833
23
796
419
818
60
2,711
568
353
24
871
419
512
61
1,165
771
778
25
451
771
639
62
188
257
232
26
1,337
771
1,350
63
284
568
1,680
27
1,687
771
798
64
563
419
655
28
977
419
808
65
2,701
628
1,540
29
813
568
703
66
1,194
352
937
30
438
568
84
67
1,094
771
780
31
682
419
762
68
2,788
568
1,380
32
622
568
349
69
479
568
727
33
1,322
628
767
70
1,381
568
405
34
437
568
383
71
321
771
942
35
1,576
568
1,020
72
3,837
419
362
36
827
628
710
73
2,861
628
2,840
37
3,603
568
1,020
74
694
368
2,400
75
807
419
1,000
SOURCE: Data provided by Idaho Department of Health and Welfare, unpublished material, 2004.
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Superfund and Mining Megasites: Lessons from the Coeur d’alene River Basin
intake from soils, dusts, water, air, and food is calculated from measured media concentrations and added to background default levels in non-measured media. The factor by which the estimated intake exceeds the IOC is obtained by dividing the result by 1.85 μg lead/kg body weight/day. The percentage of locations for which exposure estimates are less than a factor of 2 above the IOC is taken as the percentage of children whose blood lead values are less than 10 μg/dL.
BATCH OPERATION OF THE INTEGRATED EXPOSURE UPTAKE BIOKINETIC MODEL
The 75 homes’ data were used for blood lead estimates using the batch mode capability of the integrated exposure uptake biokinetic (IEUBK) model. For these comparisons, the estimated blood lead level at an age of 20 months was obtained. This age matches closely the age corresponding to maximum blood lead concentration and also corresponds approximately to the 16 kg body weight for which the OMOEE IOC computation is made.
IMPLEMENTATION OF THE O’FLAHERTY MODEL
The physiologically based, transport limited biokinetic model of O’Flaherty (O’Flaherty 1998) was applied to the 75 homes’ data for comparison with the other models. Such comparisons are not exact because of differences in how the models specify input of exposure regimes and the way bioavailability is incorporated in the computations. Another impediment is the sensitivity of the O’Flaherty model to year of birth for the individual being simulated. As noted in the TRW adult lead model review (EPA 2001, Appendix K), a variety of model parameters may be adjusted in the exposure specifications to establish baseline conditions against which variations in soil and dust lead concentrations may be examined. For the O’Flaherty model implementation here (Advanced Continuous Simulation Language [ACSL] platform) the following variable values were used for model runs: year of birth, yob = 1980; frlung = 0.32 (bioavailability of inhaled lead—same as IEUBK); cair2 = 0.1 μg/m3 (same as IEUBK); concentration of lead in water, cwater = 4 μg/L (same as IEUBK); rfood2 = 20 μg of lead/day ingested by adult; rfood3 = 15 μg lead/day ingested by child; and the concentration of lead in infant formula, cfmla = 0.01 μg/L. For tabulation in Table 6-3, the midpoint between blood lead at ages 12 and 24 months was used.
ADAPTATION OF MODELS FOR PREDICTIONS UNDER THE BUNKER HILL SUPERFUND SITE “BOX MODEL” CONDITIONS
The study of von Lindern et al. (2003) established a set of IEUBK model conditions that best fit the observed blood lead distribution for
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children living within the Bunker Hill Superfund site (BHSS). Discussion of this model and an evaluation of its application to predictions of blood lead levels for children living in the Coeur d’Alene River basin outside the BHSS box is detailed in the body of the report. Important points for the present comparison of model results are as follows: (1) the soil and dust exposure regime was weighted as 40% from household dusts, 30% from the residential soil, and 30% derived from the community-wide soils; and (2) bioavailability for soil and dust ingestion was set at 18%.
Soil lead values for the 75 homes’ data (BHSS box conditions) were tabulated on a geographical location basis as the average between the individual residential lot surface-soil value and the geometric mean soil value for the community where the residence was located. The latter values were derived from the human health risk assessment for operable unit 3 (TerraGraphics et al. 2001, Table 6-48). To account for the lower bioavailability of lead in soils and dusts used in the box model, concentration values for these inputs were reduced to 60% of their original values before each model’s invocation. This corresponds approximately to the change in bioavailability used in the box model version of the IEUBK model, since the default bioavailability from soil in the IEUBK is 30%. This approach was adopted because bioavailability, the fraction of lead intake that is taken up in the blood, could not be adjusted in the ATSDR model. The modification of the soil concentration achieves the same effect, because the model exhibits a linear response over the concentration ranges of interest. In the O’Flaherty model, the user cannot specify bioavailability, but the ACSL program constants were adjusted to reflect 40% dust and 60% soil inputs to the exposure module of the program. The O’Flaherty model uses age-specific soil/dust-ingestion rate functions that are not accessible in the executable program structure but whose average value is about 60% of the average IEUBK default ingestion regime.
REFERENCES
ATSDR (Agency for Toxic Substances and Disease Registry). 2000. Health Consultation. Coeur d’Alene River Basin Panhandle Region of Idaho Including Benewah, Kootenai and Shoshone Counties. Office of Regional Operations, Region 10, Agency for Toxic Substances and Disease Registry, U.S. Public Health Service, Department of Health and Human Services [online]. Available: http://www.atsdr.cdc.gov/HAC/PHA/basinres/bas_toc.html [accessed Jan. 4, 2005].
EPA (U.S. Environmental Protection Agency). 2001. Review of Adult Lead Models: Evaluation of Models for Assessing Human Health Risks Associated with Lead Exposures at Non-Residential Areas of Superfund and Other Hazardous Waste Sites. OSWER #9285.7-46. Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency, Washington, DC. August 2001 [online]. Available: http://www.epa.gov/superfund/programs/lead/products/adultreview.pdf [accessed Jan. 3, 2005].
O’Flaherty, E.J. 1998. A physiologically based kinetic model for lead in children and adults. Environ. Health Perspect. 106(Suppl. 6):1495-1503.
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TerraGraphics/URS Greiner/CH2M Hill. 2001. Final Human Health Risk Assessment for the Coeur d’Alene Basin Extending from Harrison to Mullan on the Coeur d’Alene River and Tributaries, Remedial Investigation/Feasibility Study. Prepared for Idaho Department of Health and Welfare, Division of Health, Idaho Department of Environmental Quality, U.S. Environmental Protection Agency Region X, Seattle, WA, by TerraGraphics Environmental Engineering, Inc, URS Greiner in association with CH2M Hill [online]. Available: http://www.epa.gov/r10earth/offices/sf/BH_HHRA_final/TableOfContents.pdf [accessed Jan. 3, 2005].
URS Greiner, Inc., and CH2M Hill. 2001. Final (Revision 2) Remedial Investigation Report, Remedial Investigation Report for the Coeur d’Alene Basin Remedial Investigation/ Feasibility Study. URSG DCN 4162500.6659.05a. Prepared for U.S. Environmental Protection Agency, Region 10, Seattle, WA, by URS Greiner, Inc., Seattle, WA, and CH2M Hill, Bellevue, WA. September 2001.
von Lindern, I.H., S.M. Spalinger, V. Petroysan, and M. von Braun. 2003. Assessing remedial effectiveness through the blood lead: Soil/dust relationship at the Bunker Hill Superfund Site in the Silver Valley of Idaho. Sci. Total Environ. 303(1-2):139-170.
Representative terms from entire chapter:
flow measurements