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PUBLIC HEALTH ASSESSMENT

INITIAL RELEASE

CALLAWAY AND SON DRUM SERVICE
LAKE ALFRED, POLK COUNTY, FLORIDA


APPENDIX A: FIGURES

Site Location in Florida
Figure 1. Site Location in Florida

Site Location in Lake Alfred
Figure 2. Site Location in Lake Alfred

Site Layout
Figure 3. Site Layout

Sampling Locations
Figure 4. Sampling Locations


APPENDIX B: TABLES

Table 1. Maximum concentrations of organic contaminants in on-site groundwater
Contaminants of Concern (COC) Maximum Concentration (mg/L) Sample I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/L) Source
Gamma Chlordane 0.036J TW-04 1/5 0.03 (CREG) ATSDR 2000
Chlorophenol 100JN TW-05 1/5 50 (Ch. RMEG) ATSDR 2000
4, 4'- DDE 0.27N TW-05 1/5 0.1 (CREG) ATSDR 2000
1,2-Dichloroethylene 160 CGW-02 2/17 70 (LTHA) ATSDR 2000
3 and/or 4-Cresol 78 TW-05 1/5 4 (GWCTL) FDEP 1999
Tetrachloroethylene 950 CGW-02 2/17 0.7 (CREG) ATSDR 2000
Trichloroethylene 110 CGW-02 2/17 3 (CREG) ATSDR 2000
Vinyl Chloride 33 CGW-02 2/17 0.02 (CREG) ATSDR 2000
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
µg/L = micrograms per liter of groundwater
J - Estimated value
N - Presumptive evidence of presence of material
Ch- Indicates the standard is based on a child's exposure concentration


Table 2. Maximum inorganic contaminant concentrations in on-site groundwater
Contaminants of Concern (COC) Maximum Concentration (mg/L) Well I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/L) Source
Aluminum 270,000 TW-05 3/8 20,000 (Ch. EMEG) ATSDR 2000
Arsenic 68 TW-05 2/8 0.02 (CREG) ATSDR 2000
Barium 3,400 TW-05 2/8 700 (Ch. RMEG) ATSDR 2000
Cadmium 6.4JN TW-05 1/8 2 (CH. EMEG) ATSDR 2000
Chromium 530 TW-05 4/15 30 (Ch. RMEG) ATSDR 2000
Lead 740 TW-05 5/15 15 (GWCTL) FDEP 1999
Mercury 0.92 TW-05 0/8 2 (LTHA) ATSDR 2000
Nickel 55 TW-05 0/8 200 (Ch. RMEG) ATSDR 2000
Selenium 10J TW-05 0/8 50 (Ch. EMEG) ATSDR 2000
Thallium 9JN TW-05 1/8 0.5 (CREG) ATSDR 2000
Vanadium 1,100 TW-05 2/5 30 (Ch. EMEG) ATSDR 2000
µg/L = micrograms per liter
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
N.A.- Not analyzed
J - Estimated value
N - Presumptive evidence of presence of material
Ch- Indicates the standard is based on a child's exposure concentration


Table 3. Maximum concentrations of organic contaminants in on-site surface soil (0-6 inches bgs) or sediment
Contaminants of Concern (COC) Maximum Concentration (mg/kg) Sample I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/kg) Source
Gamma Chlordane 0.023 SS-03 0/10 2 (CREG) ATSDR 2000
Chlorophenol N.D. --- 0/11 300 (Ch. RMEG) ATSDR 2000
4, 4'- DDE 0.017 SS-05 0/11 2 (CREG) ATSDR 2000
1,2-Dichloroethylene N.D. --- 0/11 10,000 (Ch. EMEG) ATSDR 2000
3 and/or 4-Cresol N.D. --- 0/11 3000 (Ch. RMEG) ATSDR 2000
Tetrachloroethylene N.D. --- 0/11 500 (Ch. RMEG) ATSDR 2000
Trichloroethylene N.D. --- 0/11 6 (SCTL) FDEP 1999
Vinyl Chloride N.D. --- 0/11 0.3 (CREG) ATSDR 2000
bgs- below ground surface
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
mg/kg = micrograms per kilogram of soil
N.D.- Not detected
Ch- Indicates the standard is based on a child's exposure concentration
Note: The one surface water sample taken from the western side of the site was contaminated with dichloroethylene (250 µg/L).


Table 4. Maximum concentrations of inorganic contaminants in on-site surface soil (0-6 inches bgs) or sediment
Contaminants of Concern (COC) Maximum Concentration (mg/kg) Sample I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/kg) Source
Aluminum 12,000 SS-03 0/10 100,000 (Ch. EMEG) ATSDR 2000
Arsenic 6 SS-03 3/10 0.5 (CREG) ATSDR 2000
Barium 34 SD-03 0/10 4000 (Ch. RMEG) ATSDR 2000
Cadmium 2.9 SD-01 0/10 10 (CH. EMEG) ATSDR 2000
Chromium 1500 SS-04 1/10 200 (Ch. RMEG) ATSDR 2000
Lead 5,300 SS-04 1/10 400 (SCTL) FDEP 1999
Mercury N.D. --- 0/10 3.4 (SCTL) FDEP 1999
Nickel 3.2J SS-03 0/10 1000 (Ch. RMEG) ATSDR 2000
Selenium 0.92J SS-03 0/10 390 (SCTL) FDEP 1999
Thallium N.D. --- 0/10 5 (Ch. RMEG)) ATSDR 2000
Vanadium 32 SS-03 0/10 200 (Ch. EMEG) ATSDR 2000
bgs- below ground surface
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
mg/kg = milligrams per kilogram of soil
Ch- Indicates the standard is based on a child's exposure concentration
N.D.- Not detected
J - Estimated value


Table 5. Maximum concentrations of organic contaminants in off-site groundwater
Contaminants of Concern (COC) Maximum Concentration (mg/L) Sample I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/L) Source
Gamma Chlordane 0.13 TW-02 1/4 0.03 (CREG) ATSDR 2000
Chlorophenol N.D. --- 0/4 50 (Ch. RMEG) ATSDR 2000
4, 4'- DDE N.D. --- 0/4 0.1 (CREG) ATSDR 2000
1,2-Dichloroethylene N.D. --- 0/11 70 (LTHA) ATSDR 2000
3 and/or 4-Cresol N.D. --- 0/4 4 (GWCTL) FDEP 1999
Tetrachloroethylene N.D. --- 0/11 0.7 (CREG) ATSDR 2000
Trichloroethylene N.D. --- 0/11 3 (CREG) ATSDR 2000
Vinyl Chloride N.D. --- 0/11 0.3 (CREG) ATSDR 2000
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
It is important to note that two of the four samples came from private drinking wells south of the site. The first was the public supply well at Palm Shores Mobile Village and the second was the well Camp Hackedy.
µg/L = micrograms per liter of groundwater
N.D.- Not detected
N.A.- Not analyzed
Ch- Indicates the standard is based on a child's exposure concentration


Table 6. Maximum inorganic contaminant concentrations in off-site groundwater
Contaminants of Concern (COC) Maximum Concentration (mg/L) Well I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/L) Source
Aluminum 210,000 TW-02 2/11 20,000 (Ch. EMEG) ATSDR 2000
Arsenic 110 TW-02 1/11 0.02 (CREG) ATSDR 2000
Barium 6000 TW-02 1/11 700 (Ch. RMEG) ATSDR 2000
Cadmium 84JN TW-02 2/11 2 (CH. EMEG) ATSDR 2000
Chromium 340 TW-02 2/11 30 (Ch. RMEG) ATSDR 2000
Lead 2,200 TW-02 2/11 15 (GWCTL) FDEP 1999
Mercury 26 TW-02 2/11 2 (LTHA) ATSDR 2000
Nickel 390 TW-02 1/11 200 (Ch. RMEG) ATSDR 2000
Selenium 170J TW-02 1/11 50 (Ch. EMEG) ATSDR 2000
Thallium 27JN TW-02 1/11 0.5 (CREG) ATSDR 2000
Vanadium 420 TW-02 2/4 30 (Ch. EMEG) ATSDR 2000
µg/L = micrograms per liter
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
Ch- Indicates the standard is based on a child's exposure concentration
J - Estimated value
N - Presumptive evidence of presence of material


Table 7. Maximum concentrations of organic contaminants in surface soil (0-6 inches bgs) off-site
Contaminants of Concern (COC) Maximum Concentration (mg/kg) Sample I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/kg) Source
Gamma Chlordane N.D. --- 0/3 2 (CREG) ATSDR 2000
Chlorophenol N.D. --- 0/3 300 (Ch. RMEG) ATSDR 2000
4, 4'- DDE N.D. --- 0/3 2 (CREG) FDEP 1999
1,2-Dichloroethylene N.D. --- 0/3 10,000 (Ch. EMEG) ATSDR 2000
3- and 4-Cresol N.D. --- 0/3 3000 (Ch. RMEG) FDEP 1999
Tetrachloroethylene N.D. --- 0/3 500 (Ch. RMEG) FDEP 1999
Trichloroethylene N.D. --- 0/3 6 (SCTL) FDEP 1999
Vinyl Chloride N.D. --- 0/3 0.3 (CREG) ATSDR 2000
bgs- below ground surface
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
mg/kg = micrograms per kilogram of soil
N.D.- Not detected
Ch- Indicates the standard is based on a child's exposure concentration


Table 8. Maximum concentrations of inorganic contaminants in off-site surface soil (0-6 inches bgs) or sediment
Contaminants of Concern (COC) Maximum Concentration (mg/kg) Sample I.D. # Greater Than Comparison Value/
Total # of Samples		 Comparison Value*
(mg/kg) Source
Aluminum 5,300 SS-02 0/4 100,000 (Ch. EMEG) ATSDR 2000
Arsenic 0.68J SS-02 1/4 0.5 (CREG) ATSDR 2000
Barium 63 SS-02 0/4 4000 (Ch. RMEG) ATSDR 2000
Cadmium N.D. --- 0/4 10 (CH. EMEG) ATSDR 2000
Chromium 5.3 SS-02 0/4 200 (Ch. RMEG) ATSDR 2000
Lead 15 SS-02 0/4 400 (SCTL) FDEP 1999
Mercury N.D. --- 0/1 3.4 (SCTL) FDEP 1999
Nickel 25 SS-06 0/4 1000 (Ch. RMEG) ATSDR 2000
Selenium N.D. --- 0/4 390 (SCTL) FDEP 1999
Thallium N.D. --- 0/4 5 (Ch. RMEG)) ATSDR 2000
Vanadium 2.1 SS-02 0/3 200 (Ch. EMEG) ATSDR 2000
bgs- below ground surface
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
Ch- Indicates the standard is based on a child's exposure concentration
J - Estimated value
N.D.- Not detected


Table 9. Potential Exposure Pathways
Pathway Name Exposure Pathway Elements Time
Source Environmental Media Point of Exposure Route of Exposure Exposed Population
On-site Soil/sediment
Ingestion		 On-site soil contamination On-site soil/sediment On the property Incidental ingestion of soil/sediment On-site residents or trespassers Current/Future
On-site Soil
Inhalation		 On-site soil contamination On-site dusts from soil On the property Inhalation of dusts On-site residents or trespassers Current/Future
Ingestion of On-site groundwater On-site soil contamination Groundwater On-site wells/
Tap water		 Ingestion of contaminated groundwater On-site residents Future
Inhalation of vapors from on-site groundwater On-site soil contamination Groundwater On-site wells/
Tap water		 Inhalation of vapors from contaminated water On-site residents Future
Off-site Soil/sediment
Ingestion		 Contaminated surface water in drainage ditch Off-site soil/sediment Drainage ditch Incidental ingestion of soil/sediment Off-site residents/children Current/Future
Off-site Soil
Inhalation		 Contaminated surface water in drainage ditch Off-site dusts from soil Drainage ditch Inhalation of dusts Off-site residents/children Current/Future
Ingestion of off-site groundwater On-site soil contamination Groundwater Off-site wells/
Tap water		 Ingestion of contaminated groundwater Off-site residents Current/ Future
Inhalation of vapors from off-site groundwater Migration of on-site groundwater Groundwater Off-site wells/
Tap water		 Inhalation of vapors from contaminated water Off-site residents Current/Future


Table 10. Total Population Estimation Table
Pathway Types Estimated Total Population in Potential Exposure Pathways* Minimum Population* Maximum Population*
Potential Pathways On-site 0 0 1-50
Potential Pathways Off-site 2300 0 501-2500
Total Potential On and Off-site 2300 0 501-2500
Completed Pathways On-site 0 0 0
Completed Pathways Off-site 0 0 0
Total Completed On and Off-site 0 0 0
Potential and Completed Pathways On-site 0 0 1-50
Potential and Completed Pathways Off-site 0 0 501-2500
Total Potential and Completed On and Off-site 2300 0 501-2500


Table 11. Calculated dose of organic chemicals from residential use of on-site groundwater
Contaminant of Concern
(maximum concentration)		 Oral MRL
(mg/kg/day)		 Groundwater- Ingestion (mg/kg/day) Groundwater- Dermal (mg/kg/day) Inhalation MRL
(mg/m3)		 Groundwater- Inhalation (mg/m3)
Child Adult Child Adult Child Adult
Gamma-Chlordane
(0.000036 mg/L)		 0.0006 0.000002 0.000001 2x10-9 2x10-9 0.00002 N.S. N.S.
Chlorophenol
(0.1 mg/L)		 0.005 0.007 0.003 0.0005 0.0003 N.A. 1 1
3 and/or 4-Cresol
(0.078 mg/L)		 0.05 0.005 0.002 0.0003 0.00009 N.A. 0.78 0.78
4,4'-DDE
(0.00027 mg/L)		 0.0005 0.000018 0.000008 0.0001 0.00007 N.A. 0.003 0.003
1,2-Dichloroethylene
(0.16 mg/L)		 0.2 0.01 0.005 0.0008 0.0006 0.9 1.6 1.6
Tetrachloroethylene
(0.95 mg/L)		 0.05 0.06 0.03 0.03 0.02 0.27 10 10
Trichloroethylene
(0.11 mg/L)		 0.2 0.007 0.003 0.0008 0.0005 0.55 1.1 1.1
Vinyl Chloride
(0.033 mg/L)		 0.00002 0.002 0.0009 0.00007 0.00005 0.078 0.33 0.33
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991). Shaded cells indicate an estimated dose exceeding the appropriate MRL.
N.A.- Not available
N.S.- Not significant
The above doses were calculated using the following values and an average shower time of 0.2 hours:

Adult body weight- 70 kg
Adult water consumption- 2 liters/day
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child water consumption- 1 liter/day
Child skin surface area- 7,200cm2
mg/kg/day= milligram of contaminant per kilogram body weight per day
mg/m3= milligram of contaminant per cubic meter


Table 12. Calculated dose of metals from residential use of on-site groundwater
Contaminant of Concern
(maximum concentration)		 Oral MRL
(mg/kg/day)		 Groundwater- Ingestion (mg/kg/day) Groundwater- Dermal (mg/kg/day) Inhalation MRL
(mg/m3)		 Groundwater- Inhalation (mg/m3)
Child Adult Child Adult Child Adult
Aluminum (270 mg/L) 2 18 8 0.03 0.02 N.A. N.S. N.S.
Arsenic (0.068 mg/L) 0.0003 0.005 0.002 0.000007 0.000004 N.A. N.S. N.S.
Barium (3.4 mg/L) 0.07 0.2 0.1 0.0003 0.0002 N.A. N.S. N.S.
Cadmium (0.0064 mg/L) 0.0002 0.0004 0.0002 0.0000006 0.0000004 N.A. N.S. N.S.
Chromium (0.53 mg/L) 0.003 0.04 0.02 0.000006 0.000004 0.0005 N.S. N.S.
Lead (0.74 mg/L) N.A. 0.05 0.02 0.00007 0.00005 N.A. N.S. N.S.
Thallium (0.009 mg/L) 0.00008 0.0006 0.0003 0.000001 0.0000007 N.A. N.S. N.S.
Vanadium (1.1 mg/L) 0.003 0.07 0.03 0.0001 0.00007 0.0002 N.S. N.S.
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991). Shaded cells indicate an estimated dose exceeding the appropriate MRL.
N.A.- Not available
N.S.- Not significant
The above doses were calculated using the following values and an average shower time of 0.2 hours:

Adult body weight- 70 kg
Adult water consumption- 2 liters/day
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child water consumption- 1 liter/day
Child skin surface area- 7,200cm2
mg/kg/day= milligram of contaminant per kilogram body weight per day
mg/m3= milligram of contaminant per cubic meter


Table 13. Calculated dose of metals from ingestion of on-site surface soil
Contaminant of Concern
(maximum concentration)		 Oral MRL
(mg/kg/day)		 Soil/dust- Ingestion (mg/kg/day) Soil/dust- Dermal (mg/kg/day) Inhalation MRL
(mg/m3)		 Soil/dust- Inhalation (mg/m3)
Child Adult Child Adult Child Adult
Arsenic (6 mg/kg) 0.0003 0.00008 0.000009 N.S. N.S. N.A. N.S. N.S.
Chromium (1500 mg/kg) 0.003 0.02 0.002 N.S. N.S. 0.0005 0.00008 0.00008
Lead (5300 mg/kg) N.A. 0.07 0.008 N.S. N.S. N.A. 0.0003 0.0003
These doses were calculated using Risk Assistant software and accepted values for soil exposure parameters (EPA, 1991). Shaded rows indicate an estimated dose exceeding the appropriate MRL.
N.A.- Not available
N.S.- Not significant
The above doses were calculated using the following values and an average shower time of 0.2 hours:

Adult body weight- 70 kg
Adult soil ingestion- 100 mg/day
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child soil ingestion- 200 mg/day
Child skin surface area- 7,200cm2
mg/kg/day= milligram of contaminant per kilogram body weight per day
mg/m3= milligram of contaminant per cubic meter
The estimated doses for lead are shaded because no MRL exits for lead. Therefore, all lead doses were evaluated for health effects.


Table 14. Calculated dose of organics from residential use of off-site groundwater
Contaminant of Concern
(maximum concentration)		 Oral MRL
(mg/kg/day)		 Groundwater- Ingestion (mg/kg/day) Groundwater- Dermal (mg/kg/day) Inhalation MRL
(mg/m3)		 Groundwater- Inhalation (mg/m3)
Child Adult Child Adult Child Adult
Gamma-Chlordane (0.00013 mg/L) 0.0006 0.000009 0.000004 1x10-8 9x10-9 0.00002 N.S. N.S.
Chlorophenol (N.D.) 0.005 N.D N.D N.D N.D N.A. N.D N.D
3 and/or 4-Cresol (N.D.) 0.05 N.D N.D N.D N.D N.A. N.D N.D
4,4'-DDE (N.D.) 0.34 N.D N.D N.D N.D N.A. N.D N.D
1,2-Dichloroethylene (N.D.) 0.2 N.D N.D N.D N.D 0.9 N.D N.D
Tetrachloroethylene (N.D.) 0.05 N.D N.D N.D N.D 0.27 N.D N.D
Trichloroethylene (N.D.) 0.2 N.D N.D N.D N.D 0.55 N.D N.D
Vinyl chloride (N.D.) 0.00002 N.D N.D N.D N.D 0.078 N.D N.D
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991). Shaded rows indicate an estimated dose exceeding the appropriate MRL.
N.D.- Not detected
N.A.- Not available
N.S.- Not significant
The above doses were calculated using the following values and an average shower time of 0.2 hours:

Adult body weight- 70 kg
Adult water consumption- 2 liters/day
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child water consumption- 1 liter/day
Child skin surface area- 7,200cm2
mg/kg/day= milligram of contaminant per kilogram body weight per day
mg/m3= milligram of contaminant per cubic meter


Table 15. Calculated dose of metals from residential use of off-site groundwater
Contaminant of Concern
(maximum concentration)		 Oral MRL
(mg/kg/day)		 Groundwater- Ingestion (mg/kg/day) Groundwater- Dermal (mg/kg/day) Inhalation MRL
(mg/m3)		 Groundwater- Inhalation (mg/m3)
Child Adult Child Adult Child Adult
Aluminum (210 mg/L) 2 14 6 0.02 0.01 N.A. N.S. N.S.
Arsenic (0.11mg/L) 0.0003 0.007 0.003 0.00001 0.000007 N.A. N.S. N.S.
Barium (6.0 mg/L) 0.07 0.4 0.2 0.0006 0.0004 N.A. N.S. N.S.
Cadmium (0.084 mg/L) 0.0002 0.006 0.002 0.000008 0.000006 N.A. N.S. N.S.
Chromium (0.34 mg/L) 0.003 0.02 0.01 0.00003 0.00002 0.0005 N.S. N.S.
Lead (2.2 mg/L) N.A. 0.1 0.06 0.0002 0.0001 N.A. N.S. N.S.
Mercury (0.026 mg/L) 0.002 0.002 0.0007 0.000002 0.000002 0.0002 N.S. N.S.
Nickel (0.39 mg/L) 0.02 0.03 0.01 0.00004 0.00003 0.0002 N.S. N.S.
Selenium (0.17 mg/L) 0.005 0.01 0.005 0.00002 0.00001 N.A. N.S. N.S.
Thallium (0.027 mg/L) 0.00008 0.002 0.0008 0.00003 0.00002 N.A. N.S. N.S.
Vanadium (0.42 mg/L) 0.003 0.03 0.01 0.00004 0.00003 0.0002 N.S. N.S.
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991). Shaded rows indicate an estimated dose exceeding the appropriate MRL.
N.D.- Not detected
N.A.- Not available
N.S.- Not significant
The above doses were calculated using the following values and an average shower time of 0.2 hours:

Adult body weight- 70 kg
Adult water consumption- 2 liters/day
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child water consumption- 1 liter/day
Child skin surface area- 7,200cm2
mg/kg/day= milligram of contaminant per kilogram body weight per day
mg/m3= milligram of contaminant per cubic meter


APPENDIX C: RISK OF ILLNESS, DOSE RESPONSE/THRESHOLD, AND UNCERTAINTY IN PUBLIC HEALTH ASSESSMENTS

Risk of Illness

In this health assessment, the risk of illness is the chance that exposure to a hazardous contaminant is associated with a harmful health effect or illness. The risk of illness is not a measure of cause and effect; only an in-depth health study can identify a cause and effect relationship. Instead, we use the risk of illness to decide if a follow-up health study is needed and to identify possible associations.

The greater the exposure to a hazardous contaminant (dose), the greater the risk of illness. The amount of a substance required to harm a person's health (toxicity) also determines the risk of illness. Exposure to a hazardous contaminant above a minimum level increases everyone's risk of illness. Only in unusual circumstances, however, do many people become ill.

Information from human studies provides the strongest evidence that exposure to a hazardous contaminant is related to a particular illness. Some of this evidence comes from doctors reporting an unusual incidence of a specific illness in exposed individuals. More formal studies compare illnesses in people with different levels of exposure. However, human information is very limited for most hazardous contaminants, and scientists must frequently depend upon data from animal studies. Hazardous contaminants associated with harmful health effects in humans are often associated with harmful health effects in other animal species. There are limits, however, in only relying on animal studies. For example, scientists have found some hazardous contaminants are associated with cancer in animals, but lack evidence of a similar association in humans. In addition, humans and animals have differing abilities to protect themselves against low levels of contaminants, and most animal studies test only the possible health effects of high exposure levels. Consequently, the possible effects on humans of low-level exposure to hazardous contaminants are uncertain when information is derived solely from animal experiments.

Dose Response/Thresholds

The focus of toxicological studies in humans or animals is identification of the relationship between exposure to different doses of a specific contaminant and the chance of having a health effect from each exposure level. This dose-response relationship provides a mathematical formula or graph that we use to estimate a person's risk of illness. There is one important difference between the dose-response curves used to estimate the risk of noncancerous illnesses and those used to estimate the risk of cancer: the existence of a threshold dose. A threshold dose is the highest exposure dose at which there is no risk of a noncancerous illness. The dose-response curves for noncancerous illnesses include a threshold dose that is greater than zero. Scientists include a threshold dose in these models because the human body can adjust to varying amounts of cell damage without illness. The threshold dose differs for different contaminants and different exposure routes, and we estimate it from information gathered in human and animal studies. In contrast, the dose-response curves used to estimate the risk of cancer assume there is no threshold dose (or, the cancer threshold dose is zero). This assumes a single contaminant molecule may be sufficient to cause a clinical case of cancer. This assumption is very conservative, and many scientists believe a threshold dose greater than zero exists for the development of cancer.

Uncertainty

All risk assessments, to varying degrees, require the use of assumptions, judgements, and incomplete data. These contribute to the uncertainty of the final risk estimates. Some more important sources of uncertainty in this Public Health Assessment include environmental sampling and analysis, exposure parameter estimates, use of modeled data, and present toxicological knowledge. These uncertainties may cause risk to be overestimated or underestimated to a different extent. Because of the uncertainties described below, this Public Health Assessment does not represent an absolute estimate of risk to persons exposed to chemicals at or near Callaway and Son.

Environmental chemistry analysis errors can arise from random errors in the sampling and analytical processes, resulting in either an over- or under-estimation of risk. We can control these errors to some extent by increasing the number of samples collected and analyzed and by sampling the same locations over several different periods. The above actions tend to minimize uncertainty contributed from random sampling errors.

There are two areas of uncertainty related to exposure parameter estimates. The first is the exposure-point concentration estimate. The second is the estimate of the total chemical exposures. In this assessment we used maximum detected concentrations as the exposure point concentration. We believe using the maximum measured value to be appropriate because we cannot be certain of the peak contaminant concentrations, and we cannot statistically predict peak values. Nevertheless, this assumption introduces uncertainty into the risk assessment that may over- or under-estimate the actual risk of illness. When selecting parameter values to estimate exposure dose, we used default assumptions and values within the ranges recommended by the ATSDR or the EPA. These default assumptions and values are conservative (health protective) and may contribute to the over-estimation of risk of illness. Similarly, we assumed the maximum exposure period occurred regularly for each selected pathway. Both assumptions are likely to contribute to the over-estimation of risk of illness.

There are also data gaps and uncertainties in the design, extrapolation, and interpretation of toxicological experimental studies. Data gaps contribute uncertainty because information is either not available or is addressed qualitatively. Moreover, the available information on the interaction among chemicals found at the site, when present, is qualitative (that is, a description instead of a number) and we cannot apply a mathematical formula to estimate the dose. These data gaps may tend to underestimate the actual risk of illness. In addition, there are great uncertainties in extrapolating from high-to-low doses, and from animal-to-human populations. Extrapolating from animals to humans is uncertain because of the differences in the uptake, metabolism, distribution, and body organ susceptibility between different species. Human populations are also variable because of differences in genetic constitution, diet, home and occupational environment, activity patterns, and other factors. These uncertainties can result in an over- or under-estimation of risk of illness. Finally, there are great uncertainties in extrapolating from high to low doses, and controversy in interpreting these results. Because the models used to estimate dose-response relationships in experimental studies are conservative, they tend to overestimate the risk. Techniques used to derive acceptable exposure levels account for such variables by using safety factors. Currently, there is much debate in the scientific community about how much we overestimate the actual risks and what the risk estimates really mean.

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Agency for Toxic Substances and Disease Registry, 1825 Century Blvd, Atlanta, GA 30345
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DHHS
Department of Health and Human Services