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PUBLIC HEALTH ASSESSMENT

SOLITRON DEVICES, INCORPORATED
WEST PALM BEACH, PALM BEACH COUNTY, FLORIDA


APPENDIX A. SITE SUMMARY

Below we list the chronologic history of Solitron Devices contamination discovery and interimefforts to protect municipal water quality. The highly acid Solitron wastewaters corroded on-siteplumbing, holding tanks and portions of the city sewer, releasing solvents and metals to the soiland groundwater. Released chemicals moved in ground-water influenced by flow away from thedrainage canal north of the site and toward on-site production wells and off-site municipal supply wells (see Figure 1 for details).

On-site Well Use
1960-1992:

  • Manufacturing Production Well pumps 30,000 gallons per day

1960 - 1968 or 1969:

  • Three large wells supply cooling water for the air-conditioning system

Releases and Interim Efforts.
1969:

  • Waste stream corrodes pump in sewer-line lift station north of Blue Heron Boulevard
  • Waste stream dissolves bottom of concrete manhole and 10-inch iron sewer line in Blue Heron Boulevard north of site
  • City of Riviera Beach (CRB) Utilities repair sewer line and lift station
  • Untreated effluent discharges from damaged sewer system (time unknown, based on operational history probably between 1959 and 1969 - EPA, 1980)

1970:

  • Solitron Devices installs waste stream pH control system (July 1970)
  • Pump in municipal well PW-9 fails, pump and stand pipe severely corroded (late 1970) - "pesticide" odor from PW-9 (water sample from PW-9 analyzed for organochlorine pesticides several years later: none detected - DER 1985)
  • CRB Utilities replace PW-9 pump, well returns to service

1974:

  • PW-9 "pesticide" odor worse (within an hour of pumping); smell so intense CRB Utilities receive numerous complaints from irate consumers
  • CRB Utilities removes PW-9 from service,
  • PW-10 develops odor problems and CRB Utilities removes it from service

1980:

  • CRB Utilities plugs and abandons PW-10 and PW-9

1981:

  • EPA samples from PW-11A and PW -17 show chlorinated solvents (August 1981)

1982:

  • EPA resample shows chlorinated solvent levels in PW-11A and PW -17 increasing
  • CRB takes PW-11A and PW -17 out of service

1984:

  • FDER begins CRB Wellfield Contamination Study, study team installs 30 groundwater monitoring wells in 11 locations near suspected sources of groundwater contamination

1985:

  • FDER's sampling data identifies Solitron Devices, Trans Circuits and BMI/Textron as probable sources of CRB groundwater contamination - highest off-site solvent levels occurring between 150 and 250 feet below the land surface, metals not found in off-site groundwater
  • Solvents detected in additional CRB supply wells PW-4, PW-5, PW-6 and PW-14, primary groundwater flow direction attributed to pull of operating supply wells
  • EPA Site Screening Investigation finds discharge water from pipe at the front of the south building contains chlorinated solvents

1986:

  • CRB Utilities begins building air stripping towers

1988:

  • CRB Utilities completes air stripping towers and begins using them

1991:

  • Contamination Assessment Report determines the drainage canal north of the site acts as a groundwater high and water flows outward - away from it, a process called mounding - lower portion of the aquifer moves in response to the pumping of the public supply wells (Tomasello and Associates, 1991)

1999:

  • EPA funds assessment activities at the site under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA, or Superfund) - consultants deliver Final Site Inspection/Remedial Investigation Report, Baseline Environmental Risk Assessment (Black and Veatch, 1999) and Feasibility Study Work Plan (BBL Environmental Services, 1999)
  • Remedial Investigation Report shows on-site soil contains elevated metals only in the area southwest of the northern building
  • Feasibility Study Work Plan recommends: testing soil in 15 locations beneath northern building, sampling groundwater for 1,4 -dioxane, and sampling 10 existing monitoring wells in four locations to provide data for evaluation of natural attenuation as a remedial alternative

2000:

  • January, BBL Environmental Services submits Feasibility Study Technical Memorandum
  • April, BBL Environmental Services submits the Draft Feasibility Study with the latest soil and groundwater data from samples collected in September 1999
  • August, EPA drafts a Record of Decision, as of March 2001, it has not been signed

APPENDIX B. FIGURES AND PHOTOGRAPHS

Site location map
Figure 1. Site location map.

Locations of groundwater contamination impacting the City of Riviera Beach and Southern Lake Park
Figure 2. Locations of groundwater contamination impacting the City of Riviera Beach and Southern Lake Park.

Locations of groundwater contaminants below land surface in 1985
Figure 3. Locations of groundwater contaminants below land surface in 1985.

View across Blue Heron Boulevard, north of the site
Photo 1. View across Blue Heron Boulevard, north of the site.

View south from Blue Heron Boulevard, looking at the northwestern corner of the northern building
Photo 2. View south from Blue Heron Boulevard, looking at the northwestern corner of the northern building.

Looking north from the middle of the site, at the south side of the northern building
Photo 3. Looking north from the middle of the site, at the south side of the northern building.

Southwest corner of the northern building. Window above Donald Sikaswe's head is broken, revealing asbestos insulation around piping. Rusty metal equipment could be a physical hazard
Photo 4. Southwest corner of the northern building. Window above Donald Sikaswe's head is broken, revealing asbestos insulation around piping. Rusty metal equipment could be a physical hazard.

Looking south from the middle of the site, at the north side of the southern building
Photo 5. Looking south from the middle of the site, at the north side of the southern building.

Northwest corner of the northern building, shows good condition of the loading dock and profuse vegetation growing on exposed soils
Photo 6. Northwest corner of the northern building, shows good condition of the loading dock and profuse vegetation growing on exposed soils.

View of the neighborhood north of the site
Photo 7. View of the neighborhood north of the site.

View east of canal that flows north of Heron Boulevard. This photo was taken between 1/8 and 1/4 mile from the site
Photo 8. View east of canal that flows north of Heron Boulevard. This photo was taken between 1/8 and 1/4 mile from the site.

Air strippers at the City of Riviera Beach Water Treatment Plant
Photo 9. Air strippers at the City of Riviera Beach Water Treatment Plant.


APPENDIX C. TABLES

Table 1.

Maximum Concentrations in On-Site Groundwater (All Depths)
Contaminants of Concern Maximum Concentration
(g/L)
# Greater Than Comparison Value/ Total # of Samples Comparison Value*
(g/L) Source
Chromium 496 (MW13C - 1993) 2/22 30 (Child RMEG, Hexavalent) ATSDR 1999
Chlorobenzene 3200 (MW13B - 1993) 5/38 100 (LTHA) ATSDR 1999
1,4-Dichlorobenzene 200 (MW13B - 1993) 5/46 75 (LTHA) ATSDR 1999
1,2-Dichloroethene 320 (MW13C - 1997) 2/37 70 (LTHA - Cis) ATSDR 1999
Tetrachloroethene 85 (MW13A - 1997) 3/38 5 (MCL) ATSDR 1999
Trichloroethene 57.9 (MW13A - 1993) 5/37 5 (MCL) ATSDR 1999
Vinyl Chloride 11,000 (MW13B - 1993) 11/22 2 (MCL) ATSDR 1999

Sources:

Department of Environmental Regulation, 1987
Tomasello Consulting Engineers, Inc., 1991
REP Associates Inc., 1993
Black and Veatch, 1999

g/L = micrograms per liter

* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.


Table 2.

Maximum Concentrations in On-Site Surface Soils (0-3 Inches Deep)
Contaminants of Concern Maximum Concentration
(mg/kg)
# Greater Than Comparison Value/ Total # of Samples Comparison Value*
(mg/kg) Source
Chromium 790 1/12 200 (Child RMEG, Hexavalent) ATSDR 1999
Chlorobenzene Not Detected 0/12 1,000 (Child RMEG) ATSDR 1999
1,4-Dichlorobenzene Not Detected 0/12 20,000 (Child Intermediate RMEG) ATSDR 1999
1,2-Dichloroethene Not Detected 0/12 20,000 (Child Intermediate RMEG - Cis) ATSDR 1999
Tetrachloroethene Not Detected 0/12 500 (Child RMEG) ATSDR 1999
Trichloroethene Not Detected 0/12 60 (CREG) ATSDR 1999
Vinyl Chloride Not Detected 0/12 1 (Child EMEG) ATSDR 1999

Sources: Black and Veatch, 1999

* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.

mg/kg = milligrams per kilogram


Table 3.

Maximum Concentrations in Off-Site Groundwater (All Depths)
Contaminants of Concern Maximum Concentration
(g/L)
# Greater Than Comparison Value/ Total # of Samples Comparison Value*
(g/L) Source
Chromium 2.09 (MW6C - 1985) 0/30 30 (Child RMEG, Hexavalent) ATSDR 1999
Chlorobenzene 300 (MW1C - 1985) 2/62 100 (LTHA) ATSDR 1999
1,4-Dichlorobenzene 100 (MW1C - 1991) 0/61 75 (LTHA) ATSDR 1999
1,2-Dichloroethene 200 (PW11A - 1985) 5/61 70 (Cis - LTHA) ATSDR 1999
Tetrachloroethene Not Detected 0/61 5 (MCL) ATSDR 1999
Trichloroethene 0.95 (Riviera Beach Finished Water, 1982) 0/62 5 (MCL) ATSDR 1999
Vinyl Chloride >1000 (PW11A - 1985) 18/59 2 (MCL) ATSDR 1999

Sources:

Department of Environmental Regulation, 1985
Department of Environmental Regulation, 1987
Tomasello Consulting Engineers, Inc., 1991
REP Associates Inc., 1993
Black and Veatch, 1999

g/L = micrograms per liter

* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.


Table 4.

Maximum Concentrations in Off-Site Sediments (0-6 Inches)
Contaminants of Concern Maximum Concentration
(mg/kg)
# Greater Than Comparison Value/ Total # of Samples Comparison Value*
(mg/kg) Source
Chromium 280 1/6 200 (Child RMEG, Hexavalent) ATSDR 1999
Chlorobenzene Not Detected 0/6 1,000 (Child RMEG) ATSDR 1999
1,4-Dichlorobenzene Not Detected 0/6 20,000 (Child Intermediate RMEG) ATSDR 1999
1,2-Dichloroethene Not Detected 0/6 20,000 Child Intermediate RMEG - Cis) ATSDR 1999
Tetrachloroethene Not Detected 0/6 500 (Child RMEG) ATSDR 1999
Trichloroethene Not Detected 0/6 60 (CREG) ATSDR 1999
Vinyl Chloride Not Detected 0/6 1 (Child EMEG) ATSDR 1999

Sources: Black and Veatch, 1999: samples from 1997.

* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.

mg/kg = milligrams per kilogram


Table 5.

City of Riviera Beach - Finished Water Quality
Date Sampled Agency Results (g/L)
Vinyl Chloride 1,2-Dichloroethene Trichloroethene Chlorobenzene
8/81 EPA (1) <1 0.2 0.3 --
7/82 EPA (1) 4 1.6 0.95 0.97
1/83 FDER (2) <1 <5 <5 <5
3/84 EPA (3) <0.5 <0.5 3 --
5/84 Consultant (4) <1 <1 <1 <1
9/84 Consultant (4) 1 <1 3 <1
Vinyl Chloride
dl=.1
1,2-Dichloroethene
dl=.3
Trichloroethene
dl=.3
Chlorobenzene
dl=2.0
Tetrachloroethene
dl=.3
9/22/85 CRB bdl bdl 0.1 bdl bdl
11/7/85 CRB bdl bdl bdl bdl bdl
12/12/85 CRB bdl bdl 0.5 bdl 3.6
12/16/85 CRB bdl bdl bdl bdl bdl
1/17/86 CRB bdl bdl bdl bdl bdl
1/20/86 CRB bdl bdl bdl bdl bdl
2/7/86 CRB bdl bdl bdl bdl bdl
2/10/86 CRB bdl bdl bdl bdl bdl
3/7/86 CRB bdl bdl bdl bdl bdl
3/10/86 CRB bdl bdl bdl bdl bdl
4/11/86 CRB bdl bdl bdl bdl bdl
4/14/86 CRB bdl bdl bdl bdl bdl
5/2/86 CRB bdl bdl bdl bdl bdl
5/5/86 CRB bdl bdl bdl bdl bdl
6/6/86 CRB bdl bdl bdl bdl bdl
7/4/86 CRB bdl bdl bdl bdl bdl
7/7/86 CRB bdl bdl bdl bdl bdl
7/31/86 CRB bdl bdl bdl bdl bdl
8/4/86 CRB bdl bdl bdl bdl bdl
9/5/86 CRB bdl bdl bdl bdl bdl
9/7/86 CRB bdl bdl bdl bdl bdl
10/7/86 another lab bdl bdl bdl bdl bdl
10/10/86 another lab bdl bdl bdl bdl bdl
Air Strippers Began Operating in 1988, all chemicals bdl from 10/10/86 to 8/19/99
8/19/99 CRB bdl, dl=0.5 bdl, dl=0.5 bdl, dl=0.5 bdl, dl=0.5 bdl, dl=0.5
EPA (1) United States Environmental Protection Agency, Office of Drinking Water, Cincinnati, Ohio 1981-1982. Groundwater Supply Survey Data on Water Supplies in South Florida
FDER (2) Florida Department of Environmental Regulation, Southeast Florida District, West Palm Beach, Florida. Program Files
EPA (3) United States Environmental Protection Agency. Survey of VOCs in Community Water Supplies, February - May 1984.
Consultant (4) City of Riviera Beach, Office of Utilities Director General Files,
CRB - City of Riviera Beach, a licensed laboratory would have had to run the sample, 1999 sample done by Southern Research Laboratories NR - Not Reported bdl below method detection level


Table 6. Completed Exposure Pathways

Table 6.

Completed Exposure Pathways
PATHWAY NAME EXPOSURE PATHWAY ELEMENTS TIME
SOURCE ENVIRONMENTAL MEDIA POINT OF EXPOSURE ROUTE OF EXPOSURE EXPOSED POPULATION
Municipal Water Supply Solitron Devices Groundwater Municipal Water Supply - Tap Water Ingestion and Inhalation About 26,000 area residents 1982-1983; possibly before 1981


PATHWAY NAME EXPOSURE PATHWAY ELEMENTS TIME
SOURCE ENVIRONMENTAL MEDIA POINT OF EXPOSURE ROUTE OF EXPOSURE EXPOSED POPULATION
Private Well Water Use of Existing Private Wells Groundwater Tap water Ingestion and Inhalation Seven Identified Households, Risk of Contaminated Groundwater Use Contingent Upon Proximity of Well to Site and Well Depth Current Analytical Results Do Not Indicate Current Contamination, Possibly Future?, Past Unlikely
On-Site Surface Soil and Contaminated Dust On-Site Surface Soil Soil On-site Inhalation and Incidental Ingestion About 300 Nearby Residents Depends on Future Land Use Changes Future


Table 8.

Calculated dose (mg/kg/day) from residential use of on-site groundwater
Contaminant of Concern
(maximum concentration)
mg/L
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
Chromium 0.496 None 0.03 0.01 0.00004 0.00003 Int. 0.0005 - -
Chlorobenzene 3.2 Int. 0.4 0.2 0.09 0.05 0.03 None 32 32
1,4-Dichlorobenzene 0.2 Int. 0.4 0.01 0.006 0.006 0.004 Int. 0.2
Chr. 0.1
2 2
1,2-Dichlorobenzene 0.32 None 0.02 0.009 0.009 0.006 None 3.2 3.2
Tetrachloroethene 0.085 Acute 0.05 0.006 0.002 0.002 0.002 Acute 0.2
Chr. 0.04
0.85 0.85
Trichloroethene 0.0579 Acute 0.2 0.004 0.002 0.0004 0.0003 Acute 2
Chr. 0.1
0.58 0.58
Vinyl Chloride 11.0 Chr. 0.00002 0.7 0.3 0.02 0.01 Acute 0.5
Chr. 0.03
110 110

Scenario Time-frame: Future
Land Use Conditions: Residential
Exposure Medium: Groundwater
Exposure Point: On-site tap water
Receptor Population: Residents
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991).
N.D.- Not detected
N.A.- Not applicable
N.S.- Not significant

The above doses were calculated using the following values:
Adult body weight- 70 kg
Adult water consumption- 2 liters/day
Adult shower time- 0.2 hours
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child water consumption- 1 liter/day
Child shower time- 0.2 hours
Child skin surface area- 7,200cm2


Table 9.

alculated dose (mg/kg/day) from residential contact with on-site soil
Contaminant of Concern
(maximum concentration)
mg/kg
Oral MRL
(mg/kg/day)
Soil- Ingestion (mg/kg/day) Inhalation MRL
(mg/m3)
Soil- Inhalation (mg/m3)
Child Adult Child Adult
Chromium 790 None 0.01 0.001 Int. 0.0005 0.00004 0.00004
Chlorobenzene ND Int. 0.4 - - None - -
1,4-Dichlorobenzene ND Int. 0.4 - - Int. 0.2
Chr. 0.1
- -
1,2-Dichlorobenzene ND None - - None - -
Tetrachloroethene ND Acute 0.05 - - Acute 0.2
Chr. 0.04
- -
Trichloroethene ND Acute 0.2 - - Acute 2
Chr. 0.1
- -
Vinyl Chloride ND Chr. 0.00002 - - Acute 0.5
Chr. 0.03
- -

Scenario Time-frame: Future
Land Use Conditions: Residential
Exposure Medium: Groundwater
Exposure Point: On-site tap water
Receptor Population: Residents
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991).
N.D.- Not detected
N.A.- Not applicable
N.S.- Not significant

The above doses were calculated using the following values:
Adult body weight- 70 kg
Adult soil consumption- 100 mg/day
Adult shower time- 0.2 hours
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child soil consumption- 200 mg/day
Child shower time- 0.2 hours
Child skin surface area- 7,200cm2


Table 10.

Calculated dose (mg/kg/day) from residential use of off-site groundwater
Contaminant of Concern
(maximum concentration)
mg/L
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
Chromium 0.02 None 0.001 0.0006 8.2 x 10-7 0.00001 Int. 0.0005 - -
Chlorobenzene 0.3 Int. 0.4 0.02 0.009 0.002 0.003 None 3 3
1,4-Dichlorobenzene 0.1 Int. 0.4 0.007 0.003 0.001 0.002 Int. 0.2
Chr. 0.1
1 1
1,2-Dichlorobenzene 0.2 None 0.01 0.006 0.003 0.004 None 2 2
Tetrachloroethene ND Acute 0.05 - - - - Acute 0.2
Chr. 0.04
- -
Trichloroethene 0.01 Acute 0.2 0.0006 0.0003 0.00003 0.00005 Acute 2
Chr. 0.1
0.1 0.1
Vinyl Chloride >1.0 Chr. 0.00002 0.07 0.03 0.002 0.001 Acute 0.5
Chr. 0.03
10 10
Finished Water,
Vinyl Chloride 0.004
Chr. 0.00002 0.0003 0.0001 0.000008 0.000005 Acute 0.5
Chr. 0.03
0.04 0.04

Scenario Time-frame: Future
Land Use Conditions: Residential
Exposure Medium: Groundwater
Exposure Point: On-site tap water
Receptor Population: Residents
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991).
N.D.- Not detected
N.A.- Not applicable
N.S.- Not significant

The above doses were calculated using the following values:
Adult body weight- 70 kg
Adult water consumption- 2 liters/day
Adult shower time- 0.2 hours
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child water consumption- 1 liter/day
Child shower time- 0.2 hours
Child skin surface area- 7,200cm2


Table 11.

Calculated dose (mg/kg/day) from residential contact with off-site soil
Contaminant of Concern
(maximum concentration)
mg/kg
Oral MRL
(mg/kg/day)
Soil- Ingestion (mg/kg/day) Inhalation MRL
(mg/m3)
Soil- Inhalation (mg/m3)
Child Adult Child Adult
Chromium 280 None 0.004 0.0004 Int. 0.0005 0.00002 0.00002
Chlorobenzene ND Int. 0.4 - - None - -
1,4-Dichlorobenzene ND Int. 0.4 - - Int. 0.2
Chr. 0.1
- -
1,2-Dichlorobenzene ND None - - None - -
Tetrachloroethene ND Acute 0.05 - - Acute 0.2
Chr. 0.04
- -
Trichloroethene ND Acute 0.2 - - Acute 2
Chr. 0.1
- -
Vinyl Chloride ND Chr. 0.00002 - - Acute 0.5
Chr. 0.03
- -

Scenario Time-frame: Future
Land Use Conditions: Residential
Exposure Medium: Groundwater
Exposure Point: On-site tap water
Receptor Population: Residents
These doses were calculated using Risk Assistant software and accepted values for groundwater consumption, shower inhalation exposure and dermal exposure parameters (EPA, 1991).
N.D.- Not detected
N.A.- Not applicable
N.S.- Not significant

The above doses were calculated using the following values:
Adult body weight- 70 kg
Adult soil consumption- 100 mg/day
Adult shower time- 0.2 hours
Adult skin surface area- 23,000cm2
Child body weight- 15 kg
Child soil consumption- 200 mg/day
Child shower time- 0.2 hours
Child skin surface area- 7,200cm2

g.w. = groundwater
N.D. = not detected
* The air concentration is given in milligrams per cubic meter because the values for inhalation studies in the Toxicologic

Profile are given in these units. The air concentration is not a dose, therefore it is the same for adults and children.


APPENDIX D. 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 hazardouscontaminant is associated with a harmful health effect or illness. The risk of illness is not ameasure of cause and effect; only an in-depth health study can identify a cause and effectrelationship. Instead, we use the risk of illness to decide if a follow-up health study is neededand to identify possible associations.

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

Information from human studies provides the strongest evidence that exposure to a hazardouscontaminant is related to a particular illness. Some of this evidence comes from doctorsreporting an unusual incidence of a specific illness in exposed individuals. More formal studiescompare illnesses in people with different levels of exposure. However, human information isvery limited for most hazardous contaminants, and scientists must frequently depend upon datafrom animal studies. Hazardous contaminants associated with harmful health effects in humansare 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 hazardouscontaminants are associated with cancer in animals, but lack evidence of a similar association inhumans. In addition, humans and animals have differing abilities to protect themselves againstlow levels of contaminants, and most animal studies test only the possible health effects of highexposure levels. Consequently, the possible effects on humans of low-level exposure tohazardous contaminants are uncertain when information is derived solely from animalexperiments.

Dose Response/Thresholds

The focus of toxicological studies in humans or animals is identification of the relationshipbetween exposure to different doses of a specific contaminant and the chance of having a healtheffect from each exposure level. This dose-response relationship provides a mathematicalformula or graph that we use to estimate a person's risk of illness. The actual shape of the dose-response curve requires scientific knowledge of how a hazardous substance affects different cellsin the human body. There is one important difference between the dose-response curves used toestimate the risk of non-cancer illnesses and those used to estimate the risk of cancer: theexistence of a threshold dose. A threshold dose is the highest exposure dose at which there is norisk of illness. The dose-response curves for non-cancer illnesses include a threshold dose that isgreater than zero. Scientists include a threshold dose in these models because the human bodycan adjust to varying amounts of cell damage without illness. The threshold dose differs fordifferent contaminants and different exposure routes, and we estimate it from informationgathered in human and animal studies. In contrast, the dose-response curves used to estimate therisk of cancer assume there is no threshold dose (or, the cancer threshold dose is zero). Thisassumes a single contaminant molecule may be sufficient to cause a clinical case of cancer. Thisassumption is very conservative, and many scientists believe a threshold dose greater than zeroalso exists for the development of cancer.

Uncertainty

All risk assessments, to varying degrees, require the use of assumptions, judgments, andincomplete data. These contribute to the uncertainty of the final risk estimates. Some moreimportant sources of uncertainty in this public health assessment include environmental samplingand analysis, exposure parameter estimates, use of modeled data, and present toxicologicalknowledge. These uncertainties may cause risk to be overestimated or underestimated. Becauseof the uncertainties described below, this public health assessment does not represent an absoluteestimate of risk to persons exposed to chemicals at or near the Solitron Devices site.

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

There are two areas of uncertainty related to exposure parameter estimates. The first is theexposure-point concentration estimate. The second is the estimate of the total chemicalexposures. In this assessment we used maximum detected concentrations as the exposure pointconcentration. We believe using the maximum measured value to be appropriate because wecannot be certain of the peak contaminant concentrations, and we cannot statistically predict peakvalues. Nevertheless, this assumption introduces uncertainty into the risk assessment that mayover- or under-estimate the actual risk of illness. When selecting parameter values to estimateexposure dose, we used default assumptions and values within the ranges recommended by theATSDR 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 themaximum exposure period occurred regularly for each selected pathway. Both assumptions arelikely to contribute to the over-estimation of risk of illness.

There are also data gaps and uncertainties in the design, extrapolation, and interpretation oftoxicological experimental studies. Data gaps contribute uncertainty because information iseither not available or is addressed qualitatively. Moreover, the available information on theinteraction among chemicals found at the site, when present, is qualitative (that is, a descriptioninstead of a number) and we cannot apply a mathematical formula to estimate the dose. Thesedata gaps may tend to underestimate the actual risk of illness. In addition, there are greatuncertainties 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. Humanpopulations are also variable because of differences in genetic constitution, diet, home andoccupational environment, activity patterns, and other factors. These uncertainties can result inan over- or under-estimation of risk of illness. Finally, there are great uncertainties inextrapolating from high to low doses, and controversy in interpreting these results. Because themodels used to estimate dose-response relationships in experimental studies are conservative,they tend to overestimate the risk. Techniques used to derive acceptable exposure levels accountfor 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.


CERTIFICATION

This Solitron Devices Inc., Site Public Health Assessment was prepared by the Florida Department of Health under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health assessment was begun.

Debra Gable
Technical Project Officer
Division of Health Assessment and Consultation (DHAC)
ATSDR


The Division of Health Assessment and Consultation, ATSDR, has reviewed this health consultation, and concurs with its findings.

Richard Gillig
Chief, SSAB, DHAC, ATSDR

Table of Contents

  
 
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