PUBLIC HEALTH ASSESSMENT
SOLITRON DEVICES, INCORPORATED
WEST PALM BEACH, PALM BEACH COUNTY, FLORIDA
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
Figure 2. Locations of groundwater contamination impacting the City of Riviera Beach and Southern Lake Park.
Figure 3. Locations of groundwater contaminants below land surface in 1985.
Photo 1. View across Blue Heron Boulevard, north of the site.
Photo 2. View south from Blue Heron Boulevard, looking at the northwestern corner of the northern building.
Photo 3. Looking north from the middle of the site, at the south side of the northern building.
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.
Photo 5. Looking south from the middle of the site, at the north side of the southern building.
Photo 6. Northwest corner of the northern building, shows good condition of the loading dock and profuse vegetation growing on exposed soils.
Photo 7. View of the neighborhood north of 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.
Photo 9. Air strippers at the City of Riviera Beach Water Treatment Plant.
| Contaminants of Concern | Maximum Concentration (µg/L) | # Greater Than Comparison Value/ Total # of Samples | Comparison Value* | |
|---|---|---|---|---|
| (µg/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
µg/L = micrograms per liter
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
| 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
| Contaminants of Concern | Maximum Concentration (µg/L) | # Greater Than Comparison Value/ Total # of Samples | Comparison Value* | |
|---|---|---|---|---|
| (µg/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
µg/L = micrograms per liter
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
| 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
| Date Sampled | Agency | Results (µg/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 |
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
| 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 |
| 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
| 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
| 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
| 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.
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
