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PUBLIC HEALTH ASSESSMENT

TRANS CIRCUITS, INCORPORATED
LAKE PARK, PALM BEACH COUNTY, FLORIDA


APPENDIX A. SITE SUMMARY

Below we list the chronologic history of Trans Circuits (TC) and Solitron Devices (SD)contamination discovery and interim efforts to protect municipal water quality. Liquid wastesfrom both sites released solvents and metals to the soil and groundwater. Released chemicalsmoved in the shallowest groundwater at both sites under the influence of natural flow to the eastand northeast. When this shallowest water moved deeper in the aquifer, pull toward the City ofRiviera Beach (CRB) public supply wells influenced its flow. At these deeper levels,contaminants from Trans Circuits moved to the southeast while Solitron Devices chemicalsmoved northeast. The largest cluster of CRB municipal wells is along Old Dixie Highway (see Figure 2, Appendix B for details).

Releases and Interim Efforts

Solitron Devices Early History, 1969 - 1980

1969:

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

1970:

  • Pump in municipal well (public supply well (PW)) 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, smell likely chlorobenzene or sulfur metabolites - Department of Environmental Protection 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 notices of odors 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 (these wells are located just north of SD)

Trans Circuits Early History, 1976 - 1981

  • Etched Products manufactures electronics onsite from 1976 to 1978, sells property to TC in 1978
  • Wastewater disposal not documented for period from 1976 to 1981, lack of sanitary sewers at that time means effluent was likely discharged to the ground or septic tank. Either practice could have introduced contaminants to groundwater for a period of approximately five years

Both Sites - 1981 and Later
1981:

  • EPA samples show chlorinated solvents or their breakdown products in PW-11A (plausible source - SD) and PW -17 (plausible source - TC) (August 1981)
  • TC builds the wastewater discharge pond north of their building. Designed for evaporation, it has a synthetic membrane liner

1982:

  • TC evaporation pond inadequate to hold 336,000 gallons of effluent per month, part of the membrane liner is removed from the pond, 10/6/82 Memo from John Martin to Rick Reis (both of Department of Environmental Protection) - pond full and overflowing to the railroad tracks, Department of Environmental Protection Notice of Violation - no monthly monitoring reports, liquid and industrial waste treatment and disposal system operated without Department of Environmental Protection permit, fluoride and nitrate above allowable levels in groundwater, Department of Environmental Protection issues orders of corrective action
  • TC builds a wastewater treatment plant to treat the electroplating wastewater and adds a centrifuge to dewater chemical sludge which was taken to a landfill - effluent exceeds limits for copper, fluoride and lead, sample not analyzed for VOCs
  • EPA resample shows chlorinated solvent levels in PW-11A and PW -17 increasing
  • CRB takes PW-11A and PW -17 out of service

1983:

  • FDER conducts TC site reconnaissance, no samples collected. Sludge observed in perc. pond
  • Flooding problems prompt the construction of a 3-foot high retaining wall around the TC pond. Rain, along with mechanical and electrical problems frequently result in discharge of effluent above the recommended state guidelines

1984:

  • FDER begins CRB Wellfield Contamination Study, study team installs 30 groundwater monitoring wells in 11 locations near suspected sources of groundwater contamination
  • TC begins monitoring wastewater for VOCs as a condition of the 1984 discharge permit from FDER
  • TC loses appeal to administrative hearing officer in September and agrees to stop using their inadequate treatment process until improvements are made

1985:

  • FDER's sampling data identifies SD, TC 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. TC is indicated as responsible for the contamination of the CRB PW-17, due to:
    • - detection of tetrachloroethene and trichloroethene in effluent and monitoringwell samples (2/85 grab sample),
      - the southeasterly groundwater flow direction from the site at that time,
      - the vertical distribution of the contamination in the aquifer, and
      - the absence of other sources in the vicinity
  • 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
  • TC, Inc. signs a consent agreement with FDER to remediate groundwater. Manufacturing processes at TC cease, and no effluent is discharged after that time to the percolation pond. TC purchases a Laboratory Computer, Well Drilling Equipment and pays a balance of $873 as a $100,000 "donation" to FDER for industrial wastewater discharge violations

1986:

  • Goldberg, Zoino and Associates (GZA) prepare TC Contamination Assessment Plan, seven on-site wells are tested on a monthly basis
  • CRB Utilities begins building air stripping towers

1987:

  • Groundwater treatment system (recovery well and air-stripping tower) installed on TC property to reduce solvent levels in groundwater

1988:

  • CRB Utilities completes air stripping towers and begins using them

1989:

  • NUS Corp. Completes a TC Screening Site Inspection (SSI) for the EPA, and they recommend a Phase II SSI
  • GZA submits a TC Summary Report of the Recovery system with summary data from 10 quarterly rounds of on-site groundwater samples
  • Groundwater treatment system (recovery well and air-stripping tower) on TC property groundwater is disengaged because solvent levels on and near the site are significantly reduced. However, FDER declines signing off on the Consent Order because metals and VOCs are still being detected in offsite groundwater

1990:

  • Groundwater remediation system on TC property is dismantled
  • Southeast Department of Environmental Protection District requests help from the Site Investigation Section in characterizing migration of groundwater contamination from the TC site

1991:

  • TC Screening Site Inspection Report (Phase II) completed for the EPA by the Jacobs Engineering Group

1992:

  • FDER completes groundwater investigation for TC site which includes 12 onsite groundwater samples
  • Black and Veatch (B&V) Waste Science and Technology Corp. completes TC Site Inspection Prioritization for EPA and recommends surface soil analysis for the site

1994:

  • EPA completes a TC site sampling investigation, with five surface soil and six subsurface soil samples

1998:

  • B&V Special Projects Corp. complete the TC Expanded Site Investigation for the EPA. They install 16 permanent monitoring wells; and take and analyze 10 surface soil samples, 35 subsurface samples, and 35 groundwater samples.

1999:

  • B&V Special Projects Corp. submits the TC Draft Screening Level Ecological Risk Assessment of TC, Inc. Site
  • B&V Special Projects Corp. completes samples for the TC RI/FS (Remedial Investigation, Feasibility Study) and submits the Draft Data Evaluation and Summary Report Volumes 1, 2 & 3, November, 1999.
  • B&V Special Projects Corp. completes SD 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.
  • B&V Special Projects Corp. Feasibility Study Work Plan for SD recommends: testing soil in 15 locations beneath northern building, and sampling 10 existing monitoring wells in four locations to provide data for evaluation of natural attenuation as a remedial alternative

2000:

  • B&V Special Projects Corp. submits the TC Draft Remedial Investigation/Feasibility Study Report, Volumes 1, 2 & 3 January 2000.
  • B&V Special Projects Corp. submits the TC Final Remedial Investigation/Feasibility Study Report, Volumes 1, 2 & in May 2000.
  • In June 2000, B&V Special Projects Corp. submits a Remedial Alternative Screening Technical Memorandum for Groundwater
  • In August 2000, B&V Special Projects Corp. submits a Draft Feasibility Report
  • In November 2000, B&V Special Projects Corp. submits Final Feasibility Report
  • In December 2000, EPA submits Draft Record of Decision

APPENDIX B. FIGURES AND PHOTOGRAPHS

Site location map
Figure 1. Site location map.

Map of contaminants
Figure 2. Map of contaminants.

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

Entering the town of Lake Park, intersection of Old Dixie Highway and Silver Beach Road
Photo 1. Entering the town of Lake Park, intersection of Old Dixie Highway and Silver Beach Road.

Residential area south of Tri-City Industrial Park, just south of Silver Beach Road
Photo 2. Residential area south of Tri-City Industrial Park, just south of Silver Beach Road.

Site viewed from the north, Australian Pines are in the pond and in front of the building, 11/30/99
Photo 3. Site viewed from the north, Australian Pines are in the pond and in front of the building, 11/30/99.

Site viewed from corner of Brandt and Newman Roads, July 1999
Photo 4. Site viewed from corner of Brandt and Newman Roads, July 1999.

Closeups of two doorframes on the rear of the building. Doors have been removed
Photo 5. Closeups of two doorframes on the rear of the building. Doors have been removed.

Closeup of doorframe on the east side of the building. Door has been removed
Photo 6. Closeup of doorframe on the east side of the building. Door has been removed.

View of east side of site looking north along Brandt Street
Photo 7. View of east side of site looking north along Brandt Street.

Air stripping towers at the City of Riviera Beach Utilities, July 1999
Photo 8. Air stripping towers at the City of Riviera Beach Utilities, July 1999.

Air stripping tower on the north side of the building, doorframe visible in the background, door has been removed
Photo 9. Air stripping tower on the north side of the building, doorframe visible in the background, door has been removed.


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
1,2-Dichloroethene 450 J (M104 10/91) 3/22 70 (LTHA) ATSDR 1999
Fluoride 67,300 (Pd 8/85) 62/148 4,000 (PDWS) FDEP 1999
Lead 343 (Ps 8/85) 66/132 15 (PDWS) FDEP 1999
Nickel 140J (TC-MW2D-SA3 6/99) 1/4 100 (LTHA) ATSDR 1999
Tetrachloroethene 2250 (Ps 7/85) 97/156 0.7 (CREG) ATSDR 1999
Trichloroethene 1287 (M-104 12/86) 57/154 3 (CREG) ATSDR 1999

Sources:

Department of Environmental Regulation, 1987, 1992,
Goldberg, Zoino and Associates, Inc., 1990,
Black and Veatch Special Projects Corp., 1999.

J = Approximate Value; quantitative QC out of range
g/L = micrograms per liter

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

PDWS - Primary Drinking Water Standard - Enforceable Florida Standards
CREG - Cancer Risk Evaluation Guide for one in one million excess cancer (ATSDR)
LTHA - Lifetime Health Advisory (ATSDR)


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
1,2-Dichloroethene ND 0/9 1,000 (RMEG) ATSDR 1999
Fluoride NA
Lead 110 (SS05, 7/97) 0/9 400 (SCTL, direct contact, children) EPA 1994a
Nickel 25 0/9 1000 (C-RMEG) ATSDR 1999
Tetrachloroethene ND 0/9 10 (CREG) ATSDR 1999
Trichloroethene ND 0/9 60 (CREG) ATSDR 1999

Sources:

Goldberg, Zoino and Associates, Inc., field screening for purgeable halocarbons all results showed concentrations less than 1 mg/kg, the detection level for the field-sampling equipment,
Black and Veatch Special Projects Corp., 1999.

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

mg/kg = milligrams per kilogram
ND = Not Detected
NA = Not Analyzed

CREG - Cancer Risk Evaluation Guide for one in one million excess cancer (ATSDR)
SCTL - Soil Cleanup Target Levels (FDEP)
RMEG - Reference Dose Media Evaluation Guide (ATSDR)


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
1,2-Dichloroethene 1,200J (M-110, 10/91) 8/81 70 (LTHA) ATSDR 1999
Fluoride 20,400 (DER4D, 10/91) 11/144 4,000 (PDWS) FDEP 1999
Lead 110 (M-102, 1987) 14/140 15 (PDWS) FDEP 1999
Nickel 380 (TCMW11D-SA4 6/99) 2/40 100.............................(LTHA)
Tetrachloroethene 890J (MW110, 10/91) 21/245 0.7 (CREG) ATSDR 1999
Trichloroethene 3000 (MW110, 10/91) 17/243 3 (CREG) ATSDR 1999
Trichloroethene 0.95 (Riviera Beach Finished Water, 1982) 3 (CREG) ATSDR 1999
Vinyl Chloride 4 (Riviera Beach Finished Water, 1982) 1 (PDWS) FDEP 1999

Sources:

Department of Environmental Regulation, 1985, 1992,
Goldberg, Zoino and Associates, Inc., 1990,
Black and Veatch Special Projects Corp., 1999.

J = Approximate Value; quantitative QC out of range
g/L = micrograms per liter
* Comparison values used to select chemicals for further scrutiny, not for determining the possibility of illness.
PDWS - Primary Drinking Water Standard - Enforceable Florida Standards
CREG - Cancer Risk Evaluation Guide for one in one million excess cancer (ATSDR)
LTHA - Lifetime Health Advisory (ATSDR)


Table 4.

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
- - Not Reported
bdl below method detection level


Table 5.

Completed Exposure Pathways
PATHWAY NAME EXPOSURE PATHWAY ELEMENTS TIME
SOURCES ENVIRONMENTAL MEDIA POINT OF EXPOSURE ROUTE OF EXPOSURE EXPOSED POPULATION
Municipal Water Supply Trans circuits
(trichloroethene)*
Groundwater Municipal Water Supply - Tap Water: Ingestion and Inhalation About 26,000 area residents 1982-1983;
possibly before 1981
(but, no data)

* Past and present Public Well (PW) analyses show PW-17, which is down-gradient from Trans Circuits, shows (and has shown)trichloroethene which has not been found in public wells near Solitron Devices. PW-11, near Solitron Devices, has the highest PW level ofvinyl chloride followed by PW-6 and PW-4&5. These wells and their levels of vinyl chloride correspond to proximity with Solitron Devices, (closest equals highest). PW-17 has never shown vinyl chloride.


Table 6.

Potential Exposure Pathways
PATHWAY NAME EXPOSURE PATHWAY ELEMENTS TIME
SOURCE ENVIRONMENTAL MEDIA POINT OF EXPOSURE ROUTE OF EXPOSURE EXPOSED POPULATION
Private Well Use of Off-site Private Wells Groundwater Tap water Ingestion and Inhalation Seven Households, Risk of Contaminated Groundwater Use Contingent Upon Proximity of Well to Site and Well Depth Past and Possibly Future
Future Use of New Wells Future Use of New On-site or Off-site Wells Groundwater Tap Water or Other Use of Private or Limited-use Wells Ingestion and Inhalation Residents or Workers Using Contaminated Groundwater Future
On-Site Subsurface Soil On-Site Subsurface Soil Soil 2.5 to 5 feet below the land surface On-site Incidental Ingestion Depends on Future Land Use, Possibly Construction or Utilities Workers Future


Table 7.

Calculated dose (mg/kg/day) from residential use of on-site groundwater
Contaminant of Concern
(maximum concentration)
g/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
1,2-Dichloroethene 450J Acute 1
Int. 0.3
0.03 0.01 0.002 0.001 None 4.5 4.5
Fluoride 67,300 None 4.5 1.9 0.006 0.004 None - -
Lead 343 None 0.02 0.01 0.0003 0.00002 None - -
Nickel 380 None 0.012 0.005 0.00001 0.00003 Chr 0.002 - -
Tetrachloroethene 2250 Acute 0.05 0.15 0.06 0.06 0.04 Acute 0.2
Chr. 0.04
22.5 22.5
Trichloroethene 1287 Acute 0.2 0.09 0.04 0.009 0.006 Acute 2
Chr. 0.1
12.9 12.9
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 Child body weight- 15 kg
Adult water consumption- 2 liters/day Child water consumption- 1 liter/day
Adult shower time- 0.2 hours Child shower time- 0.2 hours
Adult skin surface area- 23,000cm2 Child skin surface area- 7,200cm2
* 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.
g/L = microgram per liter of water
mg/kg/day = milligrams per kilogram per day
mg/m3 = milligrams per cubic meter


Table 8.

Calculated 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 - Dermal
(mg/m3)
Child Adult Child Adult
1,2-Dichloroethene ND Acute 1
Int. 0.3
- - None - -
Fluoride NA None - - None - -
Lead 110 None 0.02 0.01 None 0.00003 0.00002
Nickel ND None -- - Chr 0.002 - -
Tetrachloroethene ND Acute 0.05 - - Acute 0.2
Chr. 0.04
- -
Trichloroethene ND Acute 0.2 - - Acute 2
Chr. 0.1
- -
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 Child body weight- 15 kg
Adult soil consumption- 100 mg/day Child soil consumption- 200 mg/day
Adult shower time- 0.2 hours Child shower time- 0.2 hours
Adult skin surface area- 23,000cm2 Child skin surface area- 7,200cm2
* 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.
mg/kg = milligram per kilogram of soil
mg/kg/day = milligrams per kilogram per day
mg/m3 = milligrams per cubic meter


Table 9.

Calculated dose (mg/kg/day) from residential use of off-site groundwater
Contaminant of Concern
(maximum concentration)
g/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
1,2-Dichloroethene 1,200 Acute 1
Int. 0.3
0.08 0.03 0.004 0.003 None 12 12
Fluoride 20,400 None 1.36 0.6 0.002 0.001 None - -
Lead 110 None 0.007 0.003 0.00001 0.000007 None - -
Nickel 180 None 0.0 0.0000 Chr 0.002 - -
Tetrachloroethene 890 Acute 0.05 0.06 0.03 0.02 0.016 Acute 0.2
Chr. 0.04
8.9 8.9
Trichloroethene 3,000 Acute 0.2 0.2 0.09 0.02 0.01 Acute 2
Chr. 0.1
30 30
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:
The above doses were calculated using the following values:
Adult body weight- 70 kg Child body weight- 15 kg
Adult water consumption- 2 liters/day Child water consumption- 1 liter/day
Adult shower time- 0.2 hours Child shower time- 0.2 hours
Adult skin surface area- 23,000cm2 Child skin surface area- 7,200cm2
* 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.
g/L = microgram per liter of water
mg/kg/day = milligrams per kilogram per day
mg/m3 = milligrams per cubic meter


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 hazardous contaminant isassociated with a harmful health effect or illness. The risk of illness is not a measure of cause andeffect; only an in-depth health study can identify a cause and effect relationship. Instead, we use therisk of illness to decide if the site needs a follow-up health study and to identify possible associations.

The greater the exposure to a hazardous contaminant (dose), the greater the risk of illness. The amountof a substance required to harm a person's health (toxicity) also determines the risk of illness. Exposureto a hazardous contaminant above a minimum level increases everyone's risk of illness. Only inunusual 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 doctors reporting anunusual incidence of a specific illness in exposed individuals. More formal studies compare illnesses inpeople with different levels of exposure. However, human information is very limited for mosthazardous contaminants, and scientists must frequently depend upon data from animal studies. Hazardous contaminants associated with harmful health effects in humans are often associated withharmful health effects in other animal species. There are limits, however, in only relying on animalstudies. For example, scientists have found some hazardous contaminants are associated with cancer inanimals, but lack evidence of a similar association in humans. In addition, humans and animals havediffering abilities to protect themselves against low levels of contaminants, and most animal studies testonly the possible health effects of high exposure levels. Consequently, the possible effects on humansof low-level exposure to hazardous contaminants are uncertain when information is derived solely fromanimal experiments.

Dose Response/Thresholds

The focus of toxicological studies in humans or animals is identification of the relationship betweenexposure to different doses of a specific contaminant and the chance of having a health effect from eachexposure level. This dose-response relationship provides a mathematical formula or graph that we useto estimate a person's risk of illness. The actual shape of the dose-response curve requires scientificknowledge of how a hazardous substance affects different cells in the human body. There is oneimportant difference between the dose-response curves used to estimate the risk of non-cancer illnessesand those used to estimate the risk of cancer: the existence of a threshold dose. A threshold dose is thehighest exposure dose at which there is no risk of illness. The dose-response curves for non-cancerillnesses include a threshold dose that is greater than zero. Scientists include a threshold dose in thesemodels because the human body can adjust to varying amounts of cell damage without illness. Thethreshold dose differs for different contaminants and different exposure routes, and we estimate it frominformation gathered in human and animal studies. In contrast, the dose-response curves used toestimate 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. Thisassumption is very conservative, and many scientists believe a threshold dose greater than zero alsoexists for the development of cancer.

Uncertainty

All risk assessments, to varying degrees, require the use of assumptions, judgments, and incompletedata. These contribute to the uncertainty of the final risk estimates. Some more important sources ofuncertainty in this public health assessment include environmental sampling and analysis, exposureparameter estimates, use of modeled data, and present toxicological knowledge. These uncertaintiesmay cause risk to be overestimated or underestimated. Because of the uncertainties described below,this public health assessment does not represent an absolute estimate of risk to persons exposed tochemicals at or near the Trans Circuits site.

Environmental chemistry analysis errors can arise from random errors in the sampling and analyticalprocesses, resulting in either an over- or under-estimation of risk. We can control these errors to someextent by increasing the number of samples collected and analyzed and by sampling the same locationsover several different periods. The above actions tend to minimize uncertainty contributed fromrandom 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 thisassessment we used maximum detected concentrations as the exposure point concentration. We believeusing the maximum measured value to be appropriate because we cannot be certain of the peakcontaminant concentrations, and we cannot statistically predict peak values. Nevertheless, thisassumption introduces uncertainty into the risk assessment that may over- or under-estimate the actualrisk of illness. When selecting parameter values to estimate exposure dose, we used defaultassumptions and values within the ranges recommended by the ATSDR or the EPA. These defaultassumptions and values are conservative (health protective) and may contribute to the over-estimationof risk of illness. Similarly, we assumed the maximum exposure period occurred regularly for eachselected 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 oftoxicological experimental studies. Data gaps contribute uncertainty because information is either notavailable or is addressed qualitatively. Moreover, the available information on the interaction amongchemicals found at the site, when present, is qualitative (that is, a description instead of a number) andwe cannot apply a mathematical formula to estimate the dose. These data gaps may tend tounderestimate the actual risk of illness. In addition, there are great uncertainties in extrapolating fromhigh-to-low doses, and from animal-to-human populations. Extrapolating from animals to humans isuncertain because of the differences in the uptake, metabolism, distribution, and body organsusceptibility between different species. Human populations are also variable because of differences ingenetic constitution, diet, home and occupational environment, activity patterns, and other factors. These uncertainties can result in an over or underestimation of risk of illness. Finally, there are greatuncertainties in extrapolating from high doses to low doses, and controversy in interpreting theseresults. Because the models used to estimate dose-response relationships in experimental studies areconservative, they tend to overestimate the risk. Techniques used to derive acceptable exposure levelsaccount 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.


CERTIFICATION

This Trans Circuits, 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

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