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PETITIONED PUBLIC HEALTH ASSESSMENT

BURLINGTON NORTHERN LIVINGSTON COMPLEX
(a/k/a BURLINGTON NORTHERN RAIL YARD)
LIVINGSTON, PARK COUNTY, MONTANA


APPENDIX A: FIGURES

Burlington Northern Rail Yard Site Location Map
Figure 1. Burlington Northern Rail Yard Site Location Map

Location of private and city wells
Figure 2. Location of private and city wells

Mission Wye area
Figure 3. Mission Wye area

River sediment sampling locations
Figure 4. River sediment sampling locations

Ambient air monitoring sites
Figure 5. Ambient air monitoring sites

Burlington Northern Rail Yard
Figure 6. Burlington Northern Rail Yard



APPENDIX B: DATA TABLES

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Table 3.

On-site soil gas contaminants at BNRYc
Substance Maximum level detected in Comparison Values
electric shop areas drainline areas Value Source
(ug/m3)
cis-1,2-DCE 36,000 100,000 800*
(200 ppb)
Intermediate EMEG
Chlorobenzene NDd 92,000 NONE  
2-chlorotoluene ND 4,500 NONE  
TCE 48,000 49,000 0.6 CREG
PCE 1,900,000 1,300,000 2 CREG
1,1,1-TCA 650 920 4,000*
(700 ppb)
Intermediate EMEG

* Conversion factor for air:

Cug/m3 = Cppb

X MWg/mole


24.45
where
C = Concentration
MW = Molecular Weight

 

Table 4.

Off-site soil gas contaminants at BNRY
Substance Highest level detected Reference Comparison Value Source
PCE 14 ug/m3 16 2 ug/m3 CREG
TCE 9.6 ug/m3 16 0.6 ug/m3 CREG


Table 5.

Mean levels of on-site airborne organic compounds
Substance Level
detected
Reference Comparison Values
Value Source
On-site organic compounds (in ug/m3)
Acenaphthene 0.0039 16 NONE  
Acenaphthylene 0.0033 16 NONE  
Anthracene 0.0034 16 NONE  
Benzo (b) fluoranthene 0.0037 16 NONE  
Chrysene 0.0032 16 NONE  
Fluoranthene 0.0052 16 NONE  
Fluorene 0.0076 16 NONE  
Napthalene 0.9 5 10*
(2 ppb)
Chronic EMEG
Phenanthrene 0.67 5 NONE  
PCE 1.52 16 2 CREG
Pyrene 0.0044 16 NONE  

* Conversion factor for air:

Cug/m3 = Cppb

X MWg/mole


24.45
where
C = Concentration
MW = Molecular Weight


Table 6.

Mean levels of off-site airborne organic compounds
Substance Level detected Reference Comparison values
Value Source
Off-site volatile organic compounds (in ug/m3)
PCE 1.47 - 1.55
4
2 CREG
4.7 - 10.2 (upwind of BNRY) 16
1.0 (downwind of BNRY)

Table 7.

Mean levels of on-site airborne metals
Metal Upwind Downwind Reference Comparison value
ug/m3 Value (ug/m3) Source
Antimony 0.021 0.020 16 NONE  
Arsenic 0.001 0.006 16 0.0002 CREG
Barium 0.010 0.015 16 NONE  
Bromine 0.003 0.013 16 NONE  
Cadmium 0.008 0.024 16 0.0006 CREG
Chlorine ND 0.174 16 NONE  
Copper 0.004 0.004 16 NONE  
Germanium 0.001 0.001 16 NONE  
Indium 0.016 0.013 16 NONE  
Iron 0.406 0.161 16 NONE  
Lanthanum 0.188 0.086 16 NONE  
Lead 0.005 0.070 16 NONE  
Molybdenum 0.106 0.106 16 NONE  
Palladium 0.015 0.003 16 NONE  
Rubidium 0.003 0.004 16 NONE  
Selenium 0.001 ND 16 NONE  
Silver 0.010 0.004 16 NONE  
Strontium 0.014 0.013 16 NONE  
Sulphur 0.130 0.042 16 NONE  
Tin 0.018 0.022 16 NONE  
Titanium 0.050 0.046 16 NONE  
Vanadium 0.001 0.002 16 NONE  
Yttrium 0.003 0.002 16 NONE  
Zinc ND 0.089 16 NONE  
Zirconium 0.018 0.017 16 NONE  


Table 8.

On-site groundwater samples
Substance Highest levels detected Reference Comparison values
Value Source
On-site
Volatile organic compounds
(in parts per billion; ppb)
Chloroform 4.6 16 400 Chronic EMEG (adult)
TCE 200 8 5 MCL
1,1,1-TCA 0.85 16 200 LTHA / MCL
PCE 2,200 9 5 MCL
Ethylbenzene 11 16 700 LTHA / MCL
sec-butylbenzene 5.5 16 NONE  
Chlorobenzene 3,000 9 100 LTHA / MCL
Cis-1,2-DCE 2,550 1 70 LTHA / MCL
Trans-1,2-DCE 31 1 100 LTHA / MCL
2-chlorotoluene 190 16 100 LTHA
4-chlorotoluene 6 9 100 LTHA
1,2-dibromo-3-chloropropane 32 9 0.2 MCL
1,2-DCB 88 16 600 LTHA / MCL
1,3-DCB 16 16 600 LTHA
1,4-DCB 220 9 75 LTHA / MCL
Isopropylbenzene 6.9 16 NONE  
Xylenes 36 8 7,000 Intermediate EMEG (adult)
On-Site
Semivolatile organic compounds
(in parts per billion; ppb)
Naphthalene 45 16 20 LTHA
1-methylnaphthalene 250 8 NONE  
2-methylnaphthalene 170 8 NONE  
Dibenzofuran 21 10 NONE  
Fluorene 12 10 1,000 RMEG (adult)
Phenanthrene 9 10 NONE  
bis(2-ethylhexyl)-phthalate 5,600 10 6 MCL
Metals
(in parts per billion; ppb)
Arsenic 7 1 10 Chronic EMEG (adult)
Barium 100 1 2,000 RMEG (adult)
Cadmium 4 1 20 Chronic EMEG (adult)
Lead 20 1 15 MCL
Selenium 6 1 70 Chronic EMEG (adult)


Table 9.

Off-site groundwater samples
Substance Maximum levels detected Reference Comparison values
Value Source
Off-site Groundwater
Volatile organic compounds
(in parts per billion; ppb)
TCE 30 10 5 MCL
PCE 530 1 5 MCL
Cis-1,2-DCE 190 16 70 LTHA / MCL
Trans-1,2-DCE 26 10 100 LTHA / MCL
Toluene 2 9 200 Intermediate EMEG (child)
Chlorobenzene 13 16 100 LTHA / MCL
Metals
(in parts per billion; ppb)
Arsenic 5 16 3 Chronic EMEG (child)
Barium 100 1 700 RMEG (child)
Cadmium 4 16 7 Chronic EMEG (child)
Lead 20 1 15 MCL


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Table 10.

tream sediment and gravel from the Yellowstone River: March 7 and March 21, 1990e
Substance Level detected Comparison Values
River gravel River sediment Value Source
Organic compounds
(ppm)
2-Chlorotoluene 21 BDLf 1,000 RMEG (child)
m+p-xylene .018 BDL NONE  
o-xylene .014 BDL NONE  
TPHs 325 425 NONE  
Toluene BDL .022 1,000 Intermediate EMEG (child)
Metals
(ppm)
Arsenic BDL 13 20 Chronic EMEG (child)
Barium BDL 130 4,000 RMEG (child)
Chromium BDL 16 300 RMEG (child)
Lead BDL 6 NONE  


g">

Table 11.

VOCs and Metals in private water well samplesg
Substance Level detected Comparison Values
Value Source
VOCs (ug/L)
Chloroform 1.2h 100 Chronic EMEG (child)
PCE 96 5 MCL
TCE 15 5 MCL
cis-1,2-DCE 99 70 LTHA / MCL
Chlorobenzene 3.5 100 LTHA / MCL
Metals (ug/L)
Arsenic 15 3 Chronic EMEG (child)


Table 12.

Indoor air sampling results
Sampling Dates August 1989 October
1989
November 1990 February,
March 1992
January,
February 1993
Comparison value
References (16) (16) (16) (16) (16) Value Source
  Concentrations in ug/m3  
cis-1,2-DCE NAi NA BDL 0.22-0.63 NA 800*
(200 ppb)
Intermediate
EMEG
trans-1,2-DCE NA 6 BDL 0.22 - 0.39 NA 800*
(200 ppb)
Intermediate
EMEG
Ethylbenzene NA NA 50 Basement NA NA 1,000*
(300 ppb)
Intermediate
EMEG
PCE BDLj BDL BDL 0.56-27.9 Upstairs 4.5 - 19 2 CREG
0.58-82.1 Basement
1,1,1-TCA 6,000 -18,000 1 - 3 NA NA NA 4,000*
(700 ppb)
Intermediate
EMEG
TCE BDL BDL 73 - 567 Basement 0.09-3.33 Upstairs NA 0.6 CREG
0.075-2.71 Basement
Toluene 8,000-45,000 BDL BDL NA NA 4,000*
(1000 ppb)
Chronic
EMEG
Xylene NA NA 139 Basement NA NA 200*
(50 ppb)
Acute
EMEG
Vinyl chloride NA NA NA 0.64 - 0.8 NA   EPA
Cancer
Class: A

* Conversion factor for air:

 

Cug/m3 = Cppb

X MWg/mole


24.45

where
C = Concentration
MW = Molecular Weight

 

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Table 13.

Levels of VOCs, SVOCs, and total metals detected in on-site surficial soil: April and May 1992k
Substance Range
(ppm)
Comparison value Exceed health
guideline?
Volatile Organic Compounds (VOCs) Value (ppm) Source  
PCE 0.0052 - 0.018 7,000 RMEG (adult) NO
Methylene chloride 0.0105 - 1.5 40,000 Chronic EMEG (adult) NO
TCE 0.0066 - 0.039 1,000 Intermediate EMEG (adult) NO
Chloromethane 0.034 NONE   NONE EXISTS
Semi-Volatile Organic Compounds (SVOCs)
Fluoranthene 0.42 - 27 30,000 RMEG (adult) NO
Pyrene 0.44 - 27 20,000 RMEG (adult) NO
Benzo(b)fluoranthene 0.48 - 29 NONE   NONE EXISTS
Phenanthrene 0.66 - 3.6 NONE   NONE EXISTS
Chrysene 0.66 - 3.3 NONE   NONE EXISTS
Benzo(a)anthracene 0.69 - 2.7 NONE   NONE EXISTS
Benzo(a)pyrene 0.71 - 2.3 0.1 CREG YES
Indeno(1,2,3-cd) pyrene 0.48 - 1.5 NONE   NONE EXISTS
Benzo(ghi)perylene 0.48 - 1.7 NONE   NONE EXISTS
Naphthalene 0.70 - 1.0 NONE   NONE EXISTS
Anthracene 0.34 200,000 RMEG (adult) NO
Dibenzo(a,h)anthracene 0.77 NONE   NONE EXISTS
Total metals
Arsenic 5 - 29 200 Chronic EMEG (adult) NO
Barium 72 - 890 50,000 RMEG (adult) NO
Cadmium 1 - 4 500 Chronic EMEG (adult) NO
Chromium 4 - 220 4,000 RMEG (adult) NO
Lead 18 - 1,250 NONE   NONE EXISTS
Selenium 8 1,000 Chronic EMEG (adult) NO
Silver 7 4,000 RMEG (adult) NO


Table 14.

Levels of VOCs, SVOCs, Pesticides, and total metals detected in off-site surficial soil: April and May 1992m
Substance Range
(ppm)
Comparison value Exceed health
guideline?
Volatile Organic Compounds (VOCs) Value (ppm) Source
PCE 0.0098 - 0.0243 500 RMEG (child) NO
Methylene chloride 0.0052 - 0.0105 3,000 Chronic EMEG (child) NO
Semi-Volatile Organic Compounds (SVOCs)
Pyrene 4.2 2,000 RMEG (child) NO
Phenanthrene 4 NONE   NONE EXISTS
Chrysene 9.6 NONE   NONE EXISTS
Pesticides
4,4'-DDE 0.011 2 CREG NO
4,4'-DDT 0.0074 - 0.018 2 CREG NO
Total metals
Arsenic 6 - 11 20 Chronic EMEG (child) NO
Barium 82 - 280 4,000 RMEG (child) NO
Chromium 6 - 19 300 RMEG (child) NO
Lead 28 - 100 NONE   NONE EXISTS


Table 15.

Yellowstone River water samples: September 20, 1989, and March 23, 1990.
Substance Level detected Reference Comparison value
Value (ppb) Source
TPHs (ppm) 0.1 - 1.9 16 NONE  
Organic compounds
(ppb)
PCE 0.91 16 5 MCL
2-Chlorotoluene 0.98 16 100 LTHA
Metals
(ppb)
Arsenic 14 - 28 16 50 MCL
Cadmium 2 16 5 LTHA / MCL


Table 16.

On-site subsurface soil contaminants at BNRY
Substance Maximum Level
Detected
Reference Comparison Values
Value Source
On-site
Volatile Organic Compounds
(in mg/kg)
TCE 1800 16 1,000 Intermediate EMEG (adult)
cis-1,2-DCE 710 16 200,000 Intermediate EMEG (adult)
1,2,4-trimethylbenzene 2 16 NONE  
n-propylbenzene 1.5 16 NONE  
sec-butylbenzene 1.5 16 NONE  
n-butylbenzene 1.9 16 NONE  
Isopropylbenzene 0.49 16 NONE  
1,1-Dichloroethene 30 16 6,000 Chronic EMEG (adult)
PCE 420 16 7,000 RMEG (adult)
Vinyl Chloride 11 16 10 Chronic EMEG (adult)
Semi-Volatile Organic Compounds
(in mg/kg)
Naphthalene 11 16 NONE  
Fluorene 17 16 30,000 RMEG (adult)
Fluoranthene 12 16 30,000 RMEG (adult)
Benzo(b)fluoranthene 9.6 16 NONE  
1,4-dichlorobenzene 220 16 NONE  
1,2-dichlorobenzene 1100 16 60,000 RMEG (adult)
Chrysene 5.5 16 NONE  
Benzo(a)anthracene 4.3 16 NONE  
Benzo(a)pyrene 3.3 16 0.1 CREG
1,3-dichlorobenzene 120 16 NONE  
Benzo(k)fluoranthene 1.1 16 NONE  
Metals
(in mg/kg)
Arsenic 48 16 200 Chronic EMEG (adult)
Barium 450 16 50,000 RMEG (adult)
Cadmium 10.2 16 500 Chronic EMEG (adult)
Chromium 120 16 4,000 RMEG (adult)
Lead 790 16 NONE  
Mercury 0.51 16 NONE  
Selenium 43 16 1,000 Chronic EMEG (adult)
 
PCB-1248 154 16 10 Chronic EMEG (adult)

 

a. One micron is equal to one-millionth of a meter or 0.000001 meter.

b. Contour plots are lines that run through sample collection points that show similar concentrations.

c. All values from reference (16).

d. ND = not detected.

e. All values from reference (16).

f. BDL = below detection limit.

g. All values from reference (16).

h. Detected at the same concentration in duplicate samples.

i. Not analyzed.

j. Below Detection Limit.

k. All values from reference (16).

l. All values from reference (16).

m. All values from reference (16).

APPENDIX C - COMPARISON VALUES

Comparison Values

ATSDR comparison values are media-specific concentrations that are considered tobe safe under default conditions of exposure. They are used as screening values inthe preliminary identification of site-specific "contaminants of concern". The latterterm may be misinterpreted as an implication of "hazard". As ATSDR interprets thephrase, a "contaminant of concern" is merely a site-specific chemical substancethat the health assessor has selected for further evaluation of potential healtheffects. Generally, a chemical is selected as a contaminant of concern because itsmaximum concentration in air, water, or soil at the site exceeds one of ATSDR'scomparison values.

However, it must be emphasized that comparison values are not thresholds oftoxicity. While concentrations at or below the relevant comparison value mayreasonably be considered safe, it does not automatically follow that anyenvironmental concentration that exceeds a comparison value would be expected toproduce adverse health effects. The purpose behind highly conservative, health-based standards and guidelines is to enable health professionals to recognize andresolve potential public health problems before they become actual health hazards. The probability that adverse health outcomes will actually occur depends on site-specific conditions and individual lifestyle and genetic factors that affect the routeand duration of actual exposure, and not on environmental concentrations alone.

Listed and described below are the various comparison values that ATSDR uses to select chemicals for further evaluation, along with the abbreviations for the most common units of measure.

 

CREG = Cancer Risk Evaluation Guides
MRL = Minimal Risk Level
EMEG= Environmental Media Evaluation Guides
IEMEG= Intermediate Environmental Media Evaluation Guides
RMEG= Reference Dose Media Evaluation Guide
RfD= Reference Dose
RfD-C= Reference Dose Concentration
EPA III= EPA Region III
DWEL= Drinking Water Equivalent Level
LTHA= Drinking Water Lifetime Health Advisory
MCL= Maximum Contaminant Level
PRG= Permissible Remediation Goal (Action Level)
PEL= Permissible Exposure Limit
TLV= Threshold Limit Value
ppm= parts per million (mg/L water or mg/kg soil)
ppb= parts per billion (ug/L water or ug/kg soil)
kg= kilogram (1,000 grams)
mg= milligram (0.001 grams)
ug= microgram (0.000001 grams)
L= liter
m3= cubic meter (used in reference to a volume of air equal to 1,000 liters)

Cancer Risk Evaluation Guides (CREGs) are estimated contaminant concentrationsexpected to cause no more than one excess cancer in a million persons exposedover a lifetime. CREGs are calculated from EPA's cancer slope factors.

Minimal Risk Levels (MRL) are estimates of daily human exposure to a chemical(i.e., doses expressed in mg/kg/day) that are unlikely to be associated with anyappreciable risk of deleterious noncancer effects over a specified duration ofexposure. MRLs are calculated using data from human and animal studies and arereported for acute (< 14 days), intermediate (15-364 days), and chronic (> 365days) exposures. MRLs are published in ATSDR Toxicological Profiles for specificchemicals.

Environmental Media Evaluation Guides (EMEGs) are concentrations that arecalculated from ATSDR minimal risk levels by factoring in default body weights andingestion rates.

Intermediate Environmental Media Evaluation Guides (IEMEG) are calculated fromATSDR minimal risk levels; they factor in body weight and ingestion rates forintermediate exposures (i.e., those occurring for more than 14 days and less than 1year).

Reference Dose Media Evaluation Guide (RMEG) is the concentration of acontaminant in air, water or soil that corresponds to EPA's RfD for thatcontaminant when default values for body weight and intake rates are taken intoaccount.

EPA's Reference Dose (RfD) is an estimate of the daily exposure to a contaminantunlikely to cause noncarcinogenic adverse health effects. Like ATSDR's MRL,EPA's RfD is a dose expressed in mg/kg/day.

Reference Dose Concentrations (RfD-C) is a concentration derived from an EPAReference Dose with assumed body and ingestion rates factored into thecalculation.

Environmental Protection Agency Region III (EPA III) values are risk-basedconcentrations which take into account factors such as body weight, toxicity, andexposure duration and frequency for non-carcinogens and carcinogens, whenapplicable.

Drinking Water Equivalent Levels (DWEL) are based on EPA's oral RfD andrepresent corresponding concentrations of a substance in drinking water that areestimated to have negligible deleterious effects in humans at an intake rate of 2L/day, assuming that drinking water is the sole source of exposure.

Lifetime Health Advisories (LTHA) are calculated from the DWEL and represents theconcentration of a substance in drinking water estimated to have negligibledeleterious effects in humans over a lifetime of 70 years, assuming 2 L/day waterconsumption for a 70-kg adult, and taking into account other sources of exposure. In the absence of chemical-specific data, the assumed fraction of total intake fromdrinking water is 20%. Lifetime health advisories are not derived for compoundswhich are potentially carcinogenic for humans.

Maximum Contaminant Levels (MCLs) represent contaminant concentrations indrinking water that EPA deems protective of public health (considering theavailability and economics of water treatment technology) over a lifetime (70 years)at an exposure rate of 2 liters of water per day (for an adult).

Permissible Remediation Goal (PRG) are levels set by EPA under Superfund thattrigger a response or action when the contaminant concentration exceeds thisvalue. Also generically known as action levels.

Occupational Safety and Health Administration's Permissible Exposure Limit (PEL)for air is an 8-hour, time-weighted average developed for the workplace. The levelof exposure may be exceeded (for brief periods), but the sum of the exposure levelsaveraged over 8 hours must not exceed the limit.

Threshold Limit Value (TLV), according to the American Conference ofGovernmental Industrial Hygienists (ACGIH), is "the time-weighted averageconcentrations for a normal 8-hour workday and a 40-hour workweek, to whichnearly all workers may be repeatedly exposed, day after day, without adverseeffect". Many of ACGIH's TLVs were adopted by OSHA for use as PELs. TLVsand PELs, which were designed to protect healthy workers, are usually much higherthan the health-based values of ATSDR and EPA, which were designed to protectthe health of the general population, including the very young and the elderly. Although the ATSDR does not base any of its community health decisions on TLVsor PELs, agency health assessors and toxicologists may sometimes mention suchvalues in Public Health Assessments or consultations as a means of putting site-specific concentrations of contaminants into some kind of meaningful perspective for the reader.


References

Agency for Toxic Substances and Disease Registry. Health Assessment Guidance Manual. Atlanta: ATSDR, March, 1992.


APPENDIX D - PCE

PCE Carcinogenicity

PCE is a nongenotoxic animal carcinogen. In chronic bioassays (1.5-2.0 yrs), massive doses of PCE administered orally (up to 1,072 mg/kg/day) or by inhalation (100-200 ppm), have produced liver cancer in mice, but not in rats; administered by inhalation (200-400 ppm), it has also caused a statistically insignificant increase in kidney tumors in male, but not female rats (22,25,33,34). However, recent re-evaluations of these studies by various government agencies and independent scientists indicate that the tumors observed in animals were probably due to species-specific mechanisms that exhibit thresholds at near-toxic levels (33,34,36,37). That is to say that the induction of cancers in mice and rats by PCE required doses in excess of anything humans might reasonably be expected to encounter, and involved certain elements of rodent biology that are not likely to be shared by humans (peroxisome proliferation, alpha-2µ-globulin accumulation, glutathione-PCE conjugate formation). The implication is that the cancers observed in laboratory animals at very high doses of PCE have little or no relevance for human risk evaluation at environmental levels of exposure that are orders of magnitude lower. In fact, a number of epidemiological studies of men and women exposed occupationally to PCE have not identified an increased risk of cancer (27).

The International Agency for Research in Cancer (IARC) classifies PCE as "possiblycarcinogenic to humans" based on "sufficient" evidence of carcinogenicity inanimals and "inadequate" evidence of carcinogenicity in humans, and the NationalToxicology Program (NTP) classifies PCE as Reasonably Anticipated to be aCarcinogen (RAC) in humans (27). However, both IARC and NTP use a "strengthof evidence" basis of classification which, in contrast to the "weight of evidence"scheme used by the EPA, largely ignores negative studies and mechanisms ofaction. EPA's carcinogen classification scheme was developed at a time when littleor no data on mechanism of action were available for consideration, with the resultthat the carcinogen category that would best accommodate such data often doesnot exist. This is the case with PCE.

EPA currently classifies PCE as a B2-C carcinogen, which is to say, somewherebetween group B2 and group C (27). This is an unorthodox classification currentlyshared by only two other chemicals, trichloroethylene and styrene. Group B2 isreserved for chemicals defined as "probable" human carcinogens based on"sufficient" animal evidence. Group C is reserved for chemicals defined as"possible" human carcinogens based on "limited" animal evidence. The only otherchoices available (i.e., Groups A, B1, D, and E) require either reliable evidence ofcarcinogenicity in humans, which does not exist for PCE, or the absence of suchevidence in animals, which does exist for PCE. However, there is no question that,at high enough doses and administered by the right route to the right species andsex, PCE can cause an elevated incidence of certain cancers by species-specificmechanisms in laboratory animals. Thus, EPA classified PCE as a B2-C carcinogennot because it could not decide whether the evidence for carcinogenicity in animalswas "sufficient" or "limited", but rather because it's classification scheme does notinclude a more appropriate category for this type of carcinogen. The AmericanConference of Governmental Industrial Hygienists (ACGIH), which does have such acategory, recently reclassified PCE as an A3 animal carcinogen, signifying that "theagent is carcinogenic in animals at a relatively high dose, by route(s) ofadministration, at site(s), of histological type(s), or by mechanism(s) that are notconsidered relevant to worker exposure" (31).

It is important to realize that formal cancer risk assessment has its limitations (23-25). Based on a withdrawn EPA risk assessment that is currently being re-evaluated (32), it has been estimated that the drinking water standard of 5 µgPCE/L corresponds to a theoretical lifetime cancer risk of 14 in a million. However,as is the case with all numerical estimates of low-dose cancer risk based on animaldata, the true risk is unknown, and may be as low as zero (35). It is, in fact, apractical impossibility to determine experimentally the carcinogenicity of chemicalsat very low doses, due to the enormous number of animals that would be requiredto achieve statistically reliable results. Instead, the assessment of cancer risk atlow doses has traditionally involved linear extrapolation from the results of high-dose animal experiments with the aid of statistical models that incorporate highlyconservative default assumptions. These include the assumptions that (1)carcinogens have no threshold, and (2) all animal carcinogens are likely to behuman carcinogens. These assumptions are clearly defensible as prudent publichealth policy when used to provide a maximal margin of safety in the face ofoverwhelming uncertainties. However, they were never intended to take priorityover new scientific data that could otherwise reduce those uncertainties. Nor werethey ever intended to be used for the prediction of actual disease incidence.

The ATSDR recognizes that no single mathematical model is appropriate in all casesand that existing mathematical models for low-dose extrapolation may not beappropriate for nongenotoxic agents. Information on the biological mechanism isneeded to determine if there are threshold exposure levels for nongenotoxic agents. The ATSDR, therefore, evaluates the relevance of the animal data to humans on acase-by-case basis. In the case of PCE, the available animal cancer data appear toreflect species-specific mechanisms that exhibit thresholds at near-toxic levels and,therefore, have little or no relevance for the evaluation of human risk atenvironmental levels of exposure. However, in the absence of compelling data tothe contrary, the ATSDR policy considers it prudent to presume that a substancewhich causes cancer in animals may also pose a potential carcinogenic risk tohumans, and that exposure to the substance should be minimized (30). (For aperspective on cancer risk assessment, see reference 41.)




APPENDIX E

PUBLIC HEALTH HAZARD CONCLUSION CATEGORIES
ATSDR PUBLIC HAZARD CONCLUSION CATEGORIES
CATEGORY DEFINITION CRITERIA
A. Urgent public health hazard This category is used for sites that pose an urgent public health hazard as the result of short-term exposures to hazardous substances • evidence exists that exposures have occurred, are occurring, or are likely to occur in the future AND
• estimated exposures are to a substance(s) at concentrations in the environment that, upon short-term exposures, can cause adverse health effects to any segment of the receptor population AND/OR
• community-specific health outcome data indicate that the site has had an adverse impact on human health that requires rapid intervention AND/OR
• physical hazards at the site pose an imminent risk of physical injury
B. Public health hazard This category is used for sites that pose a public health hazard as the result of long-term exposures to hazardous substances • evidence exists that exposures have occurred, are occurring, or are likely to occur in the future AND
• estimated exposures are to a substance(s) at concentrations in the environment that, upon long-term exposures, can cause adverse health effects to any segment of the receptor population AND/OR
• community-specific health outcome data indicate that the site has had an adverse impact on human health that requires rapid intervention
C. Indeterminate public health hazard This category is used for sites with incomplete information • limited available data do not indicate that humans are being or have been exposed to levels of contamination that would be expected to cause adverse health effects; data or information are not available for all environmental media to which humans may be exposed AND
• there are insufficient or no community-specific health outcome data to indicate that the site has had an adverse impact on human health
D. No apparent public health hazard This category is used for sites where human exposure to contaminated media is occurring or has occurred in the past, but the exposure is below a level of health hazard • exposures do not exceed an ATSDR chronic MRL or other comparable value AND
• data are available for all environmental media to which humans are being exposed AND
• there are no community-specific health outcome data to indicate that the site has had an adverse impact on human health
E. No public health hazard This category is used for sites that do not pose a public health hazard • no evidence of current or past human exposure to contaminated media AND
• future exposures to contaminated media are not likely to occur AND
• there are no community-specific health outcome data to indicate that the site has had an adverse impact on human health


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  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #