• Home
• About ATSDR
• Press Room
• A-Z Index
• Glossary
• Employment
• Contact Us
• CDC

ATSDR en Español

Search:

Skip directly to: content | left navigation | search

---

Find a Publication

1. ATSDR > Public Health Assessments & Consultations

PETITIONED PUBLIC HEALTH ASSESSMENT

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

APPENDIX A: FIGURES

Figure 1. Burlington Northern Rail Yard Site Location Map

Figure 2. Location of private and city wells

Figure 3. Mission Wye area

Figure 4. River sediment sampling locations

Figure 5. Ambient air monitoring sites

Figure 6. Burlington Northern Rail Yard

APPENDIX B: DATA TABLES

Table 3: On-site soil gas contaminants at BNRY^c

* 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

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

Table 10: Stream sediment and gravel from the Yellowstone River: March 7 and March 21, 1990^e

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

Table 11: VOCs and Metals in private water well samples^g

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

Table 13: Levels of VOCs, SVOCs, and total metals detected in on-site surficial soil: April and May 1992^k

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 1992 ^m

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 to be safe under default conditions of exposure. They are used as screening values in the preliminary identification of site-specific "contaminants of concern". The latter term may be misinterpreted as an implication of "hazard". As ATSDR interprets the phrase, a "contaminant of concern" is merely a site-specific chemical substance that the health assessor has selected for further evaluation of potential health effects. Generally, a chemical is selected as a contaminant of concern because its maximum concentration in air, water, or soil at the site exceeds one of ATSDR's comparison values.

However, it must be emphasized that comparison values are not thresholds of toxicity. While concentrations at or below the relevant comparison value may reasonably be considered safe, it does not automatically follow that any environmental concentration that exceeds a comparison value would be expected to produce adverse health effects. The purpose behind highly conservative, health-based standards and guidelines is to enable health professionals to recognize and resolve 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 route and 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 concentrations expected to cause no more than one excess cancer in a million persons exposed over 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 any appreciable risk of deleterious noncancer effects over a specified duration of exposure. MRLs are calculated using data from human and animal studies and are reported for acute (< 14 days), intermediate (15-364 days), and chronic (> 365 days) exposures. MRLs are published in ATSDR Toxicological Profiles for specific chemicals.

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

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

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

EPA's Reference Dose (RfD) is an estimate of the daily exposure to a contaminant unlikely 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 EPA Reference Dose with assumed body and ingestion rates factored into the calculation.

Environmental Protection Agency Region III (EPA III) values are risk-based concentrations which take into account factors such as body weight, toxicity, and exposure duration and frequency for non-carcinogens and carcinogens, when applicable.

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

Lifetime Health Advisories (LTHA) are calculated from the DWEL and represents the concentration of a substance in drinking water estimated to have negligible deleterious effects in humans over a lifetime of 70 years, assuming 2 L/day water consumption 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 from drinking water is 20%. Lifetime health advisories are not derived for compounds which are potentially carcinogenic for humans.

Maximum Contaminant Levels (MCLs) represent contaminant concentrations in drinking water that EPA deems protective of public health (considering the availability 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 that trigger a response or action when the contaminant concentration exceeds this value. 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 level of exposure may be exceeded (for brief periods), but the sum of the exposure levels averaged over 8 hours must not exceed the limit.

Threshold Limit Value (TLV), according to the American Conference of Governmental Industrial Hygienists (ACGIH), is "the time-weighted average concentrations for a normal 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect". Many of ACGIH's TLVs were adopted by OSHA for use as PELs. TLVs and PELs, which were designed to protect healthy workers, are usually much higher than the health-based values of ATSDR and EPA, which were designed to protect the 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 TLVs or PELs, agency health assessors and toxicologists may sometimes mention such values 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 "possibly carcinogenic to humans" based on "sufficient" evidence of carcinogenicity in animals and "inadequate" evidence of carcinogenicity in humans, and the National Toxicology Program (NTP) classifies PCE as Reasonably Anticipated to be a Carcinogen (RAC) in humans (27). However, both IARC and NTP use a "strength of evidence" basis of classification which, in contrast to the "weight of evidence" scheme used by the EPA, largely ignores negative studies and mechanisms of action. EPA's carcinogen classification scheme was developed at a time when little or no data on mechanism of action were available for consideration, with the result that the carcinogen category that would best accommodate such data often does not exist. This is the case with PCE.

EPA currently classifies PCE as a B2-C carcinogen, which is to say, somewhere between group B2 and group C (27). This is an unorthodox classification currently shared by only two other chemicals, trichloroethylene and styrene. Group B2 is reserved 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 other choices available (i.e., Groups A, B1, D, and E) require either reliable evidence of carcinogenicity in humans, which does not exist for PCE, or the absence of such evidence 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 and sex, PCE can cause an elevated incidence of certain cancers by species-specific mechanisms in laboratory animals. Thus, EPA classified PCE as a B2-C carcinogen not because it could not decide whether the evidence for carcinogenicity in animals was "sufficient" or "limited", but rather because it's classification scheme does not include a more appropriate category for this type of carcinogen. The American Conference of Governmental Industrial Hygienists (ACGIH), which does have such a category, recently reclassified PCE as an A3 animal carcinogen, signifying that "the agent is carcinogenic in animals at a relatively high dose, by route(s) of administration, at site(s), of histological type(s), or by mechanism(s) that are not considered 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 µg PCE/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 animal data, the true risk is unknown, and may be as low as zero (35). It is, in fact, a practical impossibility to determine experimentally the carcinogenicity of chemicals at very low doses, due to the enormous number of animals that would be required to achieve statistically reliable results. Instead, the assessment of cancer risk at low doses has traditionally involved linear extrapolation from the results of high-dose animal experiments with the aid of statistical models that incorporate highly conservative default assumptions. These include the assumptions that (1) carcinogens have no threshold, and (2) all animal carcinogens are likely to be human carcinogens. These assumptions are clearly defensible as prudent public health policy when used to provide a maximal margin of safety in the face of overwhelming uncertainties. However, they were never intended to take priority over new scientific data that could otherwise reduce those uncertainties. Nor were they ever intended to be used for the prediction of actual disease incidence.

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

Next Section          Table of Contents

Agency for Toxic Substances and Disease Registry, 1825 Century Blvd, Atlanta, GA 30345
Contact CDC: 800-232-4636 / TTY: 888-232-6348 

Department of Health and Human Services