DRAFT
Guidance in Developing Health Criteria
for
Determining Unreasonable Risks to Health
October, 1990
Office of Drinking Water
U.S. Environmental Protection Agency
Washington, DC 20460
Printed on Recycled Paper
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Purpose
The purpose of this guidance is to provide information and
recommendations on the health based criteria that should be
considered in determining an unreasonable risk to health (URTH)
for drinking water contaminants. This guidance will assist States
having primacy in the issuance of a variance or exemption from a
Maximum Contaminant Level (MCL). In this guidance, EPA is
providing several ways that an URTH value might be determined.
Actual values are stated for various contaminants with an upper
bound URTH level that is recommended.
This document provides EPA's guidance to States on determining
URTH values. It-does not establish or affect legal rights or
obligations. It does not establish a binding norm and is not
finally determinative of the issues addressed. Agency decisions
in any particular case will be made applying the law and
regulations on the basis of specific facts and actual action.
Background
Under Sections 1415 and 1416, respectively, of the Safe
Drinking Water Act (SDWA) of 1974, as amended in 1986, States with
primacy may grant a variance or exemption to a public water supply
(PWS) from an MCL if the State finds that the variance or exemption
will not result in an unreasonable risk to health to persons served
by the PWS.
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In 1979, EPA developed a guidance document on the issuance of
variances or exemptions. This document listed four criteria to be
considered in determining the *unreasonableness1 of risk:
1. The degree to which the MCL is or will be exceeded and
the health effects resulting therefrom;
2. The duration of the requested variance or exemption;
3. Historical data (how long the problem has existed); and
4. The type of population exposed.
Utilizing these criteria, an URTH level was generally
determined as any concentration of a contaminant that was greater
than two times the MCL.
After the 1986 Amendments of the SDWA, the 1979 URTH guidance
was reevaluated. This document replaces the 1979 guidance and has
expanded on the above criteria to better characterize the potential
health risks that may result with the exceedance of an MCL.
Under SDWA section 1415, a variance may be issued to a PWS
only after the system has applied the best technology or treatment
technique that the Administrator finds available. A variance is
usually granted to a system because the characteristics of the raw
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water supply available to the system are such that the system
cannot meet the requirements of the MCL(s) despite application of
the best available technology. At the time a variance is granted,
Section 1415(A)(i) provides that the primacy Stats shall prescribe
a schedule for compliance with the MCL(s). The compliance schedule
may include increments of progress and the implementation of
additional control measures by the PWS to meet the MCL(s).
Under SOW A section 1416, an exemption for a PWS may be granted
if the PWS is unable to comply with an MCL or treatment technique
for a drinking water contaminant. The inability to comply may be
due to compelling factors such as economic constraints. An
exemption is granted for one year with an exten-sion for two
additional years, if necessary. In instances where a PWS serves
500 or less service connections, an exemption may be renewed for
one or more 2-year periods if the system demonstrates that it is
taking all practicable steps for compliance.
Approach for Developing Health Criteria
In developing the Health Criteria for determining URTH, the
toxicity exhibited by each contaminant is evaluated individually.
This is done^ in part, by considering any available risk assess-
ments conducted for each contaminant. The various types of risk
assessments that could be considered are discussed below. In
evaluating the assessments, carcinogenic risks should be compared
with risks for non-cancer health effects. This comparison serves
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to balance the potential- risks. Thus, the consideration of one
type of risk such as cancer would not exclude the consideration of
another endpoint of toxicity such as reproductive effects.
Risk Aas<
The Environmental Protection Agency (EPA) regulates contami-
nants that may pose an adverse health risk and are known or
anticipated to occur in water. Because of the chemical make up
and behavior of a given contaminant, each contaminant may elicit
a toxic response that differs from another contaminant. The
toxicity for a given contaminant is considered in developing the
Maximum Contaminant Level Goal (MCLG), a non-enforceable health
goal. Under the SOW A, the MCL, or enforceable standard, is set as
close to the MCLG as feasible. Usually the MCL will equal the
MCLG. In some cases (e.g., carcinogens), however, the MCL may
exceed the MCLG based on feasibility. Although the MCL may be
somewhat higher than the health goal, it represents a level of
acceptable risk that the Agency considers to be reasonable.
Thus, MCLs are determined for each contaminant considering
the toxicity exhibited by that contaminant, technological
capabilities, costs and residual risk. Since MCLs are determined
contaminant by contaminant, the level above an MCL that constitutes
an unreasonable risk to health should also be evaluated
v ,
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The mechanism for producing a toxic response for a given
contaminant may be considered as threshold or non-threshold. For
a threshold response, exposure to a specific dose can result in a
toxic outcome, whereas for non-threshold response, exposure to any
level can theoretically lead to a toxic outcome. However, the
hypothetical risk at low levels can be very small. Most non-
cancer health effects are thought to result from a threshold level.
The biological mechanism for carcinogenesis is not well understood;
therefore, a non-threshold mechanism is assumed. EPA assesses the
health risks for threshold effects differently from non-threshold
effects.
Threshold; A quantitative risk assessment for threshold
contaminants can be derived through first determining a Reference
Dose (RfD). The RfD can be summarized as an estimate of a daily
exposure to the human population, including sensitive subpopula-
tions, that is not likely to produce any adverse health effects
over a lifetime. The RfD is calculated by dividing a no- or
lowest-observed-adverse-effect level (NOAEL or LOAEL) by
uncertainty factors. The NOAEL or LOAEL is identified from an
experimental study of appropriate exposure duration in humans or
animals reflecting a sensitive endpoint in a sensitive species.
The uncertainty factors may range from 1 to 10,000 or more,
depending on the data base for the chemical. The uncertainty
factors are used to account for differences in response to toxicity
within and between species. Additional factors may be used when
a NOAEL has not been identified or to account for data base
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quality.
For threshold contaminants, the RfD serves as the basis of
the MCLG. The RfD is adjusted for a 70-kg adult consuming an
average of 2 liters of water per day over a lifetime (70 years).
The resulting value is called a Drinking Water Equivalent Level
(DWEL), and assumes that all of the exposure comes from drinking
water. Since this often is not the case, the DWEL is adjusted by
an assumed or actual exposure (the relative source contribution;
RSC) from drinking water. If actual data are not available, a
range of 20 to 80% may be used for the RSC. This final value is
the MCLG.
In addition to the RfD, risk assessments are also conducted
for less-than-lifetime exposures to drinking water contaminants.
These are expressed by EPA in non-enforceable Health Advisories
(HAs). The HAs are based on non-cancer endpoints of toxicity and
are developed for exposures of one day, ten days, longer-term (up
to seven years) , as well as lifetime (70 years) . They are calcu-
lated in a manner similar to the RfD with the exception that the
NOAELs and LOAELs are identified from studies where the exposure
duration is comparable to that which the HA represents in terms of
percentage of lifetime exposed. In addition, less-than-lifetime
HAs are calculated for a 10 kg child consuming 1 liter of water per
day. Other sources of exposure are generally not considered since
water is assumed, to be the major source o£ exposure for a short
period such as an accidental spill. One-day HAs are based on acute
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exposure studies of 1 to. 7 days. 'The Ten-day HA is derived from
human or animal studies with 30 days exposure or less. The Longer-
term HA, calculated for both a child and an adult, is derived from
subchronic studies based on exposure periods correlating to
approximately 10 percent of an individual's lifetime. Assuming a
70-year lifetime, the Longer-term HA correlates to an exposure
period of up to 7 years. The Lifetime HA is determined in the same
way as the MCLG.
Non-threshold: The EPA assumes, in the absence of any
contrary data, that carcinogenicity is a toxic response that does
not have a threshold. In other words, any exposure can lead to a
carcinogenic response. The EPA evaluates contaminants that may be
carcinogenic qualitatively as well as quantitatively. Table l
summarizes the EPA cancer classification scheme. This scheme
qualitatively ranks chemicals as to their carcinogenic potential
in humans based on weight of evidence presented in the available
toxicological and epidemiological literature.
If toxicological evidence leads to the classification of a
contaminant as a human (Group A), probable human (Group B) or in
some instances possible human (Group C) carcinogen, mathematical
models can be used to calculate a theoretical upper-bound excess
cancer risk associated with the ingestion of the contaminant in
drinking water. Using these models, risks from oral exposure can
be estimated for excess cancers compared to the population (e.g.,
one in 10,000 [10*4] to one in one million [10**]). The 10"* to 10"
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6 risk range is the target for setting MCLs for human or probable
human carcinogens. Often data used in these estimates come from
lifetime exposure studies in animals.
MCLGs for non-threshold contaminants are set at zero as an
aspirational goal. The MCL, then, is set as close to zero as
feasible, generally falling in the excess cancer risk range of 10"
4 to 10"6. MCLGs for Group C contaminants are usually derived from
the RfD approach with an additional uncertainty factor of 1 to 10
to account for possible carcinogenicity. If an RfD is not
available for a Group C contaminant, the HCLG nay be set in the
range of 10"5 to 10"6.
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Group A; Human carcinogen
Sufficient evidence in epidemiologic or occupational studies to
support causal association between exposure and cancer in humans.
Group B; Probable human carcinogen
Limited evidence in human studies (Group Bl) and/or sufficient
evidence from animal studies (Group B2)
Group Ct Possible human carcinogen
Limited evidence from animal studies and inadequate or no data in
humans
Group D; Not classifiable
Inadequate or non human and animal evidence of carcinogenicity
Group E; No evidence of carcinogenicity for humans
No evidence of carcinogenicity in at least two adequate animal
tests in different species or in adequate human and animal studies
Source: USEPA 1986. Federal Register 51:33992-34003. Sept. 24.
Risk Assessments for Determining URTH
The above risk assessment methodologies used to develop HAs,
MCLGs and MCLs are used in determining the health criteria for URTH
levels. As stated earlier, contaminants classified as carcinogens
may also exhibit noncancer related health effects such as
reproductive texicity. Thus, the risk assessments for both cancer
and noncancer effects must be compared.
Exposure duration should also be considered. The risk
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assessments for both cancer and noncancer effects are time
dependent. Cancer assessments usually assume a lifetime exposure,
while the risk assessments for noncancer effects cover less-than-
lifetime and lifetime exposures. Ideally, the variance or exemption
period will cover a less-than-lifetime exposure period. In
addition, past exposure to a given contaminant may not be known.
Some of the values for URTH provided in this document are based on
the Longer-term HA which assume exposures of seven years or less.
Therefore, EPA recommends that variances or exemptions not exceed
seven years when URTH is based on noncarcinogenic health effects.
The risk assessments for URTH are presented as a range from
the MCL to an upper-bound (least stringent) level. The EPA
recommends that the upper-bound not be exceeded when determining
URTH. However, the State may determine URTH to lie within or
outside the range based on site-specific considerations. These
considerations may include, for example, site-specific exposures,
past exposure (if known), population sensitivity or volatility of
the contaminant.
The types of risk, assessment values used in developing the
range of health criteria are:
1. The MCLG and MCL.
2. The Longer-term Health Advisory for a child.
3. DWEL.
4. Cancer classification.
5. The 10"* cancer risk level.
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6. MCLG multiplied by a factor of one to ten for Group c
contaminants.
When determining the upper-bound URTH level, EPA considered
that :
for threshold contaminants where the MCL is based on
0 Acute toxicity: the MCL is appropriate to use for URTH
whenever the MCL for a contaminant is based on an acutely toxic
response and there is little margin of safety above the MCL. Where
there is a greater margin of safety, some exceedance of the MCL
based on scientific judgment may be reasonable.
0 Subchronic and chronic toxicity: the Longer-term HA for
a child could be used for URTH. This level of exposure is
considered protective of a potentially sensitive subgroup over a
seven year period.
0 the DWEL may be used for URTH when data to calculate a
Longer-term HA are not available.
for nonthreshold contaminants
0 where the MCL is set at or above the 10"* excess cancer
risk, the MCL is appropriate for URTH.
0 where the MCL is set at a concentration less than the
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10 risk level, the 10" cancer risk level may be used for URTH if
this value does not exceed the DWEL or Longer-term HA for a child.
The lower of these values would then be recommended as URTH.
0 where the MCL for a Group C contaminant includes an
additional safety factor of 1 to 10, the removal of the factor
could be used as URTH, provided that the Longer-term HA for a child
or DWEL is not exceeded. The lower of these values would be
recommended as URTH.
Table 2 summarizes examples of how the above strategy can be
applied and lists the recommended risk assessments that could be
considered in determining URTH levels for drinking water
contaminants. Following Table 2 is a more complete description of
those values for each contaminant and EPA's recommendations for
which of these values should be applied as the URTH level.
ISSUES TOR COKMBHT
EPA is seeking comment on the proposed approach for
determining URTH. The following table and chemical specific
discussions are provided as examples of how this approach could be
applied. Issues to address include:
1. Is it appropriate to base URTH on the Longer-term HA for
£ child fcr threshold contaminants?
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2. Is it appropriate to base URTH on the 10"4 cancer risk for
nonthreshold contaminants? Could a higher risk such as 10"3 be
justified for a short period of time if noncancer risks were not
exceeded?
3. Is it reasonable to limit the URTH for noncarcinogens to
seven years? Should the same guidance be recommended for
carcinogens?
4. Should other types of risk assessments not mentioned here
be considered for determining URTH?
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Table 2. DEVELOPMENT OF URTH RANGE (MGIL)
Compound
INORGANICS
Asbestos
>10 (jm
Cadmium
Copper
Fluoride
Mercury
Nitrate
Nitrite
Nitrate/Nitrite
Selenium
MICROBIOLOGICAL
Total Coliforms
ORGANICS
Acrylamide
Alachlor
Atrazine
Benzene
MCLG
•
7 MFL
0.005
1.3
4
0.002
10
1
10
0.05
0
0
0
0.003
0
Longer-
Term
HA
MCL Child
7 MFL ~
0.005 0.005
1.3
4
0.002 ~
10 10
1 1
10
0.05
5%/1% -
TT 0.02
0.002 -
0.003 0.06
0.005 (10 day
Cancer t(T**»
DWEL Class Risk
A 700
0.02 B1
D
D
0.01 D
D
..
_
0.1
—
0.007 B2 0.001
0.4 B2 0.04
0.2 C
A 0.1
URTH Level
Group C Recommended
MCLGxW V EPA
70 7 MFL
0.005
1.3
5
0.01
10 child
1 child,
10 child
0.1
5%/1%
0.001
0.04
0.03 0.03
-0.01
Carbofuran
= 0.2)
0.04 0.04 0.05
0.2
0.05
(Continued on next page)
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Table 2. DEVELOPMENT OF URfH RANGE fMG/L) (Continued]
Compound
MCLG MCL
Longer-
Term
HA
Child DWEL
Cancer 1O***
Class Risk
URTH Level
Group C Recommended
MCLGxIO tiy EPA
Carbon Tetrachloride
Chlordane
2.4-D
DBCP
cis-1,2-DCE
trans-1,2-DCE
o-DCB
p-DCB
^ichloroethane
1,1-Dichloroethylene
1,2-Dichloropropane
0 0.005 0.07
0 0.002 »
0.07 0.07 0.1
0 0.0002 --
0.07 0.07 3
0.1 0.1 2
0.6 0.6 9
0.075 0.075 10
0 0.005 0.7
0.007 0.007 1
0 0.005 -
0.03 B2
0.002 B2
D
0.4
0.4
0.6
4
4
0.4
B2
D
D
D
C
B2
C
B2
0.03
0.003
0.003
0.2 0.75
0.04
0.02 0.07
0.06
0.03
0.003
0.1
0.003
0.4
2
9
0.75
0.04
0.07
0.06
Epfchlorohydrin
Ethylbenzene
EDB
Heptachlor
Heptachlor Epoxide
LJndane
Methoxychlor
Monochlorobenzene
PCBs
TT 0.07
0.7 1
0.00005 -
0.0004 0.005
0.07
3
B2
D
B2
0.02 B2
0
0.7
0
0
0 0.0002 0.0001 0.0004 B2
0.0002 0.0002 0.03 0.01 C
0.4 0.4 0.5 2 D
0.1 0.1 2 0.7 D
0 0.0005 0.001 - B2
fnti.
inued on next page)
0.4
0.00004 -
0.0008 -
0.0004 ~
0.003 0.002
0.0005 -
0.07
1
0.00005
0.0008
0.0004
0.002
0.5
2
0.0005
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Table 2. DEVELOPMENT OF URTH RANGE (MGIL) (Continued!
Compound
Tetrachloroethylene
Toxaphene
2.4.5-TP
1,1,1 -Trichloroethane
Trichloroethylene
Vinyl Chloride
Xylenes
MCLG
0
0
0.05
0.2
0
0
10
MCL
0.005
0.003
0.05
0.2
0.005
0.002
10
Longer-
Term
HA
Child
1
~
0.07
40
—
0.01
40
DWEL
0.5
0.003
.0.3
1
0.3
—
60
Cancer
Class
B2
B2
D
D
B2
A
D
TO4*" Group C
Risk MCLGxIO
0.07
0.003
—
..
0.3
0.0015 -
..
URTH Level
Recommended
toy EPA
0.07
0.003
0.07
1
0.3
0.002
40
TT = Treatment technique
TBD = To be determined
** = 10^ Lifetime Risk
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INORGANICS
Asbestos
The EPA proposed an MCLG of 7 and an MCL of 7 million fibers
per liter (MFL) for asbestos fibers greater than 10 /m in length
based on equivocal evidence of carcinogenicity in male rats
following ingestion of chrysotile fibers. There are insufficient
data to determine a Longer-term Health Advisory for a child or a
drinking water equivalent level. Asbestos is classified in Group
A: Human carcinogen for inhalation, according to EPA's
classification scheme. The 10"4 excess cancer risk estimated for
asbestos is 700 MFL. There is limited evidence that asbestos may
be carcinogenic by ingestion. It is unlikely that asbestos, if
found in the water, would exceed 7 MFL; thus, URTH may be
considered any concentration above the MCL.
Cadmium
The EPA proposed an MCLG of 0.005 and an MCL of 0.005 mg/L
for cadmium based on renal dysfunction. The Longer-term Health
Advisory for a child is also 0.005 mg/L, and the drinking water
equivalent level is 0.02 mg/L. cadmium is classified in Group Bl:
probable human carcinogen by inhalation with no evidence of
carcinogenicity by ingestion according to the EPA's classification
scheme. Based on this information and the bioaccumulative
potential for cadmium, an upper-bound unreasonable risk to health
level of 0.005 mg/L based on the MCLG and the Longer-term Health
Advisory is recommended for a period of up to 7 years.
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Copper
The EPA proposed an MCLG of 1.3 and an MCL of 1.3 mg/L for
copper based on acute gastrointestinal effects in humans.
A Longer-term Health Advisory for a child and the drinking water
equivalent level has not been determined. Copper is classified in
Group D: not classifiable for human carcinogenicity according to
the EPA's classification scheme. Based on this information, an
upper-bound unreasonable risk to health level of 1.3 mg/L is
recommended based on acute toxicity.
Fluoride
The EPA promulgated an MCLG of 4 and an MCL of 4 mg/L for
fluoride based on crippling skeletal fluorosis in humans. Only
two cases of crippling skeletal fluorosis have been observed in
this country associated with the consumption of drinking water
containing fluoride levels of 8 mg/L or more.
It is generally believed that the consumption of approximately
20 mg of fluoride per person per day over at least a twenty year
period will increase the risk of crippling skeletal fluorosis.
Thus, persons who chronically consume inordinately large amounts
of water, i.e., 4 liters/day, (perhaps 1% of the population) would
be at risk of crippling skeletal fluorosis at a level greater than
5 mg/L. Based on this information, an upper bound unreasonable
risk to health level of 5 mg/L is recommended.
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Marcurv
The EPA proposed an MCLG of 0.002 and an MCL of 0.002 mg/L
for mercury based on absence of toxicity in rats following
subchronic exposure to mercury. The Longer-term Health Advisory
for a child has not been determined, but the drinking water
equivalent level is 0.01. Mercury is classified in Group D: not
classifiable as to human carcinogenicity according to the EPA's
classification scheme. Based on this information, an upper-bound
unreasonable risk to health level of 0.01 based on the drinking
water equivalent level is recommended for a period of up to
7 years.
Nitrate as M. Nitrate and Nitrate + Nitrite (measured as Nl
Nitrate
The EPA proposed an MCLG of 10 and an MCL of 10 mg/L (N) for
nitrate based on acute toxicity in infants following ingestion of
water with nitrate.
Infants and particularly those with gastrointestinal disease
(e.g., diarrhea) are considered the most sensitive members of the
population. The consumption of biologically contaminated water
(e.g., £. coin may contribute to the problem, resulting in
diarrhea which may render an infant much more sensitive to nitrate
and/or nitrite toxicity.
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Nitrate in drinking"water at levels in excess of the current
10 mg/L MCL has been responsible for serious methemoglobinemia and
mortality in some infants under the age of approximately six
months.
Based on this information the URTH value for infants up to
6 months of age is 10 mg/L nitrate (as N) . Based on available
epidemiology data, the URTH value for nitrate for all individuals
except infants up to 6 months of age is 20 mg/L (as N) . In
addition, biological water quality standards must be met in both
cases.
Nitrite
Nitrate is toxic because it is metabolized within the human
body to yield nitrite, which in turn reacts with hemoglobin to
yield methemoglobin (i.e., nitrate per se does not react with
hemoglobin). Nitrite may also occur in drinking water. The URTH
level for nitrite should not exceed 1 mg/L as N based on
methemoglobin formation following short-term exposure.
Nitrate and Nitrite
As both nitrate and nitrite may occur in drinking water and
as exposure to either may lead to methemoglobinemia, it is
reasonable to conclude that the toxicity of nitrate and nitrite
•j
may be additive. As a consequence, the URTH level for combined
levels of nitrate and nitrite should not exceed 10 mg/L (i.e., the
sun of nitrate and nitrite, as nitrogen, shall not exceed 10 mg/L).
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Selenium
The EPA proposed an MCLG of 0.05 mg/L and an MCL of 0.05 mg/L
for selenium based on a human study evaluating selenium deficiency.
The Longer-term Health Advisory for a child is not established, but
the drinking water equivalent level is 0.1 mg/L. Selenium is
classified in Group D: not classifiable as to human
carcinogenicity according to the EPA's classification scheme.
Based on this information, an upper-bound unreasonable risk to
health level of 0.1 mg/L based on the drinking water equivalent
level is recommended for a period of up to 7 years.
MICROORGANISMS
Total Coliforms
The EPA promulgated an MCLG of 0 and an MCL of 5%/l%
detections for total col i forms based on acute gastrointestinal
disorders. Based on the acute pathogenicity implied by the
presence of total col i forms, an upper-bound unreasonable risk to
health level is any exceedance of the criteria specified for the
MCL.
ORGXKICS
The EPA proposed an MCLG of zero and a treatment technique
for acrylamide based on carcinogenicity. The Longer-term Health
Advisory for a child is 0.02 mg/L, and the drinking water
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equivalent level.is O.OQ7. Acrylamide is classified in Group B2:
probable human carcinogen according to the EPA's classification
scheme. The 10~*. excess cancer risk estimated for aery 1 amide is
0.001 mg/L. Based on this information, &n upper-bound unreasonable
risk to health level of 0.001 mg/L based on the 10'4 excess cancer
risk is recommended.
Alaehlor
The EPA proposed an MCLG of zero and an MCL of 0.002 mg/L for
alachlor based on feasibility based on carcinogenicity. The
Longer-term Health Advisory for a child has not been calculated,
but the drinking water equivalent level is 0.4 mg/L. Alachlor is
classified in Group B2: probable human carcinogen according to
the EPA's classification scheme. The 10"4 excess cancer risk
estimated for alachlor is 0.04 mg/L. Based on this information,
an upper-bound unreasonable risk to health level of 0.04 mg/L based
on the 10"* excess cancer risk is recommended.
Atratine
The EPA proposed an MCLG of 0.003 and an MCL of 0.003 mg/L
for atrazine based on cardiac effects in dogs fed atrazine for one
year. The Longer-term Health Advisory for a child is 0.05 mg/L,
and the drinking water equivalent level is 0.2 mg/L. Atrazine is
classified in Group C: possible human carcinogen according to the
EPA's classification scheme. EPA applied an additional 10-fold
uncertainty f*etrvr in calculating the MCLG for atrazine to account
for possible carcinogenicity; without ttiis additions! factor, the
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MCLG would have been 0.03 mg/L. • Based on this information, an
upper-bound unreasonable risk to health level of 0.03 mg/L based
on the removal of.the extra 10-fold UF and the Longer-term Health
Advisory for a child is recommended for a period of up to 7 years.
Benzene
The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for benzene based on feasibility. There are insufficient data to
calculate a Longer-term Health Advisory for a child or a drinking
water equivalent level for non-cancer health effects. However, a
Ten-day Health Advisory of 0.2 mg/L has been estimated. Benzene
is classified in Group A: human carcinogen according to the EPA's
classification scheme. The 10*4 excess cancer risk estimated for
benzene is 0.1 mg/L. Ordinarily, the 10"4 excess cancer risk would
be recommended for the upper bound URTH. However, the 10~* risk of
0.1 mg/L is virtually the same as the Ten-day Health Advisory of
0.2 mg/L. Also, taking into consideration that benzene is also
classified in Group A, the upper bound urth for this compound is
recommended at the 10"5 cancer risk of 0.01 mg/L.
Carbofuraii
The EPA proposed an MCLG of 0.04 and an MCL of 0.04 mg/L for
carbofuran based on absence of cholinesterase or reproductive
effects in dogs fed carbofuran one year. The Longer-term Health
Advisory for a child is 0.05 mg/L, and the drinking water
equivalent level is 0.2 mg/L. Carbofuran is classified in Group E:
no evidence of human carcinogenicity according to the EPA's
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classification scheme. .Based on this information, an upper-bound
unreasonable risk to health level of 0.05 mg/L based on the Longer-
term Health Advisory is recommended for a period of up to 7 years.
Carbon tetrachloride
The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for carbon tetrachloride based on carcinogenicity. The Longer-
term Health Advisory for a child is 0.07 mg/L, and the drinking
water equivalent level is 0.03 mg/L. Carbon tetrachloride is
classified in Group B2: probable human carcinogen according to the
EPA's classification scheme. The 10"4 excess cancer risk estimated
for carbon tetrachloride is 0.03 mg/L. Based on this information,
an upper-bound unreasonable risk to health level of 0.03 mg/L based
on the drinking water equivalent level is recommended.
Chiordan•
The EPA proposed an MCLG of zero and an MCL of 0.002 mg/L for
chlordane based on carcinogenicity and technological feasibility.
The Longer-term Health Advisory for a child has not been
calculated, but the drinking water equivalent level is 0.002 mg/L.
Chlordane is classified in Group B2: probable human carcinogen
according to the EPA's classification scheme. The 10"* excess
cancer risk estimated for chlordane is 0.003 mg/L. Based on this
information, an upper-bound unreasonable risk to health level of
0.003 mg/L based on the 10"* cancer risk is recommended.
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The EPA proposed an MCLG of 0.07 and an MCL of 0.07 mg/L for
2,4-D based on liver and kidney effects in animals. The Longer-
term Health Advisory for a child is 0.1 -ng/L, and the drinking
water equivalent level is 0.4 mg/L. 2,4-D is classified in
Group D: not classifiable as to human carcinogenicity according
to the EPA's classification scheme. Based on this information, an
upper-bound unreasonable risk to health level of 0.1 mg/L based on
the Longer-term Health Advisory is recommended for a period of up
to 7 years.
DBCP
The EPA proposed an MCLG of zero and an MCL of 0.0002 mg/L
for DBCP based on carcinogenicity. The Longer-term Health Advisory
for a child and the drinking water equivalent level has not been
calculated. DBCP is classified in Group B2: probable human
carcinogen according to the EPA's classification scheme. The 10*4
excess cancer risk estimated for DBCP is 0.003 mg/L. Based on this
information, an upper-bound unreasonable risk to health level of
0.003 mg/L based on the 10*4 cancer risk is recommended.
ei«-l. 2-Diehloroetlivlene
The EPA proposed an MCLG of 0.07 and an MCL of 0.07 mg/L for
cis-l,2-DCE based on absence of effects in a subchronic study in
animals. The Longer-term Health Advisory for a child is 3 mg/L,
and the drinking water equivalent level is 0.4 mg/L. cis-l,2-DCE
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is classified in Group D: not classifiable as to human
carcinogenicity according to the EPA's classification scheme.
Based on this information, an upper-bound unreasonable risk to
health level of 0.4 mg/L based on the drinking water equivalent
level is recommended for a period of up to 7 years.
trans—l,2—Dlchloroethvlene
The EPA proposed an MCLG of 0.1 and an MCL of 0.1 mg/L for
trans-l,2-DCE based on absence of effects in a subchronic study in
animals. The Longer-term Health Advisory for a child is 2 mg/L,
and the drinking water equivalent level is 0.6 mg/L. trans-1,2-
DCE is classified in Group D: not classifiable as to human
carcinogenicity according to the EPA's classification scheme.
Based on this information, an upper-bound unreasonable risk to
health level of 2 mg/L based on the Longer-term Health Advisory is
recommended for a period of up to 7 years.
o-Dichloroben«ene
The EPA proposed an MCLG of 0.6 and an MCL of 0.6 mg/L for o-
dichlorobenzene (DCS) based on absence of effects in a subchronic
study in rodents. The Longer-term Health Advisory for a child is
9 mg/L, and the drinking water equivalent level is 3 mg/L. o-
DCB is classified in Group D: not classifiable as to human
carcinogenicity according to the EPA's classification scheme.
Based on this information, an upper-bound unreasonable risk to
haalth level of 3 sg/L based cr. the Longer-term Health Advisory is
recommended for a period of up to 7 years.
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p-Dichlorobenaene
The EPA promulgated an MCLG of 0.075 and an MCL of 0.075 rag/L
for p-dichlorobenzene (p-DCB) based on kidney effects observed in
rats exposed to p-DCB for two years. The Longer-term Health
Advisory for a child is 10 mg/L, and the drinking water equivalent
level is 3 mg/L. p-DCB is classified in Group C: possible human
carcinogen according to the EPA's classification scheme. EPA
applied an additional 10-fold uncertainty factor to the MCLG for
p-DCB to account for possible carcinogenicity; without this
additional uncertainty factor, the MCLG would have been 0.75 mg/L.
Based on this information, an upper-bound unreasonable risk to
health level of 0.75 mg/L based on removal of the extra 10-fold UF
is recommended for a period of up to 7 years.
The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for 1,2-dichloroethane based on carcinogenicity. The Longer-term
Health Advisory for a child is 0.7 mg/L, and the drinking water
equivalent level has not been calculated. 1,2-Dichloroethane is
classified in Group B2: probable human carcinogen according to
the EPA's classification scheme. The 10*4 excess cancer risk
estimated for 1,2-DCE is 0.04 mg/L. Based on this information, an
upper-bound unreasonable risk to health level of 0.04 mg/L based
on the 10*4 excess cancer risk is recommended.
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1.i-Dichloroethvlena
The EPA promulgated an MCLG of 0.007 and an MCL of 0.007 mg/L
for 1,1-dichloroethylene based on mild liver effects and possible
carcinogenicity. The Longer-term Health Advisory for a child is
1 mg/L, and the drinking water equivalent level is 0.4 mg/L. 1,1-
DCE is classified in Group C: possible human carcinogen according
to the EPA's classification scheme. EPA applied an additional 10-
fold uncertainty factor to the MCLG for 1,1-DCE; without this
additional factor, the MCLG would have been 0.07 mg/L. Based on
this information, an upper-bound unreasonable risk to health level
of 0.07 mg/L based on removal of the extra 10-fold UF is
recommended for a period of up to 7 years.
1.2-DiehloroproDan*
The EPA proposed an MCLG of zero and an MCL of 0.005 mg/L for
1,2-dichloropropane (DCP) based on carcinogenicity. The Longer-
term Health Advisory for a child and the drinking water equivalent
level have not been calculated* 1,2-DCP is classified in Group B2:
probable human carcinogen according to the EPA's classification
scheme. The 10"* excess cancer risk estimated for 1,2-DCP is
0.06 mg/L. Based on this information, an upper-bound unreasonable
risk to health level of 0.06 mg/L based on the 104 excess cancer
risk is recommended.
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Epichlorohvdrin
The EPA proposed an MCLG of zero and a treatment technique
for epichlorohydrin based on carcinogenicity and technological
feasibility. The Longer-term Health Advisory for a child is
0.07 mg/L, and the drinking water equivalent level is also
0.07 mg/L. Epichlorohydrin is classified in Group B2: probable
human carcinogen according to the EPA's classification scheme.
The 10"4 excess cancer risk estimated for epichlorohydrin is
0.4 mg/L. Based on this information, an upper-bound unreasonable
risk to health level of 0.07 mg/L based on the Longer-term Health
Advisory is recommended for a period of up to 7 years.
Ethvlbenaene
The EPA proposed an MCLG of 0.7 and an MCL of 0.7 mg/L for
ethylbenzene based on kidney and liver effects in animals. The
Longer-term Health Advisory for a child is 1 mg/L, and the drinking
water equivalent level is 3 mg/L. Ethylbenzene is classified in
Group D: not classifiable as to human carcinogenicity according
to the EPA's classification scheme. Based on this information, an
upper-bound unreasonable' risk to health level of 1 mg/L based on
the Longer-term Health Advisory is recommended for a period of up
to 7 years.
Bthvlene dibreaide (BDBi
The EPA proposed an MCLG of zero and an MCL of 0.00005 mg/L
for EDB based on carcinogenicity. The Longer-term Health Advisory
for a child and the drinking water equivalent level have not been
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calculated. EDB is classified -in Group B2: probable human
carcinogen according to the EPA's classification scheme. The 10"'
excess cancer risk estimated for EOB is 0.00004 mg/L. Based on
this information and considering that the MCL for EDB is at the 10"
4 risk level, an upper-bound unreasonable risk to health level of
0.00005 mg/L is recommended.
Heptachlor
The EPA proposed an MCLG of zero and an MCL of 0.0004 mg/L
for heptachlor based on carcinogenicity. The Longer-term Health
Advisory for a child is 0.005 mg/L, and the drinking water
equivalent level is 0.02 mg/L. Heptachlor is classified in Group
B2: probable human carcinogen according to the EPA's
classification scheme. The 10"* excess cancer risk estimated for
heptachlor is 0.0008 mg/L. Based on this information, an upper-
bound unreasonable risk to health level of 0.0008 mg/L based on
the 10"4 excess cancer risk is recommended.
Heptachlor epoxide
The EPA proposed an MCLG of zero and an MCL of 0.0002 mg/L
for heptachlor epoxide based on carcinogenicity. The Longer-term
Health Advisory for a child is 0.0001 mg/L, and the drinking water
equivalent level is o.ooo4 mg/L. Heptachlor epoxide is classified
in Group B2: probable human carcinogen according to the EPA's
classification scheme. The 10*4 excess cancer risk estimated for
heptachlor epoxide is 0.0004 mg/L. Based on this information, an
upper~tour.d unreasonable risk t© health level of 0.0004 mg/L based
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on the 10"* excess cancer" risk is recommended.
Lindan*
The EPA proposed an MCLG of 0.0002 and an MCL of 0.0002 mg/L
for lindane based on liver and kidney effects in rodents. The
Longer-term Health Advisory for a child is 0.03 mg/L, and the
drinking water equivalent level is 0.01 mg/L. Lindane is
classified in Group C: possible human carcinogen according to the
EPA's classification scheme. EPA applied an addition 10-fold
uncertainty factor to the MCLG to account for possible
carcinogenicity; without this additional factor, the MCLG would be
0.002 mg/L. Based on this information, an upper-bound unreasonable
risk to health level of 0.002 mg/L based on removal of the 10-fold
UF is recommended for a period of up to 7 years.
Mathoxvchlor
The EPA proposed an MCLG of 0.04 and an MCL of 0.04 mg/L for
methoxychlor based on reproductive effects in rodents. The Longer-
term Health Advisory for a child is 0.5 mg/L, and the drinking
water equivalent level is 2 mg/L. is classified in Group D:
not classifiable as to human carcinogenicity according to the EPA's
classification scheme. Based on this information, an upper-bound
unreasonable risk to health level of 0.5 mg/L based on the Longer-
term Health Advisory is recommended for a period of up to 7 years.
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Monochlorob«nz«n<
The EPA proposed an MCLG of 0.1 and an MCL of 0.1 mg/L for '
monochlorobenzene based on liver and kidney effects in a subchronic
study with rodents. The Longer-term Health Advisory for a child
is 2 mg/L, and the drinking water equivalent level is 0.7 mg/L.
Monochlorobenzene is classified in Group D: not classifiable as
to human carcinogenicity according to the EPA's classification
scheme. Based on this information, an upper-bound unreasonable
risk to health level of 2 mg/L based on the Longer-term Health
Advisory is recommended for a period of up to 7 years.
Polychlorinated biphenvls (PCBs)
The EPA proposed an MCLG of zero and an MCL of 0.0005 mg/L
for PCBs based on carcinogenicity. The Longer-term Health Advisory
for a child is 0.001 mg/L, and the drinking water equivalent level
has not been calculated. PCBs are classified in Group B2:
probable human carcinogen according to the EPA's classification
scheme. The 10"4 excess cancer risk estimated for PCBs is
0.0005 mg/L. Based on this information, an upper-bound
unreasonable risk to health level of 0.0005 mg/L based on the 10"4
risk is recommended.
Tetracaicroernvi«n«
The EPA proposed an MCLG of zero and an MCL of 0.005 mg/L for
tetrachloroethylene based on carcinogenicity. The Longer-term
Health Advisory for a child is 1 mg/L, and the drinking water
equivalent level is Or5 mg/L. Tetrachloroethylene is classified
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in Group B2: probable human carcinogen according to the EPA's
classification scheme. The 10~4 excess cancer risk estimated for
tetrachloroethylene is 0.07 mg/L. Based on this information, an
upper-bound unreasonable risk to health level of 0.07 mg/L based
on the 10"4 excess cancer risk is recommended.
Toxaphene
The EPA proposed an MCLG of zero and an MCL of 0.003 mg/L for
toxaphene based on carcinogenicity. The Longer-term Health
Advisory for a child has not been calculated, but the drinking
water equivalent level is 0.003 mg/L. Toxaphene is classified in
Group B2: probable human carcinogen according to the EPA's
classification scheme. The 10** excess cancer risk estimated for
toxaphene is 0.003 mg/L. Based on this information, an upper-
bound unreasonable risk to health level of 0.003 mg/L based on the
10"* excess cancer risk is recommended.
2.4.5-TP
The EPA proposed an MCLG of 0.05 and an MCL of 0.05 mg/L for
2,4,5-TP based on absence of effects in a dog study. The Longer-
term Health Advisory for a child is 0.07 mg/L, and the drinking
water equivalent level is 0.3 mg/L. 2,4,5-TP is classified in
Group D: not classifiable as to carcinogenicity according to the
EPA's classification scheme. Based on this information, an upper-
bound unreasonable risk to health level of 0.07 mg/L based on the
Longer-term Health Advisory is recommended for a period of up to
7 years.
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1.1,l-Trichloro«thane
The EPA promulgated an MCLG of 0.2 and an MCL of 0.2 mg/L for
1,1,1-trichloroethane based on liver and kidney effects in animals.
The Longer-term Health Advisory for a child is 40 mg/L, and the
drinking water equivalent level is 1 mg/L. 1,1,1-Trichloroethane
is classified in Group D: not classifiable as to carcinogenicity
according to the EPA's classification scheme. Based on this
information, an upper-bound unreasonable risk to health level of
1 mg/L based on the drinking water equivalent level is recommended
for a period of up to 7 years.
Trichleroethvlene
The EPA promulgated an MCLG of zero and an MCL of 0.005 mg/L
for trichloroethylene based on carcinogenicity. The Longer-term
Health Advisory for a child has not been calculated, but the
drinking water equivalent level is 0.3 mg/L. Trichloroethylene is
classified in Group B2: probable human carcinogen according to the
EPA's classification scheme. The 10"4 excess cancer risk estimated
for trichloroethylene is 0.3 mg/L. Based on this information, an
upper-bound unreasonable risk to health level of 0.3 mg/L based
on the 10*4 excess cancer risk is recommended.
Vinvl Chloride
The EPA promulgated an MCLG of zero and an MCL of 0.002 mg/L
for vinyl chloride based on carcinogenicity. The Longer-term
Health Advisory for a child is 0.01 mg/L; a drinking water
equivalent level has not been calculated. Vinyl chloride is
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classified in Group A: .human car'cinogen according to the EPA's
classification scheme. The 10"4 excess cancer risk estimated for
vinyl chloride is 0.0015 mg/L. Based on this information, an
upper-bound unreasonable risk to health level of 0.002 mg/L based
on the MCL, which slightly exceeds the 10"4 excess cancer risk is
recommended.
The EPA prbposed an MCLG of 10 and an MCL of 10 mg/L for
xylenes based on body weight effects in rats. The Longer-term
Health Advisory for a child is 40 mg/L, and the drinking water
equivalent level is 60 mg/L. Xylenes are classified in Group D:
not classifiable as to human carcinogenicity according to the EPA's
classification scheme. Based on this information, an upper-bound
unreasonable risk to health level of 40 mg/L based on the Longer-
term Health Advisory is recommended for a period of up to 7 years.
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