NC0024406_Comments on Draft Permit_20170221

/r•� DUKE
ENERGY.
February 20, 2017
Mr. Sergei Chernikov, PhD
Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Richard E. Baker Jr., P. E. P. M. P
Director of Environmental Programs
EHS - Coal Combustion Products
526 S. Church Street
Mail Code:EC13K
Charlotte, NC 28202
(704)-382-7959
RECEIVEDINCDEQIDWR
FEB 21 2017
Water Quality
permitting Section
Subject: Comments on the Draft NPDES Permit for Belews Creek Steam Station — Dated January 16, 2017
Permit No. NCO024406
Stokes County
Dear Dr. Chernikov:
Duke Energy Carolinas LLC, (Duke Energy) submits the following comments on the draft National Pollutant
Discharge Elimination System ("NPDES") Permit for Belews Creek Steam Station, issued for public comment by
the North Carolina Department of Environmental Quality ("NCDEQ") on January 16, 2017. Duke Energy
appreciates NCDEQ's efforts to develop the Draft Permit, which address novel issues associated with surface
impoundment decommissioning and modifications required to allow for continued operations while complying with
various Federal and State mandates. Finalizing this wastewater permit is a critical step to advance that process by
authorizing decanting and dewatering of the ash basin and permitting replacement treatment options. In addition to
these general comments, Duke Energy offers the following comments and requests for modification and/or
clarification on specific provisions of the Draft Permit:
Duke Energy requests modification of the May 1, 2017 compliance date for Dry Fly Ash conversion
identified on pages 6 and 8. The NPDES renewal application submitted August 29, 2016 on page 6 of 9
of Attachment #3 (Narrative Description) outlines the current wet handling of fly ash. Fly ash is sluiced to
the ash basin during equipment failure or immediately following outages. Construction projects have been
commissioned to make the necessary modifications to convert the fly ash handling system to 100% dry
handling but they will require time beyond May 1, 2017 to complete. As a result, Duke Energy noted in its
justification for alternate ELG compliance schedule that it could comply with the zero discharge of fly ash
ELG by the earliest ELG applicability date, November 1, 2018. The ELG rule states the no discharge of
fly ash transport water is to be "as soon as possible" determined by the Permitting authority The
ELG rule defines "as soon aspossible" as "...November 1 2018 unless the permitting authority
establishes a later date..." N423.11[0). Duke Energy requests the Dry Fly Ash compliance date be
changed to November 1, 2018.
2. Duke Energy requests removal of the Thallium limitations identified on pages 5, 7,10,11,12,13, and
14. Duke Energy requests that the limits for Thallium be removed from the permit for the following
reasons:
a. There is no adopted numeric water quality criterion for Thallium in North Carolina. With no
adopted criteria, the State has not provided any opportunity for public involvement or comment on
recommended constituent levels used in determining permit requirements. Unlike the defined
opportunity to comment on proposed criteria during the triennial review, the only means for public
involvement in this case is through commenting on specific permitting actions. The NCDEQ has
previously indicated no limits for metals would be included in permits for constituents without numeric
criteria. NCDEQ recently acknowledged this in issuance of the company's Sutton permit in which
NCDEQ proposed to include an effluent limit for Aluminum but withdrew that limit in the final permit
"because ...North Carolina does not have [an] Al standard...". North Carolina just completed an

12
update to its standards through the triennial review process but did not propose any standards for
Thallium.
The conclusion reached in the IRIS Toxicological Review (USEPA, 2009), which DEQ seeks to
base the limit on, was the available toxicity database for Thallium contains studies that are
generally of poor quality. Please see Attachment 1 - Evaluation of Toxicological Information of
Thallium prepared by Haley and Aldrich for DEC. This information is included in the attachment to
these comments and should be considered part of our comments on the DRAFT permit. In the USEPA
Integrated Risk Information System (IRIS) Chemical Assessment Summary for Thallium, it was stated
"The available toxicity database for thallium contains studies that are generally of poor quality"
(USEPA, 2012a). In addition, there is currently not an oral chronic reference dose (RfD) toxicity value
for Thallium established by the USEPA IRIS or from an USEPA Provisional Peer -Reviewed Toxicity
Value (PPRTV) assessment, which would be used to establish water quality criteria. Due to the
significant uncertainty surrounding the study selection used to establish the values for the 2002 water
quality criteria and uncertainty to the relevance of adverse effects of Thallium, the values used for the
derivation of the 2002 Federal Water Quality Criteria for Thallium are questionable and greatly
overestimates potential risks associated with Thallium exposure. This is supported by other regulatory
and authoritative agencies concluding that the dataset is currently insufficient for derivation of non -
cancer value for Thallium. In addition. current intakes of Thallium for a substantial part of the
population exceed the provision screening value with no reported adverse effects reported. which also
suggests that the current value is unrealistic for purposes of regulatory decision making.
There is no record of a determination that any limit on Thallium is necessary to protect
narrative criteria. To the contrary, the record indicates that the receiving water currently meets
narrative criteria, despite a long history of similar discharges, indicating that effluent limits are not
necessary to protect narrative criteria or designated uses. The NCDEQ has not provided any
documentation that the factors required for consideration in developing a BPJ limit for Thallium have
been considered.
3. On page 2, a statement was added to the permit related to Outfall 003A and the construction ofa lined
retention basin. This statement reads "Upon completion of construction all waste streams previously
discharged to ash basin, will be re-routed to the new retention basin-. It is Duke Energy's intent to
continue to discharge some permitted flows.. including remediated groundwater, to the ash basin until
regulatory deadlines require all flows to the ash basin to cease. Duke Energy requests that this
statement be modified to allow for this activity to continue until regulatory deadlines require all
flows to be rerouted from the ash basin.
4. The DRAFT permit contains Aluminum limitations on pages 5 and 7. Duke Energy requests that the
limits for Aluminum be removed from the permit for the following reasons:
a. NCDEQ has proposed to impose limits based on references to Aluminum in the EPA National
recommended criteria table. The EPA acknowledges their criteria are not meant to be used for
regulatory purposes but are to be used as a guide to help States adopt their own, properly noticed and
approved standards. With no adopted criteria, the State has not provided any opportunity for public
involvement or comment on recommended constituent levels used in determining permit requirements.
Unlike the defined opportunity to comment on proposed criteria during the triennial review, the only
means for public involvement in this case is through commenting on specific permitting actions.
NCDEQ acknowledged this in issuance of the company's Sutton permit in which NCDEQ proposed to
include an effluent limit for Aluminum but withdrew that limit in the final permit "because ...North
Carolina does not have [an] Al standard...". Furthermore, there is no justification provided for setting
the Daily Maximum Limit equal to the Monthly Average. NCDEQ states there is no acute standard;

therefore, there should be no Daily Maximum limit imposed. Duke Energy requests the proposed limits
for Aluminum be removed until NCDEQ adopts properly noticed water quality standards.
5. On page 5, Total Lead is listed twice on the parameter list. Duke Energy requests removal of one of the
references to Total Lead.
6. Cadmium, chromium, and zinc limitations are identified on pages 5 and 7. Duke Energy requests the
monitoring requirements for these metals be removed from the permit for the following reasons:
a. The NPDES Permit issued on October 12, 2012 removed requirement for monitoring of cadmium,
chromium, and zinc based upon statistical analysis of historical effluent data. Reasonable Potential
Analysis (RPA) performed on these outfalls for the draft permit as outlined in NCDEQ's Fact Sheet
included cadmium, chromium, and zinc. The analysis did not indicate reasonable potential to violate
the surface water quality standards or EPA criteria for these parameters.
Iron and copper limitations are identified on pages 5, 7, and 9. The word "chemical" has been omitted
from Footnotes #10 on page 6 and 8 and Footnote #6 on page 9. Previous permits for Belews Creek
applied limits for copper during "chemical" metal cleaning. Condition A(15) in the draft permit states that
it has been demonstrated that the presence of ions of copper, iron, nickel, and zinc in the Ash Basin have
not measurably increased at Belews Creek Steam Station and lists in #6 the chemicals are used for boiler
cleaning. Duke Energy requests that the analysis for iron and copper be clarified to apply only during
chemical metal cleaning activities for both Outfall 003 and Outfall 003A, and that the word
"chemical" be added to Footnote #10 on pages 6 and 8 and Footnote #6 on page 9. Additionally,
please add footnote notation #10 to Total Iron in the Table on page 5.
8. Contributing flows to Outfall 005 consists of once through non -contact cooling water and stormwater. The
DRAFT permit requires monitoring for Total Dissolved Solids, Total Suspended Solids, and Hardness.
Duke Energy requests these sampling requirement be removed and the sampling parameters be
consistent with Condition A(1).
9. Total Suspended Solids monitoring requirements are identified on page 17. Duke Energy requests that
the monitoring requirement be removed to reflect Conditions in A(1) or reduced to monthly.
10. The footnotes identified on page 15 begin with #2 which makes the footnote notation for pH and total
mercury to not match the assumed intent. Duke Energy requests clarification of this Section.
11. Duke Energy requests the monitoring requirements for Arsenic and Selenium on page 17 be removed
from the permit. Reasonable Potential Analysis (RPA) performed on these outfalls for the draft permit as
outlined in NCDEQ's Fact Sheet included arsenic and selenium. The analysis did not indicate reasonable
potential to violate the surface water quality standards or EPA criteria for these parameters.
12. There is a proposed Chloride limitation identified on pages 10, 11, 12, 13, and 14. There is no justification
provided for setting the Daily Maximum Limit equal to the Monthly Average. NCDEQ states there is no
acute standard; therefore, there should be no Daily Maximum limit imposed. Duke Energy requests that
the Daily Maximum limit be removed.
13. A Molybdenum limitation is identified on page 7. Duke Energy requests that the limits for
Molybdenum be removed from the permit for the following reason:
a) NCDEQ has proposed to impose limits based on references to Molybdenum in the EPA National
recommended criteria table. The EPA acknowledges their criteria are not meant to be used for

regulatory purposes but are to be used as a guide to help States adopt their own, properly noticed
and approved standards. With no adopted criteria, the State has not provided any opportunity for
public involvement or comment on recommended constituent levels used in determining permit
requirements. Unlike the defined opportunity to comment on proposed criteria during the triennial
review, the only means for public involvement in this case is through commenting on specific
permitting actions. Furthermore, there is no justification provided for setting the Daily Maximum
Limit equal to the Monthly Average. NCDEQ states there is no acute standard; therefore, there
should be no Daily Maximum limit imposed. Duke Energy requests the proposed limits for
Molybdenum be removed until NCDEQ adopts properly noticed water quality standards.
14. On page 3, there is a permit condition which requires Duke Energy to perform and submit EPA Form 2C
sampling. EPA 2C samples were collected from Outfall 001 on June 1, 2016 and submitted with the permit
renewal application. Duke Energy is asking for clarity that the requirement for new EPA Form 2C
data for this Outfall be changed from within 180 days from permit effective date to 180 days prior to
the permit expiration date.
15. During the period beginning upon the commencement of operations of the new Retention Basin (Outfall
003A) and lasting through decommissioning of the Ash Basin (Outfall 003), there will be contributing
flows from Ash Basin for operation/maintenance for stormwater, decanting, and dewatering, and Retention
Basin for normal plant operations that discharge through Outfall 003/003A. Duke Energy requests
clarification on effluent limitations and monitoring requirements for Outfall 003/003A during the
transition when plant operational flow through the retention basin and the decanting/dewatering of
ash basin for decommissioning will comingle at this outfall.
16. Toxicity testing requirements are identified on pages 5, 7, 9, and in permit condition A(17). Duke Energy
has never failed a toxicity tests at the Belews Creek plant and monthly testing during normal operations is
not supported. Duke Energy requests that Toxicity testing remain a quarterly requirement until ash
basin dewatering commences.
17. Based upon further review, Duke Energy requests removal of coverage from the area previously
identified at S-07 (Outfall 107) from the permit. This request is based on refined analysis in accordance
with Duke's Standard Operating Procedure for review of Areas of Wetness, and sampling data that
confirms lack of pollutants associated with plant activities. Analytical data indicates that there is no
presence of Boron or Selenium and only detectable levels of Arsenic in the one part per billion range.
18. On page 23, there is a section related to "New Identified Seeps". Duke Energy requests that this section
should include the statement "If new seeps are identified the facility shall follow the procedures
outlined above. The deadline for new seeps shall be calculated from the date of the seep discovery."
19. In condition A. (31.) FGD Treatment, the permit contains a prescriptive requirement for additional
sampling associated with FGD treatment. As opposed to a permit condition stating the laboratory
analysis, frequency and sample locations for assessing the performance of the FGD treatment system,
Duke Energy request this condition be replaced with a requirement for Duke Energy to develop a
study plan for approval by NCDEQ to be submitted within six months of the effective date of the
permit. This would allow the sampling locations to be based on the final design of the system and the
required laboratory analysis to provide useful information on the performance of the system. As the permit
condition is currently written, it is Duke Energy's position that the laboratory analysis for the following
parameters provide no value and will be problematic to perform:

15
L Turbidity (light transmission) analysis for high solids and nutrient rich in -process stream will
provide no value in assessing the performance of the treatment system. In addition, turbidity provides
an indirect, gross estimate of total suspended solids (TSS), which is unnecessary when TSS analysis is
conducted.
2. Conductivity is a surrogate characteristic and unnecessary when samples are being analyzed for total
dissolved solids (TDS) and chlorides.
3. ORP is a transient and relative value. In-situ measurement of ORP is required for assessing the
reducing waters in the treatment system and the scrubber. Duke Energy would, therefore, recommend
using the in-situ scrubber ORP monitor for SP -1, and in process ORP readings for SP -2 and SP -3. ORP
readings from the effluent of the ultrafiltration system (SP -4) provide no value and would require
additional equipment.
4. There is no accepted agreed upon valid test for the measurement of total residual oxidants in FGD
wastewaters. Any measurement of total residual oxidants will only provide a relative value and could
only be used to identify trends.
20. On page 1 of 31, please clarify that the discharge from Outfall 003 to the Dan River is via an effluent
channel previously designated by the Department.
Duke Energy welcomes any further discussion on our comments or the Draft Permit and requests the opportunity
to discuss the comments outlined in this letter with you prior to the permit being finalized to assure any
remaining questions are adequately addressed. If you have any questions, please contact Joyce Dishmon at 336-
623-0238 or [e-mail].
Sincerely,
Richard E. Baker, Jr., P.E., PMP
Director of Environmental Programs -CCP
Duke Energy
Attachment
Cc: Ms. Karen Higgins — Belews Creek Public Hearing officer
1617 Mail Service Center
Raleigh, NC 27699-1617

Attachment I
11 F,:tlZ111111
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FEB 21 2017
WaterQuality
Permitting Section
Evaluation of Toxicological Information of
Thallium prepared by Haley and Aldrich for

Thallium Toxicity Value Review
EVALUATION OF THE TOXICITY VALUE FOR THALLIUM
I. Current Screening Provisional Toxicity Value
There is not currently an oral chronic reference dose (RfD) toxicity value for thallium established by the
United States Environmental Protection Agency (USEPA) Integrated Risk Information System (IRIS) or
from an USEPA Provisional Peer -Reviewed Toxicity Value (PPRTV) assessment. The USEPA PPRTV
document for thallium (TI) concluded that it is inappropriate to derive a provisional subchronic or
chronic provisional RfD (p-RfD) for thallium; however, USEPA states that information is available which,
although insufficient to support derivation of a provisional toxicity value under current guidelines, may
be of limited use to risk assessors (USEPA, 2012). The PPRTV document contains a separate Appendix A
that provides rationale for the derivation of a subchronic and chronic "screening provisional oral
reference dose" for thallium compounds of 0.00004 mg TI/kg-day and 0.00001 mg TI/kg-day,
respectively. Appendix A of the PPRTV document also notes that, "Users of screening toxicity values in
an appendix to a PPRTV assessment should understand that there is considerably more uncertainty
associated with the derivation of a supplemental screening toxicity value than for a value presented in
the body of the assessment (USEPA, 2012a)." The screening p-RfD is expressed in units of milligrams of
thallium per kilogram of body weight per day (mg TI/kg-day).
Due to limitations in the toxicology database and general poor quality of available studies, the USEPA
IRIS Toxicological Review of Thallium and Compounds (USEPA, 2009) also concluded that reference
doses or reference concentrations could not be derived for human health following thallium exposures.
2. Information on Human Exposure to Thallium
The conservative nature of the p-RfD can be illustrated by considering the amount of thallium ingested
daily by Americans in their diet. It is estimated by the World Health Organization (WHO) and the U.S.
Agency for Toxic Substances for and Disease Registry (ATSDR) that a 70 kilogram adult ingests
approximately 0.005 mg thallium per day in the diet, especially from consumption of home-grown fruits
and green vegetables (WHO, 1996; ATSDR, 1992). This is equivalent to a daily dose of 0.00007 mg TI/kg-
day. The USEPA supplemental p-RfD for thallium is 1E-05 mg/kg -day (0.00001 mg/kg -day). This is seven
times lower than the estimated dietary intake. In other words, use of this dose -response value to
evaluate natural dietary exposure to thallium would indicate a hazard that is unlikely to exist.
Stated another way, assuming that an average adult weighs 70 kg, and using the screening level p-RfD of
0.00001 mg/kg bw-day, it could be concluded that an adult should not consume more than 0.0007 mg
TI/day, which is well below the estimated dietary intake of 0.005 mg thallium per day in the diet.
Currently, there have not been substantial reports of toxicological effects associated with typical dietary
ingestion of TI in the general population, suggesting that the use of the "screening provisional oral
reference dose" greatly overestimates the potential risks associated with oral exposure to TI
compounds.
The 90`h percentile adult urinary thallium elimination from the National Health and Nutrition
Examination Survey (NHANES) (CDC, 2016) is 0.380-0.390 micrograms per liter (ug/L) which is about
0.760-0.780 ug/day in the urine alone. This suggests that greater than 10% of Americans, and probably
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Thallium Toxicity Volue Review
closer to 50% of Americans, ingest more than the screening level p-RfD. From the IRIS assessment
conducted in 2009, a reviewer stated that there is no evidence that thallium in the current U.S. diet
poses any threat, and the adoption of this screening level p-RfD would produce unnecessary concern if
the above calculation is correct. This indicates the poor quality of the existing data, and brings into
question the validity of the analysis using the available data on thallium used by USEPA (USEPA, 2009).
3. Derivation of the Current Screening Provisional Toxicity Value
Below is a summary of the data and assessment that was used by USEPA in the derivation of the oral
chronic screening level p-RfD for thallium.
3.1 HAZARD EVALUATION/STUDY SELECTION
Note: Human or animal studies examining the carcinogenicity of thallium following oral exposure are
not available. The cancer weight -of -evidence (WOE) provided in the IRIS review (USEPA, 2009) is listed
as "Inadequate Information to Assess Carcinogenic Potential (both oral and inhalation)."
3.3.1 Human Studies
Most information on thallium toxicity in humans comes from poisonings, suicide attempts, or accidental
exposures. Symptoms observed after acute exposures to high doses of thallium in humans include
alopecia (hair loss), gastrointestinal disturbances, and neurological symptoms such as paresthesia and
neuropathy. Epidemiologic studies of either the general population or occupationally exposed groups
are limited by inadequate study design, undefined exposure parameters, and inconclusive associations
between thallium exposure and specific health effects. Therefore, USEPA (2012a) concluded in the
PPRTV document that "available human studies do not support oral RfD derivation."
3.1.2 Animal studies
Studies in animals show that oral exposure to thallium produces effects similar to those observed in
humans, most notably, alopecia. Other findings observed in animal studies include biochemical
changes, lipid peroxidation, liver and kidney damage, and histopathologic changes in the brain and
nerves. The doses at which these systemic effects were observed range from 0.2 —1.8 mg TI/kg-day
(ATSDR, 1992). Reproductive and developmental studies in animals show some evidence of adverse
effects upon oral exposure to thallium at doses of 0.08 mg TI/kg-day —1.6 mg TI/kg-day; however,
available studies have significant limitations and the same effects have not been observed in humans
(ATSDR, 1992).
Only four repeat -dose oral toxicity studies with more than one dose level are available in animals. Of
these four studies, three were not considered adequate for RfD derivation (USEPA, 2009).
3.1.3 Conclusion
The conclusion reached in the IRIS Toxicological Review (USEPA, 2009) was that the available toxicity
database for thallium contains studies that are generally of poor quality. One animal subchronic study
conducted by the Midwest Research Institute (MRI, 1988) was selected as a candidate principal study for
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Thallium Toxicity Value Review
RfD derivation but was found to include critical limitations such as high background incidence of
alopecia, lack of histopathological examination of skin tissue in low -and mid -dose groups, and
inadequate examination of objective measures of neurotoxicity, thus making it difficult to select
appropriate endpoints. On this basis, a RfD for thallium salts was not derived by IRIS (USEPA, 2012a).
3.2 BASIS FOR PROVISIONAL SCREENING ORAL CHRONIC P -RFD
As indicated above, the PPRTV assessment (USEPA, 2012a) does not derive a typical provisional toxicity
value for thallium but rather uses the limited toxicological information to develop a screening level
value.
3.2.1 Study Selection
A 90 -day Good Laboratory Practice (GLP) oral gavage study in male and female rats conducted with
thallium sulfate by MRI (1988) was selected as the principal study for the screening level p-RfD. Doses
were approximately 0, 0.008, 0.04, and 0.2 mg TI/kg-day.
3.2.2 Selection of Point of Departure
Several critical endpoints were considered, but ultimately USEPA (2009) considered only two endpoints
to be appropriate for a screening level p-RfD development:
® Hair follicle atrophy in female rats that also had alopecia; and
® Clinical observations related to animal coat, eyes, and behavior.
The clinical observation endpoint was discounted because the underlying basis for the observations is
unknown. Hair follicle atrophy was determined to be most consistent with the atrophic changes
observed in cases of human thallium poisoning and may be best indication for human response to
thallium exposure.
MRI (1998) concluded that the minor dose-related changes in the study did not affect the health status
of the treated animals and were not toxicologically significant. MRI considered the highest dose (0.2 mg
TI/kg-day) as the no -observed -effect level (NOEL). However, USEPA conducted its own analyses of the
raw data from the study to come up with different conclusions. Of the 12 high -dose females with
alopecia, 5 instances were not totally attributed to barbering behavior. Histopathologic examinations
revealed atrophy of the hair follicles in two high -dose female rats that also had alopecia. It was noted
that there were no discernable differences in either the severity or distribution pattern of alopecia
across control and treated groups (USEPA, 2009).
The high dose (0.2 mg TI/kg-day) was identified by USEPA as the LOAEL. Because histopathology of skin
tissue from the low -and mid -dose groups was not conducted, the NOAEL for this endpoint cannot be
determined with certainty. Given the low incidence of hair follicle atrophy in females in the high dose
group and absence of cases of hair follicle atrophy in male rats, USEPA (2012a) assumed that the mid -
dose could be used to approximate a NOAEL for skin histopathology.
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Thallium Toxicity Value Review
Therefore, the estimated NOAEL of 0.04 mg TI/kg-day was used as the point of departure (POD) for hair
follicle atrophy (USEPA, 2012a).
3.2.3 Uncertainty Factors
Using the NOAEL of 0.04 mg TI/kg-day for hair follicle atrophy and using an uncertainty factor (UF) of
3000, the screening level p-RfD was calculated to be 0.00001 mg TI/kg-day. Justification for the applied
OF is summarized in table below.
Table 1: Uncertainty Factors Applied by USEPA in Screening Level p-RfD Derivation
Uncertainty Factor
Justification
10
Extrapolation from laboratory animals to humans since no information is
available to characterize the toxicokinetic differences between experimental
animals and humans.
10
Variation in human susceptibility in the absence of information on the
variability of response to thallium in the human population.
10
Lack of adequate developmental toxicity studies and a two -generation
reproductive study, and additional uncertainty associated with the limited
data available on neurotoxicity.
3
Extrapolation from subchronic to chronic exposure duration. Effects on the
coat/skin as well as other clinical observations occur within weeks of exposure
to thallium (does not required chronic exposure in order to manifest).
Composite OF = 3000
Note that there are considerable and critical limitations with the principal study selected by USEPA
(2009) including:
High background of incidence of alopecia (POD selected)
r Lack of histopathological examination of skin tissue in low -and mid -dose groups
Inadequate examination of objective measures of neurotoxicity
4. Other Available Sources for Derivation of Toxicity Values for Thallium
The following sections describe sources consulted for information on the toxicology of thallium.
4.1 WORLD HEALTH ORGANIZATION
The World Health Organization (WHO) (1996) concluded that in the general population, environmental
exposure to thallium does not pose a health threat. The total intake has been estimated to be less than
5 ug/day with the vast majority coming from foodstuffs; drinking -water and air generally contribute very
small amounts of thallium. Concentrations of thallium in urine may be considered a relatively reliable
indicator of exposure. Exposure to thallium resulting in urine concentrations below 5 ug/liter is unlikely
to cause adverse human health effects. The estimated daily oral intake corresponding to a urinary
thallium concentration of 5 ug/liter in urine is approximately 10 ug thallium in.the form of a soluble
compound. Assuming an average adult body weight of 80 kg (USEPA, 2014), this would be equivalent
to 0.000125 mg/kg -day which is a 10 -fold factor above the USEPA screening level p-RfD. The WHO
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Thallium Toxicity Value Review
Task Group thus concluded that `inview of the considerable uncertainties in the evaluation, it was not
possible to recommend a health -based exposure limit. Until better information on the dose -response
relationship becomes available, it seems prudent to keep human exposures at levels that lead to urinary
concentrations of less than 5 ug/liter." In reviewing the animal studies, the WHO Task Group also noted
that, "it appears that an intake of 0.01 mg/kg -day may be associated with adverse effects. No doses
lower than this have been tested."
ATSDR (1992) notes, "Data on effects of intermediate duration oral exposure in animals do not reliably
identify the most sensitive target organ or the threshold for adverse effects. No data on effects of
chronic -duration oral exposure to thallium were located. Therefore, intermediate -duration and chronic -
duration oral minimum risk levels (MRLs) were not derived for thallium." (Vote that review of the MRI
1988 study (originally Stoltz 1986) was conducted by ASTDR but not used in the derivation of the MRL.
4.3 USEPA OFFICE OF WATER
USEPA's Maximum Contaminant Level (MCL) (USEPA, 2012b) for drinking water is 2.0 ug/L or 0.002
mg/L. The USEPA Human Health Water Quality Criteria (HHWQC) (USEPA, 2015) for thallium is 0.24 ug/L
or 0.00024 mg/L for the consumption of water and organisms from a surface water body, and is 0.47
ug/L or 0.00047 mg/L for the consumption of organisms only. These levels were derived based on the
90 -day subchronic study in rats (MRI, 1988).
4.4 CALIFORNIA EPA
In California, the MCL and Public Health Goal (PHG) for thallium in drinking water are currently set at 2.0
and 0.1 ug/L, respectively (CalEPA, 1999, 2004). The Office of Environmental Health Hazard Assessment
(OEHHA) prepared the PHG for thallium in drinking water also using the MRI (1988) study in which
alopecia was observed in both male and female rats and consistent with other reports of toxicity of
thallium in both experimental animals and in humans. OEHHA determined that the incidence of
alopecia in female rats at the highest dose of 0.25 mg/kg -day represented a biologically significant
effect. Therefore, the no -observed -effect -level (NOEL) was identified to be the administered mid -dose
level of 0.04 mg TI/kg-day. For the calculation of the PHG, a cumulative uncertainty factor of 3,000 was
incorporated to account for the use of a subchronic study, uncertainty in inter -and intra -species
extrapolation and the steep dose -response curve. Based on these uncertainty factors, OEHHA derived a
PHG for thallium in drinking water of 0.0001 mg/L (0.1 ug/L). OEHHA notes that USEPA chose to
consider the dose that resulted in alopecia and increased serum enzymes indicated of liver damage as a
NOAEL, which is why the federal values are higher than those estimated by OEHHA.
4.5 CANADIAN COUNCIL OF MINISTERS OF THE ENVIRONMENT
The Canadian Council of Ministers of the Environment (1999) also adopted the USEPA screening level p-
RfD based on the MRI (1988) study as a provisional tolerable daily intake (TDI) for derivation of health -
based soil quality guidelines for thallium at contaminated sites in Canada.
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Thallium Toxicity Value Review
4.6 EUROPEAN UNION
No data were available on thallium or thallium compounds on the European Chemical Agency (ECHA)
Portal where the Registration, Evaluation, Authorization and Restriction of Chemical Substances (REACH)
Registration Dossiers are posted (ECHA, 2016). Thus, no derived no effect level (DNEL) is available for
thallium from this source.
4.7 OTHER
No other relevant data were located with respect to thallium toxicity since the publication of the USEPA
PPRTV assessment that could better inform the dose -response assessment and toxicity value derivation
for thallium.
S. Critique of Toxicity Value for Thallium
The current screening level p-RfD currently being used by USEPA as a toxicity value is a highly
conservative and inappropriate value for use in evaluating human health risks from oral chronic
exposure to thallium on the basis of: 1) the lack of appropriate toxicological studies on subchronic and
chronic exposures to thallium that provide relevant data and endpoints to be used in a dose -response
assessments; 2) the fact that other regulatory authorities (ATSDR, WHO) have concluded that sufficient
data on thallium does not exist and have not generated toxicity values for thallium and have placed a
low priority on development of additional toxicology data for thallium; 3) the study and POD using
alopecia as the endpoint as selected for the derivation of the screening level p-RfD by USEPA (2012a)
results in significant uncertainty to the applicability of the effects to human exposure to thallium; and 4)
the screening level p-RfD greatly overestimates the risk associated with human exposures as compared
to the typical ingestion of thallium in foods.
5.1 TOXICOLOGY DATABASE ON THALLIUM
The toxicity database for thallium in consideration of a dose -response assessment and derivation of a
toxicity value is limited. Low confidence in the screening level p-RfD is attributed to the limited
database including the lack of studies addressing the known toxic effects of thallium including
neurotoxicity, developmental toxicity, and endocrine effects, and failure of the MRI (1988) study to
identify a NOAEL of all relevant endpoints are considered. It is questionable as to whether a screening
level p-RfD should have been derived and if such an analysis is even valid knowing the database
limitations resulting in the application of such high uncertainty factors, given USEPA's own discussion of
the limitations in the PPRTV document (USEPA, 2012a).
5.2 OTHER REGULATORY SOURCES/VALUES
Most regulatory sources acknowledge the paucity of data for thallium and have not derived toxicity
values. USEPA IRS, WHO, and ATSDR have not generated oral chronic RfDs for thallium. For those that
have, the MRI (1988) study has been identified as the principal study despite the fact that it has not
been published in a peer-reviewed journal, did not provide statistical analyses, and the study did not
show a statistically significant dose -response effect for alopecia in male rats.
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Thallium Toxicity Value Review
On the Priority List of Hazardous Substances established by ATSDR last updated February 12, 2016,
thallium is listed as #275 out of 275 compounds indicating its low priority and concern for review
(htti)://www.atsdr.cdc.eov/SPL/). In addition, the National Toxicology Program (NTP) (2016a) has
reviewed petitions and proposals for conducting additional toxicology studies on thallium to decrease
the limitations and uncertainty with the current toxicology database but in a recent meeting on June 15,
2016, the NTP scientific board placed low priority on moving forward with these efforts.
One could infer that the low priority established by regulatory authorities on continued development
and review of the toxicology data for thallium indicates a low concern of the potential for human health
risk effects of oral exposures to thallium as compared to other compounds.
5.3 STUDY SELECTION AND POD
It has been questioned as to whether alopecia is considered an adverse event and should have been
used as the POD for the screening level p-RfD. USEPA has stated: "Whether alopecia is itself an adverse
effect merits consideration. In humans, alopecia is generally reversible upon cessation of thallium
exposure. Alopecia, however, appears to be a part of a continuum of dermal changes observed
following thallium exposure, as well as one of a spectrum of effects on target organs that include the
nervous and gastrointestinal systems. For these reasons, alopecia supported by two cases of hair follicle
atrophy is considered an adverse effect (USEPA, 2009)." USEPA (2009) acknowledged that other factors
such as caging and husbandry can cause alopecia in laboratory rodents; however, the incidence was
clearly elevated in both male and female rats over controls. Further, to the extent that alopecia was due
to barbering, research has shown that barbering in rodents can reflect a stress -evoked behavioral
response. For these reasons, some IRIS reviewers thought it was reasonable to use the alopecia as a
"biomarker" for adverse effects until additional studies are conducted to better identify adverse effects
of thallium exposures in animals and/or humans.
NTP (2016b) has also noted that the dose selection for the subchronic study was deemed inappropriate
for evaluation of alopecia since the 14 -day range -finding study performed prior to the 90 -day study
indicated hair follicle alterations together with decreases in body weight at a dose of 2.5 mg/kg -day of
thallium sulfate; however, a dose of ten times lower than that which effects were noted, 0.25 mg/kg -day
thallium sulfate was chosen as the high dose in the subchronic study. Further, review of the results also
show that there were challenges in distinguishing between normal hair cycling, self -barbering, and
incidences of true alopecia.
Since hair follicle histopathology and self -barbering is not a standard assessment in subchronic studies, it
is difficult to know whether what was observed in the MRI study (1988) is within the range of normal or
truly adverse. Therefore, the use of this endpoint as the POD brings considerable uncertainty to the
screening level p-RfD derived using these data.
No other studies have been identified by reviewers that could bring more certainty and validity to the
current screening level p-RfD proposed by USEPA (2012a).
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Thallium Toxicity Value Review
6. Final Assessment
Due to the significant uncertainty surrounding the study selection and uncertainty to the relevance of
adverse effects in the selected study and POD, the screening level p-RfD value as provided in Appendix A
of the USEPA PPRTV document for thallium (USEPA, 2012a) greatly overestimates potential risks
associated with exposure to TI. This is supported by other regulatory and authoritative agencies
concluding that the dataset is currently insufficient for derivation of a non -cancer value for TI. In
addition, current intakes of TI for a substantial part of the population exceed the provision screening
value with no reported adverse effects reported, which also suggests that the current value is unrealistic
for purposes of regulatory decision making.
Therefore, it seems most appropriate to establish a screening level based on the level of thallium in the
diet; clearly exposure to thallium at this level are without adverse effects. Using the information from
WHO (1996) that the estimated daily oral intake corresponding to a urinary thallium concentration of
5 ug/liter in urine is approximately 10 ug thallium in the form of a soluble compound, and assuming
an average adult body weight of 80 kg (USEPA, 2014), a RfD of 0.000125 mg/kg -day can be calculated,
which is a 10 -fold factor above the USEPA screening level p-RfD. This value is still a conservative
derivation, considering that it is well below the intake of 0.01 mg/kg -day that WHO indicated was the
lowest associated with adverse effects.
7. References
1. ATSDR. 2004. Toxicological Profile for Cobalt. U.S. Department of Health and Human Services,
Public Health Service, Agency for Toxic Substances and Disease Registry. Available at:
http://www.atsdr.cdc.gov tox rofiles P.as ?id=309&tid=49
2. CDC. 2016. National Health and Nutrition Examination Survey. U.S. Center for Disease Control and
Prevention. Available at: htt2:j/www.cdc.goyZnchs/nhanes/
3. CalEPA. 1999. Public Health Goal for Thallium in Drinking Water. Office of Environmental Health
Hazard Assessment (OEHHA). Available at:
http://oehha.ca.xovlmedialdownloadsjpesticides/report/thalf 1 odf
4. CalEPA. 2004. Update of Public Health Goal (PHG)-Thallium. Office of Environmental Health Hazard
Assessment (OEHHA). Available at:
hit oehha.ca. ov medialdownloads/`pesticides/reportltha111104.pdf
5. Canadian Council of Ministers of the Environment. 1999. Canadian soil quality guidelines for the
protection of environmental and human health: Thallium (1999). In: Canadian environmental quality
guidelines, 1999, Canadian Council of Ministers of the Environment, Winnipeg. Available at:
htt ce -rc e.ccme.ca download en 215
6. ECHA. 2016. ECHA Portal for Registration, Evaluation and Authorisation of Chemicals (REACH)
Registered Substances. European Chemicals Agency (ECHA). Available from:
htt echa europ a.eu information -on -chemicals re gistered-substances
November 2016 8

Thallium Toxicity Value Review
7. OEHHA. 1999. Public Health Goal for thallium in drinking water. Office of Environmental Health
Hazard Assessment, Berkeley and Sacramento, CA. Accessible at
http://www.oehha.ca.gov/waterZphg/index.htmI
8. NTP. 2016a. NTP Board of Scientific Counselors Meeting. Webinar presentation. Thallium
Compounds. June 15. See: http://ntp.niehs.nih.pov/about/org/bsc/meetings/past/index.html
9. NTP. 2016b. Draft NTP Board of Scientific Counselors Meeting. NTP Research Concept: Thallium
Compounds. June 15-16. Available at:
http•//ntp niehs nih Zov/nt /about ntplbsc/?016/lune/meeting%20materialslthallium-
compounds 508. df
10. USEPA. 2009. Toxicological Review of Thallium and Compounds -In Support of Summary
Information on the Integrated Risk Information System (IRIS). September. Available at:
https://cfpub.eSLa.gov/ncea/irisZiris documents/documentsltoxreviews11012tr.pdf
11. USEPA. 2012a. Final Provisional Peer Reviewed Toxicity Values for Thallium and Compounds.
Superfund Health Risk Technical Support Center, National Center for Environmental Assessment,
Office of Research and Development, US Environmental Protection Agency, Cincinnati, OH.
Available at: httr)s:,/Phhnnrtv.orn! ,o_Zissue _pa �erslThalliumSolubleSalts. �df
12. USEPA. 2012b. USEPA 2012 Edition of the Drinking Water Standards and Health Advisories, Spring
2012. U.S. Environmental Protection Agency. Available at:
htt : /rais.ornl.aoyjdocuments/2012 drinking water pdf
13. USEPA. 2014. Human Health Evaluation Manual, Supplemental Guidance: Update of Standard
Default Exposure Factors. OSWER 9200.1-120. February 6, 2011. U.S. Environmental Protection
Agency. Available at: http:/ nepis epa goy/Exe/ZVPDF li/P100NQNA PI)F?Dockev-P100NQNA.PDF
14. USEPA. 2015. Human Health Ambient Water Quality Criteria. U.S. Environmental Protection
Agency. Available at: https:l/www.epa.eov/woclnationaI-recommended-water-gualltK-cr!terla-
human-health-criteria-table
15. WHO. 1996. Thallium. Environmental Health Criteria 182. World Health Organization. Available
at: http://www.inchem.ore/documents/ehc/ehc/ehcl82.htm
November 2016
9I -Ar CH

November 2016 comment letter on Belews
Creek DRAFT NPDES permit

PDUKE
V11 ° ENERGY®
November 14, 2016
Dr. Sergei Chernikov
Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Subject: Comments on the Draft NPDES Permit for Belews Creek Steam Station
Permit No. NCO024406
Stokes County
Dear Dr. Chernikov:
Richard E. Laker, Jr.
Director
ENS-C:CP Environmental Programs
526 S. Church Street
Mail Cade: EC 13K
Charlotte, NC: 28202
[phone]
Duke Energy Carolinas LLC, (Duke Energy) submits the following comments on the draft National Pollutant
Discharge Elimination System Permit for Belews Creek Steam Station, issued for public comment by the North
Carolina Department of Environmental Quality ("NCDEQ") on November 15, 2016. Duke Energy appreciates
NCDEQ's efforts to develop the Draft Permit, which address novel issues associated with surface impoundment
decommissioning and modifications required to allow for continued operations while complying with various
Federal and State mandates. Finalizing this wastewater pen -nit is a critical step to advance that process by
authorizing decanting and dewatering of the ash basin and permitting replacement treatment options. In addition to
these general comments, Duke Energy offer the following comments and requests for modification and/or
clarification on specific provisions of the Draft Permit:
I. Thallium limitations are identified on pages 5, 7, 10, 11, 12, 13, and 14. Duke Energy requests that the
limits for Thallium be removed from the permit for the following reasons:
a) There is no adopted numeric water quality criterion for Thallium in North Carolina. With no
adopted criteria, the State has not provided any opportunity for public involvement or comment on
recommended constituent levels used in determining permit requirements. Unlike the defined
opportunity to comment on proposed criteria during the triennial review, the only means for public
involvement in this case is through commenting on specific permitting actions. The NCDEQ has
previously indicated no limits for metals would be included in permits for constituents without numeric
criteria. NCDEQ recently acknowledged this in issuance of the company's Sutton permit in which
NCDEQ proposed to include an effluent limit for Aluminum but withdrew that limit in the final permit
"because ...North Carolina does not have [an] Al standard...". North Carolina just completed an
update to its standards through the triennial review process but did not propose any standards for
Thallium.
b) The conclusion reached in the IRIS Toxicological Review (USEPA, 2009), which DEQ seeks to
base the limit on, was the available toxicity database for Thallium contains studies that are
generally of poor quality. Please see Attachment 1 - Evaluation of Toxicological Information of
Thallium prepared by Haley and Aldrich for Duke Energy. This information is included in the
attachment to these comments and should be considered part of our comments on the DRAFT
permit. In the USEPA Integrated Risk Information System (IRIS) Chemical Assessment Summary for
Thallium, it was stated "The available toxicity database for thallium contains studies that are generally
of poor quality" (USEPA, 2012a). In addition, there is not currently an oral chronic reference dose
(RID) toxicity value for Thallium established by the USEPA IRIS or from an USEPA Provisional
Peer -Reviewed Toxicity Value (PPRTV) assessment, which would be used to establish water quality

Page 12
criteria. Due to the significant uncertainty surrounding the study selection used to establish the values
for the 2002 water quality criteria and uncertainty to the relevance of adverse effects of Thallium , the
values used for the derivation of the 2002 Federal Water Quality Criteria for Thallium are questionable
and greatly overestimates potential risks associated with Thallium exposure. This is supported by
other regulatory and authoritative agencies concluding that the dataset is currently insufficient for
derivation of a non -cancer value for Thallium. In addition, current intakes of Thallium for a
substantial part of the population exceed the provision screening value with no reported adverse effects
reported, which also suggests that the current value is unrealistic for purposes of regulatory decision
making.
There is no record of a determination that any limit on Thallium is necessary to protect
narrative criteria. To the contrary, the record indicates that the receiving water currently meets
narrative criteria, despite a long history of similar discharges, indicating that effluent limits are not
necessary to protect narrative criteria or designated uses. The NCDEQ has not provided any
documentation that the factors required for consideration in developing a BPJ limit for Thallium have
been considered.
2. On page 2 of 29, 1— Outfall 003A, contributing flows to the Retention Basin do not include cooling tower
blowdown.
3. Duke Energy intends to construct two new lined coal pile collection basins location on the southwest and
northeast comers of the coal pile to collect stormwater runoff. These ponds will be in addition to the
existing north and south coal yard sumps currently discharging to the Ash Basin. The new coal pile basins
will be utilized to reroute the contact stormwater to the new Retention Basin. Duke Energy requests that
this language be added to the permit.
4. During the period beginning upon the commencement of operations of the new Retention Basin (Outfall
003A) and lasting through decommissioning of the Ash Basin (Outfall 003), there will be contributing
flows from Ash Basin for operation/maintenance for stormwater, decanting, and dewatering, and Retention
Basin for normal plant operations that discharge through Outfall 003/003A. Duke Energy requests
clarification on effluent limitations and monitoring requirements for Outfall 003/003A during the
transition when plant operational flow through the retention basin and the decanting/dewatering of
ash basin for decommissioning will comingle at this outfall.
5. On page 2 of 29, 1— Outfall 003A, the emergency overflow from the Retention Basin (rain in excess of
designed storm event) will be infrequent. Duke Energy requests that the emergency overflow be listed
as a contributing flow to the Ash Basin.
6. On page 5 of 29, Section A(3), (Outfall 003 — normal operations/decanting), Duke Energy requests
clarification that additional physical/chemical units are only required when process of pumping to
decant is employed.
7. On page 7 of 29, Section A(4), (Outfall 003 — dewatering), it is unclear how the flow limit of 2.0 MGD was
developed. For a facility the size of Belews Creek, this flow limit is too restrictive. Duke requests that
the flow limit be clarified to only apply to interstitial water treated through additional
physical/chemical treatment system.
8. On pages 4 and 7 continuous pH and TSS monitoring is included for decanting and dewatering activities. It
is requested that this requirement be restricted to in -process monitoring and allow for these parameters to
be limited by the routine monitoring.

Pa! 13
9. On page 18 of 29, Duke Energy requests that Toxicity testing remain a quarterly requirement until
dewatering commences. Duke Energy has never failed a toxicity tests at the Belews Creek plant and
monthly testing during normal operations is not supported.
Duke Energy welcomes any further discussion on our comments or the Draft Permit. If you have any questions,
please contact Joyce Dishmon at 336-394-5524 or [e-mail].
Sincerely,
/lI :� j /�
Richard E. Baker, Jr., P.E., PMP
Director, EHS-CCP Environmental Programs
Duke Energy
Attachment
Cc: Ms. Karen Higgins — Belews Creek Public Hearing officer
1617 Mail Service Center
Raleigh, NC 27699-1617
Bc: Keeley McCormick, EHS Professional II
Joyce Dishmon, Sr. Env Specialist
Shannon Langley, NRCH15

Attachment 1
Evaluation of Toxicological Information of
Thallium prepared by Haley and Aldrich for
November 2016 comment letter on Belews
Creek DRAFT NPDES permit

Thallium Toxicity Value Review
EVALUATION OF THE TOXICITY VALUE FOR THALLIUM
1. Current Screening Provisional Toxicity Value
There is not currently an oral chronic reference dose (RfD) toxicity value for thallium established by the
United States Environmental Protection Agency (USEPA) Integrated Risk Information System (IRIS) or
from an USEPA Provisional Peer -Reviewed Toxicity Value (PPRTV) assessment. The USEPA PPRTV
document for thallium (TI) concluded that it is inappropriate to derive a provisional subchronic or
chronic provisional RfD (p-RfD) for thallium; however, USEPA states that information is available which,
although insufficient to support derivation of a provisional toxicity value under current guidelines, may
be of limited use to risk assessors (USEPA, 2012). The PPRTV document contains a separate Appendix A
that provides rationale for the derivation of a subchronic and chronic "screening provisional oral
reference dose" for thallium compounds of 0.00004 mg TI/kg-day and 0.00001 mg TI/kg-day,
respectively. Appendix A of the PPRTV document also notes that, "Users of screening toxicity values in
an appendix to a PPRTV assessment should understand that there is considerably more uncertainty
associated with the derivation of a supplemental screening toxicity value than for a value presented in
the body of the assessment (USEPA, 2012a)." The screening p-RfD is expressed in units of milligrams of
thallium per kilogram of body weight per day (mg TI/kg-day).
Due to limitations in the toxicology database and general poor quality of available studies, the USEPA
IRIS Toxicological Review of Thallium and Compounds (USEPA, 2009) also concluded that reference
doses or reference concentrations could not be derived for human health following thallium exposures.
2. Information on Human Exposure to Thallium
The conservative nature of the p-RfD can be illustrated by considering the amount of thallium ingested
daily by Americans in their diet. It is estimated by the World Health Organization (WHO) and the U.S.
Agency for Toxic Substances for and Disease Registry (ATSDR) that a 70 kilogram adult ingests
approximately 0.005 mg thallium per day in the diet, especially from consumption of home-grown fruits
and green vegetables (WHO, 1996; ATSDR, 1992). This is equivalent to a daily dose of 0.00007 mg TI/kg-
day. The USEPA supplemental p-RfD for thallium is 1E-05 mg/kg -day (0.00001 mg/kg -day). This is seven
times lower than the estimated dietary intake. In other words, use of this dose -response value to
evaluate natural dietary exposure to thallium would indicate a hazard that is unlikely to exist.
Stated another way, assuming that an average adult weighs 70 kg, and using the screening level p-RfD of
0.00001 mg/kg bw-day, it could be concluded that an adult should not consume more than 0.0007 mg
TI/day, which is well below the estimated dietary intake of 0.005 mg thallium per day in the diet.
Currently, there have not been substantial reports of toxicological effects associated with typical dietary
ingestion of TI in the general population, suggesting that the use of the "screening provisional oral
reference dose" greatly overestimates the potential risks associated with oral exposure to TI
compounds.
The 901h percentile adult urinary thallium elimination from the National Health and Nutrition
Examination Survey (NHANES) (CDC, 2016) is 0.380-0.390 micrograms per liter (ug/L) which is about
0.760-0.780 ug/day in the urine alone. This suggests that greater than 10% of Americans, and probably
November 2016
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Thallium Toxicity Value Review
closer to 50% of Americans, ingest more than the screening level p-RfD. From the IRIS assessment
conducted in 2009, a reviewer stated that there is no evidence that thallium in the current U.S. diet
poses any threat, and the adoption of this screening level p-RfD would produce unnecessary concern if
the above calculation is correct. This indicates the poor quality of the existing data, and brings into
question the validity of the analysis using the available data on thallium used by USEPA (USEPA, 2009).
3. Derivation of the Current Screening Provisional Toxicity Value
Below is a summary of the data and assessment that was used by USEPA in the derivation of the oral
chronic screening level p-RfD for thallium.
3.1 HAZARD EVALUATION/STUDY SELECTION
Note: Human or animal studies examining the carcinogenicity of thallium following oral exposure are
not available. The cancer weight -of -evidence (WOE) provided in the IRIS review (USEPA, 2009) is listed
as "Inadequate Information to Assess Carcinogenic Potential (both oral and inhalation)."
�,1-1 human dies
Most information on thallium toxicity in humans comes from poisonings, suicide attempts, or accidental
exposures. Symptoms observed after acute exposures to high doses of thallium in humans include
alopecia (hair loss), gastrointestinal disturbances, and neurological symptoms such as paresthesia and
neuropathy. Epidemiologic studies of either the general population or occupationally exposed groups
are limited by inadequate study design, undefined exposure parameters, and inconclusive associations
between thallium exposure and specific health effects. Therefore, USEPA (2012a) concluded in the
PPRTV document that "available human studies do not support oral RfD derivation."
3.1.2 Animal studies
Studies in animals show that oral exposure to thallium produces effects similar to those observed in
humans, most notably, alopecia. Other findings observed in animal studies include biochemical
changes, lipid peroxidation, liver and kidney damage, and histopathologic changes in the brain and
nerves. The doses at which these systemic effects were observed range from 0.2 —1.8 mg TI/kg-day
(ATSDR, 1992). Reproductive and developmental studies in animals show some evidence of adverse
effects upon oral exposure to thallium at doses of 0.08 mg TI/kg-day —1.6 mg TI/kg-day; however,
available studies have significant limitations and the same effects have not been observed in humans
(ATSDR, 1992).
Only four repeat -dose oral toxicity studies with more than one dose level are available in animals. Of
these four studies, three were not considered adequate for RfD derivation (USEPA, 2009).
3.1.3 Conclusion
The conclusion reached in the IRIS Toxicological Review (USEPA, 2009) was that the available toxicity
database for thallium contains studies that are generally of poor quality. One animal subchronic study
conducted by the Midwest Research Institute (MRI, 1988) was selected as a candidate principal study for
November 2016 2

Thallium Toxicity Value Review
RfD derivation but was found to include critical limitations such as high background incidence of
alopecia, lack of histopathological examination of skin tissue in low -and mid -dose groups, and
inadequate examination of objective measures of neurotoxicity, thus making it difficult to select
appropriate endpoints. On this basis, a RfD for thallium salts was not derived by IRIS (USEPA, 2012a).
BASIS FOR PROVISIONAL SCREENING ORAL CHRONIC P -RFD
As indicated above, the PPRTV assessment (USEPA, 2012a) does not derive a typical provisional toxicity
value for thallium but rather uses the limited toxicological information to develop a screening level
value.
3.2.1 Study Selection
A 90 -day Good Laboratory Practice (GLP) oral gavage study in male and female rats conducted with
thallium sulfate by MRI (1988) was selected as the principal study for the screening level p-RfD. Doses
were approximately 0, 0.008, 0.04, and 0.2 mg TI/kg-day.
3.2.2 Selection of Point of Departure
Several critical endpoints were considered, but ultimately USEPA (2009) considered only two endpoints
to be appropriate for a screening level p-RfD development:
Hair follicle atrophy in female rats that also had alopecia; and
Clinical observations related to animal coat, eyes, and behavior.
The clinical observation endpoint was discounted because the underlying basis for the observations is
unknown. Hair follicle atrophy was determined to be most consistent with the atrophic changes
observed in cases of human thallium poisoning and may be best indication for human response to
thallium exposure.
MRI (1998) concluded that the minor dose-related changes in the study did not affect the health status
of the treated animals and were not toxicologically significant. MRI considered the highest dose (0.2 mg
TI/kg-day) as the no -observed -effect level (NOEL). However, USEPA conducted its own analyses of the
raw data from the study to come up with different conclusions. Of the 12 high -dose females with
alopecia, 5 instances were not totally attributed to barbering behavior. Histopathologic examinations
revealed atrophy of the hair follicles in two high -dose female rats that also had alopecia. It was noted
that there were no discernable differences in either the severity or distribution pattern of alopecia
across control and treated groups (USEPA, 2009).
The high dose (0.2 mg TI/kg-day) was identified by USEPA as the LOAEL. Because histopathology of skin
tissue from the low -and mid -dose groups was not conducted, the NOAEL for this endpoint cannot be
determined with certainty. Given the low incidence of hair follicle atrophy in females in the high dose
group and absence of cases of hair follicle atrophy in male rats, USEPA (2012a) assumed that the mid -
dose could be used to approximate a NOAEL for skin histopathology.
November 2016 3 ��ICH

Thallium Toxicity Value Review
Therefore, the estimated NOAEL of 0.04 mg TI/kg-day was used as the point of departure (POD) for hair
follicle atrophy (USEPA, 2012a).
Uncertainty Factors
Using the NOAEL of 0.04 mg TI/kg-day for hair follicle atrophy and using an uncertainty factor (UF) of
3000, the screening level p-RfD was calculated to be 0.00001 mg TI/kg-day. Justification for the applied
OF is summarized in table below.
Table 1: Uncertainty Factors Applied by USEPA in Screening Level p-RfD Derivation
Uncertainty Factor ! Justification
10 Extrapolation from laboratory animals to humans since no information is
available to characterize the toxicokinetic differences between experimental
animals and humans.
10 Variation in human susceptibility in the absence of information on the
variability of response to thallium in the human population.
10 Lack of adequate developmental toxicity studies and a two -generation
reproductive study, and additional uncertainty associated with the limited
data available on neurotoxicity.
3 Extrapolation from subchronic to chronic exposure duration. Effects on the
coat/skin as well as other clinical observations occur within weeks of exposure
to thallium (does not required chronic exposure in order to manifest).
Composite OF = 3000
Note that there are considerable and critical limitations with the principal study selected by USEPA
(2009) including:
High background of incidence of alopecia (POD selected)
Lack of histopathological examination of skin tissue in low -and mid -dose groups
Inadequate examination of objective measures of neurotoxicity
4. Other Available Sources for Derivation of Toxicity Values for Thallium
The following sections describe sources consulted for information on the toxicology of thallium.
4.1 WORLD HEALTH ORGANIZATION
The World Health Organization (WHO) (1996) concluded that in the general population, environmental
exposure to thallium does not pose a health threat. The total intake has been estimated to be less than
5 ug/day with the vast majority coming from foodstuffs; drinking -water and air generally contribute very
small amounts of thallium. Concentrations of thallium in urine may be considered a relatively reliable
indicator of exposure. Exposure to thallium resulting in urine concentrations below 5 ug/liter is unlikely
to cause adverse human health effects. The estimated daily oral intake corresponding to a urinary
thallium concentration of 5 ug/liter in urine is approximately 10 ug thallium in the form of a soluble
compound. Assuming an average adult body weight of 80 kg (USEPA, 2014), this would be equivalent
to 0.000125 mg/kg -day which is a 10 -fold factor above the USEPA screening level p-RfD. The WHO
November 2016 4

Thallium Toxicity Value Review
Task Group thus concluded that "in view of the considerable uncertainties in the evaluation, it was not
possible to recommend a health -based exposure limit. Until better information on the dose -response
relationship becomes available, it seems prudent to keep human exposures at levels that lead to urinary
concentrations of less than 5 ug/liter." In reviewing the animal studies, the WHO Task Group also noted
that, "it appears that an intake of 0.01 mg/kg -day may be associated with adverse effects. No doses
lower than this have been tested."
ATSDR (1992) notes, "Data on effects of intermediate duration oral exposure in animals do not reliably
identify the most sensitive target organ or the threshold for adverse effects. No data on effects of
chronic -duration oral exposure to thallium were located. Therefore, intermediate -duration and chronic -
duration oral minimum risk levels (MRLs) were not derived for thallium." Note that review of the MRl
1988 study (originally Stoltz 1986) was conducted by ASTDR but not used in the derivation of the MRL.
4.3 USEPA OFFICE OF WATER
USEPA's Maximum Contaminant Level (MCL) (USEPA, 2012b) for drinking water is 2.0 ug/L or 0.002
mg/L. The USEPA Human Health Water Quality Criteria (HHWQC) (USEPA, 2015) for thallium is 0.24 ug/L
or 0.00024 mg/L for the consumption of water and organisms from a surface water body, and is 0.47
ug/L or 0.00047 mg/L for the consumption of organisms only. These levels were derived based on the
90 -day subchronic study in rats (MRI, 1988).
4.4 CALIFORNIA EPA
In California, the MCL and Public Health Goal (PHG) for thallium in drinking water are currently set at 2.0
and 0.1 ug/L, respectively (CaIEPA, 1999, 2004). The Office of Environmental Health Hazard Assessment
(OEHHA) prepared the PHG for thallium in drinking water also using the MRI (1988) study in which
alopecia was observed in both male and female rats and consistent with other reports of toxicity of
thallium in both experimental animals and in humans. OEHHA determined that the incidence of
alopecia in female rats at the highest dose of 0.25 mg/kg -day represented a biologically significant
effect. Therefore, the no -observed -effect -level (NOEL) was identified to be the administered mid -dose
level of 0.04 mg TI/kg-day. For the calculation of the PHG, a cumulative uncertainty factor of 3,000 was
incorporated to account for the use of a subchronic study, uncertainty in inter -and intra -species
extrapolation and the steep dose -response curve. Based on these uncertainty factors, OEHHA derived a
PHG for thallium in drinking water of 0.0001 mg/L (0.1 ug/L). OEHHA notes that USEPA chose to
consider the dose that resulted in alopecia and increased serum enzymes indicated of liver damage as a
NOAEL, which is why the federal values are higher than those estimated by OEHHA.
4.5 CANADIAN COUNCIL OF MINISTERS OF THE ENVIRONMENT
The Canadian Council of Ministers of the Environment (1999) also adopted the USEPA screening level p-
RfD based on the MRI (1988) study as a provisional tolerable daily intake (TDI) for derivation of health -
based soil quality guidelines for thallium at contaminated sites in Canada.
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Thallium Toxicity Value Review
4.6 EUROPEAN UNION
No data were available on thallium or thallium compounds on the European Chemical Agency (ECHA)
Portal where the Registration, Evaluation, Authorization and Restriction of Chemical Substances (REACH)
Registration Dossiers are posted (ECHA, 2016). Thus, no derived no effect level (DNEL) is available for
thallium from this source.
4.7 OTHER
No other relevant data were located with respect to thallium toxicity since the publication of the USEPA
PPRTV assessment that could better inform the dose -response assessment and toxicity value derivation
for thallium.
S. Critique of Toxicity Value for Thallium
The current screening level p-RfD currently being used by USEPA as a toxicity value is a highly
conservative and inappropriate value for use in evaluating human health risks from oral chronic
exposure to thallium on the basis of: 1) the lack of appropriate toxicological studies on subchronic and
chronic exposures to thallium that provide relevant data and endpoints to be used in a dose -response
assessments; 2) the fact that other regulatory authorities (ATSDR, WHO) have concluded that sufficient
data on thallium does not exist and have not generated toxicity values for thallium and have placed a
low priority on development of additional toxicology data for thallium; 3) the study and POD using
alopecia as the endpoint as selected for the derivation of the screening level p-RfD by USEPA (2012a)
results in significant uncertainty to the applicability of the effects to human exposure to thallium; and 4)
the screening level p-RfD greatly overestimates the risk associated with human exposures as compared
to the typical ingestion of thallium in foods.
5.1 TOXICOLOGY DATABASE ON THALLIUM
The toxicity database for thallium in consideration of a dose -response assessment and derivation of a
toxicity value is limited. Low confidence in the screening level p-RfD is attributed to the limited
database including the lack of studies addressing the known toxic effects of thallium including
neurotoxicity, developmental toxicity, and endocrine effects, and failure of the MRI (1988) study to
identify a NOAEL of all relevant endpoints are considered. It is questionable as to whether a screening
level p-RfD should have been derived and if such an analysis is even valid knowing the database
limitations resulting in the application of such high uncertainty factors, given USEPA's own discussion of
the limitations in the PPRTV document (USEPA, 2012a).
5.2 OTHER REGULATORY SOURCES/VALUES
Most regulatory sources acknowledge the paucity of data for thallium and have not derived toxicity
values. USEPA IRS, WHO, and ATSDR have not generated oral chronic RfDs for thallium. For those that
have, the MRI (1988) study has been identified as the principal study despite the fact that it has not
been published in a peer-reviewed journal, did not provide statistical analyses, and the study did not
show a statistically significant dose -response effect for alopecia in male rats.
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Thallium Toxicity Value Review
On the Priority List of Hazardous Substances established by ATSDR last updated February 12, 2016,
thallium is listed as #275 out of 275 compounds indicating its low priority and concern for review
(http://www.atsdr.cdc.gov/SPL/). In addition, the National Toxicology Program (NTP) (2016a) has
reviewed petitions and proposals for conducting additional toxicology studies on thallium to decrease
the limitations and uncertainty with the current toxicology database but in a recent meeting on June 15,
2016, the NTP scientific board placed low priority on moving forward with these efforts.
One could infer that the low priority established by regulatory authorities on continued development
and review of the toxicology data for thallium indicates a low concern of the potential for human health
risk effects of oral exposures to thallium as compared to other compounds.
5.3 STUDY SELECTION AND POD
It has been questioned as to whether alopecia is considered an adverse event and should have been
used as the POD for the screening level p-RfD. USEPA has stated: "Whether alopecia is itself an adverse
effect merits consideration. In humans, alopecia is generally reversible upon cessation of thallium
exposure. Alopecia, however, appears to be a part of a continuum of dermal changes observed
following thallium exposure, as well as one of a spectrum of effects on target organs that include the
nervous and gastrointestinal systems. For these reasons, alopecia supported by two cases of hair follicle
atrophy is considered an adverse effect (USEPA, 2009)." USEPA (2009) acknowledged that other factors
such as caging and husbandry can cause alopecia in laboratory rodents; however, the incidence was
clearly elevated in both male and female rats over controls. Further, to the extent that alopecia was due
to barbering, research has shown that barbering in rodents can reflect a stress -evoked behavioral
response. For these reasons, some IRIS reviewers thought it was reasonable to use the alopecia as a
"biomarker" for adverse effects until additional studies are conducted to better identify adverse effects
of thallium exposures in animals and/or humans.
NTP (2016b) has also noted that the dose selection for the subchronic study was deemed inappropriate
for evaluation of alopecia since the 14 -day range -finding study performed prior to the 90 -day study
indicated hair follicle alterations together with decreases in body weight at a dose of 2.5 mg/kg -day of
thallium sulfate; however, a dose of ten times lower than that which effects were noted, 0.25 mg/kg -day
thallium sulfate was chosen as the high dose in the subchronic study. Further, review of the results also
show that there were challenges in distinguishing between normal hair cycling, self -barbering, and
incidences of true alopecia.
Since hair follicle histopathology and self -barbering is not a standard assessment in subchronic studies, it
is difficult to know whether what was observed in the MRI study (1988) is within the range of normal or
truly adverse. Therefore, the use of this endpoint as the POD brings considerable uncertainty to the
screening level p-RfD derived using these data.
No other studies have been identified by reviewers that could bring more certainty and validity to the
current screening level p-RfD proposed by USEPA (2012a).
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Thallium Toxicity Value Review
6. Final Assessment
Due to the significant uncertainty surrounding the study selection and uncertainty to the relevance of
adverse effects in the selected study and POD, the screening level p-RfD value as provided in Appendix A
of the USEPA PPRTV document for thallium (USEPA, 2012a) greatly overestimates potential risks
associated with exposure to TI. This is supported by other regulatory and authoritative agencies
concluding that the dataset is currently insufficient for derivation of a non -cancer value for TI. In
addition, current intakes of TI for a substantial part of the population exceed the provision screening
value with no reported adverse effects reported, which also suggests that the current value is unrealistic
for purposes of regulatory decision making.
Therefore, it seems most appropriate to establish a screening level based on the level of thallium in the
diet; clearly exposure to thallium at this level are without adverse effects. Using the information from
WHO (1996) that the estimated daily oral intake corresponding to a urinary thallium concentration of
5 ug/liter in urine is approximately 10 ug thallium in the form of a soluble compound, and assuming
an average adult body weight of 80 kg (USEPA, 2014), a RfD of 0.000125 mg/kg -day can be calculated,
which is a 10 -fold factor above the USEPA screening level p-RfD. This value is still a conservative
derivation, considering that it is well below the intake of 0.01 mg/kg -day that WHO indicated was the
lowest associated with adverse effects.
7. References
1. ATSDR. 2004. Toxicological Profile for Cobalt. U.S. Department of Health and Human Services,
Public Health Service, Agency for Toxic Substances and Disease Registry. Available at:
vvw.amlc.gov/toxprofiles/TP.asp?id=309&'id= 49
2. CDC. 2016. National Health and Nutrition Examination Survey. U.S. Center for Disease Control and
Prevention. Available at: http;/Iwww.cdc.gov/nchslnhanes!
3. CalEPA. 1999. Public Health Goal for Thallium in Drinking Water. Office of Environmental Health
Hazard Assessment (OEHHA). Available at:
hi.tp:/ioehha.ca.eovjmedia/downloads/pesticides/report/thaIf 1.pdf
4. CaIEPA. 2004. Update of Public Health Goal (PHG)-Thallium. Office of Environmental Health Hazard
Assessment (OEHHA). Available at:
http://oehlia.ca.9ov/media/download��esticides/report/thall1104.pdf
5. Canadian Council of Ministers of the Environment. 1999. Canadian soil quality guidelines for the
protection of environmental and human health: Thallium (1999). In: Canadian environmental quality
guidelines, 1999, Canadian Council of Ministers of the Environment, Winnipeg. Available at:
htt ce -rc e.ccme.ca download eri 215
6. ECHA. 2016. ECHA Portal for Registration, Evaluation and Authorisation of Chemicals (REACH)
Registered Substances. European Chemicals Agency (ECHA). Available from:
htt echa.euro a.eu information -on -chemicals re istered-substances
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Thallium Toxicity Value Review
7. OEHHA. 1999. Public Health Goal for thallium in drinking water. Office of Environmental Health
Hazard Assessment, Berkeley and Sacramento, CA. Accessible at
http:/iwww.ochha.ca.goy/water/phg/index.html
8. NTP. 2016a. NTP Board of Scientific Counselors Meeting. Webinar presentation. Thallium
Compounds. June 15. See: http.jlntp.niehs.nih.govJabouljorg/bsc/meeting5Jpast/index.html
9. NTP. 2016b. Draft NTP Board of Scientific Counselors Meeting. NTP Research Concept: Thallium
Compounds. June 15-16. Available at:
htt@:(lntp.niehs.nih.eovintp/about ntplbscJ2016/iunefinee#ing%20materialslthallium-
compounds 508. df
10. USEPA. 2009. Toxicological Review of Thallium and Compounds -In Support of Summary
Information on the Integrated Risk Information System (IRIS). September. Available at:
http Ilcfrrul,enctincea!irisPiris docume- 'dociiments/toxreviewsf101.2tr.pdf
11. USEPA. 2012a. Final Provisional Peer Reviewed Toxicity Values for Thallium and Compounds.
Superfund Health Risk Technical Support Center, National Center for Environmental Assessment,
Office of Research and Development, US Environmental Protection Agency, Cincinnati, OH.
Available at: httr)s_? hhr)ortv.orn!.p.ov/issue Dap ers/ThalliumSolubleSalts.pdf
12. USEPA. 2012b. USEPA 2012 Edition of the Drinking Water Standards and Health Advisories, Spring
2012. U.S. Environmental Protection Agency. Available at:
http://rais.ornf.gov/documents/2012 drinking water.pdf
13. USEPA. 2014. Human Health Evaluation Manual, Supplemental Guidance: Update of Standard
Default Exposure Factors. OSWER 9200.1-120. February 6, 2011. U.S. Environmental Protection
Agency. Available at: ,Lt nepis.epa.gov/Exe/ZyPDF.cgijP100NQNA.PDF?Docket'= P100NQNA.PDF
14. USEPA. 2015. Human Health Ambient Water Quality Criteria. U.S. Environmental Protection
Agency. Available at: htt s: www.e a. ov w c national -recommended -water- uaIit -criteria-
human-health-criteria-table
15. WHO. 1996. Thallium. Environmental Health Criteria 182. World Health Organization. Available
at: ttp://www.inchem.orp/documents/ehc/eh(,,`
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