HomeMy WebLinkAboutSmuggler Superfund - Technical Advisory CommitteeThornas S. Dunlop, Director
SMUGGI,ER MOUNTAIN TAC As Environmental
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FINAL REPORT, 1/27/93 Health Departm130 S. Galena
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SMUGGLER MOUNTAIN TAC 2
FINAL REPORT, 1/27/93
PREFACE
In 1986 the Smuggler Mountain Superfund Site in Aspen,
Colorado was officially placed on the National Priority List. This
listing led to a sequence of events typical for superfund sites
culminating in a Record of Decision in which EPA proposed certain
remedial actions. These events included several Site
investigations, including the analysis of soil samples which
indicated elevated concentrations of some metals, particularly
lead, in the vicinity of residences. While these events were
unfolding, an opposition to EPA's actions developed in the
community which eventually spread to include most, if not all, of
the citizens of the area. one of the catalysts for the opposition
was a blood lead survey performed by the Colorado Health Department
which found that the blood -lead concentrations in the pre-school
children at the Site were below that for the general U.S.
population. This, and other information prompted the local
government to withdraw from a previously negotiated settlement and
put a stop to further progress toward clean-up.
In an effort to resolve the differences between the Aspen
community and EPA, a meeting was held in Washington, DC on Feb. 28,
1.992 with Senators Wirth and Brown of Colorado, a delegation from
Aspen and EPA officials. One of the agreements to emerge from this
meeting involved the formation of a Technical Advisory committee
consisting of scientists familiar with the issues at stake at the
Site. The membership of the Committee ,was agreed upon jointly by
Aspen and the EPA.
The charge to the Committee was to review documents pertaining
to lead and to the Site; to receive testimony from experts
representing Aspen and the EPA; and to answer three questions
relating to: the level of present human risk, the future human
risk, and any public health measures that should be taken. The
Committee met in Aspen on Oct. 26, 27, and 28, 1992 to hear the
testimony and to decide upon its answers to the three questions.
On Oct. 28, 1992, the Committee released its findings at a
press conference. These findings are contained in the Executive
Summary of this document which was released to the media on Oct.
28. The remainder of the report is a critical review of pertinent
information. The format of this report follows the steps in the
risk assessment process recommended by the National Academy of
Science/ National Research Council Committee on the Institutional
Means for Assessment of Risks to Public Health.
The purpose of this report is to provide the basis for the
SMUGGLER MOUNTAIN TAC 3
FINAL REPORT, 1/27/93
findings and recommendations of the committee contained in the
Executive Summary.
While the process used to arrive at these findings can be used
fruitfully at other sites, it is important to emphasize that the
findings are unique to the Smuggler Mountain Site® Indeed, this
experience emphasizes the importance of evaluation on a site -by -
site basis.
The Smuggler Mountain Technical Advisory Committee
Willard R. Chappell, Ph.D.,Chair
Rufus Chaney, Ph.D.
Paul Hammond, DVM, Ph.D.
Mary Ellen Mortensen, M.D.
Alice Stark, M.P.H., Dr. P.H.
Iain Thornton, Ph.D.
SMUGGLER MOUNTAIN TAC 4
FINAL REPORT, 1/27/93
PREFACE.................................................Z
TABLEOF CONTENTS ................... o .... * .......... o..o4
i. MEMBERSHIP OF TECHNICAL ADVISORY COMMITTEE ..............6
I. EXECUTIVE SUMMARY .......................................7
ii. BACKGROUND .............................................10
II.A. The Site.......o ....................... 000 .............. 10
II.B. The Technical Advisory Committee (TAC) .................11
II.C. The Structure of the Report ............................12.
III. HAZARD IDENTIFICATION ..................................13
IV. DOSE -RESPONSE ASSESSMENT ...............................14
V. EXPOSURE, ASSESSMENT ....................................15
V.A. Sources of Contamination ......................... o ..... 15
V.B. Pathways of Exposure ...................................16
V.C. Confounding Factors ....................................19
V.D. External Dose ................ 6 ......................... 21
V.E. Absorption/Bioavailability ..............................21
V.F. Internal Dose ...........................................26
Vi. RISK CHARACTERIZATION .................................. 27
VI.A. Comparison With Other Studies ..........................28
VI.B. Possible Explanations of
Differences from Other Sites ...........................29
VI.B.1. Absorption/Bioavailability ............................29
VI.B.2. Attenuated Pathway ...................................31.
VI.C. Predictions of EPA's UBK Model ......................... 32
VI.D. TAC's Characterization of the Risk .....................33
SMUGGLER MOUNTAIN TAC
FINAL REPORT, 1/27/93
VII. RISK MANAGEMENT ........................................34
VII.A. EPA's Proposed Remediation ............................34
VII.B. Tae's Recommendations .................................35
VIII. REFERENCES ...........................................36
TABLE1 ....................................... o ...... 43
SMUGGLER MOUNTAIN TAC
FINAL REPORT, 1/27/93 1. 1
i. MEMBERSHIP OF SMUGGLER MOUNTAIN TECHNICAL ADVISORY COMMITTEE
Rufus Chaney, Ph.D.
U.S. Department of Agriculture
10910 Dresden Drive
Beltsville, MD 20705
Willard R. Chappell, Ph.D., Chair of TAC
Professor of Physics
Director, Master of Science of Environmental Sciences Program
University of Colorado at, Denver
Campus Box 136
P.O. Box 173364
Denver, CO 80217-3364
Paul Hammond, DVM, Ph.D.
University of Cincinnati Medical Center
3223 Eden Avenue
Cincinnati, OH 45267
Mary Ellen Mortensen, M.D.
Associate Professor, Clinical Pediatrics
The Ohio State University, and
Director, Central Ohio Poison Center
Division of Clinical Pharmacology/Toxicology
700 Children's Drive
Columbus, OH 43205
Alice Stark, M.P.H., Dr. P.H.
Director, Bureau of Environmental and
Occupational Epidemiology
New York State Department of Health
2 University Place, Room 130
Albany, NY 12237
Iain Thornton, Ph.D.
Director, Global Environmental Research Centre
Imperial College of Science, Technology and Medicine
56 Queen's Gate
London, England SW7 5JR
SMUGGLER MOUNTAIN TAC 7
FINAL REPORTO 1/27/93
SMUGGLER MOUNTAIN TAC
FINAL REPORTP 1/27/93
good nutritional status can reduce soil ingestion and/or reduce
lead absorption by children. The areas adjacent to the mobile
homes, houses, and condominiums in the study Site appear to be well
maintained. Characteristics of the community on this Site suggest
that the children are likely to have good nutritional status.
Recent estimates of soil/dust ingestion are in the range of 40 to
50 mg/day (median) in contrast to the 200i mg/day used in Superfund
Risk Assessments. If these new ingestion rates are used, along
with the Environmental Protection Agency's bioavailability
assumptions, the children's blood lead concentrations that were
observed would have been predicted.
The TAC will now respond to the questions posed. We emphasize that
the answers are specific to the unique conditions at the Smuggler
Mountain Site.
QUESTION No. 1: Does the existing site-specific data and
scientific literature provide adequate evidence which confirms that
the soil lead in the Smuggler Mountain superfund site poses a
current realistic health threat (i.e., unacceptable risk of disease
or impairment) to any of the residents on or near the Site?
ANSWER: The Committee unanimously concludes that the answer is no.
QUESTION No. 2: If the answer to question i above is no, is there
a reasonable probability of such a threat developing in the future?
ANSWER: The Committee unanimously, agrees that there is a
possibility
ility of a future threat, but the likelihood is small. if
the demographics, land use and environmental conditions remain
essentially unchanged at the Site, we do not anticipate any future
realistic health threat.
QUESTION No. 3: Having made this health threat assessment,, what is
the TACfs recommended public health action, if any, in order to
protect the current and future health of residents from the soil
lead effects?
ANSWER: The Committee unanimously agrees that since there is a
small possibility of future risk, the following recommendations are
prudent:
1. A program of blood lead surveillance should be instituted for
young children. At a minimum, the frequency of testing and
interventions should be consistent with the program for
children with low risk of high lead exposure as described on
Page 93 in "Preventing Lead Poisoning in Young Children" (CDC,
1991).
2. Although the Committee unanimously agrees that there is no
need for soil removal from the Site, the berm (the mound of
waste material adjacent'to the mobile home park and the
Smuggler tennis courts) deserves special attention. Because
SMUGGLER MOUNTAIN TAC
FIVAL REPORT, 1/27/93
101
of extreme contamination of the berm, it should be capped and
covered with clean soilo then planted with appropriate
vegetation. Monitoring should be instituted to ensure the
integrity of the cap and actions taken, if necessary, to
correct any breach of the integrity. As an interim measure,
the surrounding fence should be extended to completely enclose
the berm. Common -use areas, such as Molly Gibson Park,
presently comprised of exposed mine waste, should be
appropriately covered.
3. If owners wish to have vegetable gardens, these should be
planted in raised beds with at least 12 inches of clean soil.
4. Soil testing should be made available upon request by
residents.
5.
proposed changes in Site use should be reviewed by the City
and County Health Departments to evaluate possible changes in
soil exposure to young children.
6. If studies demonstrate that lead -bearing materials at this
Site have or can be made to have very low bioavailability, the
above recommendations should be reviewed and, perhaps,
modified.
SMUGGLER MOUNTAIN TAC 10
FINAL REPORT1 1/27/93
The Smuggler Mountain site has supported mining and milling
operations, primarily for silver and lead, since 1879. Most of the
activity occurred between 1879 and 1918. The operations at the
Smuggler, Molly Gibson, and Free Silver mines and the Cowenhoven
Tunnel have resulted in mine and mill (tailings) waste which were
deposited between the western side of Smuggler Mountain and the
Roaring Fork River. Some of these waste materials were leveled
when residential development took place and lie under or adjacent
to these developments.
The Smuggler Mountain geology is characterized by glacial,
alluvial, and colluvial sediments overlying sedimentary bedrock.
Outcrops of limestone, dolomite, sandstone and shale are common on
the slopes of Smuggler Mountain and contribute to the abundance of
calcium carbonate in the native soils which provide for a natural
buffering capacity and relatively high Ph values in the soils (ICF
Clement, 1986).
The Site is approximately 110 acres in size and is about 1
mile northeast of downtown Aspen, Colorado in Pitkin County. Aspen
is at an altitude of 7928 feet above sea level. The average annual
precipitation inAspen is 19.2 inches. The total annual snowfall
is 147 inches.
In 1981, David Boon, then a graduate student at Colorado State
University (CSU), took samples of soils in and around the area of
the Smuggler Mobile Home Park (Boon and Soltanpour, 1992).. The
purpose of the sampling was to test the fertility of the soils.
Several routine soil tests were conducted. These tests indicated
that the soil pH values ranged from 7.0 to 8.0 (saturated pastes),
with a mean of 7.5 indicating that nearly all the soils tested are
calcareous. In addition, a routine metals analysis on the soils
performed by the CSU laboratories, found very high levels of some
metals, particularly lead, zinc,
, and cadmium in some of these
samples. These results came to the attention of the local
government and recommendations were made to the site residents
regarding cautionary steps to avoid exposure to the contaminants.
In 1983 EPA visited the site to determine if it qualified as
a superfund site under the Comprehensive Environmental Response,
Compensation, and Liability Act of 1980 (CERCLA) , often referred to
as the Superfund Act. In 1984 EPA proposed the listing on the
National Priority List (NPL) of the Smuggler Mountain site and in
1986 the site was officially listed on the NPL. There were two
"operable units" (OU) defined within the Site. OU -1 consisted of
approximately 75 acres, primarily the residential areas at the base
of Smuggler Mountain. OU®2 was approximately 35 acres, exclusively
containing the Smuggler Mine and surrounding mine property. It is
OU®1 that is the focus of this report.
SMUGGLER MOUNTRIN TAC
FIXIAL REPORT, 1/27/93
Since 1986 EPA or its contractors have carried out the site
investigations mandated by CERCLA and developed a Record of
Decision (ROD) which outlined the selection of the site remedy.
This ROD has undergone revisions described in two Explanation of
Significant Differences (ESD) issued in 1989 and 1990. The
proposed remedies include the excavation of contaminated soils and
the use of a geo-textile liner covered with 1 foot of clean fill
and topsoil.
I
II.B. The Technical Advisory Comaittee (TAC)
In 1990 Pitkin County repealed settlement ordinances between
local government, EPA, and the State of Colorado because of -the
iesire of local citizens and local officials to more clearly
understand the health risk question prior to accepting a remedy.
The EPA decided to withdraw plans for Site clean-up for two year�*
to allow for the completion of studies to better clarify the health
risk.
on Feb. 28, 1992, EPA representatives, Senators Wirth and
Brown of Colorado, and a delegation from Aspen met to discuss a
number of community concerns relating to the Smuggler Mountain
Site. At this meeting the various parties agreed to the formation
of a Technical Advisory Committee (TAC) that was to consist of
scientists familiar with the issues involved in the dispute. This
committee would convene and review various site specific and lead
related documents and provide an independent assessment of the
health risk resulting from the presence of high concentrations of
mM tals in the soils at the Site.
in particular, the TAC would be asked to answer the following
three questions:
1. Does the existing site specific data and scientific
literature provide adequate evidence to confirm that the soil
lead in the Smuggler Mountain Superfund Site (Site) poses a
current realistic health threat (i.e., unacceptable risk of
disease or impairment) to any of the residents on or near the
Site?
a. If so, what is the primary evidence and the main
rationale for attributing a current realistic health
threat to the soil lead on the Site?
b. Also, what comprises this health threat (spectrum of
potential risk) stemming from exposure to the soil lead?
2. If the answer to question number one above is no, is there
a reasonable probability of such a threat developing in the
future?
a. If so, please provide information outlined in parts a.
SMUGGLER MOUNTAIN TAC 171
FINAL REPORTO 1/27/93
and b. in question I above.
b. If not, provide a summary of . the evidence and
rationale to support this conclusion.
3. Having made this health threat assessment, what is the
TAC's recommended action, if any, in order to protect the
current and future public health of the residents from the
lead?
The Technical Advisory committee has been asked to consider
several questions regarding the level of health risk from the
Smuggler Mountain Superfund Site. The executive summary provides
the Committee's answers to the questions posed above. This report
is meant to provide a more detailed explanation of the logic behind
these Answers. Because the questions relate to the issue of human
health risk, the format of this report will follow the
categorization of risk assessment adopted by the National Academy
of Sciences /National Research Council (NAS/NRC) Committee on the
Institutional Means for Assessment of Risks to Public Health (NAS,
1983).
The characterization of the potential adverse health effects
of human exposures to environmental hazards.
The NAS Committee stated that risk assessments contain some or
all of the following four steps: Hazard Identification, Dose -
Response Assessment, Exposure Assessment and Risk Characterization.
The NAS Committee further observed that
Regulatory actions are based on two distinct elements,
risk assessment, and risk__management. Risk
assessment is the use of the factual base to define the
health effects of exposure of individuals or populations
to hazardous materials and situations. Risk management
is the process of weighing policy alternatives and
selecting the most appropriate regulatory actions,
integrating the results of risk assessment with
engineering data and with social, economic, and political
concerns to reach a decision (NAS, 1983).
The three questions that the Technical Advisory Committee has
been asked to address involve both risk assessment (Questions I and
2) and risk management .(Question 3). Therefore, the TAC has
decided to structure the report in terms of the four steps of risk
assessment defined by the NAS Committee and risk management.
SMUGGLER MOUNTAIN TAC 13
FINAL REPORT61 1/27/93
The National Academy of Sciences Committee (1983) defined
Hazard Identification as:
Ae process of determining whether exposure to an agent can
cause an increase in the incidence of a health condition
(cancer, birth defect, etc.) - it involves characterizing the
nature and strength of the evidence of causation.
The adverse effects of lead on human health have been known
for centuries. As noted in the CDC (19 91) document, lead has, been
shown to have an adverse effect on virtually every system in the
body. These effects include (CDC, 1991; Davis, J., 1992) effects
on the heme system (f rank anemia, reduced hemoglobin production,
increased urinary ALA, erythrocyte protoporphyrin elevation, and
ALA -D inhibition) , ef f ects on the central and peripheral nervous
systems (encephalopathy, slowed nerve conduction velocity, and
ef f ects on cognitive development) , renal system ef f ects (chronic
nephropathy), reproductive effects (delayed physical development,
and low birth weight) , cardiovascular ef f ects (elevated blood
pressure), and gastrointestinal effects (c6lic)o These and other
adverse health effects (e.g., decreased hearing acuity) have been
demonstrated, to a greater or lesser degree of certainty, in
occupational and/or environmental health studies on humans.
Therefore, as noted by Houk (1992), we have a greater confidence in
the human health hazards presented by lead than we do f or those
compounds where only animal studies are available.
On the other hand, while human studies involve the species of
interest, there are many possible confounders and covariates
involved that can make proper interpretation of such studies
fifficult. in the case of lead, however, the fact that there have
been several such studies (Davis, J., 1992) with similar results
lends additional credibility to these findings. Moreover, as noted
by Davis, J. (1992), experimental studies of laboratory animals
have "'demonstrated parallels in the developmental neurotoxicity in
lead in children, primates and rodents."
As noted by CDC (1991) lead is "particularly harmful to the
developing brain and nervous system of fetuses and young children."
Of particular concern are the adverse effects on development
involving decreased IQ, hearing acuity and growth, at very low
blood lead levels. Several studies (Davis, J., 1992) in Boston,
Cincinnati, Cleveland, Port Pirie, Australia have shown decreased
cognitive ability and other neurobehavioral effects in young
children attributable to lead exposure. The cognitive effects may
be substantial, e.g., an average I.Q. drop of 7.2 points going from
an integrated postnatal blood lead of 0.5 Amol/L (10µg/dl) to 1.5
Amol/L (30 Ag/dl) (McMichael, et al., 1988). The general consensus
among experts seems to be that the risk of adverse effects on the
central nervous system becomes apparent as the 24 month or
integrated 2 year blood lead profile rises above 10 Ag/dl.
SMUGGLER MOUNTAIN TAC 14
FINAL REPORTI 1/27/93
In addition to the vulnerability. of children because of the
development of the central and peripheral nervous system, the
apparent higher absorption and retention of lead by children also
supports the conclusion that the target group for lead toxicity are
pre-school age children.
Thus, there is considerable evidence that lead is a hazard and
that the group most at risk is that of pre-school age (generally
less than 6 years) children.
The NAS Committee defined Dose -Response Assessment as:
The process of characterizing the relation between the dose of
an agent administered or received and the incidence of an
adverse health effect in exposed populations and estimating
the incidence of an effect as a function of human exposure to
the agent.
The CDC document (1991) indicates that there are several dose -
response curves for lead depending on the adverse effect of
interest. The more obvious and dramatic the effect, the higher the
threshold. EPA's Air Quality Criteria Document (US EPA, 1986)
Viscusses some of the dose response relationships for specific
ffects such as erythrocyte protoporphyrin, coporphyrin in urine
znd ALA -D in blood.
The blood lead level has long been used as a measure of
internal dose and/or internal exposure. While there are some
disadvantages to the use of blood lead as an internal dose (e.g.,
the half-life of lead in blood is on the order of 30 days, and
therefore may not give a measure of cumulative dose), both animal
and human studies have shown that blood lead increases with
external dose, and the response increases with increasing blood
lead.: Moreover, as noted in the Butte study (Bornschein, et al.,
1992), there is a high correlation among blood leads measured at
different times in a given child.
As noted by CDC (1991) and Davis, Jr (1992), there are several
adverse effects which have an "apparent" threshold blood lead level
at or below 10 Ag/dl. While these effects are subtle, and not
apparent on clinical examination, they are demonstrable in large
epidemiological studies which compare the results for relatively
large numbers of children with low exposures to relatively large
numbers of children with higher exposures® Since the history of
lead has been a decrease in the blood lead concentration defined as
the level of "concern," due to the development of increasingly
sensitive measures of exposure and effect, it would not be
surprising to see another lowering of the level of "concern"
sometime in the future.
SMUGGLER MOUNTAIN TAC 15
FINAL REPORTOP 1/27/93
TNomittee defined Exposure Assessment as;
The process of measuring or estimating the intensity,
frequency, and duration of human exposures to an agent
currently present in the environment or of estimating
hypothetical exposures that might arise from, the release of
new chemicals into the environment. Tn its most complete
form, it describes the macfnitude, duration, schedule, and
route of exposure; the size, nature and classes of human
populations exposed- and the uncertainties in all estimates.
f
SMUGGLER MOUNTAIN TAC if
FINAL REPORT, 1/27/93
V.B. Pathways of Exposure5-
The primary pathway of interest for lead exposure at Smuggler
Mountain is presumed to be the ingestion of soil and dust by
children. As noted by CDC (1991):
Rs a part "of normal play and hand-to-mouth exploratory
aFtivities ' young children may inhale or ingest lead'from
soil or dust. ingestion of dust and soil during meals
and playtim,e activity appears to be a more significant
pathway than inhalation for young children (EPA, 1986).
The pathway from soil lead to blood lead is discussed in the
Butte report (Bornschein, et al., 1992). It involves a complex
interaction between outdoor soil lead, indoor house lead, lead on
the hands of children, and, finally, blood lead or internal
exposure or dose (blood lead is sometimes considered to be a
measure of'internal exposure and other times to be an internal dose
measure).
Several studies have documented this pathway in different
settings. Ono of the key factors in estimating the risk of this
exposure pathway is the amount of soil/dust ingested by young
children. EPA uses a default value of 100 mg/day for children in
its Uptake Biokinetic (UBK) Model, but as a matter of policy uses
200 mg per day for evaluating the risk at superfund sites (Porter,
1989).
As recently as 1985, on the basis of experimental evidence it
could be concluded that an average value of 100 mg per day was
appropriate and supported by the best available research in respec
to children between 1 and 4 years of age. This value was based o
the results of studies by Binder et al. (1986), and Clausing, e
al. (1987) using elements such as Aluminum, silicon, and titaniu
as stable markers. This f igure of 100 mg per day conf irme
estimates proposed in rather an arbitrary fashion in a series o
earlier publications. LaGoy (19empted to use these result
as a basis for a risk assessment and concluded that a value of 10ii
mg per day could be used as a soil ingestion rate for an averag
child between 1 and 4 years, with a maximum rate of ingestion o
500 mg per day. He selected the higher value on the basis o
prudence rather than scientific merit. With regard to infants i
the first year of life, he concluded that 50 mg could be used as a
estimate of the average soil ingestion rate. For older childre
and adults he then assumed that soil ingestion would be reduced
at least 50% and suggested 50 mg per day as an average with
maximum of 250 mg per day. It is emphasized that LaGoy's estimate
of soil/dust ingestion by children of I 'to 4 years of age wer
based on the results of experimental studies available at tha
time, but the values for younger and older children and adults wer
derived mainly by making,intuitive assumptions.
More recent experimental work has since been undertaken to
SMUGGLER MOUNTAIN TAC 1.7
FINAL REPORT, 1/27/93
Calabrese et al. (1 990) providethe first published estimates
if amounts of soil ingested by adults, using data collected as part
of the validation exercise for the study reported above in
children. They refer to this as a pilot study and to the, results
as being of a preliminary nature, as they are based on only 6
adults (3 males and 3 females aged 26 to 41 years) over a 3 week
period. They reported median values ranging from 1 to 65 mg of
soil/dust ingested per day, depending on the element used as a
tracer, (i.e., 1 mg per day if silicon was used, 52 mg if aluminum
was used, 65 mg if yttrium was used and no ingestion at all if
zirconium was used). The average of the four median tracer values
is 30 'Tag per day. However, the very limited nature of this study
is noted together with the disparity between the estimates, for
adult soil/dust ingestion according to the tracer element used.
Davis, et al. (199o) published the results of a population -
based estimate of soil ingestion in 104 normal children between the
age of 2 and 7 years, using the elements aluminum, silicon and
titanium as stable markers. Aluminum provided a median value of 2,5
mg of soil ingested per day, silicon 59 mg and titanium 81 mg per
day. In the'light of the findings of Calabrese et al. (1989), it
appears that titanium can no longer be accepted as a reliable
tracer.
Van Wijnen et al. (1990) studied soil/dust ingestion in 1 to
SMUGGLER MOUNTAIN TAC 18
FINAL REPORT, 1/27/93
5 year old children in the inner cities and suburbs of Amsterdam
and Utrecht, Netherlands, by measuring titanium, aluminum and acid -
insoluble residue in soil and feces. They attempted to correct the
results for non -soil sources of these elements by using data for
parallel hospitalized children. The "limiting tracer method" that
they adopted at all times uses the lowest of the three separate
estimates to calculate soil ingestion. For around "200 children
sampled from day-care centers, geometric mean soil intakes ranged
from 0 to 90 mg per day. For children younger than 1 year, these
estimates were lower, ranging up to 30 mg per day. It is noted
that this study assumed a daily average stool (feces) dry weight of
15 g. on the basis of the later findings of Thompson and Burmaster
(1991) outlined below, it is likely that the use of this figure in
calculations of soil ingestion will lead to an excessive value,
over estimating soil/dust ingestion by as much as a factor of 2.
Thompson and Burmaster (1991) published a re-evaluation of
data collected by Binder et. al (1986). This re-evaluation used
actual stool weights, rather than the assumed figure of 15 g used
by Binder. The result of this more detailed and accurate approach
was to lower both mean and median soil ingestion values by a factor
of 2.' Using the elements aluminum and silicon, which seemed to
provide the most reliable data, these authors calculated an overall
average median soil ingestion rate for children of 59 mg per day.
On the basis of the above it is now proposed that previous
estimates of 100 mg per day as an average soil/dust ingestion rate
for children were too large. The reason for these estimates were
due to incomplete experimental procedures used in the early
investigations. In the light of more recent evidence, it would
seem reasonable to assume a median value of approximately 50 mg per
day for children within the age groups of I to 7 years.
In calculations on lead ingested as dust and soil, the U.S.
E.P.A. (Porter, 1989) assumed that children ingest twice as much
dust as adults. While it may be argued that this is based on
intuitive rather than experimental procedures, nonetheless it may
be assumed that adults certainly would not be expected to ingest
more soil/dust than children (although it should be noted than in
some sub -cultures, deliberate soil ingestion has been practiced).
This assumption is supported by,the results of Calabrese et al.
(1990), where on the basis of very limited evidence a median value
of 30 mg per day was estimated.
In conclusion, on the basis of the evidence available at this
time, the following assumptions of median soil/dust ingestion
values are recommended as being reasonable:
5.0 mg per day for the 1 to 7 year old child,
25 mg or less per day for children under 1 year of age,
25 mg per day for adults.
SMUGGLER MOUNTAIN TAC 1.9
FINAL REPORT, 1/27/93
A 0
v.c. Confounding Factor3
A substantial and consistent literature exists (stark et al
1978, Stark et al 1982, Chatterjee and Geltman 1972, Lansdown et al
1974, Nullian et al 1956, Rennert et al 1970, Rummo et al 1979,
Schroeder 1989, Schroeder et al 1985) which identifies a set of
demographic and behavioral factors that are associated with blood
lead concentrations in children independent of environmental
exposure levels. The characteristics associated with increased
blood level concentrations are those that tend to impair the
ability of a family to provide the necessary care, and supervision
for a young child. These characteristics are not always, directly
SMUGGLER MOUNTAIN TAC 20
FIVAL REPORTO 1/27/93
SMUGGLER HOURTRIN TAC 21
FXNAL REPORT, 1/27/93
Moreover, these differences are all in the direction (e.g., Aspen
residents earn higher wages) that would tend to lower the amount of
exposure by the Smuggler Mountain children (Bornschein, et al.,
1992).
I
SMUGGLER MOUNTAIN TAC 22
FINAL REPORTI 1/27/93
lead ingested with meals could be due in part to a co -precipitation
of lead with calcium -phosphate formed in the duodenum. This last
suggestion was based on research conducted to clarify the role of
diet constituents on absorption of 203Pb by human volunteers. If
the test meal contained about 50% of the daily Ca intake, Pb
absorption was reduced from 60% on fasting to 5-15%; if the test
meal contained about 50% of the daily P intake, Pb absorption was
reduced from 60 to 45%; but if both were present in the test meal,
absorption was reduced to as low as 1.5% (Blake and Mann, 1983;
Heard et al., 1983; Heard and Chamberlain, 1982). Bioavailability
of dietary Zn was reduced in cow's milk compared to human milk
because higher Ca in cow's milk than human milk caused extensive
coprecipitation of Zn when acid treated cow's milk was raised to
the pH of the small intestine (Nelson et al., 1987) ., One would
expect Pb coprecipitation to be much more extensive than Zn
coprecipitation, but this has not been studied (see discussion of
pyromorphite formation below).
in a series of papers by Ruby, et al. (1992), Davis, A., et
al. (1992), and Hemphill, et al. (1991), the bioavailability of
lead in soils and other materials from the Butte, MT area was
investigated both theoretically and in laboratory animal studies
using rabbits. The predominant lead forms in these samples were
found to be lead sulfide, lead sulfate (anglesite) and lead
sulfides with rinds of anglesite. More than 80% of the soil lead
in these samples occurred as either anglesite (60-70%) or sulfide
(10-25%) (Ruby, et al., 1992). Besides the evaluation of chemical
speciation of Pb in the soil materials, these authors conducted in
vitro bioavailability assays which attempted to simulate the
conditions of the stomach and then the small intestine. They
looked at the kinetics of release of Pb from the soil materials and
from pure minerals, and found that PbSO4 and PbS could not dissolve
rapidly enough to have high bioavailability. They have not
reported fully on the effects of soil properties on Pb solubility
in the simulated small intestine phase of the assay, but noted
rapid and strong adsorption/precipitation of Pb after raising the
pH of the simulated gastric compartment. The authors concluded
that the lead in these materials had a very low bioavailability.
An extensive laboratory animal study using rats was performed
by Battelle (1991) (see also Freeman et al., 1991; Freeman et al.,
1992) using mining waste soils from the Butte, MT area. These
materials were reported to contain 28% anglesite, 17% galena, 284
coronadite (a manganese lead mineral; may be simply Pb adsorbed on
Mn02) and 22% lead phosphate in one case and 53% anglesite and 24
% galena (taking only the major phases) in the other case. Varied
%-soil were mixed into purified diets and fed for 30 days. Bone,
blood, and liver were analyzed for Pb. In contrast with the linear
dose -response pattern seen with pure Pb -compounds, tissue Pb
concentrations approached a plateau with increasing soil dose.
These materials were found to have a low bioavailability (about 9%
of Pb -acetate, and Pb -acetate is presumed to be equivalent to food
Pb) in these studies as well. One of the most important
conclusions from this work is the shape of the blood Pb vs. soil
SMUGGLER HOUVTAIN TAC 23
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SMUGGLER MOUNTAIN 'SAG 24
FINAL REPORT, 1/27/93
SMUGGLER MOUNTAIN TAC 25
FINAL REPORTP 1/27/93
one of the issues that has arisen in doing laboratory animal
studies of bioavailability is the choice of the appropriate animal
model. Weis and LaVelle (1991) have noted that coprophagy and
different feeding behaviors might make rats and rabbits less than
ideal, for such experiments. Coprophagy can be partly prevented by
different cage designs and other devices.
Another possible confounding factor is the time required for
ingested 'material to pass through the GI tract, or GI Transit Time.
It would be expected that this time would be shorter for small
animals than for large animals (Mordenti and Chappell, 1989). For
example, the gut beat duration for mammals follows this behavior,
(Adolph, 1949). if this were the case, there would be less time
for materials to dissolve as they passed through the
gastrointestinal tract of a rat than for that of a small child. On
the other hand, young swine have about the same body mass as an 18 -
month -old child. However, information regarding GI transit times
in species of widely varying size is largely unavailable.
There have been,however, some recent studies of GI transit
time for humans and some laboratory animals using gamma
scintigraphy. Davis, et al. (1986) found that the major factor
affecting transit time in humans was the presence of food which
SMUGGLER MOUNTAIN TAC 26
FINAL REPORTP 1/27/93
tended to slow the transit. In another study using pigs (Hossain,
et al., 1990 the authors found that, although pigs have many
similarities regarding GI tract with humans, the gastric emptying
time in pigs is much longer than for humans (it should be noted
however, that the pigs were ingesting capsules that were roughly
10x20 mm in size).
In summary, while some very interesting work on
bioavailability has been presented, there are still many unresolved
questions as these studies relate to the Smuggler Mountain
situation. The animal studies used material which is demonstrably
different from the Smuggler Mountain tailings and soils in mineral
composition. In addition, all of the animal models have
deficiencies in the relationship to humans. The arguments based on
geochemical models, while interesting, are not convincing in the
absence of animal testing. Thus, no conclusions can be drawn
concerning the relative bioavailability of lead in the Smuggler
mountain tailings and soils.
V.F. internal Dose.
At the present time the accepted measure of internal dose or
internal exposure is blood lead (CDC, 1991). During August and
September, 1990, a blood lead survey of the residents of the
Smuggler Mountain site was carried out by the Colorado Health
Department with funding from the Agency for Toxic Substances and
Disease Registry (ATSDR) . This survey was carried out using a
methodology common to several other studies which have been done
recently, with the notable exception that no soil or dust samples
were collected in conjunction with the study. (The soil lead data
used was collected in conjunction with a previous study.)
I
The door-to-door census phase of the study identified 65
children aged 6 months through 14 years. Forty-nine of these
children (75%) participated in the study. The geometric mean blood
lead (PbB) for the 28 children aged 6 through 71 months who
participated was 2.6 pg/dl, with an arithmetic mean of 3.0 Ag/dl
and a geometric standard deviation of 1.66. For the children aged
6 years through 14 years the geometric mean PbB was 1.8 Ag/dl. -of
143 randomly selected adults, 76 (47%) submitted to blood lead
testing and the geometric mean PbB was 2.9 Ag/dl.
of the children tested, only one had a blood lead greater than
10 Ag/dl. This 14 year old male with a PbB of 13.4 Ag/d1 was
retested 3 months later and found to have a PbB of 2.1 Ag/dl. In
the report, several possible sources of exposure for this subject
were mentioned, including leaded gasoline and mine tailings
exposure while riding his motorcycle. Later investigations
revealed that leaded gasoline was used in the motorcycle and that
the subject frequently rode the motorcycle over tailings material.
It was suggested that because after being warned of the exposure,
the subject avoided the tailings area, that the much lower blood
lead on the retest was due to a curtailed exposure.
BMUGGL I ER MOUNTAIN TAC
FINAL, REPORT, 1/27/93
WA
However, there are other explanations of the elevated blood
lead on the first test, including contamination during sample
collection; namely, Pb -containing dirt on the skin, dust
contamination of the blood collection materials (needle, syringe,
or contamination of the tube into which the blood was drawn.
it is possible, but less likely that laboratory error may account
for the high blood lead. The Centers for Disease Control
Laboratory performed the blood lead analyses. This laboratory is
highly reliable and has established and conducts a national PbB
proency testing program.
A major strength of the CDH study is that the PbB
determinations provide a means to characterize health risk to
children living on the Smuggler Mountain site. Results can be
interpreted using the large body of research on the human
toxicology of Pb, without having to extrapolate from animals or
t
The CDH report includes a lengthy discussion of the study
limitations. Notably, the results represent only a single measure
of PbB, reflecting relatively recent exposure. Serial blood leads
would be necessary to more accurately draw inferences about chronic
..... and Pb body burden in each childo Apparently, historical
blood lead data were not available in the study. participants.
However,while it is true that blood leads relate to relatively
recent exposure (the half-life of lead in blood is approximately 30
days) , the time at which the study was conducted (late summer/early
fall) is the period during which the highest blood leads tend to
occur (U.S.E.P.A.0 1986).
As noted earlier, soil sampling on the Site was not done at
the same time as the blood lead survey, thereby limiting the value
of the soil samples in interpreting the blood lead concentrations.
While the report contains. the results of correlation analyses
between blood lead and soil lead concentrations, these results
should be viewed with considerable skepticism. In addition, other
potential pathways of Pb exposure in the study participants were
not evaluated, such as lead-based paint, lead concentrations in
play area soils, hand dust, interior dust, drinking water, or
dietary sources.
T I he committee concludes that, in spite of the lack of
environmental data, the blood lead survey was well-planned, well -
implemented and the results representative of the community at that
time. Moreover, because of the time period, it is unlikely that
blood leads at other times of that year would be higher than those
found in the study, unless exposure changed significantly.
The NAS Committee defined risk characterization as:
The process of estimating the incidence of a health effect
under the various conditions of human exposure described in
SMUGGLER MOUNTAIN TAC 28
FINAL REPORT, 1/27/93
exposure assessment. it is performed by combining the
exposure and dose -response assessments. The summary effects
of the uncertainties in the preceding steps are described in
this step.
Three other blood lead studies have been conducted recently in
Colorado communities where mining, milling and/or smelting
activities took place in the past. These sites were Leadville,
Telluride, and Clear Creek/Central City. Table 1 summarizes the
results of these studies.
The comparison with the Telluride and Leadville studies suffer
because of the time lag. Bornschein (1992) has pointed out the
overall decline in blood leads with time. The CDH (1992a) report
.on the Smuggler Mountain study points out numerous differences
between the Leadville and Smuggler Mountain Sites, which probably
invalidates any direct comparisons between the two sites. These
sites differ in the nature, extent and recency of mining activities
and presence of smelter operations. They also differ with respect
to the extent of contamination, the quality of soil cover, and the
possible presence of lead-based paint. Furthermore, the Leadville
study population appears tobequite different in terms of age of
housing, income status, ethnicity and, perhaps, nutrition (CDH,
1992a) . These differences underscore the importance of considering
site-specific characteristics that may influence exposure and/or
human health risks.
The studies in the Clear Creek/Central City site and the
Smuggler Mountain site were carried out at virtually the same time.
In both cases there was only mining and milling. Although the
median and maximum soil lead concentration values are significantly
higher at the Smuggler Mountain site than at the Clear
Creek/Central City site, the blood leads at Smuggler Mountain are
significantly lower (geometric mean of 2.6 gg/dl versus 5.9 µg/dl).
It is important to note that both studies used the protocol
developed in the Leadville study, with the exception -that no soil
samples were collected in the Smuggler Mountain study as, mentioned
earlier.
Unfortunately, the only large, nationwide survey of blood
leads whose data is available was the NHANES II (National Health
and Nutrition Evaluation Survey II) that was performed in the
1970s. The data from NHANES III is not yet available. The US EPA
(1989) has a model for predicting blood leads on a regional and
national scale. This model was used to predict a "baseline"
geometric mean for 2 year old children of 4.2 - 5.2 pg/dl.
Thus, the blood lead concentrations found in Aspen are below
other sites investigated in Colorado. In fact, -to the knowledge of
the TAC members, the geometric mean blood lead concentrations found
in the Smuggler Mountain study are less than those reported for any
other group that has been studied with one exception. In 1974
SMUGGLER MOUNTAIN TAC 29
FlNhL REPORT, 1/27/93
one possible source f or the dif f erences between the blood lead
concentrations Smuggler Mountain and those found at other
contaminated sites could be in the relative bioavailability of
soil -lead form at the different sites4 However, no research has
specifically tested the bioavailability of soil -Pb from Aspen.
Based on available information, the bioavailability of Aspen soil -
Pb under worst -,case fasting conditions may not be lower than found
in other areas for similar soil Pb concentrat ions. The work of
Drexler (1992) on soils from Aspen showed that little of the soil
Pb was galena or other highly insoluble or rinded (occluded)
mineral forms. These latter forms of soil Pb were found to have
low bioavailability to rats, rabbits, and in in vi tro
bioavailability extraction methods (Ruby et al., 1992; Freeman et
al., 1992; Davis, A., et al., 1992).
However, other factors which strongly affect Pb absorption in
SMUGGLER MOUNTAIN TAC 30
FINAL REPORT, 1/27/93
human volunteers may be important in explaining the low blood -Pb
levels found here. First, the presence of food in the gut has been
shown to buffer the stomach pH to much higher levels than found in
fasting (Malagelada et al., 1977) . Second, the presence of food in
the gut has been shown to remarkably reduce the absorption of Pb
compared to fasting, from 60-80% absorbed to 1-10% absorbed (James
et al., 1985; Heard et al., 1983; Rabinowitz et al., 1980).
Besides the role of food in pH buffering and reduction in
dissolution of Pb minerals, food constituents can adsorb or
coprecipitate Pb. If children in Aspen have better care and
receive meals on a regular basis, the timing of food in the stomach
rftay prevent them from reaching the high levels of Pb absorption
found in fasting humans. James et al. (1985) showed that food
consumed at least 3 hours before a Pb dose, or up to approximately
2 hours after a Pb dose substantially reduced Pb absorption, even
for • bioavailable soluble Pb salts used in their tests.
Thus, consumption of meals on a regular •. three • more time -9
1!er day can interfere with soil Pb risk compared to the worst case
inner city •w• unsupervised child who may miss one ♦ more meals
taily,. may be malnourished, and who is believed to be at risk when
soil Pb exceeds 500-1000 mg/kg (Porter, 1989).
Further, adequate Ca nutrition and Fe nutrition can minimize
Pb absorption by animals according to many studies. However, few
studies have been conducted with humans., and the studies to
evaluate effects of Fe or Ca nutritional status on Pb absorption by
children have mostly been indirect tests rather than the controlled
variable studies which were possible with adults. At least Ca
nutrition has been shown to significantly affect Pb absorption by
children.
Many studies have shown that Fe deficiency in many animal
species caused increased Pb uptake (Mahaffey and Michaelson, 1980) .
However, the effect of Fe nutritional status remains somewhat
confusing, and no clear conclusion is possible regarding children.
. Clinical trials were conducted to test whether Fe
supplementation of children with high blood Pb could reduce blood
Pb concentration. Angle et al. (1975) found a small and nearly
significant increase in blood Pb in response to FeSO4
supplementation. Their work even included a double-blind study.
Further, in an evaluation of the results of the NHANES-II results,
Mahaffey and Annest (1986) did not find a specific effect of Fe
deficiency on blood Pb concentration.
The effect of Ca nutritional status and Ca level in the diet
on Pb absorption has also been studied extensively (see Mahaffey,
1982; Mahaffey and Michaelson, 1980). Work by Six and Goyer
(1970), Mahaffey et al. (1973), and Mahaffey et al. (1977) clearly
showed that Pb uptake was enhanced much more by deficient levels of
Ca than it was decreased by supraoptimal levels of Ca. Mahaffey et
al. (1973) also found that the increase in blood Pb due to Ca
deficiency was much more pronounced at low Phi intake than at high
SMUGGLER MOUVTAIN TAC
FINAL REPORT, 1/27/93
Pb intake, indicating
dietary Cia in Pb risk -
of children may ingest
have a high incidence
M
even more importance for the ro I le of low
o children. Although all economic classes
low levels of diet Ca, poor urban children
*f low Ca intake (Mahaffey, 1982).
Further, when Ca and P are at high levels in the diet, Pb may
coprecipitate in the intestine. Pb absorption in fasted adult
humans was reduced in proportion to Ca level in the diet (Blake and
Mann, 1983). It appears that reduction in Pb absorption by humans
with normal or high intakes of Ca can be due to 1) reduction in the
Ca binding protein/carrier 'in -the intestine; 2) direct competition
between Ca and Pb uptake in the intestine; and 3) coprecipitation
M f Pb in the intestine.
The effect of dietary Ca on blood -Pb levels in children has
been assessed in several research studies which attempted to better
characterize this relationship. These included the finding that
absorption/retention of Pb from pediatric foods was significantly
reduced with increasing Ca concentration in the diet (Ziegler et
al., 1978). Mahaffey et al. (1986) noted that improved public
health measures aimed at increasing intake of Ca and dairy
products, particularly in low-income black and white urban
dwellers, might reduce Pb risk to urban children. Socioeconomic
and demographic factors of the Aspen community indicate that little
reduction in blood Pb would be expected from Ca supplementation of
Aspen children because they are likely to have adequate Ca
nutrition already.
Thus, while evidence presented concerning the relative
bioava,ilability of lead in the tailings/soil/dust material at the
Smuggler Mountain Site was either irrelevant or unconvincing, there
are other factors such as the dietary characteristics of the
population at that site which would tend to lead to lower
absorption of the lead in these materials.
VI.B.2. Attenuated Pathway
There is a significant difference in the s,oc ia 1 -economic
status of the population studied in Aspen compared to the other
sites. Unfortunately, the SES data for the Clear Creek/Central
City study has not been compiled. But, the CDH (1992a) report on
the Smuggler Mountain study does make a comparison with Leadville.
It is clear that the Smuggler Mountain population is far more
affluent than the Leadville population. While the Clear
Creek/central City population was probably somewhat more affluent
than that in Leadville, it was certainly more like Leadville than
it was like Smuggler Mountain (personal observation, W.R.Chappell) .
This relative affluence could be expected to result in child
care behaviors, nutritional status and personal and residential
hygiene practices that would tend to reduce soil/dust ingestion.
As noted in the previous sections, these factors may also impact
the kinetics of absorption of lead from the GI tract, binding of
lead to both hard and soft tissues and renal excretion.
I.Al GGL ER-VMUNTA71-&N-�'O���-2
FINAL REPORT, 1/27/93
SMUGGLER HOURTAXN TAC 33
FXNAL REPORT, 1,/27/93
34
lognormal probability distribution) the probability of finding a
child with a blood lead level above 10 pg/dl and 15 pg/dl. These
probabilities are 0.4% or 4 in a thousand for blood leads above 10
Ag/dl and 0.03% for blood lead concentrations above 15 Mcg/dl.
While the number of subjects in the Aspen study (28) was not
as large as in some studies, if the upper 95% confidence limit on
the geometric mean obtained by CDH (1992a), which is 3.1 gg/dl, is
used (with the same geometric standard deviation), then the
probabilities of finding a child above 10 and above 15 ,fig/dl are 1%
and 0.1%, respectively. That is, it is unlikely that the risk of
a child having a blood lead concentration higher than 10 or 15
µg/dl is higher than 1 in a 100 or 1 in a 1,001, respectively.
Two of the questions posed to the Committee involved the issue
of present or future realistic health threats. These questions
were:
QUESTION No. 1: Does the existing site-specif ic data and
scientif ic literature provide adequate evidence which confirms
that the soil lead in the Smuggler Mountain Superf und Site
Floses a current realistic health threat (i.e., unacceptable
risk of disease or impairment) to any of the residents on or
near the site.
ANSWER: The Committee unanimously concludes the answer is no.
QIESTION No. 2: If the answer to question I is no, is,there
a reasonable probability of such a threat developing in the
future?
ANSWER: The Committee unanimously agrees that there is a
possibility of a future threat, but the likelihood is small.
If the demographics, land use and environmental conditions
remain essentially unchanged at the Site, we do not anticipate
any future realistic health threat.
It should be noted that the Committee is not implying there is
no risk. As noted above, the risk is small, but not zero.
EPA's Proposed Remediation
The Record of Decision (ROD) proposed by EPA that describes
the remedial actions has been modified at least twice, once in
March 1989 and again in May, 1990. The May, 1990 modified -ROD
apparently proposes to place a protective cover of clean soil over
contaminated areas (those with concentrations >1000 ppm). A foot
of clean soil will be put over a geo-textile liner for individual
properties. For the condominium area, the depth of the clean soil
will be 6 inches. several institutional controls are also
proposed.
SMUGGLER MOUNTAIN TAC
FINAL REPO.T, 1/27/93
m
SMUGGLER MOUNTAIN TAC 3f
FINAL REPORTI 1/27/93
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