|
Items in cart [0] |
Questions? Call 888-624-8373 |
PAPERBACK PDF BOOK Free Resources |
||||||||||||||||
|
||||||||||||||||
|
||||||||||||||||
| ||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 15
1
InTroduction
The U.S. Environmental Protection Agency (EPA) is required under the Safe
Drinking Water Act (SDWA) to establish the concentrations of contaminants
permitted in public drinking-water supplies. There are two drinking-water
contaminant concentrations that the statute requires EPA to set the maxi-
mum contaminant level goal (MCkG) and the maximum contaminant level
(MCL). The MCkG is a health goal to be based on the best available, peer-
reviewed scientific data. It is to be set at a concentration at which no known
or anticipated adverse health effects occur, allowing for adequate margins of
safety. The MUG is not a regulatory requirement end might not tee attainable
with current technology or analytical methods. The MCL, in contrast, is an
enforceable standard. The MCL is required to be set as close to the MUG
as is technologically feasible, taking cost into consideration.
The EPA Of floe of Water is considering options for revising the cur-
rent MCL of 50 ,ug/L for arsenic in drinking water. To incorporate the most
recent scientific research into its decision, in April 2001, the Office of Water
requested that the National Research Council (NRC) review the data pub-
lished on the health effects of arsenic since the NRC's 1999 report, Arsenic
in Drinking Water. The NRC was also asked to evaluate the arsenic risk as-
sessment conducted by EPA for the proposed arsenic standard published in the
January 22, 2001, Federal Register (EPA 2001a).
15
-
OCR for page 16
6 ARSENIC IN DRINKING WA TER: 2001 UPDA TE
SUMMARY OF THE
NRC'S 1999 ARSENICINDRIN1[ING WATER REPORT
~ 1996, the NRC Subcommittee on Arsenic in Drinking Water was form-
ed and charged with reviewing EPA's 1988 risk assessment for arsenic, re-
viewing the scientific data relevant to an arsenic risk assessment, and identify-
ing data gaps. The subcommittee did not provide a formal risk assessment or
recommend anMCL. The subcommittee concluded, on the basis of epidem~o-
logical studies in Taiwan, Chile, and Argentina, that "ingestion of arsenic in
drinking water poses a hazard of cancer of the lung and bladder, in addition
to cancer of the skin." The subcommittee further concluded, "No human
studies of sufficient statistical power or scope have examined whether con-
sumption of arsenic in drinking water at the current MCL (approximately
0.001 mg/kg (milligram per kilogram) body weight per day) results in an
increased incidence of cancer or noncancer effects." Therefore, the subcom-
mittee used the available epidemiological data and information on mode of
action, uncertainty, and human susceptibility to extrapolate and estimate
cancer risks at various concentrations of arsenic in drinking water. The sub-
committee concluded that data Tom the area of southwestern Taiwan where
arsenic is endemic provided the best data for dose-response assessment.
Although data suggest an indirect mode of action, the subcommittee con-
cluded that the data are insufficient to determine a threshold below which no
effects are seen and are insufficient to depart from a linear extrapolation to
zero. The subcommittee presented the risks using numerous models. Using
the Poisson regression model, the lifetime risk for male bladder cancer at the
MCL (50 micrograms per liter Dug/ is ~ to l.5 per 1,000, and the lifetime
risk for all cancers combined could be on the order of ~ in 100.~ On the basis
of its assessment, the subcommittee concluded that "the current EPA MCL for
arsenic in drinking water of 50 ,ug/L does not achieve EPA's goal for public
health protection and therefore requires downward revision as promptly as
possible."
'Two of the 16 members of the previous subcommittee did not agree with the 1 in 100
estimate pending further analysis of the risk of lung cancer, as done for bladder cancer in
Chapter 10 of the 1999 report.
OCR for page 17
INTRODUCTION ~ 7
POLICY BACKGROUND
In ~ 976, under the SDWA, EPA proposed an interim MCL of 50 ,ug/L for
arsenic in drinking water as part of the National Interim Primary Drinking
Water Standards; that standard was originally set in 1942 and would apply
until EPA adopted a new MCL. In ~ 988, EPA conducted a risk assessment for
arsenic in drinking water and, in ~ 996, requested that the NRC independently
review the scientific database on the health effects of arsenic and evaluate the
scientific validity of that risk assessment. Arsenic in Drinking Water MARC
1999) was published in response to that request.
Summary of EPA's Actions
Following the publication of that report, EPA published a proposed ar-
senic MCL of 5 ,ug/L (EPA 2000a) in the FederaiRegister. That standard was
based on the information in Arsenic in Drinking Water MARC ~ 999) and on
epidemiological studies from southwestern Taiwan, Chile, and Argentina,
some of which were remewed in the NRC report. EPA also reviewed data
from an epidemiolog~cal study in Utah (Lewis et al. ~ 999) that was released
after the NRC (1999) report. EPA concluded that "exposure to inorganic
arsenic induces cancer in humans" and proposed a regulation on the basis of
that effect. It further concluded that "tiin the absence of a known mode of
actions, EPA has no basis for determining the shape of a sublinear dose-
response curve for inorganic arsenic" (EPA 2000a) and, therefore, proposed
using a linear type of a dose-response curve and setting an MUG of zero. On
the basis of "national and international research, the bladder cancer risk analy-
sis provided by the National Research Council (NRC) report issued by the
National Academy of Sciences (NRC 1999), and the NRC's qualitative state-
ments of overall risk of combined cancers," EPA evaluated the risk posed by
arsenic in drinking water at 3 ~g/L, 5 PAL, ~ 0 ,ug/L, and 20 ,ug/L. According
to EPA policy, an MCL is to be set "as close as feasible to the MC~G, based
on available technology and taking costs to large systems into account" (EPA
2000a). EPA determined that 3 ~g/L is technologically feasible but that the
costs associated with compliance for that concentration are notjustifiedby the
benefits. Therefore, EPA proposed an MCL of 5 ~g/L but requested public
comment on alternative MCEs of 3 PAL, 10 ~g/L, and 20 ~g/L. The effective
date for compliance for small community water systems would be 5 years after
the final rule issuance and 3 years for all other community water systems.
OCR for page 18
~ ~ ARSENIC IN DRINKING WA TER: 2001 UPDA TE
After the publication of the proposed rule, Morales et al. (2000) published a
study in which a risk assessment for mortality from several internal cancers
was presented. That risk assessment was based on reanalyses ofthe data from
southwestern Taiwan (Chen et al. 1985~. Risk estimates were calculated for
mortality from lung, bladder, and liver cancers, as well as combined cancer
deaths, using 10 different statistical models. Those models included linear,
logarithmic and square-root models, calculated with and without a Taiwanese
comparison population. EPA was considering those analyses in the finalrule-
making and, therefore, published a Notice of Data Availability in the Federal
Register (EPA 2000b) summarizing and further analyzing the information
from Morales et al. (2000~.
On December 12,2000, the EPA Science Advisory Board (SAB) issued
a report on the proposed drinking-water regulation (EPA 2000c). In its major-
ity report, the SAB commented on the scientific basis of EPA's health risk
assessment and on the economic and engineering aspects of the final rule.
Exposure assessment fortheU.S. population, costs, benefits, control technolo-
gies, and policy issues discussed by the SAB go beyond the charge to this
subcommittee and wall not be discussed here. The SAB also discussed the
differential sensitivity of children to arsenic but could not reach consensus on
whether children have an increased sensitivity to arsenic. A minority report
was written on that issue. In general, the SAB agreed with the analyses cony
ducted by the NRC Subcommittee on Arsenic in Drinking Water ARC ~ 999),
which formed part of the basis for EPA's proposed regulation. It did not
agree, however, with EPA's interpretation ofthe NRC report, stating that EPA
"may have taken the modeling activity in the NRC report as prescriptive."
T h e S A B a ~ s o s t a t e ~ t h a t E P A ~ i ~ n o t a ~ e q u a t e ~ y a ~ ~ r e s s t h e N ~ C s u b c o m m i t -
tee' s cautions about such factors as nutrition and exposure measures that were
to be considered when using the Taiwanese data for assessing risk in the U.S.
population. The SAB also concluded "that the comparison populations [used
in some analyses] were not appropriate control groups for the study area" in
the Taiwanese study, and, therefore, dose-response models that did not use the
comparison population are more appropriate. The SAB did not believe, how-
ever, that "resolution of all these factors can nor must be accomplished before
EPA promulgates a final arsenic rule." The SAB agreed that the "available
data do not yet meet EPA's new criteria for departing from linear extrapola-
tion of cancer risk."
In response to public comment and the SAB report, on January 22, 2001,
EPA issued a pending standard of 10 ,ug/L (EPA 2001a). To support this
OCR for page 19
INTRODUCTION ]9
revised proposed standard, EPA reviewed the available data and quantitatively
estimated risks using the epidem~ological data from southwestern Taiwan
(Chen et al. 1988, 1992; Wu et al. 1989) because, despite limitations, "the
Taiwan epidemiological studies provide the basis for assessing potential risk
from Tower concentrations of inorganic arsenic in drinking water, without
having to adjust for cross-species toxicity interpretation." In its ruling, EPA
discussed the implications for extrapolating from the observed range of ar-
senic concentrations in the Taiwanese population to the risk in the U.S. popu-
lation of (~) arsenic in food alluvia cooking, (2) uncertainty in exposure from
the grouping of individuals with respect to exposure, (3) nutritional aspects of
the Taiwanese population, and (4) a study in Utah, which did not find any
excess bladder or lung cancer risk after exposure was taken into account.
"tT]he best available science provides no alternative to use of a linear dose-
response process for arsenic because a specific mode (or modes) of action has
not been identified"; therefore, EPA used a Poisson model, with concentration
entered as a linear term to estimate the dose that results in a I% increased risk
(i.e., 1% benchmark dose; BMDo~), and extrapolated from that point using a
linear extrapolation. That analysis follows the EPA draft carcinogen risk
assessment guidelines (EPA 1996~. On the basis of that assumption and
estimates of water intake, EPA calculated cancer risks at various MCL op-
tions. Those risks were calculated for bladder and lung cancer combined. As
described in the proposed rule (EPA 2000a), when estimating a risk at a given
MCI option, EPA assumed that water-treatment facilities will treat water to
achieve a concentration that is 80°/O of the MCL and, therefore, calculates
risks based on 80% of the MCL. EPA made that assumption because "water
systems tend to treat below the MCL level in order to provide a margin of
safety" (EPA 2000a). For example, when estimating population risks at an
MCL of 10 ,ug/L, the actual average exposure after water treatment would be
,ug/L`. Therefore, the estimated risks presented by EPA at an MCL of 10
g/L are the risks calculated for a drinking-water concentration of ~ ~g/L.
Such an adjustment to account for the difference between the MCL and the
actual drinking-water concentrations was not done in the risk estimates of the
previous NBC subcommittee. In addition, the NRC (1999) risk estimates are
for mate bladder cancer alone, not combined cancers as presented by EPA,
and estimates calculated with and without a comparison population (i.e.,
background data) are presented in the NRC report (1999~. Given those risks,
what is known or not known about arsenic's mode-of-action, cost-benefit
analyses, and policy considerations, EPA set an MUG of 0 ~g/L and an MCL
OCR for page 20
20 ARSENIC IN DRINKING WA TER: 2001 UPDA TE
of 10 Age. Further details on the models and parameters used by EPA to
determine their risk estimates are presented in Chapter 5.
On March 23, 200 I, EPA published a notice that delays the effective date
of the arsenic rule pending further study (EPA 200 Ib). EPA's Of fice of Water
requested that the NRC update its 1999 report as part of the further study.
CHARGE TO TTIE SUBCOMMITTEE
In response to EPA's request, the NRC assigned the project to the Com-
mittee on Toxicology (COT), which convened the Subcommittee to Update
the 1999 Arsenic in Drinking Water Report. Members selected to serve on
this subcommittee have expertise in toxicology, epidemiology, cellular and
molecular toxicology, biostatistics and modeling, risk assessment, uncertainty
analyses, medicine, and public health. Five members of this subcommittee
also served on the earlier Subcommittee on Arsenic in Drinking Water. This
subcommittee is charged with the task of preparing a report updating the
scientific analyses, uncertainties, findings, and recommendations of the Ar-
senic in Drinking Water report (NRC ~ 999) on the basis of several new stud-
ies and analyses published since the 1999 report was released. Specifically,
the charge to the subcommittee was to review relevant toxicological and
health-effects studies published and relevant data developed since the 1999
NRC report, including the toxicological risk-related analyses performed by
EPA in support of its regulatory decision-making for arsenic in drinking wafer.
The subcommittee addressed only scientific topics relevant to toxicological
risk and health effects of arsenic; it did not address questions of economics,
cost-benefit assessment, control technology, or regulatory decision-making.
The subcommittee performed the following tasks in response to the
charge:
· It determined whether data from the ~ 988, ~ 989, and ~ 992 Taiwanese
studies remain the best data for dose-response assessment and risk estimation.
· It assessed whether the EPA analysis appropnately incorporates popu-
lation differences, including diet, when extrapolating from the Taiwanese
study population to the U.S. population.
· It evaluated whether the dose-response analysis conducted by EPA,
as well as any available analyses of more recent data, is adequate for estimat-
ing an effective dose for a 1% response (EDo~.
OCR for page 21
INTRODUCTION 2]
· It determined whether EPA's analysis appropriately considers and
characterizes the available data on the mode of action of arsenic and the infor-
mation on dose-response and uncertainties, when assessing the public-health
impacts.
· It determined whether EPA's risk estimates at 3, 5, ~ 0, and 20 ,ug/L are
consistent with available scientific information, including information from
new studies.
This subcommittee was not asked to assess and did not assess U.S. popu-
lation exposures. Therefore, it did not estimate the benefits or potential lives
saved in the United States at each possible regulatory level. Consistent with
the makeup ofthe subcommittee, it has addressed the scientific issues related
to the hazards from arsenic in Winking water and has avoided commenting or
making recommendations on risk-management or policy decisions to the
extent possible. To that end, the subcommittee has not recommended an
MCL, which, by definition, requires policy considerations that include evalua-
tion of risk-management options and cost-benefit analyses that are beyond the
scope ofthis subcommittee. If a particular analysis conducted by the subcom-
m~ttee has policy or risk-management decisions inherent in it, the subcommit-
tee presents the analysis as an example and indicates which parameter values
are derived from policy decisions.
It should also be noted that the subcommittee is charged with updating
Arsenic in Drinking Water MARC ~ 999) and not with reviewing it. Therefore,
the subcommittee has taken that report as a starting point and has evaluated
the information published since the release of that report.
ORGANIZATION OF THIS REPORT
Subsequent to the release of Arsenic in Drinking Water MARC 1999),
numerous new studies and analyses have been published on the health effects
of arsenic and related data, including epidemiological studies on cancer and
noncancer effects, toxicokinetic and mode-of-action studies, and reports on
arsenic risk assessments. The remainder of the report is organized into five
chapters that review those areas. To provide context for the update, each
chapter includes a brief summary of the information from the 1999 report.
Chapter 2 discusses recent data on the health effects of arsenic in humans.
Chapter 3 presents information published since the 1999 report on the toxico-
OCR for page 22
22 ARSENIC IN DRINKING WA TER: 2001 UPDA TE
kinetics and possible mode of action of arsenic. Chapter 4 addresses vanabil-
ity and uncertainty, which are to be considered when assessing the hazards of
arsenic, arising Mom intenndiv~dual vanability, dietary and nutritional factors,
exposure issues in epidemiology studies, and latency periods. Chapter 5 pro-
v~des a discussion on the modeling approaches for quantitative evaluation of
nsks. It includes analyses conducted by EPA in its proposed regulations and
the comments of the EPA Science Advisory Board (SAB) as well as analyses
conductedby this subcommittee. Chapter6 presents a summery ofthe subcom-
mittee's findings, including lifetime cancer risk estimates associated with
lifetime consumption of arsenic at different concentrations in Winking water.
REFERENCES
Chen, C.J., Y.C. Chuang, T.M. Lin, and H.Y. Wu. 1985. Malignant neoplasms
among residents of a blackfoot disease-endemic area in Taiwan: High-arsenic
artesian well water and cancers. Cancer Res. 45~11 Pt 2~:5895-5899.
Chen, C.J., M. Wu, S.S. Lee, J.D. Wang, S.H. Cheng, and H.Y. Wu. 1988. Athero-
genicity and carcinogenicity of high-arsenic artesian well water. Multiple risk
factors and related malignant neoplasms of blackfoot disease. Arteriosclerosis
8(5):452-460.
Chen, C.J., C.W. Chen, M.M. Wu, and T.L. Kuo. 1992. Cancer potential in liver,
lung, bladder and kidney due to ingested inorganic arsenic in dunking water. Br.
J. Cancer 66~5~:888-892.
EPA (U.S. EnvironmentalProtection Agency). 1996. Carcinogenic Risk Assess-
mentGuidelines.Notice. Fed.Regist.61~79~:17960-18011.
EPA (U.S. Environmental Protection Agency). 2000a. 40 CFR Parts 141 and 142.
National Primary Drinking Water Regulations. Arsenic and Clarifications to
Compliance and New Source Contaminants Monitoring. Notice of proposed
rulemalcing. Fed. Regist. 65~121~:38887-38983.
EPA (U.S. Environmental Protection Agency). 2000b. 40 CFR Parts 141 and 142.
National Primary Drinking Water Regulations. Arsenic and Clarifications to
Compliance end New Source Contaminants Monitoring. Notice of data availabil-
ity. Fed. Regist. 65~204~:63027-63035.
EPA (U.S. Environmental Protection Agency). 2000c. Arsenic Proposed Drinking
Water Regulation: A Science Advisory Board Review of Certain Elements of the
Proposal, A Report by the EPA Science Advisory Board. EPA-SAB-DWC-01-
001. Science Advisory Board, U.S. Environmental Protection Agency, Washing-
ton, DC. [Online]. Available: http://www.epa.gov/sab/fiscalOl.hun .
EPA (U.S. Environmental Protection Agency). 2001a. 40 CFR Parts 9,141 and 142.
National Primary Dnnking Water Regulations. Arsenic and Clarifications to
OCR for page 23
Representative terms from entire chapter:
southwestern taiwan
INTRODUCTION 23
Compliance end New Source Contaminants Monitoring. Final Rule. Fed. Regist.
66~14~: 6975-7066.
EPA (U.S. Environmental Protection Agency). 2001b. 40 CFR Parts 9,141 and 142.
National Prunary Drinking Water Regulations. Arsenic and Clarifications to
Compliance and New Source Contaminants Monitoring. Final rule. Delay of
effective date. Fed. Regist. 66~57~: 16134- 16135.
Lewis, D.R., J.W. Southwick, R. Ouellet-Hellstrom, J. Rench, and R.L. Calderon.
1999. Drinking water arsenic in Utah: A cohort mortality study. Environ. Health
Perspect. 107~5~:359-365.
Morales, K.H., L. Ryan, T.L. Kuo, M.M. Wu, and C.J. Chen. 2000. Risk of internal
cancers from arsenic in Mung water. Environ. Health Perspect. 108~7~:655-
661.
N1
