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Human Exposure and Health Effects
Editor’s Note: Part 1 of this series provided a
timeline for the development of a drinking water standard for arsenic. It also
summarized the political and public reactions to the U.S. EPA decision to delay
and withdraw the arsenic rule.
The discovery of exceptionally high arsenic levels in
groundwater derived from shallow “tube wells” in Bangladesh and
West Bengal, India, in 1993 brought worldwide attention to the chronic exposure
of as many as 85 million people in what has been called the largest mass
poisoning of a population in history. The publication in 2001 of the results of
a survey conducted in 1999 (Environmental Science and Technology 2001, 35, 13)
show similarly high concentrations of arsenic in well waters in Vietnam and the
water supply for the City of Hanoi. The arsenic concentrations reported in
these regions are often an order of magnitude greater than those observed in
U.S. ground and surface waters. However, indications are that arsenic may be
widespread in shallow well drinking water sources globally.
Taiwanese studies, reported in the American Journal of
Epidemiology (153, 411 ), have linked 10 to 50 µg/L arsenic
concentrations to urinary tract cancers in Taiwan. Some critics have discounted
the significance of these Taiwanese results citing lower arsenic levels and
better nutrition in the U.S.
On-going health effects studies and research reports (2001) appear to support the argument for lowering the current EPA drinking water standard for arsenic. Studies conducted by EPA, the University of North Carolina and the University of British Columbia have indicated that methylated metabolites of trivalent arsenic are genotoxic. In other words, they damage DNA in human cells.
Animal studies at the Dartmouth Medical School, reported in
Environmental Health Perspectives (109, 245 ), indicate that exposure of
rat liver cells to trivalent arsenic concentrations in the range of 5 to 70
µg/L disrupted a hormone receptor. Researchers believe that this may
explain why exposure to arsenic in drinking water is associated with Type 2
diabetes and vascular disease. To further explore this possibility, follow-up
epidemiology studies are underway on humans exposed to arsenic in drinking
Johns Hopkins University researchers have reported (J. Clin.
Invest. 2001, 108, 1,541–1,547) the results of studies aimed at
determining the mechanism linking arsenic to cancer. The exposure of cell lines
to low levels of arsenic trioxide was observed to result in al decrease in the
activity of the enzyme telomerase. This enzyme maintains the length of
chromosomal ends (telomeres). The progressive decrease in the length of the
telomeres after each healthy cell division could lead to the formation of
Arsenic was previously known to increase the risk of cancer
of the lungs, skin, bladder, liver, kidney, prostate and nasal passages. The
Public Health Service, Agency for Toxic Substances and Disease Registry (ATSDR)
has compiled a comprehensive review of studies related to arsenic and cancer.
With respect to exposure through drinking water, the ATSDR Information Center
(July, 2001) states that “An association between environmental exposure
to arsenic through drinking water and skin cancer has been observed and
confirmed; two cases of bladder cancer also were described, with latent periods
of eight to 20 years. The latent periods for two cases of skin cancer related
to arsenic in drinking-water were 20 and 23 years, and the concentrations or
uptake of arsenic were reported to be 1.2 and 1 mg per day, respectively, with
an estimated total ingested dose of about 8 g in one study. Epidemiological
studies in areas with different frequencies of black-foot disease and where
drinking-water contained 0.35-1.14 mg/L arsenic revealed elevated risks for
cancers of the bladder, kidney, skin, lung, liver and colon in both men and
Arsenic also has been associated with a broad range of
non-cancerous health effects. These include cardiovascular, neurological,
pulmonary, immunological, endocrine, reproductive and developmental effects.
Based on the health effects evidence, the EPA has classified
arsenic as a human carcinogen and has restricted or canceled many uses of
arsenic compounds in pesticides. OSHA has set a standard for arsenic in
workplace air. In assessing the health benefits of a lowered standard, EPA has
focussed on bladder and lung cancer and estimated that a 10 µg/L arsenic
drinking water MCL would
• prevent between 19 and 31 cases and 5 to 8 deaths due to bladder cancer annually,
• prevent 19 to 25 cases and 16 to 22 deaths from lung cancer annually, and reduce the incidence of noncancer health effects from arsenic exposure.
In a move aimed at still further reducing exposure of the
public to arsenic, U.S. EPA announced on February 12, 2002, a voluntary
decision by the lumber industry to “move consumer use of treated lumber
from a variety of pressure-treated wood that contains arsenic by December 31,
2003, in favor of new alternative wood preservatives.” By 2004, EPA will
not allow chromated copper arsenate (CCA) products for specified residential
In initially proposing a 5 µg/L arsenic standard, EPA
estimated that implementation of the rule nationally would cost $374 million
per year for the next 20 years. EPA estimated a $28 average annual household
cost for arsenic removal for systems serving more than 10,000 people. However,
most affected utilities utilize groundwater and serve populations less than
10,000. Since an estimated 75 percent of these smaller utilities already have
treatment plants, the incremental cost of arsenic removal for these systems
would be far lower than if the construction of new facilities were required.
Agreeing that the existing standard should be reduced, but
opposing the establishment of a 5 µg/L standard, the American Water Works
Association (AWWA) has contended that a standard below 20 µg/L cannot be
justified. Moreover, AWWA countered EPA with cost estimates of $600 million per
year to meet a 10 µg/L standard and $1.5 billion per year to meet a 5
µg/L standard. One industry spokesman suggested that some consumers would
face bill increases of as much as $1,900 annually.
While conceding the need to reduce arsenic levels, the
Association of California Water Agencies challenged the scientific
justification and economic feasibility of the previously proposed 5 µg/L
A Western Coalition of (Seven) Arid States (WESTCAS) called
for an interim standard of 20 µg/L. Arguing that compliance should be
eight years rather than the proposed three, WESTCAS has contended that no
available technologies exist for water providers to implement arsenic removal
within three years.
At issue is the cost-benefit ratio of increased arsenic
removal. It has long been recognized that the establishment of any health-based
standard is, in effect, an attempt to place a value on human life or the
quality of human life. To quantify (monetize) the benefits of avoiding
mortality from bladder and lung cancer, EPA utilizes a Value of Statistical
Life (VSL) estimate. The VSL value used by the Agency as of 1999 is $6.1
million. In addition, EPA uses a
Willingness to Pay (WTP) value to monetize the cancer cases that do not result
in a mortality. Since a WTP value for avoiding a non-fatal cancer has not been
established, EPA uses a proxy WTP estimate of $607,000 established for the
value of reducing the number of chronic bronchitis cases. Non-cancer health
effects are considered essentially non-quantifiable.
At the request of the EPA Administrator, the National
Academy of Sciences, National Research Council (NAS-NRC) appointed a new panel
to review and update the 1999 NAS-NRC report on Arsenic in Drinking Water. The
new NAS-NRC panel issued its updated report in September 2001, noting that
several hundred new relevant articles had been published sine the 1999 report
and that four major epidemiological studies had been conducted.
In their 200-page report, the NAS-NRC health effects panel
concluded that the cancer risk from arsenic has been underestimated. While in
the past EPA has used a risk level of 1 in 10,000 for establishing standards,
the NAS report indicates that, even at 3 µg/L, the risk of bladder and
lung cancer is between 4 and 7 deaths per 10,000 people. At 10 µg/L, the
risk increases to between 12 and 23 deaths per 10,000 people (Table 1). In
addition, the health effects panel cited increased evidence that arsenic causes
high blood pressure and diabetes.
Based on three new epidemiological studies conducted in
Chile and Taiwan, the panel also concluded that existing data “provide a
sound and sufficient database showing an association between bladder and lung
cancers and chronic arsenic exposure in drinking water.” style="mso-spacerun: yes"> Moreover, the earlier Taiwan data that
had been criticized as scientifically flawed by industry spokesmen, was found
to be “appropriate for use in dose-response assessment of arsenic in
Part 3 of this series will summarize currently available
data on the occurrence of arsenic in U.S. waters.