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Update: Arsenic
by Kelly A. Reynolds,
Ph.D.
Arsenic is a poisonous agent found in
nature at low levels and which makes its way to source waters
via weathering of rocks and erosion. Arsenic in plants and animals
(i.e. fish and seafood) combines with carbon and hydrogen to
form less toxic organic compounds relative to the inorganic arsenic
compounds generally associated with contaminated water. Inorganic
arsenic compounds form when arsenic combines with oxygen, chlorine
and sulfur.
Arsenic is considered a silent pollutant since there’s generally
no smell or taste associated with its presence. Furthermore,
because many of these symptoms are indicative of a number of
other illnesses, arsenic poisoning may easily go undetected
More serious health effects from arsenic exposure include skin
damage, circulatory system problems and an increased cancer risk,
especially of the skin, bladder and lungs. Early warning signs
may include stomach pain, nausea, vomiting, diarrhea and numbness
in extremities. Exposures may be through food, especially fish
and seafood, or drinking water.
Certain areas of the United States contain mineral deposits with
high levels of arsenic that can leach into drinking water sources
when groundwater flows through these deposits. The effect of
arsenic exposure on any given individual depends on a number
of factors including the ingested dose, duration of exposure,
form of the arsenic compound and the immunological status of
the person exposed—where age and general health play key
roles.
Environmental
sources
Although arsenic occurs naturally in mineral deposits throughout
the world, many industrial applications contribute to these indigenous
sources, including discharge from semiconductor manufacturing,
petroleum refining and glass manufacturing, as well as products
used as wood preservatives, animal feed additives, herbicides,
and lead- or copper-based alloys.
Although arsenic use in agriculture declined in 1994 following
a negotiated agreement with the U.S. Environmental Protection
Agency (USEPA) limiting the use of arsenic acid desiccant production
for cotton crops, demand for the compound remained unchanged
due to increased demands for preserved wood. Thus, arsenic demand
is closely tied to the economics of the home construction market,
currently a booming business in the United States.
Regulatory
issues
The current federal maximum contaminant level (MCL)—the
maximum permissible level of arsenic in water which is delivered
to any user of a public water system—was set in 1975 based
on the 1943 standard set by the U.S. Public Health Service of
50 mg/L (micrograms per liter), or 50 parts per billion (ppb).
MCLs are enforceable standards that must be maintained by public
water suppliers.
Generally, health and water industry experts agree that an MCL
of 50 ppb for arsenic does not adequately protect the public
from adverse effects of the contaminant. A recent National Academy
of Sciences report said the standard should be lowered but stopped
short of recommending the USEPA adopt the World Health Organization
limit of 10 ppb. Currently, for arsenic, there’s no U.S.
maximum contaminant level goal (MCLG)—the maximum level
of a contaminant in drinking water at which no known or anticipated
adverse effect on the health of persons would occur—since
MCLGs were not established prior to the 1986 Amendments to the
Safe Drinking Water Act.
MCLGs are non-enforceable public health goals. Arsenic, however,
is one of 83 specific contaminants for which the USEPA is required
to set an MCLG and a National Primary Drinking Water Regulation
(NPDWR). Based on risk management components such as treatment
technologies, occurrence assessment and cost /benefit analysis,
the MCL is set as close as possible to the health goal, or MCLG,
as is feasible. Therefore, proposed changes in the MCL of 50
mg/L range from 2-to-20 mg/L, which would yield an acceptable
cancer risk of 1 in 10,000 over a lifetime.
Who’s
at risk?
Recently, the Association of California Water Agencies (ACWA)
completed a survey of low-level arsenic occurrence in surface
and groundwater in California. The survey is the first of a two-part
study aimed at determining the impact on California water consumers
of a revised drinking water regulation for arsenic. The ACWA
is the largest statewide coalition of public water agencies in
the United States, with 417 public agency members serving more
than 90 percent of the state’s water. Association concerns
include how revised drinking water regulations for arsenic would
effect the cost and available resources of water in the state.
Within this study, 1,500 water samples were collected over a
12-month period, from 1993-to-1994, via 180 agencies in 27 counties.
The median value of arsenic found in the total samples was 2
mg/L, with only one source having a level above the current standard.
Half of the surface water and 65 percent of the ground water
had detectable levels of arsenic present. Depending on the new
MCL standard level, many previously compliant utilities could
now be out of regulatory compliance. Many U.S. utilities are
recognizing the cost of compliance to a lower MCL is prohibitive
and are fighting the regulatory change.
Another study sponsored by the Water Industry Technical Action
Fund (WITAF) surveyed surface and groundwater arsenic occurrence
levels nationwide to determine the rate of non-compliance to
lowered standards. The study found distinct regional variances
in arsenic occurrence. The East Coast and Southeast regions of
the U.S. had low-level arsenic occurrence in both ground and
surface water; including the Midwest, New England and Mid-Atlantic
regions which had levels less than 5 mg/L. Surface water sources
in the south central and north central U.S. and West had substantially
higher proportions of elevated arsenic occurrence compared with
the rest of the nation. Data is also available for some groundwater
supplies where arsenic concentrations less than 5 mg/L were consistently
found in the central Midwest, north central and south central
U.S. and West.1
Based on USEPA-required monitoring data from domestic water utilities,
six water systems—serving approximately 9,757 persons—reported
MCL violations of arsenic between 1994 and 1995. If the MCL was
lowered to 2 mg/L, the USEPA estimates that approximately 25
percent of all community water suppliers (11,550-to-11,890 systems)
would fail compliance. Between 6 and 17 percent (2,775-to-7,870)
are projected to violate a standard of 5 mg/L. And 1-to-3 percent
(510-to-1,360) would fail to meet an arsenic standard of 20 mg/L.
In addition, public water utilities are required to monitor and
control for arsenic to the MCL level; however, 16 percent of
the U.S. population is served by private groundwater systems
and may not be cognizant of the need for arsenic monitoring and
control. Private well owners should contact public health agencies
in their area and, if necessary, a test laboratory to determine
if arsenic is a problem in their source water. Laboratory contracted
testing may be easily performed at a cost of approximately $25-to-35
per analysis.2
Compliance
costs
According to a recent USEPA report to Congress, depending on
how arsenic is regulated, the estimated financial need for installation,
upgrade or infrastructure replacement to comply with new arsenic
standards ranges from $278.9 million to $7.126 billion.3
In the 1996 Amendments to the Safe Drinking Water Act (SDWA),
Congress directed USEPA to expand arsenic health effects research
and propose a new arsenic regulation by Jan. 1, 2000, with final
regulation to occur by Jan. 1, 2001. Congress authorized $2.5
million per year, from 1997-to-2000, for the studies. The USEPA
is currently funding research to evaluate the health effects
from arsenic exposures in drinking water. One such study is being
conducted in West Bengal, India, where a large population is
exposed to drinking water containing arsenic. This research is
due to be completed in the Fall of 2000 and aims to establish
a dose-response relationship for malignant skin tumors and other
skin ailments associated with ingestion of inorganic arsenic.
While long term research will not be completed prior to the statutory
deadline, the USEPA is committed to a reevaluation every six
years or less of all its primary drinking water regulations.
Conclusion
A variety of water treatment options are effective for arsenic
removal including activated alumina, ion exchange, lime softening,
oxidation combined with reverse osmosis (RO), ion exchange, alum
or iron coagulation with filtration, distillation and nanofiltration.
While many treatment technologies are available and effective
for arsenic removal, the choice of treatment depends on the scale,
cost requirements and water quality parameters. Point of use/
point of entry (POU/POE) systems can be effective and affordable
treatment options for individuals in lieu of the changing standard
and feasible compliance options for small systems in meeting
a new arsenic MCL.
References
1. Frey, M.M. and M.A. Edwards, “Surveying arsenic occurrence,”
Journal AWWA, 89(2): 105-117, 1997.
2. Shank-Givens, H.L., “Arsenic drinking water regulation
background information,” USEPA, Office of Ground Water and
Drinking Water, Washington, D.C., 1994.
3. USEPA, “Drinking water infrastructure needs survey: First
report to Congress,” Office of Water, USEPA 812-R-97-001,
Washington, D.C. (in January 1995 dollars) 1997.
4. U.S. Bureau of Mines, Arsenic, Mineral Commodities Summaries,
1994.
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