Overview
There is no known benefit to
human health from arsenic. The prevalence of
preventable chronic disease and death has led to
reducing the acceptable public water level of
arsenic from 50 to 10 parts per billion. The
ideal goal would be having a zero level of
tolerance, which is achievable using new
technologies for environmental remediation.
Funds from the 2009 stimulus package are now
being directed to such environmental cleanup.
Health cost savings of at least $200 annually
are achievable by reducing the incidence of
cancer by such environmental cleanup.
Furthermore, the mechanism of action for arsenic
causing disease has been elucidated.
The Metal and its
Distribution
Arsenic occurs naturally in
the earth’s crust and possesses both metallic
and non metallic properties. Arsenic is usually
found combined with elements such as oxygen,
chlorine and sulfur. Inorganic arsenic compounds
tend to be more toxic than organic compounds.
Inorganic arsenic is usually found as a solid at
ambient temperatures. Certain geological
formations contain high levels of arsenic that
can easily leach into groundwater and reach
wells and other public water supplies. Higher
levels of arsenic tend to be found more in
ground water sources than in surface water
sources of drinking water, such as lakes and
rivers. Arsenic in water is tasteless, odorless
and colorless. In the United States, the western
third of the country has more public water
systems and wells with high arsenic levels.
Chronic arsenic poisoning from water exposure is
a major public health care issue in Taiwan,
South America, and the Indian subcontinent. In
Bangladesh one of every ten adult deaths is
caused by arsenic related cancers. A total of
100 million people in the world are exposed to
high levels of arsenic in their water supply.
90% of the arsenic used for
industrial purposes is dedicated to the
manufacture of wood preservatives, while the
rest of industrial arsenic is used as pesticides
for agriculture, and in the production of glass,
non ferrous alloys, drugs, soaps and
semiconductors. Man made arsenic releases are a
by-product from copper, zinc and lead smelters.
In North America, China and Western Europe the
man made release of arsenic comes primarily from
the burning of coal.
Acceptable Levels in the
Environment
The Environmental Protection
Agency established a higher drinking water
standard for arsenic at 10 parts per billion
which went into effect in January, 2006. This
standard is equivalent to the standards adopted
by the World Health Organization and the
European Union. This standard was promulgated in
response to a congressional mandate and a
comprehensive study by the National Academy of
Sciences. Arsenic standards are based on risk
assessment models from high exposure
populations. The National Academy of Sciences
determined in 1999 that chronic exposure to
arsenic via the ingestion of drinking water led
to an increased risk in the incidence of the
following malignancies – lung, bladder, skin,
liver and kidney cancers. . The International
Agency for Research on Cancer (IARC) has
classified arsenic as a Group I human
carcinogenic substance.
Excess Injury Due to Arsenic
Exposure
The previous standard had
been 50 parts per billion, which over a 70 year
lifetime gave an individual a 1 in 100 chance of
developing a solid tumor malignancy based just
upon drinking water! This is roughly equivalent
to the risk of death over a lifetime from motor
trauma. The EPA has estimated that the reduction
in the acceptable level of arsenic in the water
supply will lead to a statistically significant
reduction in the incidence of solid tumors – for
example, it is estimated that there will be a
reduction in the incidence of lung cancer by
19-25 cases annually, and in the incidence of
bladder cancer by 19-31 cases annually.
Additionally, exposure to
arsenic increases the risk for hypertension,
diabetes and cardiovascular disease. A spectrum
of disease reduction is anticipated with
compliance to the new water standards for
arsenic. The annual savings in health care costs
will exceed $200 million.
Many parts of the United
States have high underground water
concentrations of arsenic. In New Hampshire,
where 40% of the population derives their water
supply from private wells, as much as 8% of the
population is exposed to arsenic levels of
between 10 and 50 ppb, with many wells having
arsenic concentrations of between 100 and 800
ppb.
Mechanisms of why arsenic is
so dangerous to human health are being developed
by medical researchers. It has been theorized
that arsenic alters the function of the
glucocorticoid receptor as a transcription
factor. Glucocorticoids induce cellular and
physiological effects mediated predominantly
through an interaction with the steroid receptor
hormone GR. Upon steroid binding GR is altered
which unmasks a DNA binding domain, which leads
to a translocation of the ligand bound GR to the
nucleus in a form that can interact with DNA. In
so doing GR can then led to either positive or
negative effects on transcription of specific
glucocorticoid responsive genes. It is
postulated that GR mediates suppression of tumor
promotion in skin and lung by suppressing cell
growth and inducing differentiation. Down
regulation of GR or loss of function induced by
arsenic may be permissive for tumor growth.
Furthermore it has been
proposed by researchers at the Dartmouth Medical
School that arsenic may be able to act
synergistically with other toxic and
carcinogenic agents to increase disease risk.
There is a significant increase in the risk of
malignancies when there is an increased exposure
to both arsenic and cigarette smoking.
For these reasons, the goal
is to establish a zero tolerance limit for
arsenic. It is not a compound which has been
shown to be of any value to mankind. As it is
endemic in our soil and in our water it is
essential that a cost effective method be shown
to remove arsenic and reduce the risks to
health. As with most environmental challenges
the impact of arsenic is most serious in infants
and the aged.
In surface and groundwater
arsenic occurs primarily as arsenite (+++)
(H3As03) or arsenate (+++++) (H2As04-). Arsenite
is significantly more toxic than arsenate. The
presence of oxygen oxidizes arsenite to five
valent arsenate, and therefore the oxidation
state is an important design consideration in
the treatment of water. Both these species of
arsenic are present in water as dissolved
anions. Current separation techniques require
that in order to remove arsenite it is necessary
to pre-oxidize arsenite to the arsenate species.
In order to do so many water purification
systems have a dedicated oxidation column in
order to supplement the oxidation capacity
available in adsorption media. This is a costly
and bulky solution, but is essential in order to
be able to effectively remove both forms of
inorganic arsenic.
The US Environmental
Protection Agency guidelines revised the current
Maximum Contaminant Level for arsenic to 10
parts per billion ( 10 ug/L) and sets a Maximum
Contaminant Level Goal of zero for arsenic in
drinking water. This requirement is in
enforcement for both community water systems and
non transient non community water systems. A
community water system is defined as a public
water system that serves at least 15 locations
or 25 residents regularly year round. Compliance
with this standard is voluntary for private well
owners that do not fall within the definition of
a community.
In most instances health
authorities require arsenic to be tested as part
of the suite of tests taken before a real estate
transaction can be completed. If arsenic levels
are above 10 ug/L the seller of the home may be
required to drill a new well or provide a system
or device to reduce the arsenic levels to below
the Maximum Contaminant Level (MCL).
Arsenic Remediation
Solutions
There are several commercial
solutions available in the marketplace offering
the means to clean up arsenic to below the
drinking water standard of 10 ug/liter. The
spectrum of solutions offered include such
technologies as reverse osmosis, ion exchange,
coagulation microfiltration and activated
alumina. Adsorption technologies have gained the
most favor during the past 5 years due to ease
of use, cost, and efficiency. Currently
available treatment technologies include the
following solutions:
As noted above there are
clearly multiple technologies and the end user
must decide upon factors such as cost,
availability, ease of use and convenience and
removal of waste in determining what is best for
their particular needs.
When using an adsorption
technology, which is currently the preferred
method for arsenic removal, it is best to use a
material which is non leachable. The arsenic
should remain chemically bound to the adsorbent
media such that the material is able to pass the
EPA criteria for Toxic Characteristic Leaching
Procedure Levels (TCLP). This will allow the
arsenic bound adsorbent material to be removed
in a cost effective, non hazardous fashion.
Ideally, there should be no sludge for disposal
and the adsorbent selected should be effective
over a wide range of temperature conditions and
pH, and be resistant to both microbial growth
and oxidation.