Environmental Engineering Reference
In-Depth Information
have an adverse human health effect and that are known or anticipated to occur in public
water supply systems. This law requires the EPA to determine the level of contaminants
in drinking water at which no adverse health effects are likely to occur. These nonen-
forceable health goals, based solely on possible health risks and exposure over a lifetime
with an adequate margin of safety, are called maximum contaminant level goals (MCLGs).
Contaminants are any physical, chemical, biological, or radiological substances or matter
in water.
The MCLG for arsenic is zero. The EPA has set this level of protection based on the best
available science to prevent potential health problems. On the basis of the MCLG, the EPA
has set an enforceable regulation for arsenic, called a maximum contaminant level (MCL),
and is set as close to the health goals as possible, considering cost, beneits, and the abil-
ity of public water systems to detect and remove contaminants using suitable treatment
technologies. 1
In 1975, under the SDWA, the EPA established an MCL for arsenic at 0.05 mg/L. During
the 1980s and early 1990s, the EPA considered changes to the MCL but did not make any. In
1996, Congress amended the SDWA and these amendments required that the EPA develop
an arsenic research strategy, publish a proposal to revise the arsenic MCL by January 2000,
and publish a inal rule by January 2001.
On January 22, 2001, the EPA published a inal Arsenic Rule in the Federal Register
that revised the MCL for arsenic to 0.01 mg/L (10 μg/L). Two months later, in March 2001,
the effective date of the rule was extended to provide time for the National Academy of
Science to review new studies on the health effects of arsenic and for the National Drinking
Water Advisory Council to review the economic issues associated with the standard. After
considering the reports by the two review groups, the EPA inalized the arsenic MCL at
0.01 mg/L (10 μg/L) in January 2002.
The inal rule requires all community and nontransient, noncommunity (NTNC) water
systems to achieve compliance with the rule by February 2006. Adsorptive media pro-
cesses are capable of achieving that level. 2 Likewise, the World Health Organization
(WHO), which views arsenic as a irst priority issue, set the same international arsenic
removal standard, 10 μg/L, and had numerous articles written on arsenic removal. 3
When arsenic is present above its MCL in a water supply in combination with quantities
of other organic and/or inorganic contaminants, the adsorptive media process may not be
the optimal method of arsenic removal. The economics of removing arsenic in addition to
the volume of water to be treated and how the removed arsenic is disposed also dictate
which water treatment method is selected. The EPA estimated that it would cost more than
$200 million in new technology implementation to meet the new arsenic removal levels.
Arsenic contamination in drinking water has always been there as arsenic leaches from
volcanic formations, runoff from orchards, and runoff from glass and electronics produc-
tion and wood preservatives. How ironic that arsenic contamination in drinking water
would surface when tube wells were drilled in India for the sole purpose of providing a
cleaner source of drinking water. While it takes 20 years for the symptoms to develop, the
long-term consumption of arsenic causes arcenosis, which builds up over time and can
cause cancer and death. There are >100 million people at risk for arcenosis in Bangladesh,
China (Inner Mongolia), Vietnam, Pakistan, Nepal, Myanmar, and Cambodia. 4
Arsenic occurs in two primary forms: organic and inorganic. Organic species of arsenic
are predominantly found in food stuffs. Inorganic arsenic occurs in two valence states,
As 3+ and As 5+ . It has been well established that As 3+ is more toxic in biological systems than
As 5+ , whereas the toxicity of organo-arsenicals is generally lower than that of inorganic
arsenic species.
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