137Arsenic- Inorganic Contaminant 0.010 mg/L MCL
Metalloid
Arsenic is a chemical element with symbol As and the atomic number is 33. Arsenic occurs in many
minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was
first documented by Albertus Magnus in 1250. Arsenic is a metalloid. It can exist in various
allotropes, although only the gray
form has important use in industry.
In 1974, Congress passed the
Safe Drinking Water Act. This law
requires EPA to determine the
level of contaminants in drinking
water at which no adverse health
effects are likely to occur. These
non-enforceable 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 (MCLG).
Contaminants are any physical,
chemical, biological or radiological
substances or matter in water.
The MCLG for arsenic is zero. EPA has set this level of protection based on the best available
science to prevent potential health problems. Based on the MCLG, EPA has set an enforceable
regulation for arsenic, called a maximum contaminant level (MCL), at 0.010 mg/L or 10 ppb. MCLs
are set as close to the health goals as possible, considering cost, benefits and the ability of public
water systems to detect and remove contaminants using suitable treatment technologies.
The Arsenic and Clarifications to Compliance and New Source Contaminants Monitoring Final
Rule, the regulation for arsenic, became effective in 2002. The Safe Drinking Water Act requires
EPA to periodically review and revise contaminants, if appropriate, based on new scientific data.
The regulation for arsenic will be included in a future review cycle.
The main uses of metallic arsenic is for strengthening alloys of copper and especially lead (for
example, in car batteries).
Arsenic is a common n-type dopant in semiconductor electronic devices, and the optoelectronic
compound gallium arsenide is the most common semiconductor in use after doped silicon.
Arsenic and its compounds, especially the trioxide, are used in the production of pesticides (treated
wood products), herbicides, and insecticides. These applications are declining, however.
Arsenic is notoriously poisonous to multicellular life, although a few species of bacteria are able to
use arsenic compounds as respiratory metabolites. Arsenic contamination of groundwater is a
problem that affects millions of people across the world.