Introduction
Arsenic and selenium are two widely distributed
semimetals which for different reasons have attracted
interest in connection with public health issues.
Arsenic has been known for centuries as a toxic
element: in popular imagination, it has become a
synonymous of poison. Besides the obvious behavior
of some of its compounds in acute exposure, there is an
increasing concern about the risk associated with longterm
exposure. There exists considerable evidence
suggesting that consumption of arsenic-containing
water can cause skin, bladder and lung cancer (Goyer
1996).
One of the main problems in some geographical
areas arises from groundwater contamination of either
mineral or anthropogenic origin. A number of chronic
intoxication episodes have occurred that have drawn
attention to the risk to which the population of certain
areas is exposed due to consumption of water from
contaminated wells. Thus, it has been classified as a
high-priority substance for screening in drinking water
sources. Maximum acceptable levels of total arsenic in
drinking water have been the object of some controversy,
although there is a trend toward the establishment
of lower values. WHO, in its Guidelines for