reduced to 10 mg l1. The Japanese limit for drinking
water is also 10 mg l1 while the interim maximum
acceptable concentration for Canadian drinking water is
25 mg l1. The US-EPA limit was also reduced from 50
to 10 mg l1 in January 2001following prolonged debate
over the most appropriate limit. However, this rule is
now (September 2001) being reconsidered given the high
cost implications to the US water industry, estimated at
$200 million per year. Whilst many national authorities
are seeking to reduce their limits in line with the WHO
guideline value, many countries and indeed all affected
developing countries, still operate at present to the 50 mg
l1 standard, in part because of lack of adequate testing
facilities for lower concentrations.
Until recently, As was often not on the list of constituents
in drinking water routinely analysed by
national laboratories, water utilities and non-governmental
organizations (NGOs) and so the body of information
about the distribution of As in drinking water is
not as well known as for many other drinking-water
constituents. In recent years, it has become apparent
that both the WHO guideline value and current national
standards are quite frequently exceeded in drinkingwater
sources, and often unexpectedly so. Indeed, As and
F are now recognised as the most serious inorganic contaminants
in drinking water on a worldwide basis. In
areas of high As concentrations, drinking water provides
a potentially major source of As in the diet and so its
early detection is of considerable importance.