Maximum Contaminant Levels (MCL) in ppm (mg/l
Chromium (hexavalent) (Cr16)
(See Table 4-2)
Nitrate (as N)
Table 4-1. Maximum contaminant levels of inorganic chemicals (Primary Standards)
in drinking water.
(1) Arsenic. The widespread use of inorganic insecticides and its presence
in animal foods, tobacco, and other sources make it necessary to set a limit on the
concentration of arsenic in drinking water. The toxicity of arsenic is well known. The
ingestion of as little as 100 mg usually results in severe poisoning. A concentration of
0.01 ppm should not be exceeded if other more suitable water supplies are or can be
(2) Barium. Barium is recognized as a general muscle stimulant, especially
the heart muscle. The fatal dose for man is considered to be from 550-600 mg.
Concentrations in excess of 1 mg/l are grounds for rejection of a 0water supply because
of the seriousness of the toxic effects of barium on the heart, blood vessels, and nerves.
(3) Cadmium. Cadmium is recognized as an element of high toxic potential,
but which is (as far as is known) biologically nonessential and nonbeneficial. UntiI fairly
recently, Iittle attention was paid to cadmium. Tests have shown accumulations in soft
tissues from drinking water with cadmium concentrations down to and including 0.1
mg/i. Suspicion has been cast on the presence of minute amounts of cadmium in the
kidney as responsible for adverse renal arterial changes in humans.
(4) Chromium. The level of chromate ion that can be tolerated over a
Iifetime without adverse effects on health is unknown. However, hexavalent chromium
is known to have carcinogenic (cancer-causing) potential. Chromium is a known
carcinogen agent when inhaled. A chromate concentration of 0.05 mg/l has been found
toxic to Daphnia magna (a fresh-water crustacean).