Metals, their Biological Functions and Harmful Impacts - Mining and the Environment: From Ore to Metal - page 479

TABLE 11.1
(Continued)

Metal Shortage Defi ciency Optimal Range Function Excess Toxicity

Iron (Fe) Anaemia Essential - Present in hemoglobin for oxygen

transport

Essentially non-toxic but causes taste problems in water;
may induce vomiting, kidney damage, black stool

Manganese
(Mn)

Anaemia Essential - Present in pyruvate carboxylase

required for the metabolism of sugars; involved
in synthesis of fatty acids and glycoproteins

Affects water taste. Toxic to animals at high
concentrations

Molybdenum
(Mo)

Essential - Involved in electron transfer proc-
esses; Nitrogen fi xation is also coupled to a
molybdenum process

Zinc (Zn) Growth retardation; delayed

sexual maturity

Essential - Essential in several enzymes catalyz-
ing the metabolism of proteins and nucleic acids

May affect water taste at high levels. Irritation of digestive
system, epithelium, vomiting. Toxic to some plants and fi sh

Essential Elements for Some Organisms

Chromium (Cr) Involved in glucose metabolism (insulin) Cr 6 is toxic to humans and can induce skin sensitiza-

ions. Human tolerance of Cr 3 has not been determined

Iodine (I) Essential for some organisms - Present in

thyroxine and related compounds for proper
functioning of the thyroid system

Nickel (Ni) Essential for some organisms -

Component of urease and thus a part of the
CO 2 metabolism

Selenium (Se) Essential for some organisms - Activates

glutathione peroxidase to scavenge free radicals

Valadium (V) Essential for some organisms - Regulation

of intracellular signalling; Cofactor of enzymes
involved in energy metabolism; Possible thera-
peutic agent in diabetes

.

effects. For both metal groups, however, there is a clear concentration 'window' within
which the internal metal concentration of the organism is regulated without causing detri-
mental effects.
With the exceptions of mercury and gold, most metals occur rarely or not at all in metal-
lic form under normal natural situations. Metals remaining in mine and mineral process-
ing wastes are sooner or later transformed into other chemical or physical forms. However,
unlike organic compounds, metals can not be degraded chemically or bacteriologically into
simpler constituents; metals are therefore classii ed as persistent. Metals exist in a wide variety
of physical and chemical states and several forms will coexist, depending on environmental
conditions. In rocks, metals usually occur in the form of insoluble minerals such as silicates

There is a clear concentration
'window' within which the
internal metal concentration of
the organism is regulated without
causing detrimental effects.