Chemistry Reference
In-Depth Information
CHAPTER
47
Zinc
*
HAROLD H. SANDSTEAD AND WILLIAM AU
ABSTRACT
Cu intakes are in the range of the most recent recom-
mended dietary allowance. Present data suggest the
risk of Cu defi ciency is increased when the oral intake
Zn/Cu molar ratio is >18; however, the critical level is
unknown.
Preparation of this chapter was facilitated by com-
mittee reports and reviews (e.g., the 2001 International
Program for Chemical Safety Environmental Health
Criteria Report 221, Zinc (Simon-Hettich,
et al
. 2001), the
2005 US Environmental Protection Agency Toxicologi-
cal Review of Zinc and Compounds (Choudhury
et al.,
2005), a report sponsored by the International Lead Zinc
Research Organization (Walsh
et al
., 1994), and a review
of Zn in soils and crops sponsored by the International
Zinc Association (Alloway, 2003). Other sources were
identifi ed through PubMed,
http://www.ncbi.nlm.nih.gov/
entrez/query.fcgi
, and Google Scholar,
http://scholar.google.
com/schhp?hl=en&tab=ws&q=
Zinc (Zn) is environmentally ubiquitous and essential
for life. The curve in Figure 1 represents Zn nutriture.
The left and right ascending limbs, respectively, repre-
sent risk of defi ciency or excess. At the base is the desir-
able range of intake. The actual shape of the curve is
unknown. Human Zn-defi ciency is common throughout
the life cycle, especially in populations with diets that
infrequently include animal fl esh, and thus are limited
primarily to plant products, many of which are rich in
indigestible Zn-binding ligands. One estimate suggests
20% of the world's population is at risk of Zn defi ciency.
Manifestations include abortion, teratology, prematurity,
retarded growth and development, low immunity, poor
healing, dermatitis, low physical work capacity, abnormal
neuropsychological functions, and other abnormalities.
Human Zn toxicity is considerably less prevalent.
Inhalation of Zn oxide fume generated by welding and
certain other industrial processes causes metal fume
fever, a self-limited fl ulike illness. In contrast, inhala-
tion of Zn chloride, from smoke bombs, causes severe
pulmonary injury and may be fatal. Ingestion of food
or drink contaminated by exposure to galvanized sur-
faces can cause nausea, vomiting, cramps, and diarrhea
that is seldom fatal. Uncontrolled consumption of die-
tary supplements rich in Zn represents a hazard that
is not widely appreciated; intestinal absorption of Cu
is suppressed, and Cu defi ciency can occur. A similar
phenomenon can occur when oral intakes of Zn are
physiological or near physiological, and intakes of
1 IDENTITY AND PHYSICAL/CHEMICAL
PROPERTIES
Properties of Zn include: atomic weight, 65.38;
atomic number, 30; density, 7.13 g/cm
3
; Mohs'
hardness, 2.5; melting point, 419.5°C; boiling point,
908°C; and electrical conductivity, 28.3% of the
international annealed copper standard. Crystal-
line Zn is a bluish white metal with a distorted hex-
agonal close-packed structure. There are five stable
isotopes:
64
Zn (49%),
66
Zn (28%),
68
Zn (19%),
67
Zn
(4.1%), and
70
Zn (0.62%) and 19 known radioactive
isotopes. The half-life of
65
Zn is 243.8 days, and of
69
Zn is 13.8 hours (Simon-Hettich
et al
., 2001; Choud-
hury
et al.,
2005).
*
Dr. Carl-Gustaf Elinder was the author of this chapter in the
2nd edition of the
Handbook on Toxicology of Metals
; his text provided
guidance.
