Page 472 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 29

Lead

Larry J. Thompson

INTRODUCTION environmental contamination from mining, smelting, and
recycling operations. As a result of increased regulation
Lead is a bluish white to gray heavy metal that was prob-
of lead and the decreasing use of lead-containing pro-
ably the first toxic element recognized by man and still
ducts, the overall incidence of lead poisoning (also called
has great relevance today. The chemical symbol for lead,
plumbism) in animals and humans has been decreasing.
Pb, is short for the Latin word plumbum, meaning liquid
While environmental contamination with lead does not
silver. The main source of lead is the ore named galena,
resolve readily, the overt poisoning of domestic animals
which contains lead sulfide. The main use of lead today is
from environmental sources (e.g., from contaminated
in lead-acid storage batteries, but historically it has had
forages, plants, water, or other food sources) has been
widespread usage in paints (white, yellow and red pig-
decreasing in number. Still, lead poisoning in animals is
ments) and as a gasoline additive (tetraethyl lead),
encountered with greatest frequency compared to any
although these latter uses have essentially been phased
other metal.
out. A debate still continues as to the role lead played in
the fall of the Roman Empire. Although lead was indeed
used in some Roman water pipes (the word plumbum TOXICOKINETICS
leading to our modern word plumber), the main source of
The main route of entry of lead into the body is the diges-
lead for the Romans was probably sapa, a syrup used to
tive tract with absorption dependent upon the chemical
sweeten wine and preserve fruit, which was made by boil-
form of lead and the physiological state of the animal.
ing grape juice in lead pots thereby adding lead acetate to
Organic lead compounds are, in general, more readily
the liquid. The use of lead continues in our modern world
absorbed than either inorganic lead salts or the metallic
with lead-containing solder in our electronics as well as
form of lead. Dermal absorption of organolead com-
lead-containing glass, from cathode ray tube monitors to
pounds can be significant, but the salt or metallic forms
fine crystal. Among all the metals, lead poisoning is
of lead are not absorbed dermally. The fumes from heated
encountered with greatest frequency in certain species of
lead or very fine particles (,0.5 μm) of lead can enter the
animals and poses a serious concern to animal health.
lung alveoli and be absorbed with the larger particles
This chapter describes the toxicity of lead in mammalian
lodging in the ciliated portion of the bronchial tree. These
and avian species.
larger particles can be transported up by mucociliary
action and then swallowed with absorption through the
gastrointestinal (GI) tract. Fine particles of lead and lead
BACKGROUND
salts can be solubilized in the acid environment of the
Lead is a toxic element and has not been shown to be an stomach, and the small intestine is the site of most lead
essential trace element for nutrition. The historical use of absorption. Absorption of lead from the alimentary tract
lead in gasoline, paint, construction materials, and many is usually influenced by dietary factors and by the size of
other products has resulted in lead being one of the most lead particles. High dietary fat and mineral deficiency can
significant environmental contaminants in the world. increase lead absorption by seven and 20-fold, respec-
Additional sources of lead have included lead weights tively. In an experimental study, dogs maintained on a
(e.g., for fishing or curtains), small lead trinkets and toys, high-fat, low-calcium diet absorbed significantly more
lead shot and bullets for weapons, lead arsenate pesti- lead than those kept on a balanced diet (Hamir et al.,
cides, and many other products as well as single source 1988). Young animals absorb a larger portion of the lead
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00029-5
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