Lead Listen is the chemical element with atomic number 82, symbol Pb.
Under standard conditions, the single lead body is a malleable, bluish-gray
metal that slowly whitens as it oxidizes. The word lead and the symbol Pb come
from the Latin plumbum (lead metal).
Lead belongs to group 14 and to period 6 of the periodic table. It is the
heaviest with stable elementsb.
Lead is a toxic, mutagenic, and reprotoxic element8, with no known trace element
value. It was indeed classified as potentially carcinogenic in 1980, classified
in group 2B by the International Agency for Research on Cancer (IARC) 9 then as
probably carcinogenic for humans and animals in 20049,10. Two lead salts,
chromate and arsenate, are considered to be certain carcinogens by IARC9.
Lead is an environmental contaminant, toxic and ecotoxic from low doses11. The
diseases and symptoms it causes in humans or animals are grouped under the name
"lead poisoning
Lead - relatively abundant in the earth's crust - is one of the most ancient
metals known and worked. They have been found in pigments covering prehistoric
tombs or spoils (40,000 years BC), but also objects.
Despite its high toxicity, and probably due to its ease of extraction, its great
malleability and its low melting point, it was frequently used during the Bronze
Age, hardened by antimony and arsenic found at the same mining sites. It is
mentioned in the Sumerian cuneiform scriptures - under the term a-gar512 -
almost 5,000 years ago, or in the Exodus, written about 2,500 years ago. It is
often also a by-product of silver mining.
Throughout the ages, many writings relate its presence in objects or across
cultures. The Sumerians, Egyptians, Greeks, Hebrews and even Romans knew how to
extract it. They used it to color and enamel ceramics, to weight hooks, to seal
amphorae, to make eyeshadows, to kohl or to produce everyday objects (from 4,000
to 2,000 years before our era). Lead pipes are also found on ancient Roman
sites.
In the Middle Ages, alchemists believed that lead was the oldest (and coldest)
metal and associated it with the planet Saturn. This is why lead poisoning is
called lead poisoning13.
Its toxicity was known to doctors and miners (slaves and prisoners often) of
antiquity. The Romans used it in the form of lead acetate to store and sweeten
their wine, and had realized that heavy drinkers, therefore of the aristocratic
class, suffered from intoxication.
Later, specific symptoms were described, associated with trades such as miners,
founders, painters or craftsmen making stained glass.
The death of a child in Australia at the end of the 19th century, after lead
poisoning, was the first to raise awareness in a government. It is following the
study of many cases of intoxication that regulation, recommendations and
screening have gradually been implemented in rich countries (such as Europe or
the United States). Lead was thus prohibited for the manufacture of drinking
water distribution pipes in Switzerland from 191414 but much later in other
countries (example: lead paints were prohibited in 1948 in France but the total
ban for pipes only dates from 199515).
Lead has 38 known isotopes, with a mass number ranging from 178 to 215, as well
as 46 nuclear isomers. Four of these isotopes, 204Pb, 206Pb, 207Pb and 208Pb,
are stable, or at least have been observed stable so far, since they are all
suspected of disintegrating by ¦Á decay into corresponding mercury isotopes, with
half extremely long lives16 (which would even be greater than the theoretical
half-life of its constituents, the nucleonsc, going beyond 10100 years17'd).
Lead 204 is entirely a primordial nuclide and not radiogenic. The isotopes lead
206, lead 207, and lead 208 are the end products of three decay chains,
respectively the chain of uranium (or radium, 4n + 2), actinium (4n + 3) and
thorium (4n + 0). Each of these last three isotopes is also, and above all, a
primordial nuclide, produced by supernovae as well as by collisions of neutron
stars.
The relative amount of radiogenic lead to total lead would be less than 1%.
The four stable isotopes, 204Pb, 206Pb, 207Pb and 208Pb, are present in nature
in a ratio 1.4 / 24.1 / 22.1 / 52.4 and 5 radioisotopes are also present in
trace amounts. The standard atomic mass of lead is 207.2 (1) u.
Isotopes are sometimes used for isotopic tracing of lead and during isotopic
analyzes intended to study the environmental kinetics of certain pollutants in
the environment (ex: hunting lead after having been dissolved in the blood of an
animal suffering from lead poisoning , industrial fallout lead, or tetraethyl
lead from gasoline ...) 18.
¡¡
copper aluminum lead Zinc tin nickel iron
magnesium bismuth manganese chromium cobalt titanium
¡¡
¡¡