Burt is partially correct-in the presence of organic acids, elemental
lead, as in lead shot, is rapidly oxidized by air to lead salts. The
solubility of lead salts, like most other transition metals, is
drastically dependent on pH. In basic or neutral solutions, lead salts
such as the hydroxide or sulfide are essentially insoluble. As the pH
decreases to acid ranges, the solubility increases greatly. Also, the
the presence of organic acids can futher increase solubility. Many
plants and bacteria secrete binding compounds into the environment to
increase their ability to dissolve metals. One hypothesis for the damge
done to forests by acid rain is that the decreased soil pH increases the
mobility and solubility of soil metals so that the trees get too much
metal abosrbed-though the data on this is sketchy.

As to toxic effects-in addition to causing neurologic damage, lead
exposure also damages the enzymes involved in heme biosynthesis.
Relevant to human bone and bird eggs, lead is also a fairly good chemical
mimic of calcium; frequently lead salts are mixed in with calcium salts
in biological structures such as bone, eggs, and calcium carbonate shells.
In humans, it appears that while adults absorb fairly little ingested
lead, children and infants may absorb at least 40% of the lead they ingest.

Humans have been smelting lead a long time-ice borings from Greenland
clearly show when humans in Europe first learned to smelt lead by a huge
increase in deposited lead dating back a few thousand years. Also
remember, some estimates have placed up to 10% of lead in surface
environments in North America as a residue of our love for high octane
gas and the addition of tetraethyllead to gasoline for a few decades
It is also common in solders(frequently appearing as a toxin in bad
moonshines), house paints(still a problem in neighborhoods with old
houses) and as a component in mining slags-Asarco in Tacoma left that
area with a large dusting of lead both on shore and in the material they
dumped in the sound.

Jim Neitzel
The Evergreen State College
neitzelj at elwha.evergreen.edu