Inorganic lead arising from a number of industrial
and mining sources occurs in water in the +2
oxidation state. Lead from leaded gasoline used to
be a major source of atmospheric and terrestrial lead,
much of which eventually enters natural water systems.
Despite greatly increased total use of lead by
industry, evidence from hair samples and other
sources indicates that body burdens of this toxic metal
have decreased during recent decades. This may be
the result of less lead used in plumbing and other
products that commonly come in contact with food
or drink. Acute lead poisoning in humans causes severe
dysfunction in the kidneys, reproductive system,
liver, and the brain and nervous system.
Because of its toxicity, its mobilisation as methylated
forms by anaerobic bacteria, and other pollution
factors, mercury generates a great deal of concern
as a heavy-metal pollutant. Mercury is found as
a trace component of many minerals, with continental
rocks containing an average of around 80 ppb, or
slightly less, of this element. Cinnabar, red mercuric
sulphide, is the chief commercial mercury ore. Metallic
mercury is used as an electrode in the electrolytic
generation of chlorine gas, in laboratory vacuum