Metals, their Biological Functions and Harmful Impacts - Mining and the Environment: From Ore to Metal - page 483

Each metal has its own history of discovery; and its use for and harm to life. From the
viewpoint of environmental harm, most people associate lead, mercury, arsenic, cadmium,
chromium, copper and uranium with mining.

Lead

Water pipes in ancient Rome, some of which still carry water, were made of lead. The
English words plumber and plumbing are derived from the Latin word for lead, plumbum.
Plumbum is also the source of the chemical symbol for lead, Pb. Lead has a low melting
point and volatilizes relatively easily. It is hypothesized that lead poisoning due to the use
of lead piping contributed to the fall of the Roman Empire (Gili llan 1965). Today, lead is
no longer used as piping, and its main use is in car batteries.
However the continued use of leaded gasoline in developing countries is a major health
concern, particularly because of its possible impact on children. Lead inl uences the devel-
opment and functioning of the nervous system, slowing down neural response, affecting
learning ability and behaviour (RTI 1999). Children may be exposed to lead in utero , since
embryos can receive lead from the mother's blood. They may also be exposed to lead con-
taminated dust and soil. Lead in the environment is known to be toxic to plants, animals
and microorganisms. Effects are generally locally limited, such as metropolitan areas (use
of leaded gasoline), aquatic regimes downstream of lead bearing rocks (ore bodies or mine
waste), and in the vicinity of lead smelters. In a recent case in Western Australia, thou-
sands of birds were killed and local water supplies contaminated by dust from lead con-
centrate which was being shipped from the Port of Esperance (see also Case 4.6 ). Although
the health effects of lead have been restricted to the immediate areas of lead emissions,
lead from gasoline has been widely dispersed in the environment. In fact, the oceanic dis-
tribution of lead is substantially inl uenced by man's activities (Bruland 1983). This is not
true for any other metal.

The continued use of leaded
gasoline in developing countries
is a major health concern.

Mercury

The term 'native mercury' is used for natural mercury associated with the mineral cinna-
bar. Mercury was named after the Roman god, Mercury . Mercury is also known as quicksil-
ver , from the Greek words, hydros meaning water , and argyros meaning silver, because this
silvery mineral occurs at room temperature as a liquid. The symbol for mercury, Hg, was
derived from the name, hydrargyrum . Mercury is a peculiar metal, being liquid at room
temperature, and naturally occurring in its pure form.
Under reducing conditions in the environment, ionic mercury changes to the uncharged
elemental mercury which is volatile and may be transported over long distances by air; also
it may be chemically or biologically transformed to methylmercury and dimethylmercury,
of which the former is bio-accumulative and the latter is also volatile and may be trans-
ported over long distances. Mercury is not essential for plant, animal or human life. The
main human exposure to mercury is via inhalation of the vapour of elemental mercury
and ingestion of mercury and methylmercury compounds in food.
Mercury and its compounds are toxic to humans, with toxicity varying among the dif-
ferent species ( Case 11.1 ). Methyl mercury poses the most serious threat, and can affect
various organs including the brain (NRC 2000). As with lead, human embryos receive
mercury across the placenta, potentially causing persistent damage to a child's mental
development. Mercury toxicity i rst made headlines following the release of mercuric

Mercury and its compounds are
toxic to humans, with toxicity
varying among the different
species.