Chemistry Reference
In-Depth Information
researchers, includes studies on the effect of exposure
to MeHg through consumption of contaminated fi sh
among inhabitants of the Seychelle islands. A Danish
research group is carrying out a similar project at Färö
Islands.
Inorganic arsenic occurs in high concentrations
in bedrocks and groundwater in several parts of the
world (e.g., in Taiwan, India, Bangladesh, Argentina,
and Chile). Large populations have been exposed, and
in some places mass outbreaks of severe poisonings
have occurred. Skin cancer and cardiovascular disor-
ders are common. I had the opportunity, as a WHO
consultant, to observe the disastrous effect arsenic had
had in some places in Taiwan.
In 1976, the Scientifi c Committee was one of the
sponsors of an International Conference on Environ-
mental Arsenic at Fort Lauderdale, Florida. In 1980, a
WHO Task Group Meeting on Environmental Health
Criteria for Arsenic was held in Stockholm, Sweden.
It was pointed out that there was a risk for skin dis-
ease and certain forms of cancer from drinking water
contaminated with arsenic.
The consequences apparently have not been taken
seriously. Through the use of international foreign
aid money, including Swedish, British, and the World
Bank, a massive assistance program was launched in
Bangladesh for several years with the aim to drill deep
into the bedrock to get ground water. This was badly
needed because contaminated surface water was the
main source of water. No one was aware of the risk
for arsenic poisoning. A detailed survey of the conse-
quences of the Swedish assistance project, sponsored
by SIDA (Swedish International Development Coop-
eration Agency), was recently published in a Swedish
newspaper (DN April 19, 2005). Sweden was fi nanc-
ing the drilling of approximately 12,000 wells between
1990 and 2000. In total, the drilling of approximately
a million wells was sponsored by international or-
ganizations. Now the drilling has been stopped, and
emphasis is on analytical and technical programs.
One meeting of particular importance for the Hand-
book and referred to previously (TGMT, 1979) concerned
the concept of a critical concentration of a metal in a cell
or in an organ. The metal concentration at which adverse
functional changes occur in the cell was defi ned as the
critical concentration for the cell. The critical organ concen-
tration was defi ned as the mean concentration in an organ
that would be necessary for a number of the most sensitive
cells in the organ to be affected. The term “critical organ”
was used to identify that particular organ that fi rst attains
the critical concentration of a metal under specifi ed cir-
cumstances of exposure and for a given population. This
defi nition differs from other ones used in radiation protec-
tion, in which the term “critical organ” refers to that organ
of the body whose damage results in the greatest injury to
the individual. The critical effect as defi ned by the Scien-
tifi c Committee gives possibilities of preventing more seri-
ous effects. It is also important to recognize that the critical
concentration varies between individuals and that it is,
therefore, not possible to talk about one single value only.
With some modifi cations, which have been included
in the glossary (Nordberg
et al.,
2004a), we have, when
drafting the different chapters in the new edition of the
Handbook, tried to use the aforementioned concepts.
Another topic of great importance for evaluating
exposure and risks relates to biological monitoring of
metals in, for example, blood and urine. The quality
of published data is often very poor, even if the situa-
tion has improved. The assessment of metals in trace
concentrations in biological media is fraught with dif-
fi culties from the collection, handling, and storage of
samples to chemical analyses.
A systematic approach to quality assurance aspects
related to biological monitoring was taken in a 3-year
global project by WHO/UNEP. Quality control exercis-
es were carried out with 10 participating laboratories in
different parts of the world. The Scientifi c Committee
sponsored a meeting where the different aspects of bi-
ological monitoring were discussed in detail (Clarkson
et al.
, 1988).
Metals do not break down. As a consequence, a
metal stays in the body until it is excreted. During this
time, the metal may be transformed into another more
toxic or less toxic species. Inhalation of mercury vapor
may be used as an example. Metallic mercury vapor is
released from both old and new amalgam fi llings.
It is taken up in the blood during inhalation and is oxi-
dized within minutes to divalent mercury. Parts of the
mercury vapor penetrate the blood-brain barrier and
in pregnant women also the placental barrier. In the
brain, it is oxidized into divalent inorganic mercury
and is excreted only very slowly with a biological half-
time of years. This explains why even minor inhalation
of mercury vapor from amalgam fi llings may create
health problems.
Some reports indicate a potential danger of using dental
amalgam, whereas others deny it. In some countries, the
use of amalgam has been banned. The situation is to some
extent similar to the banning of tetraethyl lead in gasoline.
Even so there are problems. Old fi llings will continue to
release mercury for many years. The symptoms many
patients complain about are nonspecifi c and are seen in
many other diseases. It would be useful to collect as much
information as possible on the health effects of amalgam in
different countries (Chapter 33, Bellinger
et al.,
2006).
Cadmium occurs naturally in the environment
and some places, around, for example, mines may be
heavily contaminated. Nowadays humans are exposed
