Chemistry Reference
In-Depth Information
industrial metal emissions. However, this is not always
suffi cient to control human exposures that are related
to global or regional spread of metals. Despite the suc-
cessful control of point sources of mercury, high lev-
els still occur in Swedish lake fi sh as a result of global
mercury cycling and the acidifi cation and sulfur pollu-
tion of Swedish lakes from European regional sources.
Restrictions in intake of certain species of Swedish lake
fi sh, particularly in pregnant women, thus still are
recommended by the Swedish Food Agency.
One way to limit human exposures to chemical
substances is by labeling. In the EU, as a result of sys-
tematic hazard identifi cation efforts, a large number of
substances have been classifi ed for hazardous prop-
erties. Classifi cation includes acute toxicity (aquatic
and terrestrial), irritation, sensitization, carcinogenic-
ity, and reproductive toxicity, and related labeling is
implemented (cf European Chemicals Bureau: www.
ecb.jrc.it).
If the risk characterization indicates that there are
substantial problems with certain uses of a metal,
authorities may suggest voluntary substitution of
such uses for less toxic substances. If control cannot be
achieved by voluntary measures, a ban of such uses of
highly toxic metal compounds may be considered. For
most metals and uses, this is not possible, but it may
be feasible to restrict the use of the most toxic metals.
Metals are indispensable in a technological society. All
metals are elements that, owing to geological condi-
tions, will be present in varying concentrations in the
earth's crust even in nonindustrialized environments.
Highly toxic metals often occur in nature together with
less toxic metals. Cadmium, for example, is found in
ores together with zinc.
In certain instances, the use of some metal com-
pounds has been successfully prohibited. Several
governments have, for example, forbidden the use of
methylmercury as a fungicide and the use of tetra-
ethyllead as an additive to motor gasoline. Cadmium
and lead compounds have been widely used as color
pigments. Severe restrictions on this practice are now
being enforced in the EU, where many uses of mercury
are also being discouraged. For example, many chlor
alkali plants are being converted to nonmercury-based
technology.
tendency toward accumulation in nature, as well as in
the human organism. We have to live with a certain
amount of exposure to metals both in industry and in
the general environment. A major problem is to deter-
mine what levels of exposure can be accepted with only
a minor, defi ned risk. This discussion focuses on the
effects on humans only. Basically, the same principles
apply when evaluating effects on the environment. For
certain metals, such risks may be the dominating ones,
implying that they should receive priority from the
standpoint of prevention and control.
Standards for chemicals may be formulated either
in terms of concentrations in environmental media
(examples are air quality standards, threshold limit
values, and drinking water standards) or in terms of
amounts of substances that may be ingested into the
body within a given unit of time (e.g., acceptable daily
intake). These concentrations and amounts should be
suffi ciently low so that the threshold dose (if one exists
and can be determined) will not be reached, or so that
the population of concern will not be subjected to
“unacceptable risk” even after a lifetime or a working
lifetime of exposure.
If a signifi cant exposure takes place via different
media, which is often the case for metals, a standard for
one media cannot be considered separately (i.e., with-
out looking into possible exposure by means of other
media). Take lead as an example. In some places, even
the exposure by ambient air, food, and/or water may
give rise to concentrations in blood close to or above
effect levels. In such situations, occupational exposures
must be limited to a very minimum, whereas at other
places where ambient levels are low, a higher occu-
pational exposure can be permitted without causing
adverse health effects.
Depending on whether the risk characterization
indicates that some persons in the population or the
work force (for occupational exposures) are at risk of
adverse health effects, risk reduction measures are rec-
ommended or legislated. Recommendations are issued
by international organizations, and various countries
or unions may issue legislation about permissible
exposure values.
Health-based exposure guidelines are issued by
international organizations such as World Health
Organization (WHO) in collaboration with Food and
Agricultural Organization (FAO). These organizations
issue acceptable daily intakes (ADIs) for food addi-
tives, tolerable daily intakes (TDIs) or provisional
tolerable weekly intakes (PTWIs) for food contami-
nants. Air pollution guidelines and drinking water
guidelines are also recommended by WHO. Recom-
mendations for essential metals have been discussed
in Chapter 9.
6.2 Controlling Human Exposures by
Guidelines and Legislated Permissible
Exposure Levels
Exposure guidelines and standards are necessary for
toxic metals, often more so than for other substances.
Metals are not disintegrated in nature and may be trans-
ported over great distances. Furthermore, they have a
