Chemistry Reference
In-Depth Information
the United Kingdom). In other instances, the authority
derives from regulation by governmental agencies at
various levels (federal, state, or local) or from collective
bargaining agreements. Before such authority is estab-
lished, there may be a need to create political pressure.
Those engaged in research must not withdraw into
an ivory tower. On the contrary, their responsibility is
to provide politicians and policy makers with unbiased
data and opinions on the basis of scientifi c judgment to
assist the development of sound prevention programs.
Researchers should also offer the public correct facts
and should oppose any exaggeration created by mass
media, misinformation inspired by industry, adminis-
trative indolence, and any forms of misinterpretation.
These are core principles of the developing fi eld of risk
communication (Gheorghe and Seiler, 1998; Lee
et al.,
1998; Sandman, 1993).
a pregnant woman carries to work has vulnerabilities
that are very different from those of an adult worker.
Children's high degree of vulnerability to toxicity
caused by metals refl ects the fact that they have excep-
tionally heavy exposures coupled with unique bio-
logical vulnerabilities. Kilogram for kilogram of body
weight, children drink more water, eat more food, and
breathe more air than adults. In the fi rst 6 months of
life, children drink seven times as much water per day
as the average adult. Children between 1 and 5 years
of age eat three to four times as much food as an adult.
The implication of these fi ndings for health is that chil-
dren have substantially heavier exposures than adults
to any metals that are present in water, food, or air
(National Academy of Sciences, 1993a).
Children's metabolic pathways, especially in the
fi rst months after birth, are immature. Their ability to
metabolize, detoxify, and excrete many substances dif-
fers from that of adults. In some instances, children are
better able to deal with chemical toxicants. More com-
monly, however, they are less well able to deal with
toxic metals, such as lead.
Children are undergoing rapid growth and develop-
ment, and these highly complex developmental proc-
esses are easily disrupted. Organ systems undergo very
rapid change prenatally, as well as in the fi rst months
and years after birth. These developmental processes
are very delicate and may be unable to repair damage
caused by environmental toxicants. If chemicals such
as lead, mercury, or solvents destroy cells in an infant's
brain, the risk is high that the resulting dysfunction
will be permanent and irreversible.
Because children have more future years of life than
most adults, they have more time to develop chronic
diseases triggered by early exposures. Many human
diseases, including neurodegenerative diseases and
many cancers, are now thought to arise through
a series of stages that require years or even decades to
evolve form the earliest initiation to the actual mani-
festation of disease (Landrigan
et al.,
2005). Recent
studies raise the hypothesis that exposures to metals
in early life may increase later risk for Parkinson's dis-
ease—in relation to manganese exposure (Logroscino,
2005; Zatta
et al.,
2003)— and for dementia—in relation
to exposure to lead (Stewart
et al.,
2002). Genetically
mediated differences in susceptibility among individ-
uals may modulate these effects.
4 PREVENTION OF THE EFFECTS OF
METAL TOXICITY IN THE GENERAL
ENVIRONMENT
4.1 General Considerations
Industrial activity during the past 200 years, and espe-
cially in the past 50 years, has caused a sharp increase in
the concentration of many metals in air, soil, water, and
other environmental media worldwide (see Dick, 1991;
Lockhart
et al.,
1992; Mage
et al.,
1996). Consequently, the
likelihood that the general public will be exposed to toxic
metals is greater than in the past and growing.
Exposure levels vary greatly, depending on geographi-
cal, cultural, and other circumstances (see WHO, 1973).
Urban environments are typically more polluted than
rural areas, and industrialization increases exposures
directly through emissions and indirectly through its prod-
ucts. Local practices—for instance, the use of lead-glazed
ceramic containers and battery recycling—may further
cause exceptionally high exposures (Romieu and Hern-
andez-Avila
,
2003). Finally, enrichment may take place in
food chains, such as the bioaccumulation of methylmer-
cury in marine food webs (Hansen and Gilman
,
2005).
4.2. The Unique Vulnerability of Infants
and Children to Poisoning by Metals
Children are especially susceptible to adverse
health effects from exposure to metals dispersed in the
environment. Infants and children have unique pat-
terns of exposure and developmentally determined
susceptibilities that differ qualitatively from those of
adults and that generally increase their risk of toxicity
(National Academy of Sciences, 1993a). The fetus that
4.3 Reduction of Exposure
4.3.1 Elimination or Reduction of Use
The most effective method for control of the
spread of a metal into the general environment is the
