Chemistry Reference
In-Depth Information
whiskey [lead], heavy fi sh consumers [mercury], dwell-
ers in districts with lead-plumbing systems [lead],
users of primitive ceramic ware [lead], children drink-
ing well water in Bangladesh [arsenic], and children
living near highways in Australia [manganese]). From
time to time new hazards are recognized—for example,
the recent recognition in the United States of the lead
hazards that result from use of imported medications
containing lead and mercury among Asian immigrants
(Markowitz
et al
., 1994).
Special attention must always be directed to deter-
mining whether young children or women of child-
bearing age are at risk of exposure. In the United States,
in certain states where there are large populations
of young children at risk of exposure to lead-based
paint and to the dust released from this paint, manda-
tory blood lead screening of all children is required at
12 months and 24 months of age.
et al.,
2002). Decreased lifetime economic productivity,
a consequence of the diminution in intelligence caused
by lead, is the principal contributor to these great
economic costs attributable to metal toxicity.
Widespread neurotoxicity could result again, if the
organic manganese compound MMT (methylcyclopen-
tadienyl manganese tricarbonyl) is allowed to be used
extensively as a fuel additive (Weiss, 2005). Manganese
is a known cause of parkinsonism in occupationally
exposed adults (Hunter, 1969; Lucchini, 2005). Lower
dose exposures to manganese have been associated
with developmental neurotoxicity (Mergler
et al.,
1999;
Normandine
et al.,
2004; Wasserman
et al.,
2004).
The potential consequences of population-wide expo-
sure to manganese emitted to the environment from the
combustion of MMT in motor fuels are poorly under-
stood. Information is especially lacking on potential
consequences of exposures to pregnant women and
young children.
5.2 Widening Implications
of Subclinical Toxicity
If a metal is in wide use and has become extensively
dispersed in the environment, the subclinical toxic-
ity that it causes can be equally widespread and can
affect the well-being and the security of entire socie-
ties. Moreover, such widespread subclinical toxicity
can be extremely costly. Such population-wide toxic-
ity occurred in nations around the world in the 20th
century as a consequence of the nearly universal use of
tetraethyl lead as an additive in motor fuel.
Between 1950 and 1975, approximately 100 million
children in the United States and hundreds of mil-
lions more worldwide were exposed to lead emitted
to the environment by the burning of leaded gasoline.
This widespread exposure produced a mean national
blood lead level in US children in the 1970s of nearly
200
5.3 Precautionary Approaches
The history of metal toxicity provides a wealth of
examples, in which opportunities for prevention were
missed, despite early warnings (Hernberg, 2000). More
than 300 years ago, a German state enacted capital
punishment for adulteration of wine with lead, and the
use of lead for water pipes was subsequently outlawed
(Eisinger, 1982). Nonetheless, these uses continued
elsewhere in the world and caused countless cases of
lead poisoning. In the early 20
th
century, the introduc-
tion of tetraethyl lead as an octane booster of gasoline
happened, despite early warnings of neurotoxicity
that were disregarded (Needleman, 2000; Rosner and
Markowitz
,
1985). Although preventive measures are
often initiated long after ample documentation of tox-
icity has been accumulated, long experience with metal
toxicity would suggest that more stringent measures
ought to be considered earlier. Typically, early studies
of the health effects of metals document the existence
of toxicity, whereas later research shows that metals
possess toxic properties at low exposure levels that had
previously been considered “safe” and that toxicity is
more widespread than had originally been imagined.
In the future, it would be prudent to compress this
cycle and to intervene on the basis of early warnings
(Harremoes
et al
., 2002).
To prevent recurrence of such disasters as the addi-
tion of tetraethyl lead to gasoline, the precautionary
principle has recently been formally introduced into
national and international law (Foster
et al.,
2000;
Grandjean, 2004). The key element of the precaution-
ary principle is that it provides justifi cation for act-
ing in the face of uncertainty. It is a tool for acting on
µ
g/L (20
µ
g/dL) (today the mean is less than 20
µ
g
/L [2
g/dL]) and comparable elevations in children
of many other nations. This widespread elevation of
blood lead levels was associated with loss of intel-
ligence that extended across entire populations and
resulted in a 50% decline in the number of truly gifted
children (IQ scores >130) and a corresponding increase
in the number of children with mental retardation (IQ
<70). This widespread loss of intelligence caused life-
long reduction in economic productivity in the affected
birth cohorts, which, in the United States, is estimated
to have cost between $110 billion and $319 billion (USD)
in each annual birth cohort (Grosse
et al.,
2002). The
costs worldwide are many times that sum. Even today,
continuing elevations of blood lead levels in many
thousands of American children are estimated to cost
$43 billion in each annual US birth cohort (Landrigan
µ
