Chemistry Reference
In-Depth Information
of lead to the atmosphere were estimated as between
400,000 and 500,000 tons (Lantzy and Mackenzie, 1979;
Nriagu, 1989), a value exceeding the natural cycling of
lead by approximately 100 times. An average sediment
enrichment factor for lead in lake and coastal sediments
of 4.1 has been reported (Salomons and Förstner, 1984).
Tetramethyl and tetraethyl lead are added to pet-
rol as antiknocking agents. During combustion in an
engine, the organic lead compounds will be split to
methyl and ethyl radicals (that prevent unwanted
chain reactions—knocking) and elementary lead. The
elementary lead is oxidized to PbO, which will react
with HBr and HCl under the formation of PbBrCl
and salts of lead, ammonium, chloride, and bromide.
Dibromo and dichloroethylene are added to the gaso-
line with the purpose of removing the lead from the
engine (combustion of the ethylene compounds yields
HBr and HCl). The lead salts formed are found in the
exhaust gas as particles, of which 95% have a diameter
less than 0.5
8.8.1 Lead in Ammunition
The use of lead in ammunition has resulted in the
dispersal of major quantities of this metal in the envi-
ronment. In Denmark alone, approximately 800-1000
tons of lead was used for this purpose each year (until
around 1990). Approximately 200 tons of these ended
up in shallow, coastal areas. Occurrences of up to 10
lead shots/m
2
are not unusual, and in some fi ords in
Western Jutland, several hundred lead shots/m
2
have
been found (Danish EPA, 1989). Extreme values of
more than 2 kg/m
2
have been found in shallow waters
in the vicinity of shooting ranges. The problem with
the dispersal of lead ammunition in the environment
through hunting has been attempted by exchanging
lead shots with steel shot, and the use of lead shot is
now forbidden in many countries. However, the deg-
radation of the lead shots that are already in the envi-
ronment proceeds fairly slowly, because the surface of
the lead shot in the anaerobic zone of the sediments
are covered with lead sulfi des that have low solubility
and prevent further degradation. In terrestrial soil, it
is assumed that half of the lead shots will be degraded
in 40-70 years, and that all of the lead shots have been
degraded in 100-300 years (Danish EPA, 1989).
m. During the decades when leaded pet-
rol was used, lead concentrations in urban air could
easily exceed 1
µ
g Pb/m
−3
; the effects on human health
from this exposure are described in Chapter 31.
The particulate lead will—depending on the size of
the particles—be transported for shorter or longer dis-
tances before it is deposited again. A minor fraction of
the emitted lead (bound in the largest particles) hits
the soil quickly and gives rise to lead contamination
along the roads. Particles with a diameter <0.5
µ
8.8.2 Effects in Birds and Mammals
Studies of rats (Mouw
et al
., 1975), pigeons (Hutton,
1980), starlings (Grue
et al
., 1986), and swallows (Grue
et al
., 1984) living near traffi cked roads while the use
of leaded petrol was at its highest showed increased
concentrations of lead in the investigated animals and
lower ALAD activity than was seen in animals from
more rural areas. The reduction in ALAD activity in
the swallows did not lead to reductions in the concen-
trations of hemoglobin, and the breeding success of the
animals was not affected (Grue
et al
., 1984).
Ducks and swans normally ingest sand, gravel, and
small stones that in the gizzard participate in grinding
the food. If the birds instead ingest lead shot, the lead
shots will dissolve in the gizzard and digestive sys-
tem. The lead taken up causes lead poisoning, and for
swans in Western Jutland, lead poisoning used to be
the most common cause of death. Lead-poisoned birds
initially have paralysis in the esophagus and digestive
system, and at later stages in the legs, neck, and wings;
concurrently, the sense of equilibrium is lost. One to
two lead shots may be a lethal dose.
m may
remain in the atmosphere for long a time, and the lead
emitted subsequent to the use of leaded petrol gave
rise to global lead contamination.
This emission of lead can be traced in different
compartments in the environment, for example, in the
Greenland ice cap and in the oceans. The prehistoric lead
concentrations in the Greenland ice cap were only a few
pg/g. From approximately 1750, lead concentrations
increased linearly, reaching approximately 60 pg/g in
1940. After leaded petrol was taken into use in the 1940s,
lead concentrations increased very rapidly, reaching lev-
els as high as 400-500 pg/g in the 1970s. When the use
of leaded petrol was gradually phased out between the
1970s and the late 1990s in North America and Europe,
the lead concentrations in the ice layers decreased cor-
respondingly (Murozumi
et al
., 1969).
Lead concentrations in the oceans show a peak in
the upper 500-1000 m because of the atmospheric dep-
osition. In the Pacifi c Ocean, peak values of approxi-
mately 10 ng Pb/L are found (Schaule and Patterson,
1981), whereas levels in the Northern Atlantic (infl u-
enced by emissions from both the North American
and the European continents) reach 40 ng Pb/L. Below
2000 m, lead concentrations typically range between 1
and 2 ng Pb/L.
µ
8.9 Manganese
Under oxidized conditions, manganese exists in a
multitude of oxy- and hydroxide forms (e.g., vernadite
-MnO
2
, hausmannite Mn
3
O
4
, feitknechtite -MnOOH)
