174
Trace Elements in Abiotic and Biotic Environments
the coating of gills and may destroy antibacterial skin mucous layer. Recently, it
has been observed that Pb concentration in fish of some sea basins is declining.
Lead contents in muscles of herring (Clupea harengus) from the Baltic Sea vary
broadly from 0.01 to 0.03 mg/kg FW, and in shells of mollusks (Mytilus edulis)
range between <0.5 and 5.3 mg/kg FW (Szefer 2002).
24.4 AIR
Concentration of Pb in air varies highly, from about 1 ng/m 3 in the Antarctic regions
to above 10,000 ng/m 3 in urban/industrial areas (Table 24.1). The common range of
natural Pb levels in air is calculated to be within the range of 0.5–10 ng/m 3 , and of
polluted air, in the range of 70–8000 ng/m 3 . Pb concentration in air acceptable by the
U.S. EPA (2008) is 150 ng/m 3 .
Lead enters into the atmosphere from both natural and anthropogenic sources,
which include the combustion of coal, oil, and gasoline; incineration of wastes; roasting and smelting processes; and cement production. On a global basis, anthropogenic
inputs of Pb, in the last century, predominated (at about 96%) its natural sources and
was estimated at about 334 kt/yr (Nriagu and Pacyna 1988). During 1955–1995, Pb
emission in European countries decreased from 62.53 to 28.39  kt/yr (Pacyna and
Pacyna 2001). As a result of the regulatory efforts of the EPA to remove Pb from
motor vehicle gasoline, emissions of Pb from the transportation sector declined by
95% between 1980 and 1999, and its levels in the air decreased by 94% between 1980
and 1999. There are prognoses that the Pb anthropogenic emission will continue
decreasing.
The chemical species of Pb emitted into air depend on its sources. PbCl 2 , PbO,
PbS, PbSiO 3 , PbSO 4 , PbCO 3 , and Pb are released from coal combustion and industry, whereas PbO is mainly released from oil combustion. The size of Pb particles
depend on its sources; the smallest, in the range of 0.1–1.0 μm, are from automobile
exhaust. Lead particles/aerosols in the atmosphere are finely deposited in terrestrial
and aquatic systems.
Lichens and mosses are very sensitive indicators of Pb aerial pollution. It has
been observed that there is a continuous decrease of Pb concentration during the
recent decades. Average Pb contents of moss sampled in Norway during 1990–1995
ranged between 0.88 and 59 mg/kg (Berg and Steinnes 1997). Mosses sampled earlier in Sweden during 1969–1985 contained more Pb, from 20 to 50 mg/kg. Mean
Pb contents of two moss species from mountains in Poland, sampled in 2000 were
higher (9.5–10.1 mg/kg) than those from Alaska (0.63 mg/kg). This suggests that the
atmospheric Pb input is higher in Poland than in Alaska (Migaszewski et al. 2009).
24.5 PLANTS
Lead occurs in all plants, but it has not yet been shown to play any essential roles in
their metabolic processes. Although even a very low Pb content may inhibit some
vital plant processes, its poisoning has seldom been observed in plants growing in
field conditions. However, Pb in plants received much attention, as a major metallic
pollutant in the environment, very toxic to plants, animals, and humans.