Lead [Pb, 82]
171
these pellets, depending on soil conditions and the climate. Lead particles become
more rapidly degraded in acid soils or water, at a high concentration of dissolved
oxygen (Mezhibor et al. 2011).
Peat bogs are good records of atmospheric Pb deposition due to a great capacity
to accumulate and strong fixation of this metal. The anthropogenic Pb deposition,
back at least to Greek and Roman times, has been traced in peat cores of several
European countries. Lead concentrations in the present-time peat bogs is about 100
times higher than in peat layer of preanthropogenic times. Accumulation of Pb in
peat bogs and soils are regarded as sink of deposited atmospheric Pb, which may be
its significant source to the fluvial systems, due to peat erosion processes (Rothwell
et al. vide Kabata-Pendias 2011).
The main Pb pollutants emitted from industries often occur in mineral forms:
PbS, PbO, PbSO 4 , and PbO·PbSO 4 . In automobile exhausts, it is mainly in the forms
of halite salts: PbBr, PbBrCl, Pb(OH)Br, and (PbO) 2 PbBr 2 . These compounds in soils
may be easily converted into other compounds and fixed by soil particles. Some Pb
species may be methylated, due to both biological and chemical processes. The Pb
contamination of roadside soils was, for quite a time, of a real environmental concern. Although Pb additives in petrol are banned in most countries, its increased
levels (up to about 7000 mg/kg) in soils along high traffic roads have been still
observed. Tetraethyl and tetramethyl Pb present in soils along highways are converted into water-soluble compounds; nevertheless, they are not significantly leached
down soil profiles (Ou et al. vide Kabata-Pendias 2011). Soils within the city of Łódź
(Poland) contain Pb up to 60 mg/kg, as effects of contaminations from the power
plant and motor traffic (Jankiewicz and Adamczyk 2007).
Other important source of Pb are paints, commonly used in home and garden
areas. The most common forms of added Pb are PbCrO 4 and PbCO 3 . Lead is added to
paints to speed up drying, increase durability, maintain a fresh appearance, and resist
moisture that causes corrosion. Soils around pylons painted with red lead before 1970
contain still elevated Pb levels, up to 783 mg/kg (Brokbartold et al. 2012).
In some countries (e.g., the United States and the United Kingdom) there are regulations, since 1978, prohibiting the use of Pb paints; however, these paints may still
be found in older properties painted prior to this regulation, and are still used in road
markings. The content of Pb is higher in soils around old houses, than in new ones.
The geometric mean Pb in 4650 garden soils of the United Kingdom is calculated
as 298 mg/kg (Thornton vide Kabata-Pendias 2011). Elevated Pb contents of garden
soils are of a special risk due to pica soil (hand-to-mouth) behavior of children. The
limit for Pb in soils of play areas is estimated at 400 mg/kg, and in surrounding sites,
up to 1200 mg/kg. However, Pb levels above 1000 mg/kg are hazardous to cattle.
Soil-quality Pb levels are estimated, based on various criteria, within the range of
60–1000 mg/kg.
The criteria for contaminated land (Dutch List 2013), following Pb concentrations in soils and groundwater, are established (in mg/kg and μg/L) as follows:
uncontaminated, 50 and 20; medium contaminated, 150 and 50; and heavily contaminated, 600 and 200. Groundwater in the United States contains Pb within the
range of 5–30 μg/L, and in the European parts of Russia its concentration is within
0.1–8 μg/L (Kabata-Pendias and Mukherjee 2007).