Lanthanides
373
The use of LAs is relatively broad in various industries, from glass production
(mainly as colorant) to electronic devices. They are also applied in catalytic converters, batteries, radars, and so on, and are added to some metallic alloys. Cerium is
added to diesel fuel for lowering of the soot ignition temperature and is relatively
slightly trapped by filter (Ulrich and Wicher vide Kabata-Pendias 2011). Especially
Nd is broadly used as a component of the alloys of high strength and applied in
various magnets, such as microphones, computer hard disks, and high-energy lasers.
Recently, it has been utilized in alloys used in the production of green energy.
57.2 SOILS
The mean contents of LAs in various soils range from the highest amounts of La
(26 mg/kg) and Ce (49 mg/kg) to the lowest levels of Yb (2 mg/kg) and Lu (0.3 mg/kg).
Relatively high LA concentrations are reported for soils of China (Table 57.2). Their
occurrence in soils shows a relation to the geologic origin and mineral composition of parent rocks. Usually their lowest amounts are in sandy soils and
the highest in loamy soils. Fine granulometric fraction reveals a great capacity for LAs, especially for their heavy fraction. Usually elements of the group
LLAs  are more abundant in soils than elements of the group HLAs. However,
HLAs are likely to be concentrated more in clay fraction than LLAs. In general,
LAs are accumulated in residual fraction, associated with oxides, phosphates,
carbonates, and silicates.
Organic compounds play a significant role in the distribution of LAs and affect
their increased levels in humus horizons of soils and in forest soil litter. Relatively
high binding activity of soluble organic matter (SOM) toward the LAs is controlled
by pH values. Due to a high capacity of organic matter to bound LAs, their contents
of peats are about 10 times higher than in the surrounding mineral soils (Stern et al.
2007). In most soils, LAs are likely to be concentrated in amorphous Fe oxide-bound
fraction (Hu et al. 2006). According to these authors, LAs with an odd atomic number are likely to predominate in water-soluble and exchangeable fractions.
All LAs are slightly mobile in soils, and their behavior is under the impact of
microorganisms. Some bacteria increase their adsorption to about 1.5% and 4%
for quartz and goethite, respectively (Perelomov and Yoshida 2008). The authors
concluded that increased amounts of LAs, in nonexchangeable forms, on mineral
surface are due to the formation of low-soluble complexes with organic substances
produced by bacteria.
The mobility of LAs in soils is variable and controlled by both soil pH and climatic factors (Tyler 2004). Their distribution in soil profiles is affected by weathering and leaching processes. Soil solutions contain relatively high amounts of ALs,
exceeding 100 times those present in rainwater. Their concentrations in soil solutions
vary for La to Lu from 188 to 1.3 ng/L (Table 57.3).
Fertilizers enriched in LAs have been commonly used in China, since 1980, to
stimulate seed germination, seedling growth, and chlorophyll content. However,
their effects on plant metabolism are variable, and environmental effects have not
been investigated (d’Aquino et al. 2009). There is an estimation that 50–100 million
tons of LAs were added to the agricultural systems of China in 2001 (He et al. vide