Molybdenum [Mo, 42]
215
Various types of industrial pollution may be responsible for elevated Mo contents in soils. Some sewage sludge contain high levels of Mo, up to about 50 mg/kg
(Lahamann vide Kabata-Pendias 2011). Also, fly ash from some coal-fired power
plants may be a potential Mo source.
Contamination of soils (Dutch List 2013), following Mo concentrations in soils
and groundwater, is established (in mg/kg and μg/L) as follows: uncontaminated, 10
and 5; medium contaminated, 40 and 20; and heavily contaminated, 200 and 100.
28.3 WATERS
The concentrations of Mo in seawater range from <0.1 to 10 μg/L. Water of the Baltic
Sea contain Mo within the range of 1.6–6.3 μg/L (Szefer 2002). Contents of Mo in terrestrial water are also highly variable, within the range of 0.04–1.3 μg/L (Table 28.1).
Molybdenum in seawater is relatively unreactive; in oxygenated conditions its
concentration is rather stable, whereas in anoxic water, it readily precipitates in
bottom sediments. The pH–Eh water regime control both Mo precipitation and
speciation. Various anionic Mo species predominate in water of different pH as fol−
2−
6−
4−
lows: pH < 5: HMoO ; pH > 5: MoO ; pH < 6: Mo O ; and Mo O (Anbar 2004).
4
4
7 24
8 26
Molybdenum easily forms various compounds with Cl and F.
Rainwater sampled in Sweden, in 1999, contained Mo within the range of 0.03–0.06
μg/L (Eriksson 2001a), whereas in rain collected above the Baltic Sea, in about the
same period, its contents varied between 0.08 and 0.27 μg/L (Szefer 2002).
Median Mo concentration in bottled water of the EU countries is 0.275  μg/L,
and is a bit higher than in tap water, estimated as 0.233 μg/L (Birke et al. 2010). As
molybdenum occurs at very low concentrations in drinking water, it is not considered necessary to set a formal guideline value. Reason for not establishing a guideline value is that Mo occurs in drinking water at concentrations well below that of
health concern (WHO 2011a).
28.4 AIR
Molybdenum concentration in the atmosphere highly vary, from <0.2 to 10 ng/m 3 , in
remote and industrial regions, respectively (Table 28.1). Its highest contents are in heavy
industrial, and especially in steel works, vicinities. Relatively high Mo concentrations
are present in airborne ash expelled usually during the combustion of fossil fuels.
Its bulk deposition in Kola Peninsula is estimated (in kg/km 2 /yr) at 0.043 in
remote areas, and 0.923 in polluted areas (Reimann and de Caritat 1998).
Range of Mo contents of moss (Hylocomium splendens) from the mountains in
Poland (0.1–0.3 mg/kg) are fairly similar to those from Alaska (<0.05–0.3 mg/kg). This
may suggest similar Mo atmospheric deposits in both regions (Migaszewski et al. 2009).
28.5 PLANTS
Molybdenum is essential to plants, but physiological requirement for this element is
relatively low. Its phytoavailability increases with soil pH, and is proportional to its
concentration in the soil solution. Molybdenum is moderately mobile in plants, and