192
Trace Elements in Abiotic and Biotic Environments
Processes governing Mn behavior in soils are complex, and may be presented as
follows (Negra et al. vide Kabata-Pendias 2011):
r Reduction: Mn 3+ → Mn 2+ , abiotic and biotic, by Fe 2+ , Cr 3+ , S, phenols, OM,
and reducing bacteria
r Oxidation: Mn 2+ → Mn 3+ , Mn 4+ , can occur under both aerobic and anaerobic conditions and is biologically mediated or autocatalytic
r Mn 3+ is the extremely reactive redox species and quickly disappears, either
by accepting or donating an electron
r Mn 2+ is either absorbed by MnO 2 , or oxidized to Mn 3+ , or Mn 4+
r Organic and phosphate ligands are involved in the Mn–redox cycling
Manganese budgets (input/output ratio) in soils of various ecosystems indicate a
predomination of leaching processes over atmospheric input. In some forests (pine,
spruce, and birch) Mn leaching from soil profiles accounts from 360 to 6100 g/ha/yr,
whereas in some agriculture ecosystems the accumulation of Mn has been observed,
within the range of 90–191 g/ha/yr (Eckel et al. 2005).
All Mn compounds are important, as they are essential in plant nutrition, and control the behavior of many other trace elements. They have also a considerable impact
on some soil properties, and in particular on Eh and pH values. Oxidizing conditions
reduce the bioavailability of trace elements, whereas reducing conditions may lead
to the easy availability of several micronutrients, which may result in their toxicity
to plants. Reducing impact of Mn compounds may also increase Ca mobility, which
resulted in soil acidification. Increased mobility of Mn with lower soil pH resulted in
its increased phytoavailability and its losses from soils (Watmough et al. 2007).
Manganese has not been considered to be a polluting metal in soils; however, the maximum allowable concentration value for Mn is estimated to range
at 1500–3000 mg/kg. Its major anthropogenic sources are municipal wastewater,
sewage sludge, and metal smelting processes. In some regions (e.g., Mississippi
River delta), alluvial sediments concentrate Mn up to 2700 mg/kg (Mielke et al.
vide Kabata-Pendias 2011). Also, soils irrigated with water affected by acid mine
drainage contain elevated amounts of Mn. Its content in soils after sludge application increased from 242 to 555 mg/kg, during five years. After longer period of Mn
addition to soils with sludge, toxic effects of Mn in some plants might be observed.
26.3 WATERS
Worldwide mean Mn concentration in seawater is calculated to range from 0.4 to
10 μg/L, with an average of about 2 μg/L (ATSDR 2002b). However, various values
are given as median Mn concentrations for ocean water (in μg/L): 0.02–0.1 (Kitano
1992); 0.2 (Reimann and de Caritat 1998); and 0.02 (Nozaki 2005). In the Baltic Sea,
Mn concentrations range from <1 to 3 μg/L (Szefer 2002). Manganese concentrations in water of Nordic Lakes of different countries vary as follows (mean values, in
μg/L): Norway, 101; Finland, 316; and Sweden, 474 (Skjelkvale et al. 2001). Rivers
of the United States contains Mn within the range of 11–51 μg/L (ATSDR 2002b).
The global riverine flux of Mn in worldwide seas is estimated at 1270 kt/yr (Gaillardet
et al. 2003). According to the calculation of Kitano (1992), Mn input to worldwide seas