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Trace Elements in Abiotic and Biotic Environments
observed. Especially sulfate-reducing bacteria can influence a rapid dissolution of
RaSO 4 , mainly under reducing conditions in sludge. Thus, Ra mobility is enhanced
under anaerobic conditions and in acid soils. In moist soils, its mobility and bioavailability are highly increased.
Some soils derived from granite and limestone, argillaceous limestones in particular, contain elevated amounts of 226 Ra. Its distribution is associated with Ca, Mg,
Al, and SO 4 (Megumi and Mamuro vide Kabata-Pendias 2011).
Also soluble organic matter (SOM) and Fe–Mn hydroxides, as well as clay minerals, have a strong affinity for Ra and significantly decrease its exchangeable fraction,
especially in neutral and alkaline pH range of soils. Apparently, 226 Ra may form
complexes on the clay surface and also within the inner space. Its mobile species in
soils amount to 1%–10% of the total contents.
35.3 WATERS
Worldwide average Ra concentration in river waters is estimated to be 0.024 pg/L,
within the range of 0.002–0.09  pg/L, with the highest values for Asian rivers
(Gaillardet et  al. 2003). Its mean concentration in seawaters is around 1  pg/L. In
general, concentrations of two radioisotopes of Ra in surface water and groundwaters are low. However, in some geographic regions, it may be elevated due to the
impact of bed rocks. Its concentrations may also be higher in waters from deep wells,
located near radioactive waste disposal sites.
The common 226 Ra content in drinking water of the United States ranges from
0.9 to 10 pCi/L (ATSDR 2002b). The maximum allowable concentration value
for Ra in drinking water of Russia was established for 0.1 pg/L (Reimann and de
Caritat 1998). Its levels are usually around 1 pCi/L; higher levels, >5 pCi/L, are
dangerous for human. Guidance level for 226 Ra in drinking water is 1 Bq/L (WHO
2011a).
Radium in water is relatively easily available to aquatic biota. Marine plants
and animals may contain Ra on the order of 100 times of that in the water media.
Especially predatory fish, from water basins with contaminated bottom sediments
(e.g., from industrial or cities effluents), have highly elevated Ra contents (ATSDR
2002b).
Significant sources of Ra are U mine tailings and processing effluents. Also water
discharged from some coal mines may contain elevated Ra levels (Pluta vide KabataPendias and Mukherjee 2007). Residues from oil and gas industries often contain
226 Ra and its daughters. Water from oil well, when discharged into the sea and mixed
with seawater, may affect the precipitation of Ra and its accumulation in bottom
sediments.
35.4 AIR
The combustion of coal is the most common and important source of Ra in the atmosphere. Radium may concentrate in fly ash, which is within the range of 1–10 pCi/g
(1 pCi equal to 0.04 Bq/g). It is estimated that a single l000-MW coal-fired power
plant will discharge about 28 mCi of total radium per year.