In another study, the mean activity concentrations of 228Th, 230Th, and 232Th in New York City air were 36, 36, and 37 aCi/m 3 (aCi=10 −18 Ci), respectively ( Wrenn et al. The atmospheric mass concentration of thorium ranged from 0.2 to 1.0 ng/m 3, with a mean value of 0.3 ng/m 3 in air samples collected from 250 sites in the United States ( Lambert and Wilshire 1979). However, plants grown at the edge of impoundments of uranium tailings containing elevated levels of thorium had a plant/soil concentration ratio of about 3 ( Ibrahim and Whicker 1988). The plant/soil transfer ratio for thorium is <0.01 ( Garten 1978), indicating that it will not bioconcentrate in plants from soil. However, leaching into groundwater is possible in some soils with low sorption capacity and the ability to form soluble complexes. In most cases, thorium will remain strongly sorbed to soil and its mobility will be very slow ( Torstenfelt 1986). The fate and mobility of thorium in soil will be governed by the same principles as in water. Thorium has been found to show significant bioconcentration in lower trophic animals in water, but the bioconcentration factors decrease as the trophic level of aquatic animals increases ( Fisher et al. The concentration of dissolved thorium in some waters may increase due to formation of soluble complexes with carbonate, humic materials, or other ligands in the water ( LaFlamme and Murray 1987). Sediment resuspension and mixing may control the transport of particle-sorbed thorium in water. In water, thorium will be present in suspended matters and sediment and the concentration of soluble thorium will be low (Platford and Joshi 1987). Thorium particles with small aerodynamic diameters (<10 micron aerodynamic diameter) will travel long distances from their sources of emission. Although atmospheric residence times for thorium and compounds were not located, judging from residence times of other metals (e.g., lead) and their compounds, they are likely to be a few days. The rate of deposition will depend on the meteorological conditions, the particle size and density, and the chemical form of thorium particles. Wet and dry deposition are expected to be mechanisms for removal of atmospheric thorium. The primary sources of thorium at the Superfund sites are perhaps from the processing and extraction of thorium, uranium, and radium from ores and concentrates ( EPA 1988a).ĭata regarding the fate and transport of thorium in the air are limited. 1987 Moffett and Tellier 1978 Platford and Joshi 1988). The major industrial releases of thorium to surface waters are effluent discharges from uranium and thorium mining, milling and processing, tin processing, phosphate rock processing, and phosphate fertilizer production facilities ( Hart et al. Uranium and thorium mining, milling and processing, tin processing, phosphate rock processing and phosphate fertilizer production, and coal fired utilities and industrial boilers are the primary anthropogenic sources of thorium in the atmosphere ( Hu and Kandaiya 1985 McNabb et al. Windblown terrestrial dust and volcanic eruptions are two important natural sources of thorium in the air ( Fruchter et al. Release of thorium to the atmosphere can occur both from natural and anthropogenic sources, and emissions from the latter sources can produce locally elevated atmospheric levels of thorium over the background. Thorium is ubiquitous in our environment. Thorium in soil will not bioconcentrate in plants.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |