This paper deals with an aspect of the chemistry of transuranium elements in soils. in order to limit its scope, it deals mainly with Am. More specifically it is concerned with the chemical extractability of 2"lam from an artifictally ‘ contaminated soil as a function of pH and several different soil components. This study is an extention of our previous work with 238pu and 242cm (Nishita 1976). As it will be discussed later, this paper provides several implications on the movement of 2"1am in the soil and its availability to plants. LITERATURE REVIEW Studies on the behavior of Am in soils are still limited. A recent review of Am in soil and plant systems by Brown (1976) indicates that more work has been done with plants. Since the present study pertains to the chemistry of Am in soils, this review is constrained to the information that May serve as background and may be helpful in assessing its behavior in soils. Origin of Am. Among the isotopes of Am, there are two that are relatively long-lived, the 433-year ?"!am and the 7,370-year 23am. Of these, 2lAm is the more important. The isotope 2"!A4m is produced in nuclear reactors by multiple neutron capture (Pigford and Ang, 1975): 239py (nyy) 240Pu (n,y) 24 !Pu iy >» 24lam The isotope 23am is produced by more complicated successive series of neutron capture. In a nuclear detonation, these isotopes can be Produced directly in another manner, i.e., through the formation of very high mass U isotopes by extremely rapid succession of neutron capture (Diamond et al., 1960; Thomas and Perkins, 1974). These U isotopes then decay rapidly to form a spectrum of transuranium elements. The proportion of radionuclides produced by these pathways differ somewhat. Whereas 239°240py and 2% am are the main transuranium @ activities from nuclear detonations, 238py, 24 1am, and the Cm isotopes are lava tPat @ activities from nuclear reactor operations (Thomas and Perkins, The major source of worldwide contamination by 241am is ascribed to the occur- rence of “41am in the fallout from nuclear detonations. The 24) py/239*240p, activity ratios of global fallout present in soils as of January 1, 1970, was 8.2 (Krey and Krajewski, 1972). The 24lam, from 24 lpy decay, is increasing in the global environment (Poet and Martell, 1972; Harley, 1975; Livingston, Schneider, and Bowen, 1975; Krey et al., 1976). Krey et al, (1976) calculated that 2"!am content of the present fallout in the soil will peak in the year 2037 and will represent 42% of the 239°240py activity. The 241am/2397240p, activity ratio of integrated global fallout in February 1974 was around 0.22, According to Poet and Martell (1972), the maximum radioactivity contribution of 7M 1Am would probably occur 70-80 years after the environmental release of Pu. Contamination Level. The actual levels of fallout 2"!Am in surface soil in the United States are estimated to be in the range of 2.4 £Ci/g (calculated from total Pu level of 20 fCi/g (Harley, 1975) by taking Am/Pu ratio into consideration). At Bikini Atoll, which was exposed to close-in fallout, ?*!Am values from 1.2 to 45 pCi/g were observed in surface soil samples collected in 1972 (Nevissi, Schell, and Nelson, 1976). The surface soil (0-1 cm) collected near the Pu processing plant at Rocky Flats in 1969 contained from 0.01 to 0.14 pCi/g. Americium-241 values from 2 x 10 " to 10.4 nCi/g have been observed in the surface sotis (0-5 cm) from Nevada Applied Ecology Group study areas at Nevada Test Site (NTS) (Romney, 1975). Measurements of the vertical distribution of ?"Jam in certain soil profiles at NTS indicate detectable amounts of it are present to a depth of 25 cm (Romney, 1975; Essington et al., 1976). From inferences made from profile distribution of Pu (Nevissi, Schell, and Nelson, 1976), Am might be detectable as deep as 75-100 cm in some soil profiles at Bikini Atoll. Americium and Pu parallel one another in behavior because of their chemical relationship. Chemical Properties. The chemical properties of Am that one, perhaps, should be cognizant of in considering its behavior in soils follow: Americium has the valence states of (0), (III), (IV), (V), and (VI) (Keenan, 1959; Penneman and Keenan, 1960; Keller, 1971). Americium is found in four oxidation states, Am (III), Am (IV), Am (V), and Am (VI), in aqueous solutions (Kehjer, 1971). The trivalent, pentavalent, and hexavalent Am occur as hydrated Am » Am0y , and Am02 ions in the absence of complexing agents. The trivalent state is the most stable one encountered in aqueous solution. The tetravalent Am is stable only in concentrated fluoride and phosphate solutions (Yanir, Givon, and Marcus, 1969), undergoing rapid disproportionation in all other solutions. The pentavalent and hexavalent Am are reduced slowly to lower valence state by the radiolysis products formed by the action of their own a-radiation (Gel'man et al., 1962; Myasoedov et al., 1974). Americium (V) disproportionates in acid solutions to form Am (VI) and Am (IV), and the latter is immediately reduced to Am (III). Americium (V) and Am (VI) are susceptible to reduction by many common reagents (Stokely and Moore, 1967). Americium is relatively stable in strong acid, but is reduced by water if the acid concentration falls below about 0.01 M (Coleman et al., 1963). Under alkaline condition, Am (VI) solution is not stable, but is reduced completely to Am (V) in 1-2 days (Cohen, 1972). In the form of simple hydrated trivalent ion, it reacts similarly to trivalent lanthanide ton and forms sparingly soluble trifluoride, hydroxide, phosphate, iodate, oxalate, and double sulfate (Penneman and Keenan, 1960; Gel'man et al., 1962; Keller, 1971). The readily soluble Am (1II) compounds include the perchlorate, nitrate, sulfate, and halides (Gel'man ef al., 1962). The tendency of Am (III) to form complexes with the anions of inorganic acids are in the following order: F > S0,2 > NO3 > Cl > C10, (Gel'man et al., 1962; Keller, 1971). It forms chelates with synthetic chelating agents such as DTPA (diethylene triaminepentaacetic acid) (Wallace, 1972a, 1972b) and very likely with a number of soil organic components (Mortensen, 1963; Kononova, 1966; Schnitzer and Khan, 1972; Stevenson, 1972). Stability constants of a number of Am chelates have been compiled by Keller (1971). The tendency of Am to form complexes with organic and inorganic ligands relative to other transuranium elements is Pu (IV) > Am (IIIT) = Cm (III) > Pu (VI) > Np (V) (Keller, 1971). 79