of metal ions. The greater 2"!Am extraction by the HNO 3-Na0H system in the alkaline pH range is a reflection of the fact that NaOH is a more effective extractant of soil organic matter than NH,OH. After the removal of organic matter, the effectiveness of the CH3COOH-NH,,OH system in extracting 24lam increased. Apparently, the stability constant of some “*lam-soil organic matter complexes were greater than that of 7"!am-acetate Treatment 1 Control complex. T 100; Dose icpmt. PERCENT OF DOSE EXTRACTABLE A 8 TT Distribution Coefficients. It is well recognized that sorption and extractability are inseparably interrelated. This relationship is usually expressed by distribution coefficients (K,), i.e., the ratio of activities in the solid phase to that in the liquid phase. Since our emphasis here has been the extractability rather than the sorption, the distribution coefficients presented (Table 2) are defined as the ratio of the activities in the liquid phase to that in the solid phase, t.e., T Bo- - ---© CH3COOH - NH AOH System YT A e——-—* HNO,-Na0H System 28, 650 + 963 30,805 + 3063 » TTT TT 100r Treatment T F Et K, 7 (A/a) (w/v) where A; = equilibrium activity in the solution phase, A_ = equilibrium activity in the solid phase, m = mass in grams, and v = volume of solution in milliliters. The K, values (Table 2) reflect,the curves shown in Figs. 1 and 2. With the HNO,-NaoH system, the minimum K, value occurred at pH 7.58, whereas it was at pH 10.20 with the CH3COOH-NHAOH system. The occurrence of the minimum extraction at the higher pH level by the latter system was considered to be due to the lower effectiveness of NH,OH compared to NaOH in extracting soil organic Treatment TV matter. g L 100; on ~~ “A ON ‘ x h. >> ~~, TTT Treatment I : GENERAL DISCUSSION Treatment Y The results provide several implications on the possible behavior of Am in soils. In a kaolinitic soil containing appreciable amounts of organic matter, Am is likely to move fairly readily by the leaching action of water under strongly acidic (pH < 3) or alkaline (pH > 8) condition. In the intermediate pH range (pH 3-8), the movement of Am is expected to be low, but it is likely to be higher on the alkaline side due to the solubilization of alkali~soluble organic matter. With the addition of a relatively weak complexing agent such as the CH,COO ions, the movement is likely to be appreciably increased in the acidic side, but not necessarily in the alkaline side of the pH range. Our unpublished results of the extraction of 239Pu have shown that complexing action of CH3;COO ions is very weak compared to citrate, tartrate, or oxalate fons. In view of this, the addition of a strong complexing or chelating agent probably will increase the Am movement on the alkaline side of the pH range as well. This, however, remains to be determined. Fig. 3. Relative effect of extracting systems on the extractability of 24am from contaminated Aiken clay loam chemically treated to remove various components In a kaolinitic soil, which is devoid or very low in organic matter content, Am is likely to move quite readily under strongly acidic condition (pH < 4), but only slightly under alkaline condition (pH > 7). In the intermediate pH 89