kg Ϫ1 (Nicholson et al., 1999), and 743 and 501 mg kg Ϫ1 (Jackson et al., 1999). Arsenic concentration in PL is Trace elements are added to poultry feed for disease prevention variable, for example Sims and Wolf (1994; and refer-and enhanced feed efficiency. High concentrations are found in poultry litter (PL), which raises concerns regarding trace element loading ences therein) reported a range in As concentration of soils. Trace metal cation solubility from PL may be enhanced by from 0 to 77 mg kg Ϫ1 . Other studies have also reported complexation with dissolved organic carbon (DOC). Mineralization As concentrations within this range, for example 30 to of organo-As compounds may result in more toxic species such as 37 mg kg Ϫ1 (van der Watt et al., 1994), 43 mg kg Ϫ1 As(III) and As(V). Speciation of these elements in PL leachates (Moore et al., 1998), and 35 mg kg Ϫ1 (Jackson et al., should assist in predicting their fate in soil. Elemental concentrations 1999). Furthermore, there is evidence that As in PL of 40 PL samples from the southeastern USA were determined. Watermay be readily soluble; 72% of total As was solubilized soluble extractions (WSE) were fractionated into hydrophobic, anfrom PL in a water extraction (Jackson and Miller, ionic, and cationic species with solid-phase extraction columns. Arse-1999). nic speciation of seven As species, including the main As poultry feed Increased concentrations of Cu and Zn in the surface additives, roxarsone (ROX; 3-nitro-4-hydroxyphenylarsonic acid) and p-arsanilic acid (p-ASA; 4-aminophenylarsonic acid), was performed horizons of soil receiving annual applications of PL have by ion chromatography-inductively coupled plasma-mass spectrome-been identified (Kingery et al., 1994). Copper and Zn try (IC-ICP-MS). Total As concentrations in the litter varied from concentrations in the surface of a soil profile that had 1 to 39 mg kg Ϫ1 , averaging 16 mg kg Ϫ1 . Mean total Cu, Ni, and Zn received PL applications over 25 yr were significantly concentrations were 479, 11, and 373 mg kg Ϫ1 , respectively. Copper higher than an unamended soil. Furthermore the results and Ni were relatively soluble (49 and 41% respectively) while only of this study suggest that Zn is fairly mobile in the profile 6% of Zn was soluble. Arsenic was highly soluble with an average (Han et al., 2000). Initial soluble As concentrations of of 71% WSE. Roxarsone was the major As species in 50% of PL Ͼ200 g L Ϫ1 were reported in runoff from a field soil samples. However, the presence of As(V) as the major species in amended with 9 Mg PL ha Ϫ1 and runoff concentrations 50% of the PL samples indicates that mineralization of ROX had 7 d after application were still Ͼ50 g L Ϫ1 (Moore et al.,

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X-ray absorption fine structure (XAFS) measurements have been made at the Cs LIII absorption edge on (1) 0.04 M acetonitrile solutions with respect to both CsBr and dibenzo-18-crown-6 ether (Cs−D18C6), (2) solids produced by drying the aforementioned Cs−D18C6 solution complex, and (3) crystalline CsBr, CsCl, and CsF powders that were used as standards. XAFS measurements have also been made at the Br K absorption edge on the same 0.04 M solution mentioned above. Due to the many difficulties associated with obtaining high-quality XAFS data on these systems, a custom-manufactured 5-mil-thick Sc foil was used in conjunction with a Soller slit assembly to improve the XAFS signal-to-noise ratio by almost a factor of 6. XAFS analyses of the Cs−D18C6 solution show the presence of a 1:1 Cs−D18C6 complex with a Br contact ion, consistent with previous references derived from 133Cs nuclear magnetic resonance investigations. For interpretation of the Cs LIII edge data, the choice of a Br counterion reduces the error in determining the presence of a single counterion among the lighter backscattering O and C atoms of the crown ether complex. Observation of the normalized XAFS data for the dried Cs−crown ether solution shows that the Cs atom's local environment changes from a 1:1 Cs−D18C6 complex to a predominantly crystalline CsBr solid phase. This recrystallization during drying illustrates the importance of in situ methods to characterize chemical speciation in solution. The ability of XAFS to directly probe the ternary Cs−D18C6−Br contact ion pair opens many exciting avenues for improving extraction methodologies.