S. Sharmasarkar et Gf. Vance, FRACTIONAL PARTITIONING FOR ASSESSING SOLID-PHASE SPECIATION AND GEOCHEMICAL TRANSFORMATIONS OF SOIL SELENIUM, Soil science, 160(1), 1995, pp. 43-55
Fractionation techniques have been applied widely to assess the behavi
or of various geological trace elements. However, relatively few studi
es have been conducted on solid-phase speciation and geochemical asses
sment of selenium (Se) through fractional partitioning. Soils collecte
d from contrasting range and mine environments of Wyoming were partiti
oned fractionally to investigate the significance of different Se frac
tions in assessing solid-phase speciation and geochemical transformati
ons. The Se fractions extracted by the partitioning technique were aqu
eous (0.25 M KCl), exchangeable (1 M KH2PO4), acid-extractable (4 M HC
l), sulfide and humic bound (KClO3 + 12 M HCl), and siliceous (15.8 M
HNO3 + 11.7 M HCLO(4) + 28.9 M HF); each fraction was also speciated f
or selenite (Se+4) and selenate (Se+6). In addition, the soil samples
were analyzed for total soil Se after a strong mixed-acid digestion (1
5.8 M HNO3 + 11.7 M HClO4 + 28.9 M HF). High percent recovery C85-104%
) was observed between total Se and sum of the partitioned fractions,
which were also significantly correlated (r = 0.99). With increasing e
xchangeable Se, there was a corresponding increase in the aqueous frac
tion (r = 0.72). A similar increasing trend was found between the exch
angeable and acid-extractable fractions (r = 0.51>. For the aqueous fr
action, Se+6 was found to be the potential species, whereas in the exc
hangeable fraction, Se+4 predominated. Both Se+4 and Se+6 were distrib
uted almost evenly in the acid-extractable fraction. Speciation data f
or sulfide and humic bound, and siliceous fractions, however, were not
conclusive. Selenium in the available and conditionally available fra
ctions increased as the weatherable fraction decreased (for both r = -
0.83). Total soil Se increased with increasing clay content (r = 0.81)
, and a reverse trend was observed with sand content (r = -0.69), sugg
esting Se is associated with the clay-sized soil fraction. Siliceous S
e was Linearly related to total soil Se (r = 0.91), suggesting the pre
sence of Se in soil minerals. This fraction was again found to increas
e with increasing clay content (r = 0.74). Average distributions of th
e five Se fractions indicated the soils were dominated by the siliceou
s Se, with aqueous fraction comprising the least abundant Se level. St
atistical analysis indicated all of the above mentioned correlations w
ere significant at the P < 0.01 or 0.001 level.