Bs. Xing et Jj. Pignatello, DUAL-MODE SORPTION OF LOW-POLARITY COMPOUNDS IN GLASSY POLY(VINYL CHLORIDE) AND SOIL ORGANIC-MATTER, Environmental science & technology, 31(3), 1997, pp. 792-799
The widely accepted dissolution (partition) model of sorption to soil
organic matter (SOM) has been challenged by evidence that SOM has a no
n-uniform sorption potential. This study presents data supporting a pr
eviously suggested alternative dual-mode model of sorption in which di
ssolution and hole-filling mechanisms take place concurrently, as in g
lassy organic polymers. The holes are postulated to be nanometer-size
Voids within the organic matrix that provide complexation sites. The m
ain focus was on sorption of chlorobenzene, 1,2-dichlorobenzene, and 1
,3-dichlorobenzene but some experiments were carried out also on 2,4-d
ichlorophenol and the herbicide metolachlor. Sorption from water to hi
gh-organic soils, humic acid particles, and poly(vinyl chloride) is no
nlinear, competitive, and predictably responsive to conditions that af
fect hole populations such as temperature and cosolvent addition. Sorp
tion to a peat soil and its components became progressively nonlinear
and competitive in the order humic acid, native peat, humin; this orde
r reflects The increasing ''glassy''-i.e., rigid, condensed-nature of
organic matter according to modern concepts of humic structure. Gas ad
sorption isotherms (N-2 at 77 K and CO2 at 273 K) reveal the presence
of internal microvoids accessible only by diffusion through the solid
phase. The degree of nonlinearity and competition correlate with the C
O2-measured microvoid volumes of the sorbents. The hole-filling mechan
ism is more important for the kinetically slow fraction.