DISTRIBUTION OF TRACE-ELEMENTS ASSOCIATED WITH DISSOLVED COMPOUNDS (LESS-THAN-0.45 MU-M-1 NM) IN FRESH-WATER USING COUPLED (FRONTAL CASCADE) ULTRAFILTRATION AND CHROMATOGRAPHIC SEPARATIONS
Mk. Pham et Jm. Garnier, DISTRIBUTION OF TRACE-ELEMENTS ASSOCIATED WITH DISSOLVED COMPOUNDS (LESS-THAN-0.45 MU-M-1 NM) IN FRESH-WATER USING COUPLED (FRONTAL CASCADE) ULTRAFILTRATION AND CHROMATOGRAPHIC SEPARATIONS, Environmental science & technology, 32(4), 1998, pp. 440-449
After tagging with Mn, Co, Fe, Zn, Ag, Cd, and Cs colloids of the diss
olved phase (<0.45 mu m) of three samples of a river water were invest
igated by way of the amount of trace elements associated with them. Us
ing coupled frontal cascade ultrafiltration and chromatographic separa
tions, the size distribution of colloids and the affinity of the collo
idal organic matter for the trace elements were investigated. The size
distribution was determined using membranes with a nominal molecular
cutoff of 100, 10, and 1 kDa (1 kDa = 1000 daltons). For each fraction
, the trace elements associated with organic complexes were studied by
the selective isolation of complexing species using a macroporous res
in (Acell plus QMA, Sep-Pak, Waters). The mass of colloids in the >10-
kDa fractions of one sample was measured from the concentrate of 200 L
. This allowed the determination of a distribution coefficient (Kc) be
tween colloids and the ''true'' dissolved phase (10-kDa filtrate). Dep
ending on the element, the percentage of colloids in each size class i
ndicated that Cs was mainly present in the 1-kDa filtrate, in contrast
to Fe and Ag, which were mainly associated with colloids of large siz
e (>100 kDa). Cd, Zn, Co, and Mn were distributed amongst all the coll
oidal fractions, including the 1-kDa filtrate. In comparison to the di
stribution of the trace elements in the different inorganic colloid si
ze classes (using a UV-irradiated natural sample), the distribution of
trace elements in the >1-KD fractions of natural samples appeared to
be controlled by organic matter. This was particularly evident for Co
and Cd and, to a lesser extent, for Mn. Using the QMA resin, it appear
ed that the variable distribution of trace elements in the different c
olloid size classes is related to their affinity with the dissolved or
ganic matter. The affinity depends on the natura and/or on the distrib
ution of functional groups in the natural organic matter isolated (abo
ut 85% of the total <0.45 mu m) or not isolated by this resin. The rea
ctivity of the colloidal phase has been determined using Kc for three
different colloid concentrations of the same sample. Kc decreased as t
he concentration increased, indicating an apparent so called ''particl
e concentration effect''.