Environmental Engineering Reference
In-Depth Information
Table 3
Distribution range (%) over the four samples for the three fractions
Element
Particulate fraction
Colloidal fraction
Dissolved fraction
Al
97-100
0-3
0
Fe
96-100
0-4
0
Cd, Cr, Pb
85-100
0-15
0
Mn
52-100
0-11
0-41
Zn
65-94
2-15
4-21
Ni
72-98
2-7
0-26
Si
52-74
1-14
26-42
TOC
0-41
3-31
44-70
Mg
33-78
3-9
2-59
Cu
22-96
2-73
3-26
Ca, Na, K
5-69
2-16
20-92
The distribution of major and trace elements was quite similar for the four
samples, except for Cu, Mn and TOC. No sample was collected after a de-icing salt
spreading which could probably change the distribution of trace metals due to
aggregation phenomenon. Four groups of chemical elements resulted from the
calculation of percentage of distribution between the fractions (Table
3
).
The results of in series partitioning highlight that Al, Fe and trace metals such
as Cd, Cr and Pb were mostly present in runoff waters as particle-associated with a
maximum of 15% of colloidal species. Both Zn and Ni were primarily in the >8 mm
size fraction but the dissolved fraction could reach up to 30%. Their distribution
was very close to those of Mn. The dissolved fraction of Si and TOC was rather
constant, between 30% and 70%. The similar colloidal fraction of Cu and organic
carbon showed the link between this metal and organic particles, as reported in the
literature. But, as the Cu particulate fraction could reach 96%, Cu could be also
linked to other colloidal or particulate fractions, as deduced from the conventional
0.45-mm cut-off.
[9]
reported similar results in stormwater: Cu, Zn, Pb and Cr were
found in particles >5 mm and Fe, Al and Si in particles >0.45 mm. Particulate Fe,
Al, Mn and Si reflect in part the presence of soil minerals such as clay minerals,
quartz and oxy-hydroxides
[9]
. The presence of colloidal Si is consistent with
observations of
[18]
in 0.45-mm filtrates of urban stormwater. The distribution of
Mg is rather different from Ca, Na and K, indicating adsorption on specific mineral
or organic constituents.
Conclusions
Pb, Cr and Cd, which are known to associate with particles, were present entirely
in the >8 mm size particles of runoff waters. Zn and Ni were distributed mostly in
particulate fractions but with dissolved (<5 kDa) and colloidal fractions up to
30%. The distribution of Cu is quite equal to Zn and Ni, with up to 70% of
colloidal Cu. Even if colloidal metals were relatively small compared to other size
