Environmental Engineering Reference
In-Depth Information
of major chemical elements and of trace metals were obtained from raw samples by
digestion with nitric acid, ultrasonic stimulation and at least 3 h of rest. Samples
were filtrated through a 0.45-mm pore size membrane (Millipore) and total concen-
trations were measured in the filtrate. Dissolved concentration was obtained by
analysis of the filtrates of the raw samples through a 0.45-mm pore size membrane
and acidification of the filtrates at pH < 2 with nitric acid. All solutions were kept
at 4°C in a refrigerator prior to analysis.
Major elements (Na, Mg, K, Ca, Si, Al, Fe, Mn) and Zn concentrations were
determined by inductively-coupled plasma-atomic emission spectrometry (ICP-
AES) (Varian Liberty 220). All results were established from duplicate analysis, the
detection limit for Zn was 10 mg/L and precision ranged from 3% to 5%. Pb, Cu,
Cd, Cr and Ni concentrations were determined by electrothermal atomic absorption
spectrometry (AAS) (Varian SpectrAA 300 or SpectrAA 220Z). All results were
established from duplicate analysis, the detection limits for Pb, Cu, Cd, Cr and Ni
were 2, 2, 0.1, 0.5 and 2 mg/L, respectively, and precision ranged from 3% to 5%.
An internal quality control solution was incorporated into each series. When the
deviation exceeded 5% for ICP-AES or 10% for AAS, the series were started over
again. The total organic carbon (TOC) was measured by oxidation and quantifica-
tion of CO
2
by infra-red spectrometry (NF EN 1484). The detection limit was
2 mg/L. The ultra-pure water employed was deionized using ion exchange columns
(Elga Maxima). All reagents were of analytical grade (Merck, Suprapur or Pro
Analysis) and all glassware in contact with the samples were washed with 10%
nitric acid and then rinsed with deionized water.
Size Fractionation of Runoff Waters
Size fractionations were implemented for four samples (one sample for each
season), using in series filtration and ultrafiltration, to characterize the distribution
of trace metals between particulate, colloidal and dissolved fractions. The upper
size limit of colloids in runoff waters is defined to be around 10 mm, as determined
by
[19]
. The lower limit is considered to be 5 kDa referred to the limit between
colloids and compounds such as dissolved species and very small natural organic
colloids (fulvic acids). A 2-L feed sample was used for in series fractionation.
Large particles were removed by settling during 24 h. Experiments were carried out
in a pressured stirred batch cell (Amicon cell). The membranes selected were
Millipore nitrocellulose membranes with 8, 1.2, 0.45, 0.22 and 0.05-mm pore sizes
for filtration and Vivascience polyethersulfone membranes with molecular weight
cut-offs of 100, 30, and 5 kDa for ultrafiltration. The membrane cut-offs were chosen
according to the procedure of
[9
, 18], and depending on the available membrane
sizes. The protocol was adapted from one sample to the next one, depending on the
results obtained for each filtration step. If the elemental concentrations were not
significantly different between two filtration steps, the corresponding cut-off was
suppressed in the next sequence. Mass balance was calculated for each step of the
