Rapp. Comm. int. Mer Médit., 37,2004
211
DETERMINATION OF THE DISSOLVED COPPER FRACTION COMPLEXED WITH SOLUBLE ORGANIC
LIGANDS IN COASTAL WATERS OF THE SARONIKOS GULF, GREECE
S. Karavoltsos*, A. Sakellari, M. Scoullos
University of Athens, Department of Chemistry, Laboratory of Environmental Chemistry, Panepistimiopolis, 157 71 Athens, Greece
* skarav@cc.uoa.gr
Abstract
This work deals with speciation of dissolved copper in seawaters of two sites in the Saronikos Gulf namely the Gulf of Elefsis and the
coast of Piraiki. The samples were UV irradiated in order to determine the inert fraction of dissolved copper corresponding to copper
complexed with dissolved colloidal organic carbon. The determined concentration of kinetically inert as for Chelex-100 resin dissolved
copper ranges widely from 1.3 to 32.1 nM, corresponding to a percentage ?uctuating between 8% and 67%, with a mean value of 37%,
of the total dissolved copper.
Keywords: copper, speciation, UV irradiation, Greece
Introduction
The chemical forms under which metals exist in seawater affect
their bioavailability and toxicity and therefore the determination of
the different species of dissolved metals is of great interest. Organic
complexation with natural organic ligands in seawaters is significant
for trace metals such as copper [1], since it may prevent metal
scavenging by suspended particulate matter and/or formation of
insoluble inorganic metal complexes, maintaining thereby enhanced
dissolved trace metal concentrations in seawater. The main purpose of
the present study is the description and evaluation of the method
employed for copper speciation and the preliminary reporting of the
results obtained.
Methodology
Five coastal sampling locations were chosen in the Saronikos Gulf,
four of which within the Elefsis Gulf (Aspropyrgos, Elefsis port,
Loutropyrgos, Nea Peramos), an industrialized area near Athens and
one station at the Piraiki coast, near Piraeus, the biggest port of
Greece. From the sampling area of Loutropyrgos seawater samples
were taken both from the surface and from near the sea-bottom. All
stations were characterised by the presence of a significant biomass of
the macroalga Ulva rigida. Nine samplings were carried out between
May and October 1998, the period when the highest biodegradation
rate of the macroalga Ulvawas observed.
Immediately after collection and transfer to the laboratory seawater
samples were filtered through 0.45Mm pore size acid-washed
celluloze nitrate filters (Millipore), kept in darkness in low-density
polyethylene containers and analysed within 24h. For the
determination of the dissolved labile copper, 500ml of each sample
were pumped through a Chelex-100 resin (200-400 mesh; Bio-Rad
laboratories, Richmond California; contact time of the sample with
the resin 7sec) and eluted with 10ml of HNO
3
-HCl 2:1M. The
concentration of copper was measured by a flameless atomic
absorption spectrophotometer (VARIAN SpectrAA 640 Z) equipped
with Zeeman background correction. For the determination of the
total dissolved metal, the filtered sample was UV irradiated for
100min before the preconcentration step. UV digestion of samples
was carried out by irradiation of solutions using a 400 W medium
pressure lamp (Cleo HPA, Philips), positioned in an aluminum lamp
housing device built in purpose, placed inside a fume cupboard cooled
by a fan. Each sample was put into a te?on beaker with quartz glass
cap, where the distance between the light source and the beaker was 2
cm. The sample was stirred continuously employing a magnetic
stirrer. The efficiency of the procedure was tested with the analysis of
CASS-4 certified reference seawater (certified copper value 0.592 ±
0.055 µg/l, measured value 0.568 ±0.067 µg/l) as well as with
synthetic solutions of Salicylic acid (1.5 mg/l; >90% decomposition)
and commercial humic acid (1.0 mg/l; Fluka Lot 45729/1) containing
a Cu(II) concentration. Although UV irradiation for 100min resulted
in the decomposition of approximately 60% of the humic acid
contained in the samples, the complexed Cu was almost fully
released, as shown by Cu analysis with DPASV. DOC was measured
by a Shimadzu-5000A TOC analyser.
Results and discussion
The concentrations of kinetically inert, as for Chelex-100 resin
dissolved copper, which is calculated by subtracting the concentration
of the labile fraction of dissolved copper from total copper, were
found to range from 1.3 to 32.1 nM in a total of 52 samples analysed.
The mean concentrations were 5.8 nM for Piraiki, 9.0 nM for
Aspropyrgos, 8.4 nM for the port of Elefsis, 5.4 nM for surface and
8.5 nM for bottom samples of Loutropyrgos and 8.1 nM for Nea
Peramos. These concentrations correspond to a percentage of inert
fraction of dissolved copper over the total dissolved copper ranging
from 8% to 67% with a mean value of 37%. By correlating these
results to those of researches from other seas [2, 3] it becomes evident
that UV irradiation accelerates the release of a major part of the inert
fraction of dissolved copper which corresponds to copper bound
predominantly to organic colloids. The percentage of this fraction in
the aforementioned cases was around 44%. Lewis and Landing [4]
showed that in seawater samples from the Black Sea following
preconcentration in a series of sequential columns where Chelex-100
was included, the percentage contribution of organically bound
copper was never less than 50%.
The concentrations of DOC ranged from 38 to 338 nM. There was
no correlation observed between the concentrations of inert dissolved
copper and those of DOC (r=0.15), due to the contribution of a single
part of dissolved organic matter to the complexation of dissolved
copper.
Inert dissolved copper measured in bottom seawater samples taken
from Loutropyrgos (mean value 8.5 nM) were higher compared to the
corresponding concentrations (mean value 5.4 nM) of surface
seawater samples. This difference is attributed to the decomposition of
the Ulva rigidabiomass accumulated at the seabed. The dissolved
organic matter released aggregates forming colloids or even
particulate matter, either through biotic mechanisms including
bacterial activity or by abiotic procedures such as adsorption on solid
surfaces, increasing the copper complexing capacity of seawater.
It is noteworthy that other researchers [5] attribute the stable
complexation of copper to relatively low molecular weight colloidal
organic ligands. The phenomena recorded require further
investigation which is currently under way.
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