Environmental Engineering Reference
In-Depth Information
Methodology
A set of 17 sediments samples was collected in the Stockholm area in December
2006. Collection was performed using piston corers. The top 2 cm was retained
for analysis. The samples include 11 samples from the outflow of Lake Mälaren
into the Baltic Sea (Lambarfjärden, Klubbensborg, Gröndal, Riddarfjärden,
Kastellholmen, Ulvsundsjön, Barnhusviken, Saltsjön, Årstadal, Årstaviken, Lilla
Värtan and in the Archipelago downstream from Stockholm) and six samples from
lakes and ponds in the Stockholm area (Trekanten, Drevviken, Bornsjön). Lake
Bornsjön is considered as a reference. Low concentrations are also expected at
Lambarfjärden owing to its location upstream from the urban area.
Samples were prepared by microwave-assisted acid digestion (Mars5, CEM,
USA) and analyzed by inductively coupled plasma-mass spectrometry (ICP-MS).
Sediment samples were dried overnight at 105°C. Dry sediments were then
sieved and the 0-75 mm fraction was retained for analysis. Approximately 0.5 g
of dry sediments was placed in microwave digestion vessels. Digestion was
performed in closed vessels after addition of 8 mL
Aqua regia
(6 mL HCl + 2
mL HNO
3
) using a two-step temperature increase to 185°C and a maximum
allowed pressure of 200 psi. The leachate was then slowly taken to dryness on a
hot plate and redissolved in 5% HNO
3
. The procedure does not provide a full
digestion, but a strong leach suitable for the study of anthropogenic metals in
sediments.
Prepared samples were analyzed by ICP-MS using a quadrupole instrument
(Elan 6,000, Perkin Elmer, USA) and standard operating conditions. Calibration
was performed by the analysis of multi-element standard solutions, except for Pt
and Rh for which solutions of individual elements were analysed due to interfer-
ence issues. Interference on Pt and Rh determination were corrected mathemati-
cally
[5, 6]
.
Several precautions and quality control steps were implemented in the study.
These include acid washing of all containers, the use of high purity acids (Suprapure
grade, Promochem AB, Sweden) and water (18 MW cm, Milli-Q, Millipore, USA),
the analysis of procedural blanks (prepared and analyzed randomly). In addition,
reference material BCR-723 was analyzed to assess the accuracy of Pt and Rh
analysis.
Trace Metal Concentrations in Surface Sediments
Copper, Zinc, Lead and Cadmium
The distribution of Cd, Cu, Pb and Zn in Stockholm sediments is presented in
Fig.
1
. Copper, zinc, lead and cadmium concentrations in surface sediments range
from 27 to 475, 76 to 1,200, 15 to 772 and 0.4 to 4.0 mg/g, respectively.
