Environmental Engineering Reference
In-Depth Information
The AET concentration is exceeded at seven sites for Ag and at one site for Sb.
Potential risk for Ag is further supported by the guideline value of 3.7 mg/g associ-
ated with frequent adverse effects to marine organisms
[10]
. The results therefore
indicate that present metal concentrations are a potential threat to aquatic ecosys-
tems in the Stockholm area.
Other metals have no defined sediment guideline values and the potential risks
associated with their elevated concentrations are therefore difficult to define.
Source Characterization
Source characterization was performed on the basis of observed spatial trends, cor-
relations and knowledge of metal uses. Elevated concentrations in the urban area
relative to reference and upstream sites indicate that most analyzed metals have
urban sources.
Automobile traffic is believed to be the main source of Pt, Rh, W and Sb owing
to a decreasing trend from a highway stormwater input at Lake Drevvikken.
A smaller concentration decrease was also found for Cu, Pb, Zn and Sn, indicating
that automobile traffic may contribute to elevated concentrations of these elements.
Other sources of Cu, Pb, Zn and Sn metals include urban surfaces (e.g. roof, galva-
nized materials, coatings, asphalt).
Elevated W, Sb, Sn, Cu, Zn and Pb concentrations at Årstadal and/or Trekanten
indicate the occurrence of location-specific sources. The sampling sites, which are
within 2 km of each other, are located in the vicinity of an industrial area character-
ized as environmentally hazardous and comprising industries and a goods
terminal.
A decreasing trend downstream from Stockholm was observed for all metals,
except Ag, indicating that Ag is release into the Baltic Sea with a higher efficiency
than other analyzed metals. This is possibly due to the use and emission of Ag as
nanoparticles
[11]
.
Conclusions
Elevated trace metal concentrations were found in sediments in Stockholm as a
result of urban contamination. Copper is present at high concentrations at most
sampling sites according to the Swedish EPA sediment concentration guideline,
while Zn and Pb are present at high concentrations at specific sites. In addition, the
apparent threshold concentrations are exceeded at several sites for Ag and at one
site for Sb. Elevated concentrations were also found for Pt, Rh and W, but no guide-
line exist for these metals. This study indicated that metals are threat to aquatic
ecosystems in the Stockholm area and emissions should be reduced to lower associ-
ated risks.
