Trace elements in Stockholm sediments

Rapport, 2007

Stockholm is Sweden’s largest city with a population of 1,200,000. As in most cities, human activities are resulting in environmental contamination and previous studies have shown the occurrence of elevated heavy metal concentrations in Stockholm sediments. The present study aims at determining the level of platinum group elements and other relevant metals in Stockholm sediments. Platinum, rhodium, antimony, cadmium, chromium, copper, lead, silver, tin, tungsten and zinc were analysed in a set of 18 sediment samples collected in the outflow of Lake Mälaren and in ponds and lakes in the Stockholm area. This study shows that these elements are found at elevated concentrations in the urban area relative to background sites. Platinum and rhodium concentrations range from 2.4 to 25 ng/g and from 0.3 to 5 ng/g, respectively. Antimony, silver, tin, tungsten have concentrations in the range 0.1 to 8.9 μg/g, 0.2 to 8.5 μg/g, 1.2 to 38 μg/g, 1.1 to 37 μg/g, respectively. Cadmium, chromium, copper, lead and zinc have concentrations of 0.4-4 μg/g, 27-77 μg/g, 27 to 475 μg/g, 15-772 μg/g and 76-1200 μg/g, respectively. Copper is present at high concentrations at most sampled sites according to Swedish EPA sediment concentration guideline. Zinc and lead are only present at high concentrations at specific sites. In addition, Ag concentrations exceed the apparent threshold concentration for Ag at several sites, whereas it is exceeded at one site for antimony. No guidelines exist for platinum, rhodium and tungsten. Sources of trace elements include automobile traffic, urban surfaces (road pavement), buildings and combustion, as well as location specific sources. The spatial distribution of trace elements in sediments demonstrates that the contamination is the result of diffuse sources and it is therefore difficult to control. Automobile traffic is a major source of trace elements, including platinum, rhodium, antimony and tungsten, and traffic reduction policies to be implemented in Stockholm may help reduced trace element input. In addition, several elements, including tungsten, antimony and lead, are locally elevated and the determination of location specific sources (possibly industrial emissions) may also allow to reduce locally elevated concentrations.