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Several polycyclic aromatic hydrocarbons (PAHs) are carcinogenic, where benzo(a)pyrene (BaP) is considered being the most carcinogenic. The PAHs are ubiquitous in an urban environment, and the levels can pose a health-risk. The sources to PAHs in an urban environment are many; traffic, industry, domestic heating, city fires are some.
Between 1999 and 2006 geochemical mapping surveys in three major Norwegian cities were completed. Surface soil samples (0-2 cm) from 719, 309 and 75 locations were collected from the cities Oslo, Bergen and Trondheim, respectively, and analyzed giving an extensive amount of PAH data. The results show clear similarities between the cities in both levels, distribution and possible sources. The median level of Sum 16 EPA PAH is 0.10 mg/kg, 0.85 mg/kg, and 0.68 mg/kg and the median BaP level is 0.01 mg/kg, 0.02 mg/kg, and 0.04 mg/kg in Oslo, Bergen and Trondheim, respectively. The inner city centers show a high density of high PAH levels, whereas the suburban areas generally show lower levels. For instance, in Trondheim the typical Sum 16 PAH level in the inner city was about ten times higher than the suburban areas.
By studying PAHs distribution and PAH ratio plots, indications of different PAH sources can be obtained. The city surface soil data indicate combustion as the general dominating source, and PAH ratio-ratio plots indicate the group of grass, wood, and coal combustion as an important source. In Oslo there are clearly different dominating PAH sources in the inner city center compared to the suburban areas. In the city center the PAH seems to be a mixture of liquid fossil fuel combustion and grass, wood and coal combustion, whereas in the suburban areas grass, wood and coal combustion dominates. Domestic heating using wood is thought to be a major source to PAH in the cities.
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