Sources and Distribution of Polycyclic Aromatic Hydrocarbons in Urban Soils: Case Studies of Detroit and New Orleans

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments. Incomplete combustion of petroleum and coal are the primary sources of elevated concentrations of urban PAHs. The purposes of the study were: 1) to determine and compare the concentration of PAHs in soils taken from two major US cities, New Orleans and Detroit; and 2) to examine the main sources of PAHs in urban soils by diagnostic PAH ratios. A total of 107 New Orleans soil samples were taken from 6 census tracts (n = 13-19 per census tract) and compared with 106 Detroit soil samples from 6 census tracts. Sampling sites included house foundations, open spaces, and soil bordering residential and busy streets. The average total PAH (sum of 17 PAH concentrations) of Detroit soils was 7,843 mu g/kg, compared to 5,100 mu g/kg for New Orleans soils. Several diagnostic PAH concentration ratios were calculated for source determination for Detroit and New Orleans, respectively: phenanthrene/anthracene ratios (2.97 and 5.36), benz(a)anthracene/chrysene ratios (0.99 and 0.85), benzo(b)fluoranthene/benzo(k)fluoranthene ratios (1.51 and 1.53), and benzo(a)pyrene/benzo(e)pyrene ratios (0.98 and 0.92). The ratios indicate that PAH concentrations are attributable to pyrolytic sources, mainly vehicle exhaust. Travel and gasoline consumption data in Detroit and New Orleans support these findings.