Polycyclic Aromatic Hydrocarbons in Urban Soils of Different Land Uses in Miami, Florida

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments and are considered as the priority pollutants by the U.S. Environmental Protection Agency. The objective of this study was to determine the depth-wise distribution (0–15, 15–30, and 30–45 cm) of 16 PAHs compounds in four urban soils of different land uses (residential, public parks, public buildings, and commercial areas) in Miami, Florida, USA. The PAHs were analyzed using a Gas Chromatograph equipped with a Flame Ionization Detector. Results showed that across use soils, total PAHs were significantly greater at surface (1,869 μg/kg) than sub-surface (478–1,079 μg/kg). Among land uses at 0–15 cm, PAHs were significantly greater in commercial areas (2,364 μg/kg) than the residential and public parks (1,508–1,595 μg/kg), but not the public buildings (2,007 μg/kg). However, at lower depths, PAHs were greater in residential soils (15–30 cm: 1,454 μg/kg; 30–45 cm: 834 μg/kg) compared with other land uses (15–30 cm: 839–1,104 μg/kg; 30–45 cm: 251–456 μg/kg). The contents of high molecular weight PAHs (HMWPAHs) were greater than the low molecular weight PAHs (LMWPAHs) in all soils at all depths. For example, at 0–15 cm, HMWPAHs were twice as much (1,039–1,602 μg/kg) as LMWPAHs (467–762μg/kg). All three source identification indices, including the predominance of HMWPAHs over the LMWPAHs, 0.42 to 0.50 ratio of fluoranthene to fluoranthene + pyrene, and 0.78 to 1.36 ratio of phenanthrene to anthracene, suggest that the dominant source of PAHs in the urban soils originated from the pyrogenic processes, particularly the burning of fossil fuel. These results can help set baseline concentrations and the exposure risk to terrestrial organisms of PAHs in the urbanized and rapidly urbanizing areas.