Polycyclic aromatic hydrocarbon concentrations and spatial distribution in the soils of Santiago de Compostela (northwestern Spain)

Abstract

Organic pollutants are commonly accumulated in urban soils, interfering with the normal functions of soils and ecosystems, and representing potential risks for human health and well-being. Here we have studied the presence of polycyclic aromatic hydrocarbons (PAHs) in 55 soils from the city of Santiago de Compostela (Spain). The soils include different land uses: urban grasslands, urban forests, urban and periurban agricultural soils. Sample preparation was carried out by miniaturized ultrasound-assisted extraction and analytical determination was performed by gas chromatography-tandem mass spectrometry. Results revealed the presence in the soils of 17 out of the 18 PAHs analyzed, with total concentration levels up to μg g−1 in 28% of the analyzed soils. The sum of their concentrations varied widely, between 4 and 4728 ng g−1, with a mean value of 508 ng g−1 (median 217 ng g−1). The sum of the 16 EPA PAHs ranged from 4 to 4216 ng g−1, with a median of 193 ng g−1. The values found are similar to other similar-sized cities with low population densities. The study of PAHs distribution with depth in one soil showed that these compounds are mainly concentrated in the top 20 cm. Spatial distribution was very heterogeneous and without a clear pattern. In general, all PAHs were strongly intercorrelated except naphthalene, whereas no correlations have been found to soil physicochemical properties. Strong correlation of PAHs with Pb was observed, suggesting a common major source for these pollutants, probably combustion by traffic and households.