Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils

The hazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or post-emission conversion of PAHs (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52°N-47°S, 71°W-118°E), to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the Σ16EPA-PAHs. The relationship of the Σ16EPA-PAHs concentrations with the Σ7OPAHs/Σ16EPA-PAHs concentration ratio (a measure of the variable OPAH sources) could be described by a power function with a negative exponent <1, leveling off at a Σ16EPA-PAHs concentration of ca. 400 ng g-1. We suggest that below this value, secondary sources contributed more to the OPAHs burden in soil than above, where primary sources dominated the OPAHs mixture. This was supported by a negative correlation of the Σ16EPA-PAHs concentrations with the con..., The concentrations of 16 EPA-PAHs and up to 15 OPAHs were taken from the literature as listed in Table 1 or specifically analyzed for this study using the method briefly described below. In the various cited studies, from which the data originated and in our new sampling in Germany and Switzerland, topsoils were sampled in a way representative for the A horizon (Argentina, China, Slovakia), at 0-0.05 m depth (Switzerland [two sites], Thailand), at 0-0.1 m depth (Brazil, Germany, Uzbekistan, Switzerland [one site]), or 0-0.15 m depth (Switzerland [one site]). The soil samples were frozen in field-fresh state or air/freeze-dried, sieved <2 mm, and stored at ‑20°C before analysis. pH was measured with a glass electrode in H2O, 0.01 M CaCl2, or 1 M KCl at a soil:solution ratio of 1:2.5. Clay concentrations were determined with the pipet method after removal of carbonates with HCl, organic matter with H2O2, and Fe oxides with dithionite-citrate-hydrogencarbonate, and wet sieving <50 μm..., If cells are empty, data is not available.