Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils

<p>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 &lt;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 contribution of the more readily biologically produced highly polar OPAHs (octanol-water partition coefficient, log K_OW &lt;3) to the Σ7OPAHs concentrations. We identified mean annual precipitation (Spearman-r = 0.33, p &lt;0.001, n = 143) and clay concentrations (r = 0.55, p &lt;0.001, n = 33) as important drivers of the Σ7OPAHs/Σ16EPA-PAHs concentration ratios. Our results indicate that at low PAH contamination levels, secondary sources contribute considerably and to a variable extent to total OPAH concentrations, while at Σ16EPA-PAHs contamination levels &gt;400 ng g^-1, there was a nearly constant ratio of Σ7OPAHs/Σ16EPA-PAHs (0.08±standard error 0.005, n = 80) determined by their combustion sources.</p>