Persistent Organic Pollutants in Native Grassland Soils along a Climosequence in North America

Abstract

Among the controls on the fate of harzardous persistent organic pollutants (POPs) in the environment, soil organic matter (SOM) and climate play an outstanding role. Thus, it may be possible to predict POP concentrations at background sites from SOM properties and climatic elements. We therefore related polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) concentrations in 18 mollic epipedons under native grassland to SOM properties (lignin‐derived phenols, polycarboxylic benzoic acids [PCBAs], aromaticity, and polarity of alkali‐extractable SOM) and climatic elements. The sum of 20 PAH (∑20PAHs) concentrations ranged from 63 to 321 μg kg−1, and that of 14 PCB (∑14PCBs) concentrations ranged from 7.9 to 93 μg kg−1, except at one contaminated site (3136 μg kg−1). On average, phenanthrene (PHEN, 38% of the ∑20PAHs concentrations) and naphthalene (NAPH, 28%) were the most abundant PAHs, congeners 28 (22% of the ∑14PCB concentrations) and 101 (17%) were the most abundant PCBs. Soil organic C (SOC) concentrations correlated with the ∑20PAHs concentrations; the C concentration in the sum of eight PCBAs, a marker for black C, correlated with the concentrations of higher molecular weight PAHs, except in soils with cyric temperature regime. The ∑14PCBs concentrations was independent of any soil property. The contribution of NAPH to the ∑20PAHs concentrations and that of the up to tetra‐chlorinated PCBs to the ∑14PCBs concentrations decreased with increasing mean annual temperature (MAT). The percentages of PCB 101 increased with increasing MAT. However, the temperature effect was not strong. Mean annual precipitation (MAP) neither effected PAH nor PCB patterns. Our results indicate that the easily measured SOC concentrations may be used to predict PAH concentrations in native grassland soils of the prairie. Including MAT improves the prediction of NAPH concentrations. The influence of MAT on PCB concentrations is obvious, but the correlation is too weak to be used for reliable predictions.