Predictivity Strength of the Spatial Variability of Phenanthrene Sorption Across Two Sandy Loam Fields
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Sorption is commonly agreed to be the major process underlying the transport and fate of polycyclic aromatic hydrocarbons (PAHs) in soils. However, there is still a scarcity of studies focusing on spatial variability at the field scale in particular. In order to investigate the variation in the field of phenanthrene sorption, bulk topsoil samples were taken in a 15 × 15-m grid from the plough layer in two sandy loam fields with different texture and organic carbon (OC) contents (140 samples in total). Batch experiments were performed using the adsorption method. Values for the partition coefficient K d (L kg−1) and the organic carbon partition coefficient K OC (L kg−1) agreed with the most frequently used models for PAH partitioning, as OC revealed a higher affinity for sorption. More complex models using different OC compartments, such as non-complexed organic carbon (NCOC) and complexed organic carbon (COC) separately, performed better than single K OC models, particularly for a subset including samples with Dexter n < 10 and OC <0.04 kg kg−1. The selected threshold revealed that K OC-based models proved to be applicable for more organic fields, while two-component models proved to be more accurate for the prediction of K d and retardation factor (R) for less organic soils. Moreover, OC did not fully reflect the changes in phenanthrene retardation in the field with lower OC content (Faardrup). Bulk density and available water content influenced the phenanthrene transport mechanism phenomenon.
KeywordsSorption Soil organic carbon Complexed organic carbon Non-complexed organic carbon Phenanthrene Field-scale Leaching risk
This research was funded as part of the large framework project Soil Infrastructure, Interfaces and Translocation Processes in Inner Space (“Soil-it-is”) by the Danish Research Council for Technology and Production Sciences, by the Danish Pesticide Leaching Assessment Programme (www.pesticidvarsling.dk), by the European Union (FEDER funds through COMPETE) and by Fundação para a Ciência e Tecnologia (FCT) through the project Pest-C/EQB/LA0006/2013. António Soares is grateful to FCT for his doctoral research grant (SFRH/BD/69565/2010) financed through POPH-QREN, Tipologia 4.1 e Formação Avançada, and subsidized by Fundo Social Europeu and Ministério da Ciência, Tecnologia e Ensino Superior. M. Paradelo is financially supported by a postdoctoral contract from the Plan I2C, Xunta de Galicia. To all financing sources, the authors are greatly indebted.
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