Significantly bipolar immigration of PFOA and PFOS into macroaggregates and microaggregates in soils under simulated natural conditions

Purpose Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in soils pose a severe threat to the soil ecosystem and human health. Soil aggregates play a critical role in the migration and transformation of pollutants. Materials and methods In this study, soil with different properties (Fluvisol and Planosol) spiked with PFOA/PFOS were incubated for 90 days, and then divided into five particle size fractions by wet sieving with low loss. The concentrations of PFOA and PFOS in soils and fractions were extracted using ultrasound-assisted extraction method with methanol as an extractant. The PFOA and PFOS were analyzed using high-performance liquid chromatography-tandem mass spectrometry (HPLC–MS/MS). Results and discussion The results showed that the ability of the soil aggregates to carry PFOA and PFOS initially decreased and then increased with decreasing particle sizes. Moreover, organic matter was the main factor influencing the PFOA and PFOS distribution in the soil aggregates, whereas soil types did not affect the accumulation capacity of PFOA and PFOS on soil particles. The macroaggregates (2000–250 µm) showed the highest accumulation capacity of PFOA and PFOS, suggesting high load of PFOA and PFOS. Additionally, the microaggregates (< 15 µm) played a dominant role in the PFOA and PFOS distribution due to the high proportion of this fraction in soil samples (51.73 ~ 62.47%). Conclusions Significantly bipolar immigrations of PFOA and PFOS into macroaggregates and microaggregates in soils were observed. This phenomenon can be explained by the fact that the particulate organic carbon (POM) can sorb the PFOA and PFOS in the macroaggregates, while the presence of SOC (highly humified) may increase the PFOA and PFOS contents in the microaggregates. Graphical Abstract