Resilience of the sorption capacity of soil organic matter during drying-wetting cycle

The sorption capacity of soil organic matter (SOM) for hydrophobic organic chemicals (HOCs) is affected by various environmental factors, such as soil water saturation and drying. In this study, we used passive sampling to investigate the changes in the sorption capacity of SOM during a drying-wetting cycle using batch sorption experiments. Dried and non-dried peat mosses were used to observe the effect of the drying process on the sorption capacity of SOM at various levels of water saturation in soil pores. At soil with non-dried peat moss, the partition coefficient between the sampler and the soil (K_sampler/soil) slightly increased with decreasing water saturation. At soil with dried peat moss, however, there were almost no differences in the K_sampler/soil among different water saturations except for 100%. The soil organic carbon-water distribution coefficients (K_OC) for dried peat moss were consistently larger than those for non-dried peat moss at all water saturation levels. However, the K_OC values obtained at 100% water saturation for both non-dried and dried peat mosses differed only by 18–29%. For fluoranthene, there was only an 18% difference between the two K_OC values at 100% water saturation, whereas it was 91% at 10% water saturation. This finding suggests that wetting SOM returns mostly its sorption capacity for HOCs after the increase in K_OC caused by extreme drying. The range in sorption capacity obtained in this study showed the resilient margin of the sorption capacity of SOM for HOCs according to microclimatic changes that would occur constantly under environmental conditions.