Effects of cation saturation, substrate addition, and aging on the mineralization and formation of non-extractable residues of nonylphenol and phenanthrene in a sandy soil

Based on the assumption that the relative density and flexibility of soil organic matter is affected by cations at the exchange sites, a sandy soil treated with Na⁺, Ca²⁺, or Al³⁺ was used to determine the long-term sorption and further mineralization and extractability of nonylphenol (NP) and phenanthrene (Phe). The sandy topsoil was percolated by either 0.1 M NaCl, CaCl₂, AlCl₃ solutions or water, then sterilized by γ radiation and spiked with ¹⁴C-labeled NP or Phe at 10 μg g^-1 of soil. Freshly spiked soils and stored under sterile conditions for 2, 5, or 9 months were used for degradation experiments. Mineralization was determined by monitoring of ¹⁴CO₂ efflux from samples that were additionally supplemented with wood flour. After 8 weeks of incubation, the sequestered xenobiotics were extracted by water and ethanol. Results showed no significant effect of cations on total respiration, while mineralization of both xenobiotics was substantially lower in Na⁺- and Al³⁺-treated soils. The wood flour addition increased respiration in all samples. The effect of wood flour on xenobiotics mineralization became less significant with time of aging. Sterile aging led to decreased mineralization and extractability of NP and Phe. Formation of non-extractable fractions of xenobiotics depended on the mineralization rate and cation saturation of soil.