Effect of structural composition of humic acids on the sorption of a branched nonylphenol isomer

By using dialysis equilibrium experiments, the sorption of a branched nonylphenol isomer [4-(1-ethyl-1,3-dimethylpentyl)-phenol] (NP111) on various humic acids (HAs) isolated from river sediments and two reference HAs was studied. The HAs were characterized by solid-state 13C direct polarization/magic angle spinning nuclear magnetic resonance (13C DP/MAS NMR) spectroscopy. Sorption isotherms of NP111 on HAs were described by a linear model. The organic carbon-normalized sorption coefficient (KOC) ranged from 2.3 × 103 to 1.5 × 104 L kg−1. Interestingly, a clear correlation between KOC value and alkyl C content was observed, indicating that the aliphaticity of HAs markedly dominates the sorption of NP111. These new mechanistic insights about the NP111 sorption indicate that the fate of nonylphenols in soil or sediment depends not only on the content of HA, but also on its structural composition.

► The sorption of a branched nonylphenol isomer (NP111) on humic acids was investigated by a dialysis technique. ► Humic acids were characterized by solid-state 13C DP/MAS NMR spectroscopy. ► A relationship between the organic carbon-normalized sorption coefficients of NP111 and the aliphaticity of humic acids was established.