Sorption properties of hydrophobically modified poly(acrylic acids) as natural organic matter model substances to pyrene

Amphiphilic natural organic matter (NOM) in soil, water and sediments plays an important role in the fate of low-soluble hydrophobic organic compounds (HOC) in the environment. Scaling NOM structural factors, which affect the transport and immobilization of HOC, is rather involved due to the complexity of the NOM materials. Sorption properties of hydrophobically modified polyacrylic (HMPA) polymers as NOM model substances for pyrene were investigated and discussed with regard to reported NOM results. Emission fluorescence spectroscopic properties of pyrene and potentiometric titrations were used to characterize the hydrophobic and acidic properties of HMPA samples. Excitation fluorescence spectroscopy allowed a speciation of pyrene molecules. Overall complexation constants β₁ and β₂ of pyrene with hydrophobic moieties (–C₈H₁₇) and (–C₁₆H₃₃) were calculated depending on the pH and electrolyte cation nature at an ionic strength of 10 mM, typical of soil solution conditions. Aggregation of HMPA molecules was detected by photon correlation spectroscopy. Normalized sorption constant K_oc values for pyrene with HMPA samples similar to reported values with NOM support recent observations on the contribution of aliphatic moieties to the binding of polyaromatic hydrocarbons (PAH). The HMPA samples also model the partitioning behavior of hydrophobic micelle-like structures of NOM.