Hydrophobic organic contaminants in marine water are mostly adsorbed onto (partitioned into) sediment organic matter (SOM). To study the impact of SOM diagenesis on sediment adsorption properties, artificial sediment with rich SOM content was incubated for more than 120 days. The sediment was sampled every week, and batch sediment adsorption tests were conducted with bisphenol A (BPA) and nonylphenol (NP) as the model pollutants. The results show that the amount of organic matter loaded in the sediment decreased by nearly 80% during incubation. For the incubated sediment, the BPA partition coefficient, Kd, decreased whereas the organic normalized partition coefficient, Koc, more than doubled. The experiments with NP show an even greater increase in Koc. Organic matter diagenesis shows a profound effect on the adsorption behavior of sediment, as the SOM residue has an increasing affinity and partition capacity for organic contaminants.

The phase transformation of iron minerals induced by aqueous Fe(II) (Fe(II)_aq) is a critical geochemical reaction which greatly affects the geochemical behavior of soil elements. How the geochemical behavior of rare earth elements (REEs) is affected by the Fe(II)_aq-induced phase transformation of iron minerals, however, is still unknown. The present study investigated the adsorption and immobilization of REEs during the Fe(II)_aq-induced phase transformation of ferrihydrite. The results show that the heavy REEs of Ho(III) were more efficiently adsorbed and stabilized compared with the light REEs of La(III) by ferrihydrite and its transformation products, which was due to the higher adsorptive affinity and smaller atomic radius of Ho(III). Both La(III) and Ho(III) inhibited the Fe atom exchange between Fe(II)_aq and ferrihydrite, and sequentially, the Fe(II)_aq-induced phase transformation rates of ferrihydrite, because of the competitive adsorption with Fe(II)_aq on the surface of iron (hydr)oxides. Owing to the larger amounts of adsorbed and stabilized Ho(III), the inhibition of the Fe(II)_aq-induced phase transformation of ferrihydrite affected by Ho(III) was higher than that by La(III). Our findings suggest an important role for the Fe(II)_aq-induced phase transformation of iron (hydr)oxides in assessing the mobility and transfer behavior of REEs, as well as for their occurrence in earth surface environments.