Relative role of aliphatic and aromatic moieties as sorption domains for organic compounds: A review

The sorption behavior of hydrophobic organic compounds (HOCs) in the environment has been the focus of numerous studies. In most of them, the role of aliphatic domains in sorption has been ignored, even although aliphatic components make up a significant portion of the soil organic matter (SOM). The objective of this review is to elucidate the role of the molecular descriptors - aromaticity and aliphaticity - of natural and engineered sorbents as sorption domains for HOCs in the environment. The data, collected from a large and diverse literature data set, show that phenanthrene, like other HOCs, has a strong affinity for aliphatic SOM domains. In many cases, sorption coefficients are higher than those with aromatic-rich sorbents. No significant correlations between either aromaticity or aliphaticity and sorption affinity were recorded for such a large and diverse data set. On the basis of the data set from our literature review of natural and engineered sorbents, we conclude that (i) aliphatic structures must be considered in the evaluation of HOC-sorption processes in the environment; (ii) neither aromaticity nor aliphaticity of SOM alone can be used to predict the sorption affinity of sorbents having wide and diverse properties; and (iii) these molecular descriptors are valuable for relatively homogeneous and chemically similar sorbents.