Thermodynamic Modeling of the Aqueous Solubility of PAHs

Solubility and Decomposition of Organic Compounds in Subcritical Water

In this article, studies on organic solubility and stability in subcritical water reported during the past 25 years have been reviewed. Data on the solubility and decomposition of organic compounds in subcritical water, a green solvent, are needed in environmental remediation, chemistry, chemical engineering, medicine, polymer, food, agriculture, and many other fields. For solubility studies, the experimental systems used to measure solubility, mathematical equations derived and applied for the modeling of the experimentally determined solubility data, and the correlation between the predicated and experimental data have been summarized and discussed. This paper also reviewed organic decomposition under subcritical water conditions. In general, the solubility of organics is significantly enhanced with increasing water temperature. Likewise, the percentage of organic decomposition also increases with higher temperature.

Spatial distribution and temporal variation of polycyclic aromatic hydrocarbons in runoff and surface water

This study aims to investigate the spatial distribution of and temporal variation in the phase distribution, emission sources, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in runoff and in surface water mixed with runoff discharge. The samples were collected at semi-rural, residential, and industrial sites in Ulsan, South Korea, from April to October 2016. The industrial site had the highest PAH concentrations in the runoff and surface water due to the higher PAH levels found in the surrounding environmental media. The PAH phase distributions were relatively similar between the sampling sites, with dissolved PAHs (2- to 4-ring species) dominant. In July, the PAHs in the surface water were more commonly found in the dissolved phase due to the higher water temperature and dissolved organic carbon concentration. The emission sources for the PAHs were identified using principal component analysis (PCA), a dimension reduction technique, and the k-nearest neighbor (KNN) classifier, a supervised learning algorithm. It was determined that the PAHs in the runoff and surface water were likely to share similar petrogenic and pyrolysis sources for most of the sampling periods. The ecological risk of the surface water was 1.5-4.5 times lower after being mixed with runoff water, mainly due to dilution effects. The ecological risk for surface water was highest in July because of the higher PAH concentrations. This study contributes to the understanding of PAHs in runoff and in surface water affected by runoff discharge.

Effects of oil dispersant on solubilization, sorption and desorption of polycyclic aromatic hydrocarbons in sediment-seawater systems

This work investigated effects of a prototype oil dispersant on solubilization, sorption and desorption of three model PAHs in sediment-seawater systems. Increasing dispersant dosage linearly enhanced solubility for all PAHs. Conversely, the dispersant enhanced the sediment uptake of the PAHs, and induced significant desorption hysteresis. Such contrasting effects (adsolubilization vs. solubilization) of dispersant were found dependent of the dispersant concentration and PAH hydrophobicity. The dual-mode models adequately simulated the sorption kinetics and isotherms, and quantified dispersant-enhanced PAH uptake. Sorption of naphthalene and 1-methylnaphthalene by sediment positively correlated with uptake of the dispersant, while sorption of pyrene dropped sharply when the dispersant exceeded its critical micelle concentration (CMC). The deepwater conditions diminished the dispersant effects on solubilization, but enhanced uptake of the PAHs, albeit sorption of the dispersant was lowered. The information may aid in understanding roles of dispersants on distribution, fate and transport of petroleum PAHs in marine systems.