Nonideal binding between dissolved humic acids and polyaromatic hydrocarbons.

Understanding how pollutants move in water is a major challenge in environmental science. Prior research has shown that dissolved organic matter (DOM) can bind with hydrophobic organic chemicals (HOCs), affecting their transport and availability. The linear dissolution concept has been used to describe these interactions, but recent findings suggest this model may not fully capture the complexity of real-world systems. No prior work had resolved whether DOM-HOC interactions are always linear or if nonlinear effects occur. This gap motivated the need to test the assumptions of linear binding. The study aimed to determine whether DOM interacts with HOCs in a nonideal way. The research also sought to evaluate the role of pH and cosolutes in these interactions. Nonlinear binding could change how scientists model pollutant behavior in water. The findings could improve predictions of chemical mobility in natural systems.

This study aimed to test the assumption that interactions between DOM and HOCs are always linear. The researchers focused on two PAHs—phenanthrene and pyrene—and two types of DOM. They used dialysis to measure sorption, desorption, and competition at different pH levels. The goal was to determine whether nonlinear effects occur in DOM-HOC binding. The study also sought to investigate how cosolutes and pH influence these interactions. By observing binding behavior under controlled conditions, the researchers could identify deviations from linear models. The findings could help refine environmental models of pollutant transport. The study aimed to provide a more accurate framework for predicting HOC mobility in natural waters.

The researchers used dialysis to study interactions between DOM and PAHs. They selected phenanthrene and pyrene as model HOCs and two DOM sources. Experiments were conducted at pH 4, 7, and 11 to assess the effect of acidity on binding. Sorption and desorption were measured using dialysis membranes. The presence of cosolutes was introduced to test their influence on binding sites. Binding coefficients were calculated to quantify the strength of interactions. Desorption hysteresis was observed by comparing initial and final desorption rates. The isotherm nonlinearity factor (n-value) was used to assess deviations from linearity. The study combined experimental measurements with theoretical analysis of binding behavior.

Nonlinear interactions between PAHs and DOM were consistently observed. The isotherm nonlinearity factor increased significantly when cosolutes were added. This suggested that cosolutes occupied specific binding sites on DOM. Desorption hysteresis was detected, indicating irreversible binding in some cases. Binding coefficients were higher at lower pH levels, suggesting stronger interactions. Desorption hysteresis was more pronounced at pH 4 than at pH 7 or 11. The n-value increased with cosolute addition, confirming nonideal binding behavior. The study showed that DOM conformation changes may explain the observed interactions. These findings challenge the assumption of linear DOM-HOC binding. The results suggest that a more complex model is needed to describe pollutant behavior in water.

The study confirmed that interactions between DOM and HOCs are not always linear. Nonlinear effects and desorption hysteresis were observed in all experiments. The presence of cosolutes increased isotherm nonlinearity, suggesting site-specific binding. Lower pH levels enhanced binding strength and hysteresis. These findings suggest that DOM conformation changes may influence interactions. The linear dissolution concept may not fully describe real-world DOM-HOC interactions. A more complete model is needed to capture the complexity of these interactions. The authors propose that DOM structural changes may explain the observed binding behavior. The study provides a foundation for improving environmental models of pollutant transport.