Biodegradation of phthalate esters in four agricultural soils: Main influencing factors and mechanisms

Phthalate esters (PAEs) are among the frequently detected organic pollutants in agricultural soils. Here, we investigated adsorption and biodegradation behaviors of di-ethyl phthalate (DEP) and dibutyl phthalate (DBP) in the soils collected from four regions in China: Changchun (CC), Changsha (CS), Cangzhou (CZ), and Yinchuan (YC). The results demonstrated that soil organic matter content crucially influenced the adsorption progress. However, the calculated degradation rates of PAEs in the four soils had no significant correlation with their adsorption capacity, suggesting that PAEs' bioavailability might be not the limiting factor governing their degradation. Furthermore, homogeneous biodegradation experiments were performed in the soil solutions extracted from different regional soils. Results showed that biodegradation of PAEs was influenced by the soil solution's pH and its concentration of dissolved organic matter (DOM). To better understand the accelerating mechanism of DOM, bacterial growth and enzyme activity in the presence of Humic acid (HA) and Fulvic acid (FA) were determined, and the degradation of PAEs by intracellular enzymes were also investigated. These results suggested that HA, FA, and other forms of DOM were actively involved in this biodegradation process in two ways: namely, via nutritional support and sequestration of PAEs. We conclude that the actual impact of soil organic matter (SOM) upon PAEs' biodegradation in soils arose from the net outcome of these two opposing effects.