Retention of 4-nonylphenol and bis(2-ethylhexyl) phthalate in soil in the Tula Valley, Hidalgo, Mexico

The reuse of wastewater for agricultural irrigation is a common practice worldwide. Among other compounds, this water contains emerging pollutants whose migration into aquifers as a result of irrigation is a concern because of their impact on health. Therefore it is of interest to study the degree to which these compounds are retained by the soil through adsorption mechanisms. The purpose of this work was to determine the degree of retention of di(2- ethylhexyl)phthalate (DEHP) and 4-nonylphenol (4-NP) in three agricultural soils (vertisol, leptosol and phaeozem) irrigated with untreated wastewater in the Tula Valley. This was performed using batch and adsorption column experiments. The results from the batch tests showed strong adsorption of DEHP by the three types of soils (Kd from 1.8 x 104 to 4.2 x 104 L/kg), and a lower adsorption for 4-NP (Kd from 15 to 80 L/kg). The Vertisol soil showed the highest adsorption capacity for both compounds, explained by its high content of clay and organic matter. In contrast to the batch studies, the column experiments indicated that the retardation factor for 4-NP was greater than that for DEHP. This suggested the presence of other mechanisms that accelerate the leaching of DEHP, such as its complexation with dissolved organic matter in the soil. These results were consistent with those observed in situ in the wells and springs in the region, where concentrations of DEHP are greater than 4-NP