Sorption and desorption of carbamazepine, naproxen and triclosan in a soil irrigated with raw wastewater: estimation of the sorption parameters by considering the initial mass of the compounds in the soil.

In conventional sorption studies, the prior presence of contaminants in the soil is not considered when estimating the sorption parameters because this is only a transient state. However, this parameter should be considered in order to avoid the under/overestimation of the soil sorption capacity. In this study, the sorption of naproxen, carbamazepine and triclosan was determined in a wastewater irrigated soil, considering the initial mass of the compounds. Batch sorption-desorption tests were carried out at two soil depths (0-10 cm and 30-40 cm), using either 10 mM CaCl(2) solution or untreated wastewater as the liquid phase. Data were satisfactorily fitted to the initial mass model. For the two soils, release of naproxen and carbamazepine was observed when the CaCl(2) solution was used, but not in the soil/wastewater system. The compounds' release was higher in the topsoil than in the 30-40 cm soil. Sorption coefficients (K(d)) for CaCl(2) solution tests showed that in the topsoil, triclosan (64.9 L kg(-1)) is sorbed to a higher extent than carbamazepine and naproxen (5.81 and 2.39 L kg(-1), respectively). In the 30-40 cm soil, carbamazepine and naproxen K(d) values (11.4 and 4.41 L kg(-1), respectively) were higher than those obtained for the topsoil, while the triclosan K(d) value was significantly lower than in the topsoil (19.2 L kg(-1)). Differences in K(d) values were found when comparing the results obtained for the two liquid phases. Sorption of naproxen and carbamazepine was reversible for both soils, while sorption of triclosan was found to be irreversible. This study shows the sorption behavior of three pharmaceuticals in a wastewater irrigated soil, as well as the importance of considering the initial mass of target pollutants in the estimation of their sorption parameters.