Autor:innen:
Mogens Thalmann | TU Braunschweig, Institut für Geoökologie | Germany
Linus Neubert | TU Braunschweig, Institut für Geoökologie | Germany
Dr. Sondra Klitzke | Umweltbundesamt | Germany
Prof. Dr. Aki Sebastian Ruhl | Umweltbundesamt | Germany
Dr. Andre Peters | TU Braunschweig, Institut für Geoökologie
Irrigation of agricultural land with reclaimed water (RW) can prevent an overexploitation of water resources and reduce competition but poses the risk of introducing pollutants to the cropland. One group of organic trace substances can be classified as persistent and mobile (PM), meaning that adsorption and decay are only weak. To date, it is unclear to which extent soils may still function as a natural buffer for these substances, protecting groundwater from contamination. The adsorption of PM substances to the soil may be affected by the composition of the soil solution, which may be altered due to irrigation with RW. Thus, the aim of this study is to examine the effect of ionic strength (IS), cation valency (mono-/divalent) and pH on the adsorption of 11 PM substances of domestic origin onto a top and a subsoil of an agricultural field in Brandenburg.
In batch experiments, we investigated two soil materials differing mainly in their organic carbon content (Corg) and texture using solutions of different IS (pure water, 0.01 M CaCl2, 0.1 M CaCl2, 0.03 M NaCl, and 0.3 M NaCl) and pH values (5.3 and 6.2 for top and subsoil, respectively, and 7.5). The PM substances examined are adamantan-1-amine, acesulfame, benzotriazole, carbamazepine, diclofenac, diatrizoic acid, oxipurinol, primidone, saccharin, sulfamethoxazole, and valsartan acid.
Acesulfame, diatrizoic acid, primidone, and saccharin did not show any sorption within the experimental setup. For the other 7 substances, significant sorption to the soil was measured, with Kd values ranging between 0.68 L kg−1 for valsartan acid and 5.89 L kg−1 for diclofenac. Changes in IS and between mono-/divalent cations only affected sorption of adamantan-1-amine, as the only cationic substance. An increase in pH from 5.3 to 7.5 reduced sorption of sulfamethoxazole, valsartan acid, diclofenac, and enhanced sorption for adamantan-1-amine in the upper horizon soil (soil A). Our results suggest that the mobility of the examined substances may vary strongly for the investigated conditions, hence making risk assessment more complex. In case the adsorption of PM substances clearly depends on the solution composition (e.g. pH and IS), caution is required when the respective laboratory Kd values are used for transport simulations.