Changes in the retention of pharmaceuticals by soil as an indicator of soil organic matter decomposition

Using freshwater and greywater for irrigation introduces pharmaceuticals (PhACs) into arable lands that lack organic matter replenishment, thus altering soil composition and affecting PhACs retention throughout the vegetation period. We conducted an incubation experiment representing a simulated vegetation period using Black Soil, which covers about 21% of the world's agricultural areas. We used PhACs with diverse physicochemical properties that cover a wide range of the characteristics typical of PhACs accumulating within the rhizosphere such as carbamazepine (CBZ), 17α-ethynylestradiol (EE2), and diclofenac-sodium (DFC) and their metabolites (trans-10,11-Dihydro-10,11-dihydroxy carbamazepine (TCBZ), estrone (E1), estriol (E3), 17β-estradiol (BE2), 17α-estradiol (LE2), and 5-hydroxydiclofenac (5HODFC)). We performed separated fixed-bed experiments (15 columns) to determine the main sorption properties of PhACs at the beginning, middle and end of the simulated vegetation period. In parallel, we were monitoring the changes in soil organic matter (SOM), characterized by the indicator physicochemical parameters (e.g. soil organic carbon (SOC), the ratio of dissolved organic carbon (DOC) to SOC and the composition of soil aliphatic and aromatic compounds). We also analysed the properties of the SMC (e.g. acidic phosphatase-, dehydrogenase enzyme activity, and the composition of the communities). Chemometric modelling has allowed us to visualize how the physicochemical properties of PhACs shape the sorption processes at different decomposition stages of SOM. With these data, we estimate how parent compounds and their metabolites are retained and released by the ever-changing organic matter medium, which might be used to simulate the temporal mobility of PhACs in agricultural systems, thereby aiding in the management of soil nutrient replenishment.

The enzyme activity showed that the microbial community was continuously transforming the soil organic carbon, leading to its decrease. During the incubation period, representing the early stages of the vegetation period, the hydrophobicity and van der Waals surface area of PhACs affected soil retention strength. By this period's end, the Hydrogen-bond donor/acceptor ratio shaped the sorption processes. The physicochemical property that dominates the adsorption clearly indicates the transformation of the available functional groups. We demonstrate the necessity of considering soil conditions over time rather than relying on a single observation, as it is inherently limited in its ability to represent the soil's actual state.

This research was supported by OTKA K142865, NKFIH 2020–1.1.2-PIACI-KFI-2021-00309; 2021–1.2.4-TÉT-2021-00029, HUSK_2302_1.2_070 INTERREG and DKOP-23_03.