Soil organic matter decomposition as a key driver of pharmaceutical retention.

Human activities release Pharmaceutically Active Compounds (PhACs) onto arable land, where they can accumulate and disrupt the ecological balance. The soil's microbial community continuously alters the composition of organic matter, as it serves as their primary nutrient source. The quality and quantity of organic matter may vary even within a single vegetation period. Observing the extent of transformation in the different phases is essential, as organic matter is primarily responsible for the soil's ability to retain micropollutants. An incubated sorption experiment was conducted simulating a vegetation period using Mollisol, to examine this question. Enzyme activity results indicate that the microbial community transforms soil organic matter, reducing its quantity and thus its ability to retain PhACs. At the beginning of the incubation period, among the physico-chemical properties of PhACs, the H-donor/acceptor counts and the size of their van der Waals surface area were the determining factors in the sorption processes. At the end of the incubation period, owing to the reduction in organic matter and the transformation of functional groups, the adsorbed PhACs decreased significantly, while desorption increased because the electrostatic interaction began to dominate the sorption processes. Consequently, the mobility rate of the PhACs with hydrophobic properties may increase in the arable land by the end of the vegetation period. The primary properties of PhACs identified should be considered when assessing soil persistence. It's vital to account for the temporal evolution of soil conditions and avoid relying on a single observation, as this only partially represents the soil's actual state.