Assessing the Removal Capacity of Three COVID-19 Pharmaceuticals from a Wastewater-Irrigated Soil

During the COVID-19 pandemic, pharmaceutically active compounds (PhACs) such as azithromycin (AZI), ivermectin (IVE), and dexamethasone (DEX) were used in developing countries with wastewater irrigation practices. This study assessed the removal of these PhACs from a soil irrigated with wastewater for over a century, considering two soil depths and three spiking concentrations (345 to 670 µg kg−1). Shifts in cumulative O2 consumption and in prokaryotic composition were also assessed in a 30-day laboratory incubation. The soil effectively removed AZI and DEX regardless of depth; however, IVE was the most persistent, being below the detection level (5.5 µg kg−1) in the topsoil (0–10 cm) after 30 days but remaining at 17% of its initial concentration in the subsoil (20–30 cm) at the highest dose. The highest removal rates occurred within the first week in accordance with the cumulative O2 consumption, positively correlated to the PhACs concentration. Significant changes in prokaryotic communities were observed at day three, where diversity diminished and the relative abundance of Methylotenera increased from 0 to 80%, yet communities returned to their baseline after seven days. These findings highlight the removal capacity of xenobiotics from soils constantly irrigated with wastewater, and the behavior of these PhACs in soils.