• Adsorption: Adsorption of pharmaceuticals onto soil media or plant roots is generally considered to be a physical process rather than a chemical reaction. However, the adsorption process can be influenced by the properties of the pharmaceuticals and the soil media or plant roots, such as pH and organic matter content.
• Uptake and metabolism by plants: Once inside the plant, pharmaceuticals may undergo metabolism, which can involve a range of chemical reactions such as oxidation, reduction, hydrolysis, and conjugation. For example, the pharmaceutical carbamazepine can be metabolized by plants through hydrolysis to form 10,11-dihydro-10,11-trans-dihydroxy carbamazepine.
• Biodegradation by microorganisms: Biodegradation of pharmaceuticals by microorganisms can involve the use of enzymes to break down the compounds into smaller molecules, which can then be used as a source of carbon and energy by the microbes. For example, the antibiotic sulfamethoxazole can be degraded by the bacterium Acidovorax sp. JS42 through the cleavage of the sulfonamide bond.
• Hydrolysis: Hydrolysis is another mechanism by which pharmaceuticals can be broken down, involving the cleavage of chemical bonds through the addition of water. For example, the beta-blocker propranolol can be hydrolyzed to form the metabolite propranolol glucuronide.
• Oxidation and reduction reactions: Oxidation and reduction reactions can also play a role in the biodegradation of pharmaceuticals, involving the transfer of electrons from one molecule to another. For example, the antibiotic tetracycline can be degraded by the bacterium Pseudomonas putida through the reduction of the compound to form the metabolite 4-epianhydrotetracycline.

It is important to note that the specific chemical reactions that occur during the removal of pharmaceuticals in constructed wetlands can depend on a variety of factors, including the specific pharmaceuticals, wetland system, and microbial community involved.