Chiral pharmaceutical drug adsorption to natural and synthetic particulates in water and their desorption in simulated gastric fluid

Natural and synthetic particulates in aquatic environments can act as a vector for chiral pharmaceutical drugs. Understanding enantiomer enrichment in the particulate phase of water matrices is essential considering the enantiospecific effects that chiral drugs can have on exposed organisms. Therefore, the enantiospecific adsorption of the cationic drugs fluoxetine and propranolol to polyhydroxyalkanoate bioplastic, polyamide microplastic, and cellulose particulates was investigated in 0.01 M calcium chloride (CaCl2) buffer and real environmental matrices. Fluoxetine enantiomers adsorbed to all particulate types under all conditions studied. Yet, propranolol only adsorbed to polyamide in 0.01 M CaCl2 buffer at pH 11, and in samples prepared using real matrices (river water and wastewater). No enantioselectivity was observed in the adsorption of fluoxetine or propranolol, or their subsequent desorption in a simulated gastric environment. Findings showed the enantiomeric composition of the adsorbed drug will reflect that of the dissolved drug assuming no degradation takes place. However, further enantiospecific adsorption studies are now needed on a broader range of chiral drugs and particulate matter found in water. Importantly, drug adsorption was considerably greater in river water and wastewater compared to 0.01 M CaCl2 buffer (2.1 to 5.3 times for fluoxetine). Most adsorption studies reported in the literature use 0.01 M CaCl2 buffer to conform with international guidelines for assessing the adsorption behaviour of chemicals. Although such conditions enable direct comparison with similar studies, they can underestimate cationic drug adsorption to particulates in engineered and natural environments. This needs consideration in future studies on drug adsorption to microplastics and other particulate matter in laboratory studies.