Bioaccumulation Kinetics of Model Ionizable Pharmaceuticals in the Freshwater Unionid Pondmussel, Ligumia subrostrata.

Though bioaccumulation of ionizable pharmaceuticals is increasingly studied, most reported aquatic tissue concentrations in field or laboratory experiments are from fish. However, higher levels of antidepressants have been observed in bivalves compared to fish from effluent-dominated and dependent surface waters. Because experimental bioaccumulation information for freshwater bivalves, for which ~ 70% of species in North America are considered vulnerable to the point of extinction, is lacking, we examined accumulation in the freshwater Pondmussel, Ligumia subrostrata, following exposure to a model weak acid, acetaminophen (mean (±SD) = 4.9 ± 1 µg L -1 ), and a model weak base, sertraline (mean (±SD) = 1.1 ± 1.1 µg L -1 ) during 14-day uptake and 7-day depuration experiments. Pharmaceutical concentrations were analyzed in water and tissue using isotope dilution LC-MS/MS. Mussels accumulated orders of magnitude higher concentrations of sertraline (31.7 ± 9.4 µg g -1 ) compared to acetaminophen (0.3 ± 0.1 µg g -1 ). Ratio and kinetic-based bioaccumulation factors of 28,836.4 (L kg -1 ) and 34.9 (L kg -1 ) were calculated for sertraline and for acetaminophen at 65.3 (L kg -1 ) and 0.13 (L kg -1 ), respectively. However, after 14 days sertraline did not reach steady state concentrations, though it was readily eliminated by L. subrostrata. Acetaminophen rapidly reached steady state conditions, but was not depurated over a 7 day period. Future bioaccumulation studies of ionizable pharmaceuticals in freshwater bivalves appear warranted. This article is protected by copyright. All rights reserved. Environ Toxicol Chem 2023;00:0-0. © 2023 SETAC.