pH influences on kinetics, bioconcentration, and internal disposition of diphenhydramine, a weakly basic pharmaceutical, in signal crayfish ( <i>Pacifastacus leniusculus</i> )

Abstract Identification of bioaccumulative chemicals has largely relied on models and empirical data describing bioaccumulation of nonionizable organic chemicals in fish, but bioaccumulation research has remained understudied in other aquatic taxa, particularly for ionizable organic chemicals. We examined the influences of pH on uptake and elimination kinetics, bioconcentration factors, and internal disposition of diphenhydramine (DPH), a weakly basic pharmaceutical, in signal crayfish Pacifastacus leniusculus. After a 10-day bioconcentration experiment (7 days of uptake, followed by 3 days of elimination) at pH 6.7 and 8.7, we analyzed DPH in water, crayfish hemolymph, and whole-body tissues using liquid chromatography with tandem mass spectrometry. We then derived a hemolymph: water partition coefficient and estimated the apparent volume of distribution (VD) for DPH in crayfish. Consistent with previous observations in freshwater and estuarine fish, pH significantly (P &amp;lt; 0.05) altered DPH tissue levels and bioconcentration factors (BCF) in signal crayfish. However, hemolymph: water partitioning and steady state and kinetic-based BCFs for DPH were lower than similar observations in fish, and apparent VD values were markedly higher in crayfish (416 − 451) than in fish and humans. Our findings indicate that signal crayfish represent a suitable crustacean model to advance an understanding of ionizable organic contaminant bioaccumulation in invertebrates.