Quantifying serotonin in four aquatic invertebrates using enzyme-linked immunosorbent assays (ELISA): Implications for assessing selective serotonin reuptake inhibitor (SSRI) effects

Selective Serotonin Reuptake Inhibitors (SSRIs) may reach effect concentrations in aquatic environments and disrupt serotonergic signalling in non-target invertebrates, yet mechanistic understanding remains limited. This study aimed to 1) explore the measurability of a key event associated with serotonin reuptake inhibition within a putative Adverse Outcome Pathway for SSRIs, 2) evaluate the feasibility and limitations of using an enzyme-linked immunosorbent assay to quantify serotonin levels across diverse aquatic invertebrates, and 3) test whether exposure to the SSRI fluoxetine can alterate these serotonin levels. Serotonin was measured in Asellus aquaticus, Tubifex tubifex, Lumbriculus variegatus, and Capitella teleta following 96-hour water exposure to 0, 10, and 100 µg/L fluoxetine. Baseline serotonin levels differed by a factor of 60 among species, but fluoxetine exposure caused no detectable changes. These findings provide baseline information and highlight the potential and methodological constraints of linking SSRI exposure to neurochemical key events in non-target organisms, thereby advancing environmental hazard assessment.