Digging into Understudied Sediments: What Lumbriculus variegatus Reveals about Fluoxetine Exposure from the Cellular to the Individual Level.

Sediments accumulate persistent and toxic compounds, yet assessing their effects on benthic species remains challenging. Especially antidepressants, such as fluoxetine, are of concern due to their sediment affinity and potential to disrupt neuroendocrine functions at low concentrations. This study investigated the chronic effects of fluoxetine in the sediment-dwelling worm Lumbriculus variegatus through two 28-day sediment exposures (0.00025-25 mg/kg) conducted in accordance with OECD 225, with modifications. Endpoints encompassed multiple biological levels, including biochemical markers of neurotoxicity (cholinesterase), oxidative stress (catalase, glutathione-S-transferase, total glutathione), damage (lipid peroxidation), energy metabolism (lipids, sugars, proteins, electron transport system), physiological responses (oxygen consumption), three novel behavioral assays (chemical avoidance, feeding, phototaxis), and conventional apical endpoints (mortality, growth, reproduction). Effects on the non-conventional endpoints occurred at environmentally relevant sediment concentrations. Additionally, oxidative stress and behavioral responses were substantially more sensitive endpoints of fluoxetine exposure than the conventional endpoints growth, reproduction, and mortality. Integrating responses across biological levels, we propose a qualitative Adverse Outcome Pathway linking molecular and cellular events to individual-level effects. Our findings demonstrate that environmentally relevant fluoxetine concentrations elicit ecologically meaningful effects in L. variegatus that current regulatory frameworks would likely overlook, emphasizing the need for standardized behavioral assays in sediment risk assessment.