Life-stage-resolved toxicological assessment and environmental relevance of triclosan in the freshwater gastropod Biomphalaria glabrata.

TCS (triclosan) is frequently detected in freshwater compartments, including surface water, sediments, biosolids, and pore water; however, its life-stage-specific toxicity in gastropod mollusks remains insufficiently characterized. To address this gap, this study aimed to determine the life-stage-dependent lethal and sublethal toxicity of TCS in Biomphalaria glabrata and identify environmentally relevant endpoints for gastropod ecotoxicology and life-stage-aware ecotoxicological assessment. We applied a life-stage-resolved framework covering embryonic development, newly hatched juveniles, acute adults, and chronic adults, assessing survival, developmental abnormalities, adult behavior, hemolymph label-free 3D imaging, AChE (acetylcholinesterase)/SOD (superoxide dismutase) activities, growth, reproduction, and histopathology. Embryos were most sensitive, with a 216 h LC₅₀ (median lethal concentration) of 0.1672 mg/L, edema at ≥ 0.20 mg/L, and blastula arrest at ≥ 0.25 mg/L. Newly hatched juveniles showed intermediate acute sensitivity (96 h LC₅₀ = 0.5818 mg/L), whereas adults were less sensitive to acute lethality (96 h LC₅₀ = 2.552 mg/L) but showed reduced escape, prolonged retraction, and visible hemocyte structural injury at ≥ 2.0 mg/L. Concentration-response modeling of the Day 21 endpoints yielded model-derived EC₅₀ (Effect Concentration) values of 0.0674 mg/L for relative body-mass change, 0.1153 mg/L for shell growth, and 0.2276 mg/L for cumulative egg-mass production. These response patterns indicate that somatic growth endpoints were more consistently responsive than reproductive output under the present experimental conditions. Overall, TCS induced stage-dependent lethal and sublethal toxicity in B. glabrata, highlighting the importance of considering the particularly sensitive embryonic stage in life-stage-aware ecological hazard assessment.