Stage-dependent developmental and reproductive toxicity of p-aminophenol in the freshwater snail Biomphalaria glabrata: Linking organ-level pathology to ecological hazard.

p-Aminophenol (PAP) is an important intermediate in the synthesis and environmental degradation of acetaminophen, and it is widely found in pharmaceutical and dyeing wastewater. However, systematic studies on its toxicity to freshwater invertebrates remain limited. In this study, Biomphalaria glabrata was used as a model organism to comprehensively evaluate the acute and chronic toxicity of PAP across three developmental stages (embryo, juvenile, and adult stages) and to identify key target organs of damage through histopathological analysis. Acute toxicity tests revealed a clear stage-dependent sensitivity gradient, with embryos being the most sensitive (216 h LC50 = 4.16 mg/L, 95 % CI = 3.94 to 4.39 mg/L), followed by juveniles (96 h LC50 = 10.87 mg/L, 95 % CI = 9.38 to 12.36 mg/L) and adults (96 h LC50 = 26.41 mg/L, 95 % CI = 22.78 to 29.58 mg/L). During a 21-day chronic exposure, PAP at concentrations of 9-13 mg/L significantly inhibited adult growth and reproduction, with egg-laying nearly completely suppressed at concentrations ≥11 mg/L. Histopathological observations revealed hepatopancreatic acinar dilation, vacuolation, and necrosis, as well as gonadal follicle atrophy and germ cell degeneration, indicating direct damage to the metabolic and reproductive systems. This study integrates multiple lines of evidence linking "developmental sensitivity, functional impairment, and organ pathology," suggesting that PAP may pose potential risks to mollusk populations under high or pulse exposure scenarios.