Abstract Synthetic chemicals with high environmental persistence, including anionic surfactants and heavy metals, pose significant risks to freshwater ecosystems. This study evaluated the sublethal toxicity of sodium dodecyl sulfate (SDS) and mercuric chloride (HgCl₂) on the freshwater planarian Girardia tigrina, a widely used ecotoxicological model. Median lethal concentrations (LC₅₀) were determined over 96 hours, revealing a time- and dose-dependent toxicity, with SDS (LC50 = 45.27 µg/L) exhibiting higher acute toxicity than HgCl₂ (LC50 = 229.16 µg/L). Sublethal concentrations (5, 10, 25 µg/L) were used to assess locomotor behavior, reproduction, regeneration, and acetylcholinesterase (AChE) activity. Both SDS and HgCl₂ impaired locomotion in a concentration- and time-dependent manner, with partial recovery after prolonged exposure, indicating potential neurophysiological compensation. Reproductive performance was severely affected, with reduced fecundity and fertility, prolonged cocoon hatching times, and complete inhibition of viable cocoons at higher concentrations. Regeneration assays revealed that SDS delayed head and eye regeneration primarily after day 3, whereas HgCl₂ induced rapid and sustained inhibition from day 2 onward. AChE activity exhibited compound-specific alterations: HgCl₂ induced a biphasic response (initial stimulation followed by suppression), whereas SDS caused sustained activation. These multifaceted effects indicate disruption of neurochemical balance, reproductive physiology, and stem cell-mediated regeneration. Collectively, the findings highlight the ecological risks of SDS and HgCl₂, emphasizing the sensitivity of planarians as sentinel species for detecting sublethal toxicological effects in freshwater environments. This study underscores the importance of evaluating behavioral, reproductive, regenerative, and biochemical endpoints to support comprehensive environmental risk assessments and inform regulatory policies on emerging pollutants.
Souza-Aguiar et al. (Tue,) studied this question.