Fast In, Faster Out: Rapid Thallium Elimination Drives Low Bioaccumulation in Coastal Gastropods

Thallium (Tl) ranks among the most toxic elements to humans, but its bioaccumulation and ecological risks in marine organisms remain poorly understood. In this study, we investigated the toxicokinetics of Tl in the intertidal snail Reishia clavigera, an ecologically and economically important gastropod native to East and Southeast Asia. Using the stable isotope ²⁰³Tl as a tracer, we quantified Tl uptake and elimination under environmentally relevant conditions across salinity (15-30‰) and temperature (7-28 °C) gradients. Despite moderate uptake rates (k_u: 0.064-0.29 L g^-1 day^-1), Tl bioaccumulation remained low due to exceptionally fast elimination (k_e: 0.79-3.37 day^-1), with biological half-lives as short as 0.21 days. Salinity suppressed Tl uptake without affecting elimination, while temperature increased both k_u and k_e. The resulting bioconcentration factors (BCF: 59-160 L kg^-1 dry weight) were two to four orders of magnitude lower than those of other trace metals, indicating inherently weak Tl retention. Tissue-specific analyses showed a higher Tl retention in viscera than in muscle, largely driven by slower elimination. Our findings resolve the apparent paradox between Tl's high mammalian toxicity and relatively lower aquatic toxicity, highlighting rapid elimination as the key controlling factor. This work underscores the importance of integrating toxicokinetics into ecological risk assessment and suggests that Tl tissue levels in marine mollusks primarily reflect short-term environmental exposure rather than chronic contamination.