Chronic Exposure to Niclosamide Disrupts Digestive Glands and Foot Tissues of Mud Snail Cipangopaludina cathayensis

Niclosamide has been the primary molluscicide for schistosomiasis control for over 50 years, but it poses significant threats to non-target large freshwater mollusks. Cipangopaludina cahayensis, a dominant species in East Asian schistosomiasis-endemic regions, was chronically exposed under environmentally relevant concentrations of niclosamide using a mesocosm approach to assess its toxic effects. Digestive glands accumulated more niclosamide than foot tissues. Prolonged exposure disrupted metabolic processes in the digestive glands, leading to tubular atrophy, inflammatory responses, and nutrient depletion. In the foot, niclosamide caused structural damage to both tissue and muscle fibers, resulting in reduced mobility. Furthermore, niclosamide impaired nutritional coupling between the digestive glands and foot, exacerbating motor dysfunction in the foot. Persistent niclosamide exposure destabilized molluscan trophic-level population dynamics, ultimately triggering multi-faceted ecological disturbances, including a decline in ecosystem resilience and disruption of key ecological functions. Our findings underscore the significant toxicological risks that niclosamide poses to freshwater mollusks and highlight the urgent need for the development of ecologically sound usage guidelines to minimize off-target effects.