Time-course physiological and transcriptomic study reveals cadmium effects on antioxidant, apoptosis, and immunity in the kidney of the freshwater snail Pomacea canaliculata

Cadmium, a common heavy metal found in batteries, coatings, and fertilizers, enters the environment through industrial waste and agricultural runoff, posing significant risks to aquatic life. However, its toxic mechanisms in aquatic invertebrates remain largely unknown. This study investigated the toxicity of cadmium chloride (CdCl₂) in the invasive freshwater snail Pomacea canaliculata. Toxicity tests showed that adult P. canaliculata exhibited high tolerance to Cd, with a 96-h LC₅₀ of 1.703 mg/L and an EC₅₀ of 0.584 mg/L. Enhanced antioxidant enzyme activities were observed in the kidney. Further examination of kidney tissues revealed a time-dependent increase in Cd bioaccumulation, reaching 61.00 ± 9.10 mg/kg and 119.62 ± 19.45 mg/kg at Days 7 and 21, respectively, under an EC₁₀ of 0.145 mg/L CdCl₂. After a 7-day depuration (Day 28), the Cd tissue burden decreased to 64.41 ± 23.13 mg/kg. We also found that the disruption of snails' behavior, cell structure, immunity, and apoptosis was potentially associated with Cd bioaccumulation and its toxicity. Comparative transcriptomics revealed that Cd exposure induced 3251, 2840, and 1574 differentially expressed genes at Days 7, 21, and 28, respectively. Enrichment analysis revealed impairment of multiple cellular functions at different phases: (1) Short-term treatment affected xenobiotic metabolism and protein degradation, leading to rapid Cd accumulation, oxidative stress, and DNA damage; (2) Long-term exposure disrupted various metabolic pathways, resulting in elevated stress levels; and (3) After depuration, reactivation of amino acid biosynthesis and ribosome function indicated a recovery phase, although the snails had not yet returned to a healthy state. Our findings enhance the understanding of the toxic mechanisms of Cd in gastropods and contribute to the development of P. canaliculata as a valuable organism for pollution and ecotoxicological studies in freshwater ecosystems.