Ecotoxicological effects of cadmium on Echinometra mathaei: Oxidative stress, genotoxicity, and biochemical responses

Cadmium (Cd), a non-essential heavy metal, poses a persistent threat to marine ecosystems. The edible sea urchin Echinometra mathaei, widely recognized as a sentinel species, was used to evaluate the effects of environmentally relevant Cd exposure. These organisms were exposed to 0, 0.01, and 0.1 mg L^-1 Cd for 28 days, and gonadal tissues were analyzed for Ca content, oxidative stress biomarkers (H₂O₂, MDA, SOD, CAT), protein and carbohydrate reserves, and genotoxic endpoints (tail intensity, tail moment, tail factor). Cd accumulated progressively in gonads, coinciding with calcium depletion, highlighting ionic disruption. Oxidative stress was evident through increased H₂O₂ and MDA levels, as well as altered antioxidant enzyme activities, which were followed by partial adaptation or enzymatic exhaustion. Protein initially increased, likely reflecting stress-induced synthesis, but declined with prolonged exposure, while carbohydrates were persistently depleted, indicating high energetic costs of detoxification. Genotoxicity peaked on day 14, confirming ROS-mediated DNA damage, with partial recovery by day 28. Integrated biomarker response (IBR) and multiple factor analysis (MFA) identified oxidative stress and genotoxicity as the most sensitive endpoints. This study presents the first comprehensive assessment of Cd toxicity in E. mathaei from Southeast Asia, revealing that reproductive tissues are highly susceptible to ionic imbalance, oxidative damage, and genomic instability. The integration of oxidative, metabolic, and genotoxic biomarkers highlights the ecological relevance of E. mathaei as a coastal bioindicator, underscoring the value of IBR and MFA in interpreting complex pollutant effects. These findings underscore the urgent need for monitoring Cd contamination in tropical marine ecosystems.