Cadmium-Induced antioxidant gene expression in

Introduction: Cadmium (Cd) is a toxic heavy metal prevalent in aquatic ecosystems, with known adverse effects on organisms through oxidative stress. Corbicula fluminea (Asian clam), a bioindicator species, is sensitive to environmental pollutants, including cadmium. This study investigates the spatial variation in cadmium exposure and its impact on antioxidant gene expression in Corbicula fluminea (C. fluminea) from the Euphrates River, Iraq. Methods: a cross-sectional study was conducted across three distinct sites with varying anthropogenic impacts (urban, agricultural, and aquaculture) along a 26-kilometre stretch of the Euphrates River. Cadmium concentrations in water and mollusc tissues were quantified using atomic absorption spectroscopy. The expression levels of antioxidant genes (MT, GST, CAT, SOD) were assessed via quantitative PCR. Statistical analyses included one-way ANOVA and Pearson correlation. Results: cadmium concentrations differed significantly among the sampling sites (p = 0.003), with the highest levels recorded in the urban area of Nasiriya. However, no significant differences were found in the expression levels of MT, GST, CAT, and SOD genes among the sites (all p > 0.05). Similarly, no significant correlations were observed between cadmium concentrations and gene expression. Conclusion: although cadmium contamination varied across sites, antioxidant gene responses in C. fluminea were not statistically significant. These findings suggest that gene expression responses in natural environments may be modulated by multiple interacting environmental factors, emphasising the need for broader and longitudinal ecological assessments. The integration of C. fluminea into environmental monitoring programs should therefore incorporate multiple biomarkers rather than relying solely on antioxidant gene expression.