Comparative Analysis Of Lead And Cadmium Toxicity On Embryonic Development And Cardiac Function In Zebrafish (Danio rerio)

Abstract

This study presents a rigorous comparative assessment of lead (Pb²⁺) and cadmium (Cd²⁺) toxicity on early life stages of zebrafish (Danio rerio). Embryos were exposed to a gradient of environmentally relevant and higher concentrations (0.1, 1, 10, 20, and 100 µg/L) to evaluate lethal (embryonic survival, hatchability) and sublethal (cardiac activity, morphological malformations) endpoints. Results demonstrated a significant, time- and concentration-dependent decrease in survival for both metals, with cadmium exhibiting marginally higher toxicity than lead at 168 hours post-fertilization (hpf) (69.2% vs. 70.0% at 1 µg/L, p < 0.05). A paradoxical, statistically significant increase in heart rate was observed across all exposure groups, indicating a pronounced stress-induced hypercardiac response (e.g., 148.0 ± 2.0 BPM for Pb²⁺ 100 µg/L vs. 122.0 ± 2.0 BPM in control at 72 hpf, p < 0.0001). Furthermore, exposure to concentrations ≥10 µg/L induced significant morphological abnormalities, with malformation rates exceeding 80% at 100 µg/L. Crucially, environmental concentrations (0.1 µg/L) induced significant sublethal cardiotoxicity (126.7 ± 2.1 BPM for Pb²⁺ and 125.7 ± 0.6 BPM for Cd²⁺ at 72 hpf) despite minimal impact on survival, highlighting the superior sensitivity of physiological endpoints over traditional lethality assays. These findings underscore the profound ecological risk posed by chronic low-level heavy metal exposure and advocate for the mandatory inclusion of sublethal biomarker analysis, particularly cardiotoxicity screening, in environmental risk assessment frameworks.