Heavy metal contamination has become a major problem that causes severe environmental and health issues due to their biosorption, bioaccumulation, and toxicity. This study was designed to evaluate heavy metal chelating abilities of alginic acid (AA) extracted from the brown seaweed Ecklonia cava and two of its derivatives prepared by the partial oxidation of the 2° OH groups (OAA) and partial carboxylation of the monomeric units (CAA) upon reducing the heavy metal biosorption in zebrafish (Danio rerio) modal. Metal ions were quantified using ICP-OES and biopolymers were characterized by FTIR and XRD analysis. All investigated biopolymers indicated potential ability for chelating Pb²⁺, Cu²⁺, Cd²⁺, As³⁺, and Ag⁺. The sorption capacities were in the order of CAA>OAA>AA. All biopolymers indicated a comparatively higher chelation towards Pb²⁺. AA, OAA, and CAA could effectively reduce Pb²⁺ induced toxicity and Pb²⁺ stress-induced ROS production in zebrafish embryos. Besides, they could reduce the biosorption of Pb²⁺ in adult zebrafish which could lead to bioaccumulation. Since alginic acid purified from E. cava and its derivatives could be utilized as seaweed derived biopolymers to purify heavy metals contaminated water and as a dietary supplement to reduce heavy metal biosorption in organisms.