Nanoremediation of tilapia fish culture using iron oxide nanoparticles biosynthesized by Bacillus subtilis and immobilized in a free-floating macroporous cryogel.

Background and aim: Contamination from increased anthropogenic activities poses a threat to human health as well as the ecosystem. To develop a nanotechnological approach to improve aqua fisheries, we synthesized magnetic hematite nanoparticle-based gel and evaluated its efficacy in a cadmium-polluted closed system to decontaminate water and improve tilapia fish health.

Methods: Green iron oxide nanoparticles were biosynthesized by the metabolite of bacillus subtilis and incorporated into polyvinyl alcohol to construct a hydrogel by cryogelation.

Key findings: The cryogel had interconnected macropores with diameters widely ranging between 20 and 200 μm and could be free-floating in water. When applied in cadmium-polluted tilapia culture, this nanogel reduced turbidity and ammonia in the aquarium, adsorbed cadmium from the water with a larger quantity on the gel's outer surface than in its center., and reduced cadmium concentration in tilapia's liver, gills, and muscles. Application of this nano-based cryogel reduced the toxic effects of cadmium on tilapia fish. It maintained hepatic and renal cell nuclear integrity as determined by comet assay. This nano-treatment also reversed the cadmium-induced elevations of plasma lipids, glucose, stress marker cortisol, the hepatic enzymes AST and ALT, and the kidney function marker urea, and improved the lymphocytopenia and other hematological functions in tilapia fish intoxicated by cadmium.