Algal blooms exacerbate cadmium/zinc bioaccumulation in filter-feeding fish in contaminated water: Mechanisms and environmental implications

Abstract

Eutrophic waters experiencing cyanobacterial blooms often contain high levels of heavy metal pollutants, including cadmium (Cd) and zinc (Zn). The transfer mechanisms of Cd and Zn within the water-algae-fish system, however, remain poorly understood. This study investigates the accumulation and transfer of Cd and Zn in a simulated water-algae‑silver carp (Hypophthalmichthys molitrix) ecosystem during Microcystis aeruginosa (M. aeruginosa) blooms. Algae demonstrated significant bioaccumulation of Cd and Zn, with Zn proving more toxic to the algae than Cd. In silver carp, the accumulation of Cd and Zn was strengthened in the intestine, liver, and skin following ingestion of M. aeruginosa enriched with these metals. This resulted in a 31% increase in Cd enrichment in the intestine, liver, and a 72% increase in the skin, compared to systems without M. aeruginosa. Zn enrichment in the liver and skin increased by 53% and 61%, respectively. However, muscle accumulation of Cd and Zn showed only minor increases of 0.59 and 3.93 mg/kg. This study elucidated that algae exacerbated the bioaccumulation of Cd and Zn in silver carp through mechanisms such as digestion, absorption, and skin mucosal contact in ecosystems experiencing M. aeruginosa blooms. The accumulation and food chain amplification of heavy metals in eutrophic water bodies increase the ecological toxicity risk to aquatic organisms and local residents. Measures should be considered to simultaneously control both eutrophication and heavy metal pollution in water bodies, with overall results contributing to the scientific management of eutrophic waters containing heavy metals.