The influence of cadmium and zinc on cadmium turnover in the zebrafish,Brachydanio rerio

Abstract

A study was made of the dynamics of non-dietary cadmium in fish exposed to different concentrations of cadmium and zinc in water. Zebrafish,Brachydanio rerio, were exposed to Cd and Zn for various periods. The fate of a short “pulse” of the radioactive tracer¹⁰⁹Cd (3 or 9 days) was studied during a post-pulse period of 53 or 83 days. The tracer elimination and accumulation were described by exponential equations. The constants obtained from regression analysis of the results were used as a tool for evaluation of the findings.

The majority of the¹⁰⁹Cd taken up in the gills during the pulse period was retained in the gill tissue and slowly transferred to the internal organs or lost to the water during the post-pulse period. The retention of tracer in the gills after a 3-day¹⁰⁹Cd pulse was increased by Zn but not influenced by Cd. Continuous exposure to stable Cd increased the rate of turnover of the retained¹⁰⁹Cd. Both Cd and Zn increased the tracer accumulation in the liver and kidney. The results also indicated that the effect of Zn on the Cd turnover might be lost if the environmental Zn is withdrawn before the start of the¹⁰⁹Cd pulse.

A tendency of increased mortality of the fish exposed to 1 μg Cd/L for 2–3 months suggested that low concentrations of Cd is toxic to the fish during chronic exposure. The increased Cd uptake and transfer in the gills, caused by Zn, could have deleterious effects on the fish. It might also reflect a change in the form of transport and in the intracellular handling of the metal, which protects the fish from Cd toxicity. However, a Zn pre-exposure did not decrease the mortality, which suggests that Zn did not protect the fish from Cd toxicity.