Evidence of Common Cadmium and Copper Uptake Routes in Zebrafish <i>Danio rerio</i>

Cadmium and copper accumulations in gills of zebrafish were measured during a 48 h exposure to 0.025 μM ¹⁰⁶Cd and 0.05 or 0.5 μM ⁶⁵Cu as a single metal or their mixtures. The gill transcript levels of genes involved in the transport of Cu (CTR1 and ATP7A), Na (NHE-2), Ca (ECaC), divalent metals (DMT1), and Zn (ZIP8) were also compared between treatments at 24 and 48 h. Cd uptake was significantly suppressed in the presence of Cu, indicating interaction between Cu and Cd at uptake sites, but Cu uptake was unaffected by Cd. The decrease in Cd accumulation rates in the presence of Cu was associated with an increase in transcript abundance of ECaC at 24 h and DMT1 at 48 h and a decrease in Zip8 transcript levels, all known as routes for Cd uptake. Fish exposed to 0.5 μM ⁶⁵Cu show an increase in gill ATP7a transcript abundance, suggesting that Cu is removed from the gill and is transferred to other organs for detoxification. A reduction in gill CTR1 transcript abundance was observed during the Cu–Cd exposure; this may be a regulatory mechanism to reduce Cu loading if Cu is entering the gills by other uptake routes, such as ECaC and DMT1