The influence of pH on the toxicity of aluminum, cadmium, and iron to eggs and larvae of the zebrafish, Brachydanio rerio.

The effects of Al, Cd, and Fe on hatching of eggs and survival of larvae were studied at different pH levels between 4 and 9 in the zebrafish (Brachydanio rerio). Aluminum and Cd were more toxic at high pH levels while Fe was more toxic at low pH levels. In the absence of added toxicants hatching was stimulated when pH was lowered from 7 to 6 but a further lowering of pH retarded hatching. The most rapid hatching was assumed to occur around pH 6.2. The effects of these metals on median time to hatch were irregular with inhibition and stimulation depending on both pH and concentration of metal. The strongest stimulation of hatch was found with 16 mg Fe liter-1 at pH 6.7. Stimulation of hatch at sublethal concentrations of these metals may be due to respiratory stress-mediated release of chorionase and such stimulation may be a more common effect of toxicants than is generally expected.