Humic substances and the water calcium content change the toxicity of malachite green
Journal of Applied Ichthyology, 19:6, 380–382 (2003)
Laboratory experiments were conducted to test interactive effects of calcium content and the presence of humic substance (HS) on malachite green (MAG)-induced toxicity in fish embryos and larvae by means of a semistatic 144-hembryo-larval-test with zebrafish (Danio rerio). Two kinds of reconstituted water samples were used to produce the test media by mixing salts into deionized water resulting in either hard water, or soft water. By adding HS two additional test media were produced. MAG was tested in concentrations of 0.05, 0.10, 0.15, 0.20, 0.25 mg/L. The toxicity ranking of MAG to embryos based on 96-h-LC50 in the different test water samples is analyzed. Increased calcium concentrations did not protect zebrafish embryos and larvae from MAG-induced toxicity. At high calcium conditions, the mortality of the embryos as well as of the larvae is reduced. Thus, at high calcium conditions the HS does affect the MAG-induced mortality. The mechanism which causes the higher toxicity of MAG in the presence of higher calcium concentrations is poorly understood. A probable explanation could be the stimulation of the calcium-binding protein calmodulin as well as the calmodulin kinase II in cell membranes in the presence of high calcium concentrations.