Humic substances and the water calcium content change the toxicity of malachite green

Abstract

Summary Laboratory experiments were conducted to test interactive effects of calcium(Ca 2+ ) 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 (›Ca ) HS), or soft water (flCa ) HS). By adding HS two additional test media were produced (›Ca + HS, flCa + HS). MAG was tested in concentrations of 0.05, 0.10, 0.15, 0.20, 0.25 mg L )1 . The toxicity ranking of MAG (mg L )1 ) to embryos based on 96-h-LC50 in the different test water samples is: ›Ca ) HS (0.061) > ›Ca + HS (0.123) ¼ flCa ) HS (0.12) ‡fl Ca + HS (0.134) and on 144-h-LC50 to larvae is: ›Ca ) HS (0.038) > ›Ca + HS (0.06) > flCa ) HS (0.077) ¼ flCa + HS (0.077). Mortality of all the groups was significantly different (P < 0.05). Increased Ca 2+ concentrations did not protect zebrafish embryos and larvae from MAG-induced toxicity. At high Ca 2+ conditions, the mortality of the embryos as well as of the larvae is reduced in the ›Ca + HS group relative to the ›Ca ) HS group. Thus, at high Ca 2+ conditions the HS does affect the MAG-induced mortality. The mechanism which causes the higher toxicity of MAG in the presence of higher Ca 2+ 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 Ca 2+ concentrations.