ASSESSMENT OF SULFATES ROLE IN ATTENUATING THE TOXIC EFFECTS OF BIVALENT HEAVY METALS AND CHROMIUM(VI) ON CULTURED MARINE ALGA DUNALIELLA TERTIOLECTA

Abstract

The issue of how the toxicant effects on microalgae depend on the composition of culture or natural water media is of major importance for bioassays and bioremediation. A high salt content in seawater can mask the presence of dangerous pollutants such as heavy metals (HM). Most studies on this topic traditionally concern divalent heavy metals. At the same time, there is evidence of possible competitive interactions between seawater sulfates and Cr(VI) at cell surface. We investigated the effects of Cr(VI), Cu(II), Cd(II), Zn(II) and Co(II) on the growth of cultured marine microalgae Dunaliella tertiolecta Butcher (1959) at varying SO42– concentrations in Goldberg medium. The cultured alga growth was estimated by the optical density of control and treated samples after cultivation in specialized vessels during 48 h. Heavy metals were added to the cultures as solutions of potassium dichromate, copper, zinc and cadmium sulfates and cobalt chloride. A decrease in SO42– concentration while maintaining the initial salinity of 33‰ caused an increase in the toxic effect of Cr(VI), but not Cu(II), Cd(II), Zn(II) and Co(II). The effective concentrations (EC50) of chromium were 21.32; 6.04; 2.01 and 0.74 mg/L in the initial medium and in media with a 5, 25 and 125-fold decrease in sulfate concentration, respectively. The EC50 values of Cu2+, Cd2+, Zn2+ and Co2+ in the initial medium were 0.54, 7.40, 3.80 and 22.00 mg/L, respectively, and did not differ significantly when SO42– concentration varied. The protective role of sulfate against the effects of Cr(VI) on different organisms in varying media may be conveniently assessed as a function of chromium to sulfate concentration ratio. In the present study, the growth of cultured D. tertiolecta was reduced by 50% when Cr(VI)/SO42? was 1:100. Reducing this proportion to 1:1700 was association with an infibition of D. tertiolecta growth only by 20%. The data suggest that seawater sulfates differentially influence the toxic effects of Cr(VI) and divalent heavy metals.