Interactions between azo dyes and selenium in their toxicity to Dunaliella Tertiolecta and Vibrio Fischeri

Abstract

In this study, the interactions between assisting chemicals, dye bath, three azo dyesand selenium in their toxicity to Dunaliella tertiolecta and Vibrio fischeri were determined.Three response parameters, including optical density at 750 nm, in vivo chlorophyll fluorescence and cell number were used to monitor the growth of algae exposed to thetested substances in batch culture. The bioluminescence was measured in a luminometer(ToxAlert by Merck).In order to understand whether the toxicity is due to the light absorption of azo dye or the dye itself, the preliminary experiments were carried out at two light intensities (37.4uE m-2s-1 and 76.8 uE m-2s-1). Algal growth was also examined with different forms and concentrations of selenium under two different light regimes. Selenite and selenate haddifferent effects on the growth of alga. When the light intensity was lowered, thestimulatory effects of all forms of selenium decreased. However, when algae were exposedto dye bath, no significant decrease was observed in the algal growth. The results reflectthat selenium is linked to energy-dependent processes and toxicity of dye bath to algae isnot due to the light absorption of colored dye bath itself. D. tertiolecta was found to be more sensitive than V. fischeri to the tested chemicals,since for all the tested chemicals with and without selenium, hormetic response wasobserved on the growth of D. tertiolecta, however, only inhibitory effect was observed on V. fischeri. Considering the average 8-d IC25, SC20 and 30-min EC25 values expressed asper cent dilution (v/v) the order of toxicity was found as Dye Bath= Remazol Black5 Reactive Yellow 37 Reactive Orange 69=Assisting chemicals. For algae, seleniumincreased the stimulatory effect of all the tested chemicals at low concentration range,whereas it decreased the inhibitory effect at high concentration range, except assistingchemicals and Reactive Orange 69. On the other hand, selenium did not change the inhibitory effect of the tested chemicals on V. fischeri. Additionally, the influences ofstimulation and inhibition of algal growth on aquatic ecosystem were discussed.