Toxic effects of synthetic and natural indigo dyes on Danio rerio reproduction

Abstract

The textile industry releases significant amounts of toxic pollutants. In the aquatic environment, the presence of these compounds can impact fauna and flora. The aim of this study was to verify if synthetic (95% purity) and natural indigo blue dye obtained from Indigofera tinctoria plants pose a risk to the aquatic fauna. To investigate ecotoxicological effects of these dyes at concentration of 100 mg.L-1, adult females and males of Danio rerio were exposed in chronic tests. At the end of the twenty-first day, reproduction was performed to evaluate the endpoints: number of eggs, egg viability, larvae survival, and gonadal histology, and the same experiments were repeated after another 21 days in clean water to evaluate the potential of biological recovery. All of the analyzed reproductive parameters were significantly reduced in the organisms exposed to both synthetic and natural indigo blue dyes in relation to the control, and males exposed to the synthetic dye, and females exposed to both natural and synthetic dyes presented gonadal histological alterations, evidencing an important chronic effect of these substances to the reproduction of D. rerio. After the biological recovery period, organisms exposed to both types of dyes showed histological improvements and they recuperated offspring production, but those exposed to the natural dye showed better reproductive performance. Overall, our findings suggested that levels of natural and synthetic indigo dyes permitted by the current legislations must be reviewed, and the substitution of synthetic by natural indigo whenever possible is recommended.