Toxicity assessment on three direct dyes (D-BLL, D-GLN, D-3RNL) using oxidative stress bioassay and quantum parameter calculation

Textile dyes and dye industrial effluents are widely known for esthetic and toxicity problems. The toxicity of three direct dyes, Direct Blending Rebine (D-BLL), Direct Blending Scarlet (D-GLN), and Direct Blending Yellow (D-3RNL), were examined by the antioxidase and lipid peroxide index. Fish (Carassius auratus) were exposed to 100 mg/L test compounds or injected with 200 μg/kg corresponding dyes, and then samples of liver were collected at different times (0.5, 1, 3, 5, 7, 10, 13, 17 and 22 d ) for analysis of superoxide dismutase (SOD), catalase (CAT), and contents of malondialdehyde (MDA). There is an obvious difference between two poisoning conditions and results indicated injection pattern have a more sensitive response. Besides, SOD, CAT and MDA levels displayed different variation trend following the prolonged duration, implying that dye metabolism generated less toxic or more active substance. The comparison among their intensity of enzyme inhibition showed that the toxicity order is D-BLL>D-GLN>D-3RNL. Additionally, three direct dye molecules were optimized based on the quantum mechanical charge density of a solute molecule interacting with a continuum description of the solvent (SMD) of Self-consistent Reaction Field Theory (SCRF) on B3LYP/LAN2BM level and the stable configurations were obtained. Wiberg bond orders were analyzed and atom in molecule (AIM) 2000 program was employed to estimate the interaction between atoms. The possible degradation pathways and toxicities were speculated based on the computations. The calculation is consistent with the experimental results and analysis.

► The chronic exposure and injection method were used for toxicity identification of dyes.
► Wiberg bond orders and atom in molecule (AIM) were employed to predict the possible degradation pathways.
► The testing was integrated with the calculation to reveal toxicity difference.
► Toxicity order of three dyes was speculated.