Toxicity studies applied to evaluate the modified zeolites adsorbent for treating copper-complex dyes from simulated dyehouse wastewater

Abstract

Textile dyes occur in wastewaters in different concentrations due to their poor fixation to fabrics. Even at low concentrations, textile dyes can cause waste streams to become highly colored. Aside from their negative aesthetic effects, certain textile dyes have been shown to be toxic, and in some cases, these compounds are carcinogenic and mutagenic. Zeolite synthesized from fly and bottom ashes and modified with hexadecyltrimethylamonium (ZMF and ZMB, respectively) were used as adsorbent to remove dyes - Solophenyl Navy and Solophenyl Turquoise and their hydrolyzed forms Solophenyl Navy Hydrolyzed and Solophenyl Turquoise Hydrolyzed, respectively, from simulated textile wastewater. The purpose of the research was to use bioassays with Lemna minor, Ceriodaphnia dubia and Chironomus tepperi to determine the acute and chronic toxicity of these dyes before and after adsorption process. The acute results indicated C. tepperi showed to be less sensitive when compared with other test organisms, showing values of 48hLC50 70.8 and 211 mgL-1 for SN and ST. On the other hand, C. dubia showed to be very sensitive to the dyes tested (48hLC50 1.25; 54.5; 0.78 and 2.56 mgL-1 for SN, ST, SNH and STH), while L. minor presented response for higher concentration of the dyes, as chlorosis, loss of roots, reduction of the size and etc., showing values of EC50 of 18.9; 69.4; 10.9 and 70.9 mgL-1 for SN, ST, SNH and STH). Chronic tests with C. tepperi showed changes in survival, growth, development and gender differences for SN and ST dyes. After adsorption treatment with ZMF the acute effects were substantially reduced for both dyes and their hydrolyzed forms, showing absence of toxicity after treatment. However, the treatment with ZMB showed no difference and/or increased toxicity in some cases. Toxicity Identification Evaluation testes were realized and showed the baseline acute effects were substantially reduced after treatment with Ethylenediaminetetraacetic acid, showing the most of the toxicants in this study are cations metals. These experimental results suggest both dyes, raw and hydrolyzed, are toxic and their removal are necessary.