RESUMEN
Global consumption of synthetic dyes is roughly 7 × 105 tons per year, of which the textile industry expends about two-thirds. Consumption of synthetic dyes produces large volumes of wastewater discharged into aquatic ecosystems. Colored effluents produce toxic effects in the hydrobionts, reduce light penetration, and alter the photosynthetic activity, causing oxygen depletion, among other effects. Some dyes, such as Congo red (CR), are elaborated with benzidine, a known carcinogenic compound. Information regarding dye toxicity in aquatic ecosystems is scarce; therefore, our study was aimed at evaluating the toxicity of CR on a battery of bioassays: the microalga Pseudokirchneriella subcapitata, the cladocerans Daphnia magna and Ceriodaphnia rigaudi, and the zebrafish Danio rerio. P. subcapitata was the most sensitive species to CR (IC50, 3.11 mg L-1); in exposed individuals, population growth was inhibited, but photosynthetic pigments and macromolecule concentrations were stimulated. D. magna was tolerant to high dye concentrations, the determined LC50 (322.9 mg L-1) is not an environmentally relevant value, but for C. rigaudi, LC50 was significantly lower (62.92 mg L-1). In zebrafish embryos, exposure to CR produced yolk sac edema, skeletal deformities, and stopped larvae hatching; lack of heart beating was the only observed lethal effect. CR affected organisms of different trophic levels diversely. Particularly, the effects observed in microalgae confirm the vulnerability of primary producers to dye-polluted wastewaters, because dyes produced toxic effects and interfered with photosynthesis. Different cladoceran species displayed different acute effects; thus, species sensitivity must also be considered when toxicity of dyes is assessed. Inhibition of fish larvae hatching is a significant effect not previously reported that warns about the toxicity of dyes in fish population dynamics. Synthetic azo colorants should be considered as emerging pollutants because they are discharged into the aquatic environment and are not currently included in the environmental regulation of several countries.
Asunto(s)
Rojo Congo/toxicidad , Pruebas de Toxicidad/métodos , Contaminantes Químicos del Agua/toxicidad , Animales , Cladóceros/efectos de los fármacos , Colorantes/toxicidad , Daphnia/efectos de los fármacos , Embrión no Mamífero , Cadena Alimentaria , Larva/efectos de los fármacos , Dosificación Letal Mediana , Microalgas , Industria Textil , Aguas Residuales , Pez Cebra/embriologíaRESUMEN
Nearly 7 00000 tons of dyes are produced annually throughout the world. Azo dyes are widely used in the textile and paper industries due to their low cost and ease of application. Their extensive use results in large volumes of wastewater being discharged into aquatic ecosystems. Large volume discharges constitute a health risk since many of these dyes, such as Congo Red, are elaborated with benzidine, a known carcinogenic compound. Information regarding dye toxicity in aquatic ecosystems is limited. Therefore, the aim of the present study was to evaluate the effect of Congo Red on survival and reproduction of Ceriodaphnia dubia. We determined the 48 h median lethal concentration (LC50) and evaluated the effects of sublethal concentrations in subchronic exposures by using as food either fresh algae or algae previously exposed to the dye. LC50 was 13.58 mg L-1. In subchronic assays, survival was reduced to 80 and 55 %, and fertility to 40 and 70 %, as compared to the control, in C. dubia fed with intoxicated cells or with the mix of intoxicated + fresh algae, respectively, so the quantity and type of food had a significant effect. We determined that Congo Red is highly toxic to C. dubia since it inhibits survival and fertility in concentrations exceeding 3 mg L-1. Our results show that this dye produces negative effects at very low concentrations. Furthermore, our findings warn of the risk associated with discharging dyes into aquatic environments. Lastly, the results emphasize the need to regulate the discharge of effluents containing azo dyes.
Asunto(s)
Cladóceros/fisiología , Rojo Congo/toxicidad , Pruebas de Toxicidad , Contaminantes Químicos del Agua/toxicidad , Animales , Cladóceros/efectos de los fármacos , Dosificación Letal Mediana , Reproducción , Aguas ResidualesRESUMEN
Discharge of dye-containing wastewater by the textile industry can adversely affect aquatic ecosystems and human health. Bioremoval is an alternative to industrial processes for detoxifying water contaminated with dyes. In this work, active and inactive biomass of the microalga Chlorella vulgaris was assayed for the ability to remove Congo Red (CR) dye from aqueous solutions. Through biosorption and biodegradation processes, Chlorella vulgaris was able to remove 83 and 58 % of dye at concentrations of 5 and 25 mg L(-1), respectively. The maximum adsorption capacity at equilibrium was 200 mg g(-1). The Langmuir model best described the experimental equilibrium data. The acute toxicity test (48 h) with two species of cladocerans indicated that the toxicity of the dye in the effluent was significantly decreased compared to the initial concentrations in the influent. Daphnia magna was the species less sensitive to dye (EC50 = 17.0 mg L(-1)), followed by Ceriodaphnia dubia (EC50 = 3.32 mg L(-1)). These results show that Chlorella vulgaris significantly reduced the dye concentration and toxicity. Therefore, this method may be a viable option for the treatment of this type of effluent.
Asunto(s)
Chlorella vulgaris/metabolismo , Colorantes/metabolismo , Rojo Congo/metabolismo , Contaminantes Químicos del Agua/metabolismo , Adsorción , Animales , Compuestos Azo/metabolismo , Compuestos Azo/toxicidad , Biodegradación Ambiental , Cladóceros/efectos de los fármacos , Colorantes/toxicidad , Rojo Congo/toxicidad , Daphnia/efectos de los fármacos , Concentración 50 Inhibidora , Industria Textil , Pruebas de Toxicidad Aguda , Aguas Residuales/química , Contaminantes Químicos del Agua/toxicidad , Purificación del AguaRESUMEN
Colour and COD removals of the azo dyes Congo Red (CR) and Reactive Black 5 (RB5) were individually evaluated in a sequential anaerobic/aerobic treatment system. Additionally, dye toxicity was assessed by using acute ecotoxicity tests with Daphnia magna as the indicator-organism. The anaerobic reactor was operated at approximately 27 °C and with hydraulic retention times of 12 and 24 h. The aerobic reactor was operated in batch mode with a total cycle of 24 h. During anaerobic step, high colour removals were obtained, 96.3% for CR (400 mg/L) and 75% for RB5 (200 mg/L). During the aerobic phase, COD effluent was considerably reduced, with an average removal efficiency of 52% for CR and 85% for RB5, which resulted in an overall COD removal of 88% for both dyes. Ecotoxicity tests with CR revealed that the anaerobic effluent presented a higher toxicity compared with the influent, and an aerobic post-treatment was not efficient in reducing toxicity. However, the results with RB5 showed that both anaerobic and aerobic steps could decrease dye toxicity, especially the aerobic phase, which removed completely the toxicity in D. magna. Therefore, the anaerobic/aerobic treatment is not always effective in detoxifying dye-containing wastewaters, sometimes even increasing dye toxicity.