When treatment increases the contaminant's ecotoxicity: A study of the Fenton process in the degradation of methylene blue.

The degradation of dyes can generate harmful by-products, thereby requiring the need to evaluate the toxicity to aquatic organisms. This study aims to evaluate the chronic ecotoxicity of methylene blue dye degraded by the Fenton process using the non-target planarian Girardia tigrina as a sensitive bioindicator of environmental contamination. The bioassays evaluated the lethality of several concentrations of the untreated and degraded dye methylene blue (MB), as well as, their sub-lethal effects on locomotion, feeding, regeneration, and reproduction. In both acute and chronic tests, the degraded dye had a stronger toxic effect when compared to the untreated dye. This negative effect after treatment was mainly associated with the presence of residual hydrogen peroxide and iron (and consequently the hydroxyl radical formed). We conclude that the utilization of the Fenton process using less oxidizing agents should be considered as important alternatives for the protection of aquatic ecosystems, without compromising the efficient removal of MB.

Fenton-type process using peracetic acid: Efficiency, reaction elucidations and ecotoxicity.

Recent studies on Fenton-type processes involving peracetic acid (PAA) stimulated further development of advanced oxidative processes (AOPs). The objective of this work was to provide new information about such processes, elucidate their reaction mechanisms both experimentally and theoretically, and verify their possible uses. The Fenton-type reaction of PAA with Fe3+ exhibited a greater dye degradation efficiency than the Fenton process, while the efficiency of the PAA reaction with Fe2+ was very close of Fenton process. Moreover, the processes photocatalyzed by solar radiation demonstrated comparable efficiencies due to the photoreduction of Fe3+ to Fe2+. By conducting theoretical calculations, it was found that the formation of oxidizing radicals during the reaction of PAA with Fe2+ was not thermodynamically favorable and, therefore, unsuitable for practical use. In contrast, the processes occurred in the PAA/Fe3+ system included thermodynamically spontaneous reactions that generated peroxyl (CH3C(O)OO•), alkoxyl (CH3C(O)•), and hydroperoxyl (HO2•) radicals. The ecotoxicological tests demonstrated that the toxicity of the PAA to the organism Dugesia tigrina can be attributed to the presence of H2O2.

Lethal and sublethal effects of the saline stressor sodium chloride on Chironomus xanthus and Girardia tigrina.

Salinization in freshwaters is gradually increasing as a result of human activities and climatic changes. Higher salt content causes stress for freshwater organisms. Sodium chloride (NaCl) is among the most frequently occurring salts in freshwater ecosystems. The objective of the present study was to investigate the lethal and sublethal effects of NaCl on freshwater ecosystems, using as test organism the dipteran Chironomus xanthus and the planarian Girardia tigrina. Acute tests showed that C. xanthus was more sensitive (48-h LC50 (median lethal concentration) of 2.97 g NaCl L-1) than G. tigrina (48-h LC50 of 7.77 g NaCl L-1). C. xanthus larvae growth rate (larvae length and head capsule width) was significantly reduced under exposure to concentrations as low as 0.19 g L-1 NaCl and higher. A delay in the emergence time (EmT50) was also demonstrated for the same concentration. Sublethal NaCl effects in G. tigrina included feeding inhibition (LOEC (lowest observed effect concentration) of 0.4 g L-1), reduced locomotion (LOEC = 0.2 g L-1), and 24-48-h blastema regeneration (LOEC = 0.2 g L-1 and 0.1 g L-1, respectively). The results demonstrated the toxicity of NaCl to C. xanthus and G. tigrina including sublethal effects that can result in negative consequences for populations in natural freshwaters under salinization.

Effects of lethal and sublethal concentrations of peracetic acid and active chlorine of calcium hypochlorite on Chironomus xanthus.

Freshwater ecosystems are vulnerable to residual concentrations of chemical agents from anthropogenic activities, and the real impacts of such compounds can only be evaluated accurately using ecotoxicological tests. The assessment of ecotoxicological effects of peracetic acid (PAA) and the active chlorine of calcium hypochlorite (Ca(ClO)2) on the insect Chironomus xanthus Meigen (Diptera: Chironomidae) is highly relevant as there are few reports on its effects in fresh water ecosystems. To our best knowledge, this is the first study to assess the chronic toxicity of the compounds to C. xanthus. The toxicity bioassays for C. xanthus included the acute effect (CL50) and the chronic effects based on body length, head width, and cumulative emergence. The results obtained in the acute effect tests indicated that the active chlorine of Ca(ClO)2 is 14 fold more toxic than PAA to C. xanthus. In sublethal evaluations, the active chlorine of Ca(ClO)2 presented higher toxicity than PAA in terms of percentage emergence, body development, and head width. In general, the results showed lower PAA toxicity relative to the active chlorine of Ca(ClO)2, demonstrating that PAA is a promising substitute for chlorinated disinfectants. In addition, the study facilitates the establishment of reference values for the safe release of effluents treated with PAA into water bodies.

Comparative ecotoxicological evaluation of peracetic acid and the active chlorine of calcium hypochlorite: Use of Dugesia tigrina as a bioindicator of environmental pollution.

Chlorine plays a primary role in the disinfection of drinking water and wastewater due to its effectiveness as a biocide; however, there is evidence of the formation of toxic byproducts from its application, and this has promoted the search for alternatives. Alternative disinfectants can be effective in the inactivation of pathogenic microorganisms and are less damaging to human health and aquatic ecosystems. However, more information is needed on the effect of residual concentrations on the environment. This work compares the ecotoxicological effects of PAA disinfectants and the active chlorine of calcium hypochlorite in relation to the organism Dugesia tigrina (planaria), in terms of the acute effects: LC50, and chronic effects: feeding, locomotion, regeneration, reproduction and fertility. The results indicated that the active chlorine was more toxic than PAA, with LC50 (96 h) of 2.63 mg.L-1 and 3.16 mg.L-1, respectively. Sub-lethal exposure to active chlorine was more toxic when compared to PAA, and there was evidence of significantly reduced feeding and locomotion, causing a greater delay in regeneration and impairment in reproduction and fertility. The results allowed the comparison of the two disinfectants using half-life constants of the compounds and the lowest observed effect level (LOEC) of the oxidants. Chlorine represents a greater risk to the ecosystem for a longer period. The results obtained in this study can help in the establishment of discharge limits for PAA in water bodies.