Abstract
Aquatic pollution caused by industrial effluents is an environmental issue, imposing deleterious impacts on the overall environment, specifically, on humans, by disrupting the balance of the ecosystem. Among all the industries, tanneries are considered some of the most polluting due to heavy use of toxic organic and inorganic compounds during leather processing, most of which find their way into rivers, lakes, and streams, thus exerting adverse effects on aquatic life, particularly on fish. Considering the huge concentrations of pollutants present in tannery effluents, toxicity evaluation is of prime importance. Therefore, bioassays are usually employed to assess the acute toxicity of industrial effluents and efficiency of effluent clean-up technologies as they provide a thorough response of test species to the substances present in the tested media. In the present study, the toxic effects of tannery effluent on common grass carp (Ctenopharyngodon idella) were studied for 96 h in laboratory conditions. The effluent was added at different concentrations, before and after treatment by constructed wetlands (CWs). During this period, mortality data was collected to calculate the 96 h-LC50 (lethal concentration inducing 50% mortality) and acute toxicity of C. idella. In addition to this, observations on change in morphological, physiological, and behavioural patterns were also made every 24 h. The present toxicity assay revealed that the raw tannery effluent changed the morphology, physiology, and behavioural response of fish. Moreover, fish exposure to raw/untreated effluent caused high acute toxicity and 100% mortality, due to the presence of high concentrations of salts and chromium (Cr) metal. While treatment of tannery effluent by CWs vegetated with different plants (B. mutica, L. fusca, and T. domingensis) significantly reduced its toxicity and fish mortality as well, and inoculation of salt and Cr-tolerant endophytic bacteria (Enterobacter sp. HU38, Microbacterium arborescens HU33, and Pantoea stewartii ASI11) further reduced (up to 90%) its toxicity level. Hence, the use of CWs for tannery effluent treatment can be recommended to favour public health and promote the overall safety of the environment.
Highlights
Industrial growth has negatively impacted the environmental quality [1], aquatic life, due to disposal of voluminous amounts of effluents into natural water resources, on a daily basis, all over the world [2,3,4]
Ctenopharyngodon idella were seriously affected by the tested raw tannery effluent, even at very low concentrations, despite making dilutions due to high toxicity of pollutants, in contrast to no adverse effects in treated effluent by constructed wetlands (CWs) technology and the control set
CWs vegetated with different plants (B. mutica, L. fusca, and T. domingensis) reduced the toxicity causing abnormal changes in morphology and physiology of fish that lead to mortality, and inoculation of endophytic bacteria
Summary
Industrial growth has negatively impacted the environmental quality [1], aquatic life, due to disposal of voluminous amounts of effluents into natural water resources, on a daily basis, all over the world [2,3,4]. Some chemicals contained in industrial effluents have been reported to be highly toxic, in a variable degree depending on the dose and exposure duration [5,6], having potential to impart serious damage to aquatic life [7,8]. Tannery effluent is extremely hazardous due to high organic loadings, solids, and metals [11], chromium (Cr), a well-known ubiquitous pollutant considered as a great menace to aquatic environments, and human beings [12]. The dark colouration and low oxygen content of tannery effluents indicates the strength of pollution, which affect the survival of aquatic organisms, especially fish, having great ecological relevance [5]
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