Acute toxicity of textile dye Methylene blue on growth and metabolism of selected freshwater microalgae

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Highlights

Abstract

Microalgae are ecologically important species in aquatic ecosystems due to their role as primary producers. The inhibition of growth of microalgae due to dye pollution results in an upheaval in the trophic transfer of nutrients and energy in aquatic ecosystems. Therefore, this investigation aimed to evaluate the toxicity of a textile dye Methylene blue (MB) on two microalgae viz. Chlorella vulgaris and Spirulina platensis. An exposure of the unialgal populations of both the microalgae towards graded concentrations of the dye showed a concentration-dependent decrease in specific growth rate, pigment and protein content. In the toxicity study of 24 –96-h, following the OECD guidelines 201, the EC50 values of C. vulgaris and S. platensis ranged from 61.81 to 5.43 mg/L and 5.83 to 1.08 mg/L respectively revealing that S. platensis exhibited a higher level of susceptibility towards the dye as compared to C. vulgaris and the latter is more tolerant to the dye toxicity even at higher concentrations. The findings indicate that the response to dye is a species-specific phenomenon. Given the differences in the cell structure and enzymatic pathways in Spirulina platensis (a prokaryote) and Chlorella vulgaris (an eukaryote), the tolerance levels can differ. After 96-h exposure of C. vulgaris to MB (100 mg/L), the chlorophyll-a, b and carotenoid content were reduced 2.5, 5.96 and 3.57 times in comparison to control whereas in S. platensis exposure to MB (10 mg/L), the chlorophyll-a and carotenoid content were reduced 3.59 and 5.08 times in comparison to control. After 96-h exposure of C. vulgaris and S. platensis to the dye (20 mg/L), the protein content was found to be 4.34 and 2.75 times lower than the control. The protein content has decreased in accordance with the increase in dye concentration.

Introduction

Dyeing was the process of colouring fibre materials so that the dye becomes an integral part of the fibre. Dyes are soluble compounds in water that can be absorbed by the fibre and retain it by chemically combining with it. It was approximated that more than 10,000 types of dyes are produced by dye industries with a production over than 7 × 105 tons annually (Ogugbue and Sawidis, 2011). Globally, China was the largest exporter of all types of textiles, followed by the European Union, India and USA (Ghaly et al., 2014). In India, out of the total production of 1,30,000 tons of dyestuff, the textiles industry consumes around 80% of the production and export the final goods to global markets (Naik et al., 2013). Production of dye stuff and pigments in India was close to 80,000 tonnes (Cervantes et al., 2001).

Textile industry plays a major role in Indian economical growth. In the year 2010, the textile export contributed 11.04 % to the total export, hence it partially fulfils the Indian economical thrust. The effluent produced during this process contains large amount of dyes (Ghaly et al., 2014). The waste water containing dyes released in to the aquatic environment creates many negative impacts. The effluents discharged from textile factories are mixtures of dyes, metals and other pollutants hence they are high in colour, pH, suspended solids (SS), chemical oxygen demand (COD), biochemical oxygen demand (BOD) (Yaseen and Scholz, 2016), metals (Sharma et al., 2007; Sekomo et al., 2012; Dos Santos et al., 2007; Shah et al., 2013) and salts. Effluent from the textile and dyeing industries release highly coloured dyes which are most obvious indicator of water pollution. The discharge of these highly coloured effluents can damage the aquatic environment (Forss and Welander, 2009). Dye molecules may block the penetration of sunlight from water surface thereby reducing the photosynthesis. Hence, production and survival of phytoplankton which forms the base of the food chain was negatively affected leading to collapse of the entire ecosystem. Dyes, coupled with synthetic intermediates and the products of their degradation, have been reported to be capable of generating aromatic compounds which are highly toxic with mutagenic and carcinogenic properties (Ito et al., 2016). The exposure of Scenedesmus quadricauda to the graded concentrations of Indigo dye, resulted in a significant reduction in the growth and biomass production. The microscopic examination of the exposed cells/filaments revealed, noticeable changes in the morphological characteristics of the microalgae (Chia and Musa, 2014). Dyes are toxic to aquatic animal health i.e., Catla catla when exposed to dyes cause micronuclei formation and histopathological changes (Jagruti, 2015). In Tilapia gills, it caused degeneration of secondary lamellae, lamellar fusion due to hyperplasia and hypertrophy of epithelial cells and in liver it leads to hyperemia, necrosis and in muscle hyperemia. Dye containing effluents increase the COD level of the receiving water which indicates a high degree of pollution.

Methylene blue was an important cationic dye and was used in many textile manufacturers and it releases aromatic amines (e.g., benzidine, methylene) and was a potential carcinogen (Boeningo, 1994). In literature, it was found that there are no reports regarding the toxicity of MB for microalgae and hence this study is the need of the hour.

Algae which forms the basis of the aquatic ecosystem are sensitive to environmental changes. Hence they are used as indicators in ecological risk assessments to assess the effect of contaminants in water (Stauber and Davies, 2000; Levy et al., 2007; Qian et al., 2008). They are sensitive to chemicals and has short life cycle (Real et al., 2003) and due to this attribute, they are used as ecological testing organism (Eguchi et al., 2004). Hence two commonly found microalgal species of naturals waters from two different family Chlorophyta and Cyanophyta were chosen to compare the toxic effects of the dye. In this study Chlorella sp. was chosen because of its abundance in aquatic ecosystem and high sensitivity to contaminants in environment (Ramadass et al., 2016). The reason behind choosing Chlorella vulgaris and Spirulina platensis was due to its high nutritional, ecological and economic properties (Tomaselli, 2004; Ali and Saleh, 2012). The aim of this study was to analyze the toxicity of the Methylene blue in microalgae. This study gives a better insight into the toxicity of the textile dye on aquatic organism and also furnishes baseline data for delineation of guidelines for effluent discharge from textile industries.

Section snippets

Chemicals

The synthetic textile dye methylene blue was bought from SD Fine chemicals limited, India. Its molecular formula was C16H18CIN3S.XH2O and molecular weight was 319.9 g/mol.

Algal species and culture conditions

Chlorella vulgaris and Spirulina platensis were obtained from the Algal Biotechnology lab, AEM, ICAR-CIFE, Mumbai. The pure culture of C. vulgaris was subcultured in sterile BG-11 media and Spirulina platensis in sterile mNRC (modified Nallayam Research Centre) medium, under photoautotrophic conditions. The indoor batch

Influence of Methylene blue on growth rates of both algae

As shown in Fig. 1, Fig. 2, Methylene blue suppressed the growth of Chlorella vulgaris and Spirulina platensis in a concentration-dependent manner during 96 h exposure reaction period. Compared with control groups, Methylene blue at all studied concentrations can significantly inhibit the growth of Chlorella vulgaris and Spirulina platensis (p < 0.05 at 24−96 h).

After 24 h exposure of C. vulgaris to MB, higher growth inhibition of 65.66 % was found at the highest exposed dye concentration

Discussion

The microalgae, which are the primary producers and occupy the base of the aquatic food chain, play a key role in the structure and function of an ecosystem. Among the aquatic organisms, the sensitivity of microalgae and cyanobacteria towards pollutant is reported to be higher. Hence, they serve as important indicators used to assess the toxicity of chemicals released to the aquatic environment (Burkiewicz, 1987). In the present study, the toxicity of MB to a green algae C. vulgaris was

Conclusions

  • (1)

    A dose-dependent growth inhibition by Methylene blue was observed in Chlorella vulgaris and Spirulina platensis. The EC50 values indicate that short-term toxicity of Methylene blue creates metabolic upheaval in both of microalgae.

  • (2)

    In the acute experiment, chlorophyll-a, chlorophyll-b, carotenoid and protein content of Chlorella vulgaris and Spirulina platensis were notably accelerated in condition of medium containing different concentrations of Methylene blue. It is evident from the findings

CRediT authorship contribution statement

Abarna Krishna Moorthy: Investigation, Writing - original draft. Bhuvaneswari Govindarajan Rathi: Conceptualization, Supervision, Project administration, Writing - review & editing. Satya Prakash Shukla: Project administration, Writing - review & editing. Kundan Kumar: Methodology. Vidya Shree Bharti: Methodology.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

The authors thank Indian Council of Agricultural Research and ICAR-Central Institute of Fisheries Education for the financial assistance and facilities provided for this work.

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