Toxicity assessment of dye containing industrial effluents by acute toxicity test using Daphnia magna

Toxicology and Industrial Health 27(1) 41–49 ª The Author(s) 2011 Reprints and permission: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0748233710380218 tih.sagepub.com

Yogendra Verma

Abstract Toxicity of dye containing effluent of tannery, textile, dyes and pulp-paper industries was evaluated in an acute toxicity test using Daphnia magna. The 48-hour EC50 values were 4.33% and 19.5% for tannery effluents (Tn1 and Tn2). Textile effluents (Tx1–Tx7) had 48-hour EC50 values; >100%, >100%, 62.9%, 63.0%, 40.3%, >100% and >100%, respectively. Dye industries (D1–D7) had 48-hour EC50 values; 14.1%, 15.5%, 24.5%, 29.7%, 23.2%, >100% and >100%, respectively. Similarly pulp-paper effluents (P1–P5) showed acute toxicity as 100%, 77.87%, 46.44%, 69.55% and 82.84%, respectively. These results showed linear relationship with high degree of confidence (r2  0.84–0.99) between immobility and test concentrations. Toxicity classification criteria showed that out of five effluents from pulp-paper mill, four were minor acutely toxic having 48-hour EC50 value in between >46%–100%. Out of seven textile effluents, four were not acutely toxic (48-hour EC50 value >100%) and three were minor acutely toxic (48-hour EC50 value in the range of 40.3%–63.0%). Similarly, out of seven dye industrial effluents, two were not acutely toxic and five minor acutely toxic. One of the two tanneries was moderately acutely toxic and another one was minor acutely toxic. Classification based on toxic unit revealed that four out of five pulp-paper effluent, three out of seven textile effluents, five out of seven dye effluents and both the tannery effluents were toxic. Overall, 66.67% effluents were found toxic and 33.33% as non-toxic. In general, tannery and dyes effluents showed more toxicity than textile and paper mill effluents. Keywords Daphnia bioassay, dye industrial effluents, acute toxicity, EC50, toxicity unit

Introduction Ecotoxicological studies on several industrial effluents all over the world have shown that effluent discharges are not safe to protect aquatic life (Rodriguez et al., 2006). Series of experiments carried out by Sponza (2002, 2003, 2006) on toxicity of different industrial effluents revealed that conventional approach of using chemical analysis are insufficient to demonstrate that the organisms of aquatic ecosystem are well protected. Effluents can remain toxic despite complying with chemical-based conditions. Bioassays, however, have the advantage of showing the total impact of the pollutants, since living materials responds to the total effect of actual and potential disruption. Therefore, biological assays have become very important tool in assessing the harmful chemical activity (ISO, 1996; OECD, 1984; US EPA, 1996). In a review on international trend in the use of bioassay,

Power and Boumphery (2004) showed that many European countries use acute and chronic toxicity test in monitoring the effluent discharge. Most of the regulatory agencies and research organizations are using the well-established conventional acute toxicity test with Daphnia in which survival/death/immobility is the most frequently monitored endpoint (ISO, 1996; OECD, 1984). Tannery, textile, dye and pulp-paper industries are voracious users of freshwater and discharge huge

National Institute of Occupational Health, Ahmedabad-380 016, India Corresponding author: Yogendra Verma, National Institute of Occupational Health, Meghaninagar, Ahmedabad-380 016, India Email: [email protected]

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Table 1. Chemicals used in various processes of textile, pulp-paper, tannery and dye industry Industries

Chemicals used

Processes

Textile

Sulfides, NaCl, Na2SO4 Dyes (Cu, Cr, Zn, Pb as colorant) H2O2, sodium hypochloride, solvents Pentachlorophenol Starch and resin Chlorophenolics, dioxins Residual chlorine, inorganic chlorides Resin acid Cu, Cr, Pb, Zn in dyes Mercury in caustic soda Chromium and dyes Sulfide H2SO4 or chrome tanning powders Chloride (use of common salt) Benzene, toluene, anthracene Organic and inorganic chemicals Dyes synthesized

Sulfur dyeing, dyeing and printing

Pulp-paper

Tannery

Dyes

volume of wastewater. These industries use dye and dye intermediates for coloring different products during various processes. Approximately 10%–15% of the dyes are released into the environment during dyeing of different substrates, such as synthetic and natural textile fibers, leather, paper, plastics etc. Due to rapid changes in customers’ demands, these industries are challenged to use high quantity of dyes and auxiliaries, which are indispensable for modern industrial setup, e.g., modern textile processing, paper, plastic, leather and cosmetic. Apart from their negative aesthetic effects on receiving aquatic ecosystem, dye-containing effluents have been reported to be toxic to aquatic organism (Bae and Freeman, 2007; Meric et al., 2005), and some of these dyes are carcinogenic and mutagenic (Mathur et al., 2005). It is reported that wastewater generated from tanneries, textile mills, dye and dye intermediates and pulppaper industries mainly have intense colors of various shades through the production of different colorcontaining dyes, and usually have high levels of COD, BOD, chlorides, sulphates, phenoloic compounds and various heavy metals (Lanciotti et al., 2004; Sponza, 2002, 2003, 2006). The common sources of metals in dye-containing industrial effluents are the use of different dyes (acid dyes: copper, lead, zinc, chrome, cobalt; basic dyes: copper, zinc, lead, chromium; direct dyes: copper, lead, zinc, chromium; mordant dyes: chrome; premetallized dye: cobalt, chrome, copper; reactive dyes: copper, chromium, lead). The metallic content in metal-containing dye is essential

Bleaching and machine cleaning Wool fiber contaminant Finishing Chlorination during pulping and bleaching Bleaching process and decoloration process Pulping process Dyeing and printing Pulping process and bleaching process Tanning, retanning and dyeing processes Breakdown of hair in the unharing process Tanning and re-tanning processes Hide and skin preservation/pickling Dye synthesis Sulfonation, chlorination, acetylation Washing of reaction kettles and floor

as colorant and responsible for the toxicity (Bae and Freeman, 2007). The responsible typical causes/ agents of aquatic toxicity are summarized in Table 1.The aim of this study was to evaluate the acute toxicity status of dye containing wastewater from pulp-paper mill, textile mill, tannery and dye industries, employing Daphnia magna bioassay, which has been used as a standard and reliable biotest for textile effluents (Meric et al., 2005; Villegas-Navarro et al., 2001) and pulp-paper (Liu et al., 2002) and tannery effluents (Cooman et al., 2003). D. magna has also been evaluated as a good organism to test chemicals and effluent toxicity (Nikunen and Maiettinen, 1985).

Materials and methods Industries, effluent sampling, handling and analysis Industries discharging dye-containing wastewater selected for the study were tannery, textile, dye and pulp-paper. Industries were selected for the study according to the following criteria: (i) all of them had wastewater treatment plant (WTP); (ii) WTP was in working condition; (iii) not very far away from the laboratory; (iv) agreed to participate on request. Grab samples of the effluents were collected at the point of outlet discharge from the wastewater treatment plants (WTPs) of two tannery (Tn1–Tn2), seven textile (Tx1–Tx7), seven dye and dye intermediate (D1–D7) and five pulp-paper (P1–P5) industries. Tannery

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industry (Tn1) is engaged in leather tanning and formed leather-based products using dyes, salts, chromium etc. and discharges colored effluents having obnoxious smell, while Tn2 used to receive primarily treated wastewater from about a dozen tanneries, and WTP was discharging finally treated wastewater. Pulp-paper industries (P1–P5) were engaged in preparing pulp from bamboo and Eucalyptus, which involves five basic steps viz. debarking, pulping, bleaching, washing and finally to paper and paper product production. The pulping, bleaching and washing processes are responsible for generating toxic waste due to use of chemicals, and discharging toxic wastewater of varying color intensity. The dye industries (D1–D7) discharge colored wastewater and were engaged in production of various dyes and dye intermediates (D1: azo pigments, auxiliaries; D2: diazo reactive dyes, disperse dyes and intermediates; D3: G salt and R salt; D4: produces acid black, red, blue violet, yellow; D5: a common effluent treatment plant receives wastewater (primarily treated) from >50 dye-producing units; D6: reactive dyes and D7: indigo carmine, allure red). All of the effluent samples were collected in amber glass bottles and transported to the laboratory at the earliest in a lightproof ice chest, and stored under refrigeration (4 C) in darkness until analysis, and bioassay was performed within 48 hours after the effluent sample had arrived in the laboratory. Dissolved oxygen (DO), conductivity and pH were measured as soon as samples arrived at the laboratory. Temperature ( C) was recorded at the sampling site.

43 Table 2. Summary of test protocol for Daphnia magna Experimental conditions

Acute test protocol

Name of the organism Age Test type Temperature Light quality Photoperiod Feeding regime Dilution water Test vessel Test solution volume Test specimen/vessel Test vessel/concentration Effluent concentrations

Daphnia magna 24 hours Static (non-renewal) 25 + 2.0 C Cool light >600 Lux 12 hours/12 hours 24 hours before experiment Reconstituted water 15 mL glass test tube 10 mL 5 daphnids in each vessel Four 100%, 75%, 50%, 25%, 12.5%, 6.25%, 3% and 1.5% 48 hours 24 and 48 hours Immobilization

Test duration Observation period End point

1985). The number of immobilized daphnids was recorded after 24 and 48 hours exposure. Daphnids unable to swim for 15 seconds after gentle stirring were considered immobile/dead (OECD, 1984). In addition, 100% survival was maintained in control group. The test protocol is summarized (Table 2) and details of the methodology is described elsewhere (Verma et al., 2003). Experiment was validated with positive control test using reference substance potassium dichromate (ISO, 1996).

Statistical analysis and calculations Daphnia culture and toxicity test D. magna Straus used in the experiment were selected from the laboratory stock culture maintained at 25 + 2 C, in 5-L borosilicate glass beakers, and fed on green algae Selenastrum sps and yeast powder. Twenty-four hours prior to the experiments, adult daphnids (gravid females) were sorted and young ones (neonates) produced from these adults were used in the study. The 24-hour and 48-hour acute toxicity (EC50) test was conducted after exposing them to various concentrations (100%, 75%, 50%, 25%, 12.5%, 6.25%, 3.0% and 1.5%) of the different industrial effluent in reconstituted dilution water (RDW) to which Daphnia culture was maintained. Toxicity test was replicated four times using batches of five neonates ( 24 hours old) received from gravid female daphnids, and placed in 15-mL glass test tube containing 10 mL test volume (Nikunen and Maiettinen,

EC50 and its 95% confidence limits were computed by probit analysis method using SPSS software. Linear regression analysis was performed to determine regression equation and correlation coefficient (r2). The correlation coefficient (r2) reflects statistical significance. In all cases, toxicity was expressed as effective concentration (EC50) and toxic unit (TU). Toxicity unit value was calculated using 48 hours EC50 value (100/48 hours EC50). The highest observed concentration causing low/no observed effect was compared with calculated EC10 value.

Results Physicochemical characteristics Physicochemical characteristics of the reconstituted dilution water (RDW) used in the experiment had pH 7.8, calcium hardness (as CaCO3) 180.0 mg/L,

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Table 3. Physico-chemical characteristics of wastewater of different industries Type of industries Tannery Tn1 Tn2 Textile Tx1 Tx2 Tx3 Tx4 Tx5 Tx6 Tx7 Dyes D1 D2 D3 D4 D5 D6 D7 Pulp-paper P1 P2 P3 P4 P5

Temperature ( C)

pH

Conductivity (mS)

DO (mg/L)

29 28

8.5 7.9

11.1 11.2

3.8 4.4

28 26 32 27 26.5 28 27

8.0 8.2 8.1 7.8 8.7 7.9 8.1

1.3 1.1 0.9 0.8 1.4 0.9 1.0

4.6 3.6 3.4 4.2 2.8 6.6 5.6

28.0 28.0 30.0 30.5 27.5 31 30

7.5 8.0 7.5 7.2 7.8 7.5 7.6

1.4 1.5 1.2 1.0 1.3 1.4 1.3

4.6 3.5 4.3 4.6 4.0 4.6 4.8

26 28 26.5 29 30

7.8 7.1 6.3 7.3 7.6

1.0 0.8 0.8 1.6 1.4

4.6 3.4 3.6 3.0 4.2

conductivity 0.7 mS and dissolved oxygen (DO) 8.1 mg/ L. The physicochemical characteristics of various industrial effluents differed substantially from one another as expected due to the different sources and different types of industries (Table 3). Dissolved oxygen concentration of the effluents ranged from 2.6 to 6.6 mg/L, pH 6.3 to 8.7; conductivity 0.8 to 11.2 mS and temperature 26.0 C to 32.0 C. The tannery effluents have often been characterized with high conductivity. Author also noticed the same in this study, which may be due to the fact that salts / common salts used during the process of hide and skin preservation and picking process results in high conductivity (11.2).

Acute toxicity test results Acute toxicity test results (24 and 48 hours EC50 values and confidence limits and TU) are summarized in Table 4. Toxicity exhibited by tannery effluents showed that 50% of the daphnids were immobile between 3.0% and 6.25% of Tn1 and 12.5% and 25% of Tn2. The 24 and 48 hours EC50 values for Tn1 were 5.91% and 4.33%, respectively. The 24 and 48 hours EC50 values for Tn2 were 49.4% and 19.5%, respectively. Thus,

Tn1 was found more toxic than Tn2. Higher the EC50 value lower is the toxicity of the substance. Contrary to tannery effluents, pulp-paper mill effluents exhibited low toxicity to daphnids. Pulp-paper mill effluent (P1) was not toxic to daphnids at full strength (100%), while effluent of P2 -P5 exhibited toxicity to some extent having 24 hours EC50 values 87.5%, 85.7%, 78.1%, 87.8%, respectively. The 48 hours EC50 values were 77.8%, 46.4%, 69.5% and 82.8% for the effluents of P2–P5 (Table 4). Dye industrial effluents D1 and D2 showed more or less similar toxicity (EC50 value 17.3% and 17.7%). Dye effluent D4 was found comparatively less toxic (Ec50 Value 46.5%) while dye effluents D6 and D7 showed no or very low toxicity (10%) at the concentration of full strength (100%). The 48 hours EC50 values were 14.1%; 15.5%; 24.5 %; 29.7 % and 23.2%, for dye effluents (D1–D7), respectively (Table 4).Textile mill effluent Tx1, Tx2, Tx6 and Tx7 showed either no toxicity or very low toxicity (10%–20% immobility) at 100% concentration; hence, EC50 value could not be calculated. The 48-hour EC50 values were 62.9%; 63.0% and 40.3%, respectively, for textile effluents Tx3, Tx4 and Tx5 (Table 4).

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Table 4. Showing 24 h and 48 h EC50 values, its 95% confidence limits and toxicity units (TU) for different types of industries discharging dye containing effluent

Industries Tannery Tn1 Tn2 Textile Tx1 Tx2 Tx3 Tx4 Tx5 Tx6 Tx7 Dyes D1 D2 D3 D4 D5 D6 D7 Pulp-paper P1 P2 P3 P4 P5

24 hours EC50 (Confidence limit 95%)

48 hours EC50 (Confidence limit 95%)

Coefficient (r2)

Slope value

NOEC (%)

EC10 (%)

Toxic unit; toxicity rating

5.91 (4.04–9.21) 49.4 (38.7–73.1)

4.33 (3.14–5.96) 19.5 (13.3–35.0)

0.91 0.94

1.61 1.16

1.5 6.2

2.3 5.46

23.1; very toxic 5.1; very toxic

>100 >100 75.9 (67.0–86.4) 91.8 (71.3–192.8) 50.2 (35.7–75.5) >100 >100

>100 >100 62.9 (55.1–70.6) 63.0 (47.9–77.6) 40.3 (29.8–55.2) >100 >100

0.97 0.66 0.98 0.98 0.96 – –

– 0.23 1.27 1.27 1.12 – –

100 75 50 25 12.5 100 100

>100 87.6 37.8 28.1 22.3 >100 >100

100

0.84 0.84 0.98 0.99 0.85 0.56 0.56

2.2 2.08 2.44 2.70 2.67 0.23 0.04

3.0 6.25 6.25 12.5 12.5 66.67 75

7.39 8.59 14.2 19.8 15.6 >100 >100

7.0; very toxic 6.5; very toxic 4.1; toxic 3.4; toxic 4.3; toxic 100 77.8 46.4 69.5 82.8

(11.5–17.4) (12.7–18.8) (21.5–28.2) (26.5–33.5) (20.7–2 5.9)

(70.4–84.6) (38.2–55.4) (62.7–76.7) (76.4–89.2)

Abbreviation: NOEC, no observed effect concentration.

Statistical correlations and significance The linear regression analysis performed, reflected statistical significance between exposure concentration and response. The correlation coefficient was (r2 ¼ 0.91 and 0.94) for tannery, (r2 ¼ 0.93–0.96) for textile, (r2 ¼ 0.84–0.99) for dye effluents and (r2 ¼ 0.80–0.99) for pulp-paper mill effluent (Table 4). These values were high for the effluents having high toxicity and low for the effluent having no or very low toxicity. The slope values ranged from 0.94 to 2.7 for the effluents that were found toxic. However, slope values were found low for the effluents having no or very low toxicity (Table 4). Higher the slope value greater is the uniformity of toxic response, greater slope values narrows the confidence limits around the EC50 value as observed in the present study (Table 4). In toxicological experiments, the time of exposure has large effect on biological responses. Longer the exposure time lesser the EC50 value and greater is the toxicity. In our study too, results showed similar pattern

having lesser 48 hours EC50 value than 24 hours EC50 (Table 4).

Acute toxicity classification Acute toxicity classification of effluent based on general criteria (Table 5) showed that tannery effluent Tn1 was moderately acutely toxic having EC50 in between 10% and 100%, and Tn2 minor acutely toxic. Out of five pulp-paper mills effluent tested, four were minor acutely toxic (48 hours EC50 range 46.4%– 82.8%) and remaining one not acutely toxic (EC50 > 100%). Further, out of seven textile effluents tested, four were not acutely toxic (48 hours EC50 > 100%) and three were minor acutely toxic (48 hours EC50 range 40.3%–62.9%). Similarly, out of seven dye and dye intermediate effluents tested, five were minor acutely toxic and remaining two not toxic (Table 5). The toxicity classification based on toxic unit (TU) as adopted by Villegas-Navarro et al. (2001) and Lanciotti et al. (2004) was also used to classify the

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Table 5. General criteria of toxicity classification based on EC50, toxic unit and toxicity rating EC50 (%); (toxicity rating)

EC50 (%)a; (toxicity rating)a

Toxic unit (toxicity rating)

>100–>75 (low toxic) 75 (toxic) 100 (not acutely toxic) 10–100 (minor acutely toxic) 1–10 (moderately acutely toxic) 14.0%), three samples (D3, D4, D5) toxic (EC50 > 23%–29%) and remaining two non-toxic (EC50 > 100%), while both the tannery effluents were very toxic (EC50 >4.33%; Table 4). Results of low exposure concentration range are suitable for determining no observed effect concentration (NOEC). Use of EC10 and EC20 values have often been chosen in effluent toxicity assessment, since these values are usually close to the acute no observed effect concentration. The observed NOEC were 100%, 50%, 12.5%, 25% and 50% for pulp-paper effluents (P1–P5), respectively. The EC10 values (>100%, 61.6%, 23.2%, 49.3% and 68.7% for the effluents P1–P5) as derived by probit analysis were close to the observed NOEC. Similarly, NOEC values were also found close to EC10 /20 for other effluents (Table 4).

Discussion Acute toxicity test application/significance Traditional acute toxicity tests are still widely used as standard eco-toxicological procedure by environmental

agencies/toxicology laboratories to assess the potential impact on the ecological system (Power and Boumphery, 2004; Rodriguez et al., 2006). Thereby, the acute toxicity tests were conducted exposing the D. magna to treated wastewater of tannery, textile, dyes and pulp-paper industries. Since eco-toxicology focuses upon the adverse effects of chemicals in the environment, acute toxicity is described by EC50/ LC50. Clearly, the EC50/LC50 value is not indicative of an acceptable level of the chemical/toxicant in the environment. Allowing an environmental concentration of chemicals/toxicants, which is predicted to kill 50% of the exposed organism, is hardly an example of good environmental stewardship.

Toxic unit and toxicity rating Assessment of industrial effluent by means of acute toxicity test seems to be sufficient for preliminary classification of effluent whether toxic or non-toxic. Effluent sample whose 48-hour EC50 value is >100% shows null or poor response of the test organism in a bioassay and could be classified as non-toxic or not acutely toxic, 10%–100% minor acutely toxic, 1%–10% moderately acutely toxic and 1 TU be considered toxic, since this would imply that full-strength effluent would adversely affect 50% or more of the exposed organisms.

Tannery effluent toxicity Tannery wastewater contains large quantities of organic and inorganic compounds, including toxic substances sulfides, chromium, dyes, chloride, sulfate, and are well known to have negative impact on

Verma

the aquatic environment. The bioassay carried out with D. magna and D. pulex revealed that both species responded in the same manner to tannery effluent (Cooman et al., 2003). Further, Cooman et al. (2003) investigated the acute toxicity of all processes involved in tannery industry and reported that all process wastewater were extremely toxic to daphnids having TU value >30. The 24-hour LC50 for D. pulex was 2.04% for beam house, 2.63% for tanning and 3.32% for final effluent. In another study, tannery effluent was found acutely toxic, having EC50 25.6%, and disinfection agent used in tannery was responsible for increased toxicity (Tisler et al., 2004). Verma et al. (2003) also reported the acute toxic response of tannery effluent having TU value >5. Talpatra and Banerjee (2005) reported 48 hours LC50 6.54%, (TU value >15) for the tannery effluent using D. magna bioassay. Thus, all these studies suggest that tannery effluents are moderately toxic to daphnids as found in the present study, having EC50 4.33% and 19.5%. Synthetic dyes are used extensively in tannery, textile, paper, printing and chemical dye industries, and have been reported to play additive role in the toxicity with other toxicants present in the specific industries (Bae et al., 2006; Sponza, 2003, 2006; Villegas-Navarro et al., 2001).

Pulp-paper mill effluent toxicity A wide variety of chlorinated compounds have been identified in the effluent of pulp-paper/kraft mills (Sponza, 2003). High COD is caused by highmolecular-weight synthetic bleaching agents and dyes present in pulp paper mill effluent. Study performed in a Kraft bleach plant by Pintar et al. (2004) showed that chemical bleaching effluent containing yellow brown colour was toxic to D. magna. Sponza (2003) found that the effluent of pulp-paper mill containing dye is toxic to fish when the color and AOX concentration is high. Liu et al. (2002) tested effluent from three paper mill containing dye and reported that pulp-paper effluent exhibited acute toxicity to D. similis EC50¼33.8%, 82.8 (52133)% and >100%. The first paper mill effluent was more toxic than the second, while the third one was not toxic. In the present study, majority (80%) of the paper mill effluent were found toxic. Slabbert and Venter (1999) reported that paper mill wastewater containing dye had EC50 value between 50% and 100%, as found in the present study.

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Dye industrial effluent toxicity Toxicity test results of the chemical dye production industry effluent showed potential toxicity. Toxicity could be attributed to a high concentration of Pb (6–9 mg/L), dye as color (SAI ¼ 3/m), Cr (5–6 mg/ L), Zn (10–12 mg/L) and total hydrocarbon (10–12 mg/L) in the effluent (Sponza, 2002). Chromium occurs in the wastewater from tannery, electroplating, dyes, textiles and pulp-paper industries, possibly playing an important role as an additive toxicant in such effluents. Meric et al. (2005) tested the Remazol Black B dye using Daphnia bioassay and reported EC50 value 75 mg/L. Bae and Freeman (2007) tested the aquatic toxicity of new direct dyes (non-genotoxic and nonmetallic azo dyes) along with metallic direct dyes C.I. Direct Black 281. They observed that four new direct dyes that do not have any metal in structure were found non-toxic, having LC50 > 100 mg/L, while C.I. Direct Blue 218 containing two copper molecule in their structure were highly toxic (24 hours LC50 6.0 mg/L; 48 hours LC50 3.66.0 mg/L), suggesting copper molecule inside dye structure play an important role in the biological toxicity.

Textile mill effluent toxicity Verma et al. (1995) reported that textile mill effluent was toxic to D. magna. The 24 hours EC50 value was 55.89 (50.64–61.69) %, TU ¼ 1.8. A study conducted by Lanciotti et al. (2004) showed that textile wastewaters contains numerous chemicals such as dyes, surfactants and metals, which cause severe pollution problem of the receiving water body. Out of 146 samples assayed with Daphnia, only 4 samples (2.74%) had shown considerable acute toxicity (EC50 value < 100%; TU value 1) to D. magna. Pioneer work carried out by Villegas-Navarro et al. (1999; 2001) on textile effluents demonstrated that the treated wastewaters of textile mills remain toxic to D. magna having TU value 2–7. Villegas-Navarro et al. (1999) reported that all the five textile industries examined produced toxic non-treated wastewater (TU value >2.1–25.4) and treated wastewater was also toxic (TU value >1.5–7.2), indicating that all the five textile industries discharged the toxic wastewater, and thus their treatment plants were not totally efficient. Further, Villegas-Navarro et al. (2001) also conducted the toxicity test of different process stages of the textile industry and reported that dyeing and chlorination stages were most toxic, and that dyes contributed to overall sample toxicity at all processes.

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Meric et al. (2005) used the D. magna bioassay to test the acute toxicity of raw and pre-oxidized textile wastewater and found sensitivity to raw wastewater. Tonkes et al. (1999) tested the effluents from nine chemical industries using whole effluent toxicity (WET) test with Daphnia and revealed that effluent of three industries were not toxic (TU value 1), one was toxic (TU value 3) and remaining five were very toxic (TU value > 4.4–42). Thus, industrial effluents containing dyes are toxic to aquatic organism.

Environmental risk assessment The possible ecological implications and/or environmental risk to Daphnia are discussed. Generally, the amount of dyes still entering in the aquatic ecosystem even today is quite small because even a small amount gives a strong color to effluent, thereby immediately noticeable in industrial effluents, even though they are toxic. It is reported in the literatures that substantially lower concentrations than the 48 hour EC50/ LC50 values have impact on survival and development of daphnids in long term and consequently have detrimental impact on aquatic communities. Although not quantified in this study, it is possible that dyes/dye products that have entered in the ecosystem could be consumed by daphnids through food. Since the exoskeleton is transparent, some dyes can be photoactivated in vivo and may cause detrimental effects. In addition to Daphnia, further concerns may be warranted for the other aquatic organisms that possess transparent or translucent bodies as part of their life cycle.

Conclusion In this study, author showed that different dyes containing industrial effluents exhibited varying degrees of toxicity to Daphnia. Tannery and dye industrial effluents were more toxic than textile and pulp-paper effluents. Result of this study reemphasized the importance of integration of bioassay in environmental monitoring. This paper shows that most of the industries dispose relatively polluted wastewater. The TU value obtained strongly suggests that the efficiency of the wastewater treatment plant (WTP) must be improved. Although not quantified in this study, the effluent that showed no toxic effects after 48 hours could be toxic after longer duration. Hence, further research is needed to evaluate the ecological long-term effects of dye-containing wastewater in the receiving aquatic ecosystem.

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Acknowledgments Author is thankful to Dr PK Nag, Director, National Institute of Occupational Health, Ahmedabad, Ex. Director of the Institute and Ex. HOD of the laboratory for their encouragement. Author is also thankful to the staff of the laboratory (MCH and AB) for the technical help rendered during the study.

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