www.elsevier.com/locate/chemosphere

Chemosphere 69 (2007) 48–54

A comparative study on characterization of textilewastewaters (untreated and treated) toxicity

by chemical and biological tests

K.P. Sharma a,*, S. Sharma b, Subhasini Sharma b, P.K. Singh a, S. Kumar a,R. Grover a, P.K. Sharma a

a Botany Department, University of Rajasthan, Jaipur 302004, Indiab Zoology Department, University of Rajasthan, Jaipur 302004, India

Received 10 November 2006; received in revised form 14 April 2007; accepted 25 April 2007Available online 20 June 2007

Abstract

Toxicity of textile wastewaters (untreated and treated) and their ingredient chemicals was quantified in terms of their chemical char-acteristics, fish (Gambusia affinis) mortality and end point growth responses of duckweed (Lemna aequinoctialis) in short-term bioassays.Other parameters of fish bioassay were erythrocyte morphology and its counts. Despite of a definite correlation between data of biolog-ical tests (LC/EC50 values) with that of chemical tests, biological tests were found to be relatively more sensitive to both wastewaters andingredient chemicals. Amongst all the examined parameters of test organisms, fish RBCs (morphology and counts) sensitivity to pollu-tants in the wastewaters was usually maximum and therefore, their study should be included in the routine fish bioassay. Other advantageof biological test such as on Lemna is even detection of eutrophic potential of wastewaters, as noted at their higher dilutions. The ingre-dient chemicals (major) contributing maximum toxicity to textile dye wastewater were, acids (HCl and H2SO4), alkali (Na2O SiO2), salt(NaNO2) and heavy metal (Cu), whereas dyes (4) were relatively less toxic.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Textile wastewaters; Fish bioassay; Duckweed bioassay; Dyes; Copper

1. Introduction

Today, pollution of aquatic habitats is a universal phe-nomenon, which is more serious in the developing coun-tries on account of discharge of mostly untreated orpartially treated municipal and industrial wastewaters intothem. The relatively higher toxicity of industrial wastewa-ters to living organisms, especially plants, is of greater con-cern since they clean aquatic ecosystems. The industries ofconcern are; textile printing industry, tanneries, distilleries,sugar industry and paper and pulp industry, since they dis-charge large volume of wastewater in the environment.

0045-6535/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.chemosphere.2007.04.086

* Corresponding author. Tel.: +91 9828418664; fax: +91 01412711654.E-mail address: sharmakp_in@yahoo.com (K.P. Sharma).

Amongst them, the textile printing industry which grewat much faster pace in the developing countries due tocheaper labour and less stringent waste disposal norms isof greater concern. For example, the magnitude of thisindustry in India can be adjudged from the fact that it con-tributes almost one-third of the total export and employ 35million people directly (Chavan, 2001).

Textile wastewater, which is a by-product of textileindustry, is a mixture of colorants (dyes and pigments)and various organic compounds used as cleaning solvents,plasticizers etc. It also contains high concentrations ofheavy metals, total dissolved solids, and has higher chemi-cal as well as biological oxygen demand. Thus, textilewastewater is chemically very complex in nature. Its dis-charge had led to complete disappearance of submergedand free-floating hydrophytes, and also selected marshy

K.P. Sharma et al. / Chemosphere 69 (2007) 48–54 49

species in the pools and a wastewater drain in the industrialarea of Sanganer town, Jaipur. Algal species richness alsodecreased markedly in them. These water bodies were alsodevoid of fauna (Chaturvedi et al., 1999; Sharma et al.,2001). Thus, textile wastewaters are highly toxic to bothflora and fauna.

The highly complex nature of textile wastewaters mayprove to be a limitation factor for complete assessment oftoxicity with chemical analysis. Biological tests in combina-tion with chemical analysis may however, be useful in deci-phering toxicity as they express living material response tothe total effect of actual and potential disruption (Chenet al., 1999). Besides, such tests also assist in developingprecautionary measures and strategy for environmentalmanagement (Slabbert, 1996).

Biological tests made on organism at different trophiclevels in the food chain may prove to be useful in forecast-ing impacts at ecosystem level. Phytoplankton, duck weeds(Blinova, 2000) and submerged macrophytes (Lee et al.,1998; Rai et al., 2003; Kumar and Prasad, 2004) are the testmaterials for monitoring toxicity of man-made chemicalson primary producers in the aquatic ecosystems, whichhave an additional advantage of detecting even stimulatoryrole of pollutants. However, duckweed such as Lemna isthe first choice of ecotoxicologists because it is wide spread,fast growing and reproduce faster. It is sensitive to manypollutants, which are assimilated from the growing medium(or aquatic environment) through the underside of the leaf(Greenberg et al., 1992; Becker et al., 2002; Sharma et al.,2006).

Among aquatic fauna, fish is favoured over other ani-mals and their mortality is the sole criteria for quantifyingpollutant toxicity (Sharma et al., 2005a,b). Recently,Sharma et al. (2006) reported higher sensitivity of fishRBCs (their counts and morphological abnormalities) toan azo dye methyl red in comparison to their mortality,and hence they may also be explored for quantifying textilewastewaters toxicity. With this background, we havedetailed physico-chemical characteristics of textile waste-waters (untreated and treated) of Sanganer, Jaipur, includ-ing of ingredient chemicals, in relation to their toxicity toduckweed and fish (mortality and RBC), to quantify poten-tial threats in terms of discharge limits imposed by the reg-ulatory authority for conventional parameters.

2. Materials and methods

Textile wastewaters released at different steps of printingin Sanganer, Jaipur were collected separately in clean plas-tic cans and transported immediately to the laboratory.These were: bleach wastewater (chlorine bleaching usingCaOCl2), screen wash (released during washing of screenafter manual printing) and wastewaters discharged atdifferent steps of fixing dyes by diazotization and silicateprocesses. During diazotization process, indigo and rapiddyes are fixed on the printed cloth by soaking them in amixture of acid (hydrochloric/sulphuric acid) and sodium

nitrite (commonly referred to as ‘Pass’) for about 15 min.Whereas soaking printed cloth for 12 h in the concentratesolution of sodium silicate bind reactive dyes in silicate pro-cess. Thereafter, three washings of printed cloth removebleeding dyes and chemicals. Textile wastewaters releasedat different steps of printing process are finally discharged(mostly untreated) in the pools and drains. Since unlikedrains, pollutants discharged during a day in textile print-ing process get mixed in the pools, therefore their waterswere collected in the morning (prior to initiation of print-ing processes on the next day) to quantify cumulative toxi-city of them. Also collected physico-chemically (FeSO4 +slaked lime + polyelectrolyte) and biologically treated dyewastewaters from effluent treatment plants (ETP) in San-ganer, Jaipur, to quantify toxicity reduction. The biologicaltreatment process which has been patented by Sharmaand Sharma (2006) comprises of neutralization of textiledye wastewaters (30000–35000 l/day) with slaked lime inthe equalizer chambers followed by microbial degradationof dyes and other organic pollutants first in a bioreactor(I day Retention Time) and then in rhizosphere of con-structed wetland of Phragmites karka (2 day RT) andfinally coagulation of suspended impurities by alum(100 mg/l) and polyelectrolyte in a clarifier and theirremoval through sand filter.

Physico-chemical characteristics of wastewaters wereanalyzed within 24 h of collection using standard methods(APHA, 1989). We examined their toxicity to a freshwaterfish Gambusia affinis (Baird and Gerard) as described ear-lier (Sharma et al., 2003). After 96 h exposure, autopsywas done for RBC counts, blood smear preparation (Leeet al., 1993) and examination of their internal organs.Almost 200 RBCs in 20 microscopic fields (10x · 100x)were observed to quantify morphological abnormality ina treatment (control/wastewater).

Lemna aequinoctialis (Welwitsch) population main-tained in the unpolluted concrete tanks of UniversityBotanical Garden was the source of plant material. Experi-ments were set in both green house (temperature =28 ± 3.5 �C) and growth chamber (temperature = 25 ±5 �C). Different dilutions (using tap water) of wastewatersamples (both untreated and treated) were filled in(two-third) separately into 1.5 l sized plastic tubs (green-house study)/200 ml sized plastic glasses (growth chamberstudy), while tap water in the control sets. Fifty Lemna

plants (100 fronds) were added in a tub, while 20 plants(40 fronds) in a glass. Frond number and oven dry weightof plants (at 60 �C for 7 days) were measured after 10 daysin five replicates of a treatment. Toxicity of wastewaterswas examined at three different occasions and data pre-sented are their mean values.

We also performed Lemna assay on ingredient chemicals(analar grade) of textile wastewaters of Sanganer viz.hydrochloric acid, sulphuric acid, sodium nitrite, copper(present in wastewaters of diazotization process), sodiumsilicate (silicate process) and few selected dyes such asC.I. Direct Blue 86, C.I. Direct Yellow 44, C.I. Drimarene

50 K.P. Sharma et al. / Chemosphere 69 (2007) 48–54

Yellow L2R and Methyl Red (C.I. 13020). Their stocksolutions prepared in distilled water were diluted with tapwater for experiment. To analyze role of nutrients on toxi-city, stock solutions of methyl red and copper sulphatewere diluted with Hoagland medium and the controls werealso run in Hoagland medium. This treatment is referred toas nutrient rich hereafter in the text. A similar study madeusing tap water as a diluent of stock solution of these twochemicals is referred to as nutrient poor hereafter in thetext. Among chemical ingredients, fish toxicity assay wasmade only for acidity (pH = 5.5 for HCl), copper andmethyl red.

LC (for fish mortality) and EC50 values (for RBC count,poikilocytosis, frond number and dry weight of Lemna)were calculated using COMPAQ personal computerBASICA version 1.13. They are mean values (with stan-dard deviation) of data obtained independently at three dif-ferent occasions for most of the textile wastewaters.

3. Results and discussion

3.1. External and internal injuries

3.1.1. Fish

The darkening of body and pronounced secretion ofmucous (a defensive mechanism) were the two most notice-able fish response in the textile wastewaters and ingredientchemicals. Dyes were deposited over the external (gills) andinternal organs (lateral line and digestive system) of fishonly in methyl red, and screen and silicate wastewaters.The gills were hemorrhaged at higher concentrations inall treatments. Additional injuries in the pass (wastewaterof diazotization process) were whitening of eye-balls, anderosion of scales from the skin and of tissue from pelvicand caudal fins. The dead fish had opened mouth andflared operculum possibly due to asphyxia on account ofdamaged gills.

RBC counts decreased with an increase in concentrationof copper, methyl red and textile wastewaters, when com-pared with control fish (58.9 ± 3.3 · 104 mm�3). Morpho-logical abnormalities (poikilocytosis) in control fish RBCs(spherical and triangular) were relatively less (<5%), in

Fig. 1. Morphological abnormalities (Poikilocytosis) in the RBCs of wastewateR = RBC membrane).

comparison to wastewater exposed fish, majority being tri-angular (30–40%) and quadrilateral (30–35%) while the restwere spherical, beaked, kidney, pentagonal and dumbleshape (Fig. 1). Other abnormalities exclusively found inpass were their hypochromic nature and some even hadvacuoles and damaged cell membrane. Thus, pass was mosttoxic to fish possibly because of maximum load of variouspollutants and acidity (Table 1). EC50 values for poikilocy-tosis were generally minimum followed by values forcounts and fish mortality.

3.1.2. Duckweed

The immediate plant responses to higher concentrationsof wastewaters (not in bleach) and ingredient chemicalswere their fragmentation into singlets (paired frond intounpaired frond) and loss of roots, while fronds turnedwhite in bleach waste. Other injuries were however, doseand time dependent, and were reduction (50–70%) in sizeand thickness of fronds, their chlorosis initiated first inmature one, but younger one in silicate wastewater andsodium silicate. Dyes were deposited on the frond (lowersurface) and root in screen wash, silicate wastewater anddye treatments.

The aforesaid injuries to fish and duckweed may be con-sidered as biomarkers of textile wastewater toxicity, as theywere also noted during bioassays of ingredient chemicals.

3.2. Relationship between physico-chemical characteristics,

and toxicity of ingredient chemicals and raw wastewaters

Acidic and neutral bleach having almost similar valuesfor chemical oxygen demand (COD) differed largely intheir toxicity to fish, the former having higher residualchlorine (3 folds) was 10–14 folds more toxic in comparisonto neutral one, whereas their toxicity to Lemna was almostsimilar, possibly due to their wide ecological amplitude(Table 1). The lowering of residual chlorine content(4.2 ppm) of neutral bleach wastewater equal to its LC50

value, along with its pH (5.5) however, resulted in instantdeath of fish. Contrast to this, control fish survived for96 h at pH 5.5. This means acidity increases residualchlorine toxicity. Thus chemical analysis forecasted lesser

r exposed fish comparison to control after 96 h of the study (N = nucleus;

Table 1Physico-chemical characteristics of textile wastewaters of Sanganer and their toxicity to fish (G. affinis) and Lemna

Wastewaters Wastewater characteristics Fish bioassay (96 h) Lemna bioassay 10th day (EC50: %)

Mortality RBC

pH EC (mS) COD (ppm) Cu (ppm) LC50 (%) EC50 (%) Frond number Dry weight

BleachAcidic 5.3 1.55 1200 88.75a 1.13 2.38 (5.71) 23.6 28.8Neutral 7.3 10.74 1430 30.8a 15.71 25.0 25.7 32.0

Screen wash 8.6 ± 0.1 4.9 ± .06 896 ± 6 0.15 ± 0.2 19.6 ± 1.1 41.3 ± 1.7 89.1 ± 71 58 ± 10Pass

Raw 1.2 ± 0.3 80.2 ± 41.8 3963 ± 1115 45.7 ± 34 0.8 ± 0.6 1.3 ± 0.9 (0.78) 1.0 ± 0.8 0.7 ± 0.01Neutral 7.6 ± 0.4 11.2 ± 7.7 3651 ± 1379 6.0 ± 1.4 3.2 ± 0.7 35.3 ± 4.5 (0.8) 5.0 ± 0.3 4.6 ± 0.3

I WashRaw 1.7 ± 0.4 19.3 ± 19.6 872 ± 116 4.5 ± 1.6 4.9 ± 4.1 0.75 ± 0.5 (0.8) 5.5 ± 4.4 5.5 ± 2.8Neutral 7.5 ± 0.2 5.2 ± 3.7 716 ± 129 1.2 ± 0.5 16.3 ± 5.0 NA (1.1) 34.6 ± 28.9 14.8 ± 2.7

II Wash: Raw 2.9 ± 0.5 4.0 ± 1.6 545 ± 132 3.7 ± 0.4 12.1 ± 1.3 NA 55.2 ± 3.4 NAIII Wash: Raw 7.2 ± 0.8 2.6 ± 0.9 291 ± 110 2.8 ± 0.6 14.9 ± 0.6 NA 107.4 ± 14 NASilicate: I wash 11.6 ± 0.1 18.6 ± 4.8 479 ± 29 Nil 4.2 ± 2.3 2.9 ± 1.0 (2.0) 6.3 ± 2.6 8.4 ± 2.2Pool waters 6.9 ± 3.1 3.9 ± 2.6 255 ± 105 0.86 ± 0.4 36 ± 18 39.7 ± 22.6 53.3 ± 31 66 ± 23

Wastewater after treatment in effluent treatment plants

Untreated wastewater 8.7 4.5 900 0.3 18.8 NA (11.42) 139.4 55.3Physico-chemical treatment 10.5 4.5 520 Nil 47.5 NA (25.1) NC 119.5Biological treatment 7.6 ± 1.0 4.4 ± 0.1 138 ± 109 Traces 39 ± 10 52.4 ± 14 (8.2) 141.2 ± 38.5 148 ± 64After alum + sand filter treatment 8.54 4.45 140.5 Nil 165.2 153.8 NC 170

a Residual chlorine content; NA = not available; NC = not calculable; Data in parenthesis are for EC50 value for poikilocytosis.

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52 K.P. Sharma et al. / Chemosphere 69 (2007) 48–54

toxicity than what actually assessed during fish bioassay.The comparatively higher sensitivity of fish (lower LC50

values) may be attributed to rapid penetration of residualchlorine in to their gills, which may be slow in Lemna

(hence low sensitivity), possibly due to presence of cell wall.Further, EC50 values for RBC counts and poikilocytosiswere higher than LC50 values of fish suggesting RBC tobe lesser sensitive to bleach. The higher fish mortality maybe ascribed to impairment of gaseous exchange throughgreater damage to gills.

The toxicity order of colored wastewaters to fish (basedon LC50 value) was: pass > silicate water � I wash > IIwash > III wash > screen wash > pools (Table 1). Further,their EC50 values for poikilocytosis (in RBCs) were usuallyminimum indicating greater physiological distress in fish,unlike bleach wastewater (Table 1). Acidic bleach waterranks almost similar to pass in terms of fish mortality whileneutral one was closer to third wash, despite the fact thatthey differed largely in their physico-chemical characteris-tics. This fact also holds true for first wash and silicatewastewater. Contrast to this, first wash and screen washalmost similar in their COD values varied largely in theirLC50 values. Thus, physico-chemical characteristics ofwastewaters alone are not sufficient to quantify theirtoxicity.

With the exception of pass, although EC50 values of dyewastewaters for Lemna were higher (low toxicity) thanLC50 values for fish, but general trend of their toxicityranking was almost similar to fish: pass > I wash > silicate

Table 2Physico-chemical characteristics (range) of ingredient chemical treatments and

Chemicals Physico-chemical characteristics of varying dilutions (rang

pH EC (mS) TH (ppm)

AcidsHCl 2.8–6.5 0.68–1.05 208–210H2SO4 2.8–6.4 0.68–1.12 207–209

SaltsNaNO2 8.1–8.3 2.5–8.42 188–236Na2OSiO2 9.9–10.1 1.59–3.09 53–68

Tap water 7.0 0.58 206

Data in parenthesis indicate EC50 values of acids in terms of pH values, and

Table 3LC and EC50 values (ppm) of methyl red and copper for fish and Lemna at d

Chemicals pH Fish bioassa

Mortality

CopperNutrient poor medium 8.5 0.25Nutrient rich medium 5.95–6.2 NA

Methyl redNutrient poor medium

i. acidic 6.0 7.3ii. alkaline 7.4–8.7 54.8

Nutrient rich medium 5.4–5.9 NA

NC = not calculable; NA = not available.

water > pools > screen wash > II wash > III wash (Table1). Thus, response of both the tested organisms to pollu-tants in wastewaters was almost identical, and therefore,they are ideal for quantifying their toxicity.

During duckweed bioassay, frond number was foundto be a more sensitive parameter in comparison to dryweight; suggesting that adverse effects on vegetativepropagation of plants were more severe than possiblyon their photosynthesis responsible for an increase intheir dry weight.

The higher toxicity of wastewaters of diazotization pro-cess may be ascribed to its major ingredients such as acids,sodium nitrite and copper, whereas of silicate wastewaterto sodium silicate, as noted in Lemna and fish (Tables 2,3). In contrast to major ingredient chemicals, dyes suchas C.I. Direct Blue 86 (EC50 = 225 ppm), C.I. Direct Yel-low 44 (EC50 = 1500 ppm) and Drimarene Yellow L2R(EC50 = 2150 ppm) were less toxic to Lemna whereasmethyl red toxicity was at par with pool waters. Similarto bleach wastewater, methyl red was less toxic to the testorganisms at pH ranging between neutral to slightly alka-line, in comparison to acidic one. Its toxicity also increasedin combination with copper (Table 4). In contrast to cop-per, nutrients had no role in reducing methyl red toxicity(at lower pH) to Lemna.

Methyl red loses its azo character a bit in acidic solu-tions on account of protonation resulting in its planarstructure (Park et al., 2005), which may increase its absorp-tion in fish in comparison to normal alkaline solution of

their toxicity to Lemna (EC50)

e) Duckweed bioassay (EC50)

Na (ppm) Frond no. Dry weight

27 0.0052 M (pH = 3.8) 0.0050 M (pH = 5.2)25 0.0025 M (pH = 4.4) 0.0045 M (pH = 4.9)

145–2900 0.009 M (0.062%) 0.015 M (0.096%)125–1250 0.014 M (0.17%) 0.029 M (0.36%)26

of salts in percentage.

ifferent nutrient and pH levels of the growing medium

y Duckweed bioassay

RBC Frond no. Dry weight

0.19 0.47 NCNA 5.48 3.13

4.98 12.1 8.541.4 23.2 56.4NA 33.9 3.2

Table 4Toxic effects of methyl red (10 ppm), copper (3.0 ppm) and theircombination at sub-lethal concentrations on Lemna counts (on 7th day),in comparison to control (nutrient rich medium)

Treatments % Reduction (counts)

Methyl red 33Copper 18Methyl red + copper 68

K.P. Sharma et al. / Chemosphere 69 (2007) 48–54 53

methyl red. The tested plant species may also respond sim-ilarly since Zhou (2001) has reported absorption of organicdyes in vegetables cultivated using textile dye wastewaters.This explains greater toxicity of methyl red in acidicsolution.

It is important to note that Lemna growth was pro-moted at lower concentrations of textile wastewaters ofpools (<40–80%), pass (<0.5–0.25%), I (<3%), II (<10%)and III (<25%) wash of diazotization process, possiblyon account of higher concentration of nutrients (filterablereactive phosphorus = 1.9–13.5 ppm; total phosphorus =5.0–16.4 ppm; NH3–N = 1.4–266 ppm; NOx = 5.6–67.2 ppm; organic nitrogen = 8.4–506.8 ppm; K = 2.8–15.8 ppm) in comparison to control plants growing in thetap water (FRP and TP = traces; NH3–N = nil; NOx =4.0 ppm; organic nitrogen = nil; K = traces). The reduc-tion in copper toxicity (higher EC50) in nutrient richmedium supports this inference.

3.3. Treated wastewaters

Neutralization of pass and 1st wash with lime decreasedtheir toxicity markedly, as evident by an increase in LC50

and EC50 values, respectively, for fish (5–15 folds) andLemna (5–32 folds) (Table 1). This has been ascribed pri-marily to reduction in acidity and copper content whichare found to be very toxic to the test organisms (Table 2).

Physico-chemical and biological treatments decreasedtoxicity of wastewaters to the tested organisms, as alsonoted for their chemical characteristics (Table 1). As evi-dent from LC/EC50 values, treated wastewaters were more(3–4 folds) toxic to fish and poikilocytosis was the mostsensitive parameter. No definite trend was recorded forEC50 values of Lemna for frond number and dry weight.The biologically treated wastewater (after alum treatment)also stimulated Lemna growth at 25% dilution. Thus,Lemna bioassay detected toxicity and stimulation of waste-waters simultaneously, as also noted for untreatedwastewaters.

It is important to note that silicate wastewater(untreated) almost similar to physico-chemically treatedwastewater in chemical characteristics were however, moretoxic to the tested organisms. Similarly, reduction in toxi-city of biologically treated wastewater was significantlyhigher after alum treatment, while their physico-chemicalcharacteristics varied little (Table 1). These findings signifyimportance of biological tests in characterizing textilewastewater toxicity.

3.4. Correlation between physico-chemical characteristics

and LC/EC50 values

LC and EC50 values of both the test organisms showedsignificant negative correlation with conductivity (r =0.53–0.59), COD (r = 0.55–0.71) and Cu (r = 0.54) whichwas positive for pH (r = 0.59–0.97), to wastewaters ofdiazotization process (untreated and neutralized) and so,they are good physico-chemical parameters for character-izing toxicity.

Pool water characteristics had significant positive corre-lations (pH: r = 0.82–0.93; EC: r = 0.78–0.90; COD: r =0.98–0.99) with LC50 and EC50 values of fish, which werenegative for number and dry weight of duckweed (pH:r = 0.92–0.98; EC: r = 0.85–0.97; COD: r = 0.81–0.97).Thus, duckweed bioassay defined pool toxicity better whencompared with fish.

Only pH had significant positive correlation (r = 0.58–0.98) with LC and EC50 values of fish and Lemna for bio-logically treated wastewaters, while their EC (r = �0.91)and COD (r = 0.89) values had significant negative correla-tion with frond number.

Present study thus established superiority of biologicaltests in deciphering wastewaters toxicity as compared totheir chemical analysis. Various external and internal inju-ries noted during fish and duckweed bioassays may assist inrapid assessment of wastewaters toxicity in the natural eco-systems, whereas their EC/LC50 values in quantifying toxi-city more accurately along with chemical attributes in thelaboratory. Duckweed bioassay has an added advantageof detecting eutrophication potential of wastewaters. Thegreater sensitivity of fish RBCs to pollutants in dye waste-waters emphasizes inclusion of their study in routine fishbioassay.

Present study documented increase in pollutants toxic-ity (residual chlorine, copper and methyl red) in the acidicmedium. The higher alkalinity of silicate wastewater maysimilarly be toxic to Lemna, since it decreased after itsneutralization (Soni, 2004). In view of these facts, we rec-ommend discharge limit of textile wastewaters close toneutral. The considerations such as dilution factor andbuffering capacity of the recipient water bodies are oflittle significance in monsoonic climate as that of India,where water flow (lotic system)/its volume (lentic system)remains low during most part of the year, except rainyseason.

Acknowledgements

We are thankful to the Council of Scientific and Indus-trial Research, New Delhi for awarding Research Asso-ciateship to Shweta Sharma, Ministry of Science andTechnology, Department of Biotechnology, New Delhifor research grants to K.P. Sharma and Subhasini Sharma,and the Head, Zoology and Botany Departments, Univer-sity of Rajasthan, Jaipur for laboratory facilities.

54 K.P. Sharma et al. / Chemosphere 69 (2007) 48–54

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