Determination of Wastewater LC50 of the Different Process Stages of the Textile Industry

Ecotoxicology and Environmental Safety 48, 56}61 (2001) Environmental Research, Section B doi:10.1006/eesa.2000.1986, available online at http://www.idealibrary.com on

Determination of Wastewater LC50 of the Different Process Stages of the Textile Industry A. Villegas-Navarro, Y. RammH rez-M., M. S. Salvador-S. B., and J. M. Gallardo Laboratorio de ToxicolognH a, Centro de InvestigacioH n BiomeH dica de Oriente, IMSS, Puebla Pue, MeH xico Received January 26, 2000

dyeing, and rinsing. The textile plants in the region of Puebla, Mexico, all employ a sequence of steps that include an initial sti!ening, preparing the "ber by removing impurities such as fuzz, powder, and oil to make the subsequent treatments more e$cient; a scouring for cotton; and bleaching (Cegarra and Romargraf, 1966). These steps are followed by dyeing, which produces a change in the color of the "ber (Cegarra et al., 1981), and rinsing to eliminate all residues from the previous stages, giving the "ber its particular quality. Each stage requires water which is "nally eliminated as wastewater carrying the chemicals used in each stage with it. It has been reported that textile plants produce highly toxic discharges (Dorn et al., 1993; Lin and Peng, 1994). Wastewater from a textile industry inhibited Cyprinus carpio growth (Rajan and Balasubramanian, 1988). Ademoroti et al. (1992) found that residual water from textile facilities carried highly concentrated pollutants and that toxicity was worsened by the presence of ClO\. Toxic heavy metals also promote the depletion of dissolved oxygen and destabilize the ability of the water to reduce microbial loads and, thus, its ability for autopuri"cation (Ademoroti et al., 1992). Rutherford et al. (1992) determined the toxicity of wastewater from three textile mills to several organisms, among them Daphnia magna, and proved that the wastewaters were toxic to all organisms due to the large amounts of chemicals used by textile facilities. Laughton et al. (1994) conducted toxicity bioassays in textile facilities in New Brunswick, Canada, using Salmo gairdneri and D. magna. They demonstrated that wastewater remained toxic despite of having been treated. Villegas-Navarro et al. (1997) determined the LC  values of treated industrial wastewater from two textile industries using D. magna and demonstrated that the treated wastewater remained toxic in both textile plants. They also found that the textile bleachers used added to the toxicity; thus an aquatic hazard assessment was conducted for branched and linear nonionic surfactants using toxicity and biodegradation measurements. Chronic toxicity of the highly branched alcohols was greater than that of the linear

Textile plants are very important sources of toxic discharges. The purpose of the research described in this paper was to use bioassays with daphnids to determine the LC50 values of textile wastewater samples taken from di4erent stages of the 5nishing textile industry. Toxicity due to dyeing, chlorination, and the absence of adequate physicochemical conditions for daphnid survival were considered. Wastewater samples corresponding to each process stage were collected at 5ve 5nishing textile industries and assayed according to previously published procedures. The sensitivity of daphnids to chemicals was assayed using sodium dodecyl sulfate and was similar to other reports (14.6 ⴞ 6.8 vs 14.5 ⴞ 2.3 mg/L). All e8uents from the 5ve company samples were toxic in terms of LC50 and exhibited very high toxicity with acute toxicity unit (ATU) levels between 2.2 and 960, indicating that the 5ve textile industries produced toxic water. The sensory characteristics indicated that the dyes contributed to overall sample toxicity at all process stages. The most toxic contaminant seemed to be ClOⴚ at levels between 0.2 and 6.8 mg/L, suggesting that further research is needed on the economic costs of stage-by-stage and total e8uent treatments.  2001 Academic Press

Key Words: Daphnia magna; wastewater; textile plants; bioassay; toxicity; LC50; residual chlorine; dyeing.

INTRODUCTION

Textile plants usually employ cotton and synthetic "bers and include an integrated printing and dyeing operation, applying a wide variety of organic dyes (Weltrowski et al., 1996; Achwal, 1997) and full range stages of fabric processes (singeing, starching, "re retarding, etc.). The main "nishing stages for synthetic "bers include washing, initial lightening, dyeing and rinsing, and natural "ber scouring, bleaching,

 To whom correspondence should be addressed at Centro de InvestigacioH n BiomeH dica de Oriente, IMSS, 19 Sur No. 4717, Col. Reforma Agua Azul, C.P. 72430, Puebla Pue, MeH xico. Fax: (2) 2-45-77-40. E-mail: [email protected].

56 0147-6513/01 $35.00 Copyright  2001 by Academic Press All rights of reproduction in any form reserved.

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LC OF TEXTILE INDUSTRY WASTEWATER 

alcohols (Dorn et al., 1993). Villegas-Navarro et al. (1999) demonstrated that NaClO found in textile e%uents is toxic to daphnids. Bioassays in situ were done to determine the impact of textile discharge into the St. Clair River using daphnids to test life cycle, reproduction rate, and survival at the sampling stations located upstream and downstream from all urban and industrial discharge points. The results indicated that routine discharge did not cause undesirable short- or long-term e!ects on daphnids (Moran et al., 1992). The purpose of the present study was to determine the textile wastewater LC at the di!erent process stages of the  "nished textile industry, distinguishing between toxicity due to dyes and ClO\ and mortality due to the absence of adequate physicochemical conditions for daphnid survival. MATERIALS AND METHODS

The aim of this work was to evaluate the toxicity of the e%uents from "ve textile industries, taking samples at each stage throughout the total process, and to establish the role of toxicity testing in identifying and measuring the toxicity of individual process streams. The number of samples taken from each textile plant varied either because each has its particular process, because the di!erent stages are not clearly de"ned, or because samples could not be taken to prevent production interruption. The requisites for carrying on the study of these industries were that the resulting information would be con"dential and that production should not be discontinued. Bioassayed wastewater was untreated, whereas in a previous and simultaneous investigation of the same textile plants, the toxicity of treated and nontreated wastewaters was evaluated, as was the e$ciency of the treatment plants (Villegas-Navarro et al., 1999). Samples of wastewater (2 L) corresponding to each process stage at the "ve textile industries were collected in polypropylene bottles, sealed according to Mexican regulation NMX-AA-003 (SCFI-NMX-AA-003, 1993), transported to the laboratory, and stored at 43C. The toxicity tests were carried out within 36 h. Chemical analyses included: pH (Corning Model 7), dissolved oxygen (YSI Model 51B), conductivity (Orion Model 520A), hardness (EDTA-Na and eriochrome black T (Fritz and Schenk, 1969)), CIO\ (orthotolidine colorimetric method, Can Spec M230; (APHA, 1976)). Both water and air temperatures were measured. The following sensory characteristics of the samples were also determined: color, odor, turbidity, presence or absence of bubbles and lather. For static tests with D. magna neonates, the methodology used was that published in Mexican Norm NMX-AA-087 (SCFI-NMX-AA-087, 1995). The quality criteria applied to the cultivation of daphnids were those published by Poirier et al. (1988). The reconstituted water solution was aerated for 48 h to obtain O concentrations higher than 3 mg/L.  The reconstituted water had the following physicochemical

parameters: pH 7.5}8.5, hardness 160}180 mg/L expressed as CaCO , conductivity 250 to 600 lS/cm, and absence of  CIO\. These conditions were adequate for the growth of daphnids. Chlorella vulgaris were used as a nutrient for the daphnids (Naylor et al., 1993; Cox et al., 1992); they were cultivated according to Stein (1973) and concentrated by centrifugation, and the pellet was kept at 43C. The pellet was rediluted with 50 mL of reconstituted water and fed to the daphnids as described previously (Villegas-Navarro et al., 1997). For the toxicity tests, daphnid neonates of the second to sixth generations less than 24 h old were used. Ten neonates were placed in individual 150-mL containers, with 100 mL of the sample, diluted or undiluted as required with reconstituted water. Sodium dodecyl sulfate (SDS) was used to determine the sensitivity of the daphnids. The LC for  SDS was established in two 48-h bioassays, one before and one after the industrial wastewater bioassays. SDS concentrations employed were 2, 4, 8, 16, and 32 mg/L. Sample toxicity tests included a 24-h preliminary test carried out to determine if the e%uent was toxic and to de"ne the concentration range to be employed in the de"nitive tests. The standard for a valid bioassay was an nomovement rate of less than 10% in the control group. In the de"nitive test, the minimum number of dilutions was 5 plus the control group. Immobile organisms were counted to calculate the 24-h LC and 48-h LC . All assays were   done in triplicate for each concentration, and a control group, except for the preliminary and SDS (Sigma) tests, which were done in duplicate. NaClO is used in the textile industry as a bleaching agent. To determine its LC , NaClO (Cloralex 6%, Allen,  Mexico) was used in the following concentrations: 0.015 to 0.48 mg/L with a growth factor of 0.6. For statistical analysis, the probit method (Goldstein, 1964) was used. The results were expressed in terms of both LC $its reliance limit at 95% and acute toxicity units  (ATU"100/LC ).  RESULTS

The 24- and 48-h LC values obtained using SDS  were 16.7$6.8 and 14.5$2.3 mg/L, respectively, and did not di!er signi"cantly from the reference result of 14.5$ 4.5 mg/L reported by Hebert (1978). Wastewaters from di!erent process stages from "ve textile industries were analyzed. Only one sample was taken from industry I. Sensory evaluation determined an acetic acid odor and a bright blue color indicating the presence of dyes, while physicochemical analyses indicated a pH of 5.2 and 0.7 mg/L ClO\ content (Table 1). This sample had 5.1 ATU at 48 h. The following samples were taken from industry II (Table 2): No. 2 "lament rinse, No. 3 moisture, No. 4 dyeing solution, and No. 5 rinse water after dyeing. Sensory

58

VILLEGAS-NAVARRO ET AL.

TABLE 1 Physicochemical Characteristics of the Sample from Industry I Physicochemical characteristic

TABLE 3 Physicochemical Characteristics of the Samples from Industry III

Sample No. 1

pH Conductivity Hardness Dissolved oxygen Residual chlorine Air temperature Sample temperature

Sample

5.2 434 152 6.4 0.7 28 78

characteristics indicated an acid odor and a yellow color for samples 4 and 5. Sample 2 contained 326 ATU with no considerable deviation in the other physicochemical parameters, but the ClO\ concentration was 6.8 mg/L, high enough to cause daphnid death (LC "0.02$0.01).  Sample 3 had 2.2 ATU and 0.4 mg/L ClO\. Some samples exhibited the presence of oil. Oil is used as a lubricant during moistening, but it causes the formation of a thin layer on the water surface in the bioassay #asks in which the daphnids become trapped, su!ocate, and die, aside from representing a chemical pollutant (Burnham et al., 1981; Vindimian et al., 1992). Sample 4 had 33 ATU, a pH of 4.9, 2.1 mg/L ClO\, an acid odor, and yellow color; the combination of all these parameters made the sample highly lethal. Sample 5 contained 6.4 ATU and adequate physicochemical parameters to keep the daphnids alive. The following samples were taken from industry III (Table 3): No. 6 impregnation stage, No. 7 dyeing stage, No. 8 rinse water from dyeing, and No. 9 bleaching. With respect to sensory characteristics, suspended solids were present in all samples, as were a starchy odor and yellow and pink colors in samples 6 and 7 respectively. Sample 8 had an acid odor and was salmon in color, while sample 9 had an ammonia odor and was beige. Samples 6 and 7 contained 2.8 and 2.1 mg/L ClO\ and 960 and 140 ATU,

TABLE 2 Physicochemical Characteristics of the Samples from Industry II

Physicochemical characteristic

No. 6

No. 7

No. 8

No. 9

pH Conductivity Hardness Dissolved oxygen Residual chlorine Air temperature Sample temperature

11.0 1220 108 15 2.8 24 69

10.0 3900 98 9 2.1 24 70

9.0 915 24 7 2 24 35

9.7 400 82 7 1.2 24 68

respectively, levels high enough to cause death in daphnids. Sample 8 had 40 ATU and its ClO\ concentration was 2 mg/L; sample 9 had 170 ATU and its ClO\ concentration was 1.2 mg/L. In the last two samples, aside from the presence of coloring matter, the ClO\ concentration was high enough to cause the death of daphnids. The following samples were taken from industry IV (Table 4): No. 10 scouring, No. 11 rinse water from No. 10, No. 12 dyeing, and No. 13 rinse water from dyeing. Numbers 10 and 11 had a starchy odor and were o!-white in color, while samples 12 and 13 had an acid odor and were slightly pink. Sample 10 had 322 ATU and a hardness of 56 mg/L. Daphnids withstand water softness and hardness but require some time for adaptation (McDonald et al., 1996). The daphnids used come from hard water and water softness could be a parameter implicated in daphnids death, aside from toxicity due to dyeing. Samples 11, 12, and 13 contained 122, 4, and 156 ATU, respectively. Their ClO\ concentrations represent a good reason for the degree of toxicity. Samples 12 and 13 were pink, indicating the presence of coloring matter. One sample (No. 14) was taken from industry V. Signi"cant sensory characteristics were an acid odor and a bright blue color, and it contained 96 ATU (Table 5).

TABLE 4 Physicochemical Characteristics of the Samples from Industry IV Sample

Sample Physicochemical characteristic pH Conductivity Hardness Dissolved oxygen Residual chlorine Air temperature Sample temperature

No. 2

No. 3

No. 4

No. 5

7.8 299 166 6.4 6.8 26 50

5.4 400 178 7 0.4 26 65

4.9 1300 176 6.7 2.1 26 75

7.6 645 172 6.4 0.2 26 50

Physicochemical characteristic pH Conductivity Hardness Dissolved oxygen Residual chlorine Air temperature Sample temperature

No. 10 No. 11 No. 12 No. 13 8.0 3870 56 2.4 0.5 27 77

10.0 1050 100 3.6 1.2 27 31

8.0 1500 180 4.3 1.2 27 70

11.0 6300 210 4.4 1.2 27 40

59

LC OF TEXTILE INDUSTRY WASTEWATER 

TABLE 5 Physicochemical Characteristics of the Samples from Industry V Physicochemical characteristic

Samples No. 14

pH Conductivity Hardness Dissolved oxygen Residual chlorine Air temperature Sample temperature

4 1020 150 8 0.2 23 55

DISCUSSION

Several samples contained suspended solids, which were eliminated by "ltering the samples before doing the tests; thus, this factor played no part in the toxicity. All e%uents from the "ve companies were toxic in terms of LC (Table 6); i.e., they had ATU values '1.0 and, in  several cases, were very toxic, 53 ATU (Lerdo de Tejada Brito and SaH nchez ChaH rez, 1993). According to these results none of the processes is atoxic, and the dyeing and chlorination stages were the most toxic. The most contaminating toxic substance found through these bioassays was ClO\ at concentrations ranging from 0.2 to 6.8 mg/L. The LC for  ClO\ is 0.02$0.01 mg/L; i.e., all samples had a high enough ClO\ concentration to induce more than 50% daphnid mortality. According to unpublished data from this laboratory ClO\ toxicity was higher than toxicity due to

TABLE 6 LC50 and ATU Values of the 14 Samples to 24 and 48 h Sample No.

24-h LC  $CI 95%

24-h ATU

48-h LC  $CI 95%

48-h ATU

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

24.3$5.5 0.5$0.01 55.0$16 3.3$0.2 16.7$7 0.1$0.04 1.0$0.3 4.2$0.9 0.7$0.2 0.4$0.1 1.2$0.3 25.0$7 0.9$0.1 1.3$0.4

4 178 2 31 6 910 99 24 151 263 85 4 107 78

19.5$5 0.3$0.03 45.0$5.3 3.0$0.1 16.0$0.6 0.1$0.03 0.7$0.3 2.5$0.4 0.6$0.2 0.3$0.1 0.8$0.3 22.0$6 0.6$0.1 1.0$0.3

5 326 2 33 6 960 140 40 170 322 122 4 156 96

Dyeing Filament rinse Moisture Dyeing Dye rinse Impregnation Dyeing Dye rinse Bleaching Scouring Scouring rinse Dyeing Dye rinse Dyeing

some of the dyes used in the textile industry. However, ClO\ has a short half-life in wastewater exposed to sunlight or containing concentrations of organic and inorganic materials and also because of its volatility (Snoeyink and Jenkins, 1990). Regarding this contaminant there are two possible treatments for its removal. One would be to treat the residual water with CaSO or Na SO    (Niino et al., 1997). This treatment is inexpensive and requires no infrastructure but it implies an additional stage in wastewater treatment and, thus, an increase in cost. It is also possible to use a di!erent textile bleaching agent, for example, O , H O , Na S O , or H PO (Cegarra et al.,         1989). The sensory characteristics indicate that the dyes contributed to the overall sample toxicity at all processes. The textile industries from which samples containing dyes were taken were industry I, sample 1, with 5 ATU; industry II, sample 4, with 33 ATU; and industry V, sample 14 with 96 ATU. The di!erences in toxicity may have been due to the use of the dye depletion dyeing technique in industry I, whereas in industries II and V dyeing is done with the impregnation technique; i.e., the dye is not necessarily depleted. This di!erence produces wastewater with di!erences in dye concentration (Rutherford et al., 1992; Ademoroti et al., 1992); therefore, sensory di!erences in dye concentration in the wastewaters may explain the di!erent degrees of toxicity for identical stages even if the toxicity of the dye used is not known. In addition, the di!erence in toxicity between samples 4 and 14 may be due to the use of di!erent "xing solutions. Industry II used ammonium hydrosul"te while industry V used ammonium sulfate. Continuing with the dyeing stage, but now for natural "bers, industry III exhibited 140 ATU, and industry IV, 4 ATU, but the largest di!erence between these is in the sensory parameters. Thus, for industry III, dissolved oxygen and temperature are adequate for daphnids while all other parameters are inadequate; for industry IV, the physicochemical parameters are adequate for life in daphnids.

CONCLUSIONS

The results using D. magna have been used only as a model to extrapolate the toxicological implications that may result from textile e%uents in the aquatic environment, but these results are not su$cient to assess the holistic health risk for a receptor aquatic ecosystem. However, the toxicity to daphnids is enough to suggest potential damage to every receptor ecosystem and emphasizes the need for adequate wastewater remedial treatments to avoid pollution and increasing concentration and to reassess methods of treatment in textile plants. The main objective of this study was to demonstrate biological toxicity for each stage and the main contaminants (dyes and ClO\) in a "nishing

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VILLEGAS-NAVARRO ET AL.

textile industry (Dorn et al., 1993). This leaves to further research the economic costs of both stage-by-stage treatment and total e%uent treatment. This last approach allows for the sophism that combining the wastewater from all stages brings about a dilution that, from the chemical standpoint, results in less chemically concentrated pollution, inducing lower toxicity. This allows the wastewater to be in compliance with the legal norms of the di!erent countries. Coccagna (1997) illustrates a similar case. However, from a biological standpoint, collecting the wastewater from all stages with their contaminants may induce antagonistic and synergetic toxicological e!ects (Ademoroti et al., 1992). All pollution should be excluded rather than diluted. One alternative is treatment at each stage, which does not necessarily have to be more complex or expensive, as textile manufacturers know what chemicals have been used and the treatment process could be speci"cally designed for those chemicals. A continuous process of combined ozonization and chemical coagulation has been employed for treatment of textile wastewater from several dyeing and "nishing plants (Lin and Lin, 1993). Ozonization was found to be highly e!ective in color removal with complete clearance of textile wastewater. The costs are further compensated by a considerable improvement in the overall quality of the treated wastewater (Lin and Liu, 1994). Ozonization is a little more expensive, and it also has a greater deleterious e!ect on aquatic environments (Leynen et al., 1998), but it can be eliminated from the residual water with KI or by aeration. The dilemma is whether to increase the economic cost or leave the cost to the environment. REFERENCES Achwal, W. B. (1997). Problems during analysis of textiles as per ecostandards and the consumer articles ordinance. Part II. Colourage 44, 31}32. Ademoroti, C. M. A., Ukponmwan, D. O., and Omode, A. A. (1992). Studies of textile e%uent discharges in Nigeria. Int. J. Environ. Stud. 39, 291}296. American Public Health Association (APHA) (1976). Standard Methods for the Examination of =ater and =astewater, 14th ed., 4.45}4.48. APHA, Baltimore, MD. Burnham, L. N., Melvin, W. W., and Buchan, R. M. (1981). Acute toxicity of an in situ shale oil process wastewater and its major components to Daphnia magna. Bull. Environ. Contam. ¹oxicol. 27, 338}343. Cegarra, J., and Romargraf, S. (1966). IntroduccioH n al blanqueo de materias textiles, pp 135}156. Barcelona. Cegarra, J., Gacen, J., Schumacher-Hamedat, U., Knott, J., Blankenburg, G., and Caro, M. (1989). Depigmentation of animal hair. Rev. Quim. ¹ext. 96, 26}31, 33, 36, 38}40. Cegarra, J., Puente, P., and Valldeperas, J. (1981). Fundamentos cientnH ,cos y aplicados de la tintura de materiales textiles, chap. 10. Universidad PoliteH cnica, Barcelona. Coccagna, L. (1997). Water reuse for textile industry. In O.cial Proceedings of the International =ater Conference, 58th, 102}108.

Cox, E. J., Naylor, C., and Calow, P. (1992). Frozen algae as food for Daphnia magna Straus in toxicity testing. Ecotoxicol. Environ. Saf. 24, 58}62. Dorn, P. B., Salanitro, J. P., Evans, S. H., and Kravetz, L. (1993). Assessing the aquatic hazard of some branched and linear nonionic surfactants by biodegradation and toxicity. Environ. ¹oxicol. Chem. 12, 1751}1762. Fritz, J. S., and Schenk, G. H., Jr. (1969). Quantitative Analytical Chemistry, 2nd ed., pp. 228}232. Allyn & Bacon, Boston. Goldstein, A. (1964). Biostatistics: An Introductory ¹ext, pp. 154}159. Collier}Macmillan Canada, Toronto. Hebert, P. D. N. (1978). The population biology of Daphnia. Biol. Rev. 53, 387}426. Laughton, R. V., Moran, T., and Roy, G. (1994). Case studies for toxicity testing and risk assessment related to the placement of textile facilities. In 21st Annual Aquatic ¹oxicity =orkshop, October 2}5, 1994, Point Edward, Ontario, Canada. Lerdo de Tejada Brito, A., and SaH nchez ChaH vez, J. J. (1993). ¹oxicidad en aguas residuales, pp. 135}138. SEDESOL, National Institute of Ecology. Direction of Standardization, Memorias de LimnologmH a, MeH xico city. Leynen, M., Duvivier, L., Girboux, P., and Ollevier, F. (1998). Toxicity of ozone to "sh larvae and Daphnia magna. Ecotoxicol. Environ. Saf. 41, 176}179. Lin, S. H., and Lin, C. M. (1993). Treatment of textile waste e%uents by ozonation and chemical coagulation. =ater Res. 27, 1743}1748. Lin, S. H., and Liu, W. Y. (1994). Continuous treatment of textile water by ozonation and coagulation. J. Environ. Eng. 120, 437}446. Lin, S. H., and Peng, C. F. (1994). Treatment of textile wastewater by electrochemical method. =ater Res. 28, 277}282. McDonald, S. F., Hamilton, S. J., Buhl, K. J., and Heisinger, J. F. (1996). Acute toxicity of "re control chemicals to Daphnia magna (Straus) and Selenastrum capricornutum (Printz). Ecotoxicol. Environ. Saf. 33, 62}72. Moran, T., Lines, M., Getty, K., and Kierstead, T. (1992). In-situ multispecies approach to environmental e!ects monitoring of a major river ecosystem. In Proceedings, Nineteenth Annual Aquatic ¹oxicity =orkshop, October 4}7, 1992. Naylor, C., Bradley, M. C., and Calow, P. (1993). Freeze-dried Chlorella vulgaris as food for Daphnia magna Straus in toxicity testing. Ecotoxicol. Environ. Saf. 25, 166}172. Niino, K., Sato, N., and Niino, M. (1997). Controlled release-type agents for removing residual chlorine in water. Jpn. Kokai Tokkyo Koho, 5 pp. Patent No. JP 11179375, Kind A2, Date 19990706, Application No. JP 97-353184, Date 1997; 1222. Poirier, D. C., Westlake, G. F., and Abernethy, S. G. (1988). Daphnia magna Acute ¸ethality ¹oxicity ¹est Protocol. Ontario Ministry of Environment, Aquatic Toxicity Unit, Water Res. Br., Rexdale, Ontario. Rajan, M. R., and Balasubramanian, M. P. (1988). E!ects of sublethal concentrations of textile industry e%uent on the food utilization and growth of the "sh Cyprinus carpio. Environ. Ecol. 6, 977}984. Rutherford, L. A., Ernst, W. R., Doe, K. G., and Hennigar, P. A. (1992). Chemical characterization, aquatic toxicity and environmental impact of untreated e%uent discharges from three textile mills in the Atlantic region. In Proceedings, 19th Annual Aquatic ¹oxicity =orkshop, Edmonton, Alberta, Canada, pp. 293}299. SCFI-NMX-AA-003: Screening ¹ests in Residual =aters. (Nov. 6, 1993). SecretarmH a de Comercio y Fomento Industrial, Diario O"cial de la FederacioH n, Mexico City.

LC OF TEXTILE INDUSTRY WASTEWATER  SCFI-NMX-AA-087: Analysis of =aters: Evaluation of Acute ¹oxicity by Means of Daphnia magna Straus (Crustacea}Cladocera), Assay Methodology. (Nov. 14, 1995). SecretarmH a de Comercio y Fomento Industrial, Diario O"cial de la FederacioH n, MeH xico City. Snoeyink, V. L., and Jenkins, D. (1990). QunH mica del agua, pp. 425}444. Limusa, Mexico City. Stein, J. R. (1973). Handbook of physiological methods: Culture Methods and Growth Measurements, p. 448. Cambridge Univ. Press, New York. Villegas-Navarro, A., RodrmH guez Santiago, M., RumH z PeH rez, F., RodrmH guez Torres, R., Dieck Abularach, T., and Reyes, J. L. (1997). Determination

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of LC from Daphnia magna in treated industrial waste waters and non treated hospital e%uents. Environ. Int. 23, 535}540. Villegas-Navarro, A., Romero GonzaH lez, M. C., Rosas LoH pez, E., DommH nguez Aguilar, R., and Sachetin Marcal, W. (1999). Evaluation of Daphnia magna as an indicator of toxicity and treatment e$cacy of textile wastewater. Environ. Int. 25, 619}624. Vindmian, E., Vollat, B., and Garric, J. (1992). E!ect of the dispersion of oil in freshwater based on time dependent Daphnia magna toxicity tests. Bull. Environ. Contam. ¹oxicol. 48, 209}215. Weltrowski, M., Patry, J., and Bourget, M. (1996). Reactive "lter for textile dyes adsorption. Adv. Chitin. Sci. 1, 462}469.