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Published online 16 October 2007
Published in J Environ Qual 36:1591-1598 (2007)
DOI: 10.2134/jeq2006.0433
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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TECHNICAL REPORTS

Bioremediation and Biodegradation

Investigation of the Toxicity of the Products of Decoloration of Amaranth by Trametes versicolor

Mihaela Gavrila,* and Peter V. Hodsonb

a Dep. of Chemical Engineering, Queen's Univ., Kingston, Ontario, Canada K7L 3N6
b School of Environmental Studies, Queen's Univ., Kingston, Ontario, Canada K7L 3N6

* Corresponding author (mihaelag{at}umich.edu).

Received for publication October 6, 2006.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and Methods
 Results and Discussion
 Conclusion
 REFERENCES
 
Trametes versicolor decolorized 2000 mg L–1 of the mono-azo substituted naphthalenic dye Amaranth with no dye sorption observed visually. The changes in the toxicity were assessed over a period of 30 d for the dye-treated viable culture, control (no dye added), and a boiled culture treated with dye, using the Microtox Acute Toxicity assay. Before dye addition, the culture filtrate had some toxicity, which increased after the dye addition. The toxicity of the dye-treated culture decreased during the treatment. The loss of toxicity occurred at the same time, with the loss of color suggesting that detoxification is associated with decoloration. The change in pH was due to natural metabolic processes and had a small effect on detoxification. Because the toxicity of the treatment was similar to that of the control at the end of the treatment, the effluent seems to be safe for release into the environment, potentially rendering this treatment suitable for industrial application.

Abbreviations: DDW, deionized distilled water • JM, Jönsson's media • MAT, Microtox Acute Toxicity


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and Methods
 Results and Discussion
 Conclusion
 REFERENCES
 
AZO DYES are a non-natural class of dyes consisting of one or more chromophoric azo groups (-N = N-) attached to sp2 hybridized carbon atoms (Chudgar, 1992). According to the Society of Dyers and Colourists (1987), there are more than 4500 commercial colorants, and over 50% of these are azodyes used primarily in the textile, paper, food, cosmetics, and pharmaceutical industries. Their production exceeds one million tons annually (Stolz, 2001).

Generally, azodyes have been reported to be mutagenic (Chung and Cerniglia, 1992; Combes and Haveland-Smith, 1982) and carcinogenic (Chung, 1983) to animals and humans. Some studies have suggested that Amaranth (FD&C Red No.2, C.I. 16185, CAS No. 915–67–3) is carcinogenic in rats (Andrianova, 1970; Wilheim and Ivy, 1953) and affects their reproduction (Collins and McLaughlin, 1972; Collins and McLaughlin 1973; Collins et al. 1975a, b). Amaranth is also considered teratogenic to small mammals such as mice or rats (FDA Report 71–23; United States Federal Drug Administration, 1972) and was banned by the United States Federal Drug Administration in 1976 for use in drugs, cosmetics, or foods (Budavari et al., 1989). The International Agency for Research on Cancer suggests that there is not enough evidence to conclusively state that Amaranth is a human carcinogen (IARC, 1987). However, due to the similarities between the metabolic systems of humans and rats, substances that are toxic to rats have been found to be toxic to humans and to the environment (Walker, 1970; Combes and Haveland-Smith, 1982; Chung, 1983).

The textile industry is a major consumer of synthetic dyestuffs and uses large volumes of water in wet processing operations. Wastewater is the main route through which the dyes used in the textile industry reach the environment. Vaidya and Datye (1982), Lieberman et al. (1988), Spadary et al. (1994), Reisch (1996), and Stolz (2001) estimated that up to 20% of the total textile dyestuff is released in waste streams during manufacturing and use processes. The presence of dyes in the process water from textile and dye industries (Maguire, 1992; Oguri et al., 1998; Kwon et al., 2003) generates colored streams that are aesthetically unacceptable for the public. Dye visible even at concentrations as low as 1 mg L–1 (Banat et al., 1996; Nigam et al., 2000). Although the dye molecules contribute little to the biological oxygen demand (Dubrow et al., 1996; Banat et al., 1996), there is a strong need to discover and use the most suitable strategies for advanced wastewater dye removal (Leidig et al., 1999; Libra et al., 2003).

Scientists have shown a growing interest in dye decoloration by white-rot fungi. Trametes versicolor degrades a wide range of xenobiotic compounds (Paice et al., 1989; Archibald et. al., 1990; Reid et. al., 1990; Archibald, 1992) and is able to decolorize dyes (Swamy and Ramsay, 1999). Recent comparison studies of different fungi suggest that T. versicolor gives superior results for the decoloration of different dyes (i.e., decolorizes to a greater extent a higher number of dyes with a more complex chemical structure) when compared with other white-rot fungi such as Phanerochaete chrysosporium (Chivukula and Renganathan, 1995; Knapp et al., 1995; Heinfling et al., 1997; Shin and Kim, 1998; Rodríguez et al., 1999; Swamy and Ramsay, 1999; Zheng et al., 1999; Schliephake et al., 2000; Stolz, 2001). The dye decoloration is the result of the destruction of the principal chromophore in the dye (-N = N-) with the formation of noncolored products. In an ideal degradation process, the resulting parent compound should be broken down into substances that are harmless to the environment.

Trametes versicolor has a complex lignolytic system. The main enzymes recognized to be an important part of this system are LiP, MnP, and laccase. The peroxidases (LiP and MnP) need H2O2 for their enzymatic cycle, which is synthesized by the mycelium. To design an industrial process for the decoloration and detoxification of industrial effluent containing dyes that would take maximum advantage of the natural characteristics of the white-rot fungi, it is important to understand the significance of the mycelium and the role of the enzymes during the decoloration process of Amaranth by T. versicolor. The results obtained in our previous work (Gavril et al., 2007; Gavril and Hodson, 2007a, 2007b) showed that peroxidases (LiP in particular) play an important role in initiating the decoloration process. The mycelium also was shown to play an important role in the fungal decoloration of the azo dye Amaranth through the synthesis and release of factors that contribute to the proper functioning of peroxidases or through the synthesis and release of enzymes. The rates of decoloration for the samples that did not contain the mycelium were significantly lower than the rates of decoloration for the treatments containing it.

Toxicity is the property that reflects the potential of a pollutant to harm a living system (Rand et al., 1995). The purpose of this study was to use toxicity as an estimate for the aquatic ecological risks of Amaranth. The risks to aquatic organisms may not be well represented by toxicity tests used to predict the risks to mammals and human health. Therefore, we chose as an alternate test suitable for aquatic species the Microtox Acute Toxicity (MAT) test. Although it cannot predict the carcinogenic effect of a substance, it can diagnose toxicity to aquatic species (Bulich, 1979; Curtis et al., 1982; De Zwart and Sloof, 1983; Ross, 1993; Johnson, 1998). Several studies showed that the results obtained using the MAT test replicate well the results obtained with standard aquatic toxicity tests (De Zwart and Sloof, 1983; Kaiser and Palibrica, 1991; Toussaint et al., 1995; Kaiser, 1998; Parvez et al., 2006). Kaiser (1998) showed a strong correlation between the fathead minnow median lethal concentration (LC50) in the standard toxicity test and bacteria EC50 in MAT test over a toxicity range of over 10 orders of magnitude in molar activity. The MAT test takes about 5% of the work involved in the standard toxicity procedures (De Zwart and Sloof, 1983); it is simple, less costly (Kaiser, 1998), and reproducible; and it eliminates the ethical problems arising from using higher-order organisms such as fish or rats (Parvez et al., 2006). The United States Environmental Protection Agency and the Department for Homeland Security have evaluated and approved this test for rapid toxicity pre-screening (USEPA, 2005; United States Department of Homeland Security, 2006).

The decoloration studies for some azo dyes have shown that the decoloration may lead to less toxic by-products (Abadulla et al., 2000; Ramsay and Nguyen, 2002), whereas the decoloration of other azo dyes may have the opposite effect (Hu, 2001; Ramsay and Nguyen, 2002).

The objective of this study was to investigate whether the dye decoloration process by the white-rot fungus T. versicolor reduces the acute toxicity of the culture filtrate containing a toxic level of azo dye Amaranth and evaluate if the release of the effluent poses a hazard to the receiving aquatic environment.


   Materials and Methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results and Discussion
 Conclusion
 REFERENCES
 
Sources of Reagents
Amaranth was purchased from Aldrich (Oakville, Ontario, Canada) and was used as purchased. Jönsson media components (Jönsson et al., 1987) (4.0 g L–1 glucose·H2O, 0.94 g L–1 diammonium tartrate, 1.0 g L KH2PO4, 0.26 g L–1 NaH2PO4·2H2O, 0.50 g L–1 MgSO4·7H2O, 0.0001 g L–1 thiamine·HCl, 0.0066 g L–1 CaCl2·2H2O, 0.005 g L–1 FeSO4·7H2O, 0.000379 g L–1 MnSO4·H2O, 0.0005 g L–1 ZnSO4·7H2O, 0.00064 g L–1 CuSO4, and 0.50 g L–1 Veratryl alcohol) were purchased from Anachemia (Montreal, Québec, Canada), Aldrich (Oakville, Ontario, Canada), BDH Chemicals Ltd. (Poole, England), Fischer (New Jersey), and J.T.Baker Chemical Company (Phillipsburg, New Jersey) and were of analytical grade. The reagents for the MAT test (bacteria Vibrio fischeri, osmotic adjusting solution, reconstitution solution, diluent, and borosilicate test cuvettes) were purchased from Strategic Diagnostic Inc. (Newark, DE) and were used as purchased.

Trametes versicolor Cultures
The cultures were prepared by inoculating the spores of T. versicolor ATCC 20869 contained on the surface of the finely chopped (average area of 1 mm2) skin collected from one quarter Petri dish culture (grown on malt agar at 30°C) into 1000 mL sterile modified Jönsson's media (JM) in a 2000-mL Erlenmeyer flask. The flasks were shaken for 16 d at 200 rpm at room temperature (about 25°C) in daylight and fluorescent lab lighting. On Day 16 of growth, the average size of the mycelium was 2 mm in diameter. The fungus was harvested and resuspended in nine 500-mL Erlenmeyer flasks (three flasks for treatment, three for control, and three for the boiled treatment) containing a fresh volume of 250 mL of JM each. The ratio of innoculum to JM was 3%. The culture that resulted was maintained for 7 d in the conditions described previously. On Day 7 of growth in the JM, the mycelium was separated from three of the flasks, and the culture filtrate obtained was boiled for at least 10 min to destroy the enzyme activity. Amaranth was added to six flasks: three contained live fungi (termed "treatments"), and three contained the boiled culture filtrate (termed "boiled treatments") to obtain a concentration of 2000 mg L–1 Amaranth. The three remaining flasks containing nontreated live fungi were the controls. Samples of 10 mL were taken from each flask before dye addition, immediately after dye addition (within 20 s from adding the dye), and every 2 d for the next 30 d. The aliquots sampled were measured for dissolved oxygen and immersed in boiling water for at least 10 min to destroy enzyme activity and stop the decoloration. The samples were stored in the refrigerator at 4°C.

Methods for Measuring the Dissolved Oxygen, pH, and Absorbance
The dissolved oxygen concentration and the pH of the culture filtrates during the treatment were monitored using a YSI 58 Dissolved Oxygen Meter (YSI Inc., Tampa, FL) and a Denver Instrument Model 250 pH/Ion/Conductivity meter (Denver Instrument Company, Denver, CO). Decoloration was monitored by measuring the absorbance of the culture filtrate at the maximum absorption wavelength for Amaranth (521 nm) using a Cary 3 UV–Visible Spectrophotometer (Varian, Palo Alto, CA) in a cuvette with the optical path-length of 10 mm. To avoid the signal saturation for high concentration of dye and to ensure that the absorbance of each sample remained within the readable range (OD = 0.05–0.8) and within the linear range of Amaranth's standard curve, samples were first diluted appropriately, and the concentration was calculated using the dilution factor.

Microtox Tests
The samples were filtered using a 0.22-µm disposable sterile syringe filter (Cameo 3N). All samples were analyzed using a M500 Analyzer (Azur Environmental, Carlsbad, CA). The experimental test units were the six flasks to which dye had been added and three controls. Each set of three flasks was a replicate of the same experiment. The assay was performed on a 2.5-mL sample at the original pH value of the aliquots and on a 2.5-mL sample at a value adjusted to pH 6 to 8, according to the MAT experimental procedure (Azur Environmental, 2001). Two analyses were performed for each flask and data point: one at the original pH and one at the adjusted pH. The confidence levels represented in the results are the intersample variability. The toxicity was obtained as the EC50 (the concentration of sample analyzed that inhibited the bacteria light production by 50%). Toxicity units are defined as 100/EC50 (Azur Environmental, 2001). To determine the performance of the test system, the negative standard used was deionized distilled water (DDW) and had no toxicity. The positive standard used was ZnSO4, and the measured toxicity was within the limits required by the test.

The toxicity of each sample is due to pH (determined by the chemical form of the solutes) and to the inherent toxicity of the chemical components. By performing toxicity assays in samples having their original pH and in neutralized samples (i.e., pH between 6 and 8), we could discern the toxicity due to the fragments resulting from the decoloration of Amaranth and determine the nature of these fragments (i.e., acidic, neutral, or basic). Therefore, the toxicity assays were performed for each sample in adjusted and nonadjusted conditions.

The limitations of the MAT test (e.g., sensitivity to the products of chlorination in regular drinking water, traces of organic solvents, and turbidity) do not apply to this work because the experiments were performed in DDW (which has no water chlorination by-products) without organic solvents and with sample filtration before analysis. The results of the toxicity assay were color corrected by measuring the absorbance of the solutions in each vial test at 490 nm using the Microtox diluent as control. Each final toxicity value was included in the data pool for each set of the experiments (culture filtrate + fungal mycelium + dye; culture filtrate + fungal mycelium; boiled culture filtrate + dye). The results were averaged, and confidence limits were calculated at 95% confidence level using SD and sample size.

Statistical Analysis
Data were subjected to a one-way ANOVA for a completely randomized design (Snedecor and Cochran, 1989). Residuals were normally distributed with constant variance. The ANOVA was conducted using the multiple means comparisons tool in JMP IN version 5.1 (SAS Institute, 2004). Significance of treatment means was determined at P < 0.05 with the Tukey-Kramer Honestly Significant Difference comparison test.


   Results and Discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results and Discussion
Conclusion
 REFERENCES
 
The toxicity of JM and Amaranth solutions in DDW having concentrations of 250, 500, 1000, 1500, and 2000 mg L–1 were assayed, and the results are presented in Fig. 1 . The toxicity of JM was assayed for its original pH and for pH adjusted between 6 and 8, according to the MAT procedure. The original pH of Amaranth solutions was already within the limits recommended by MAT and was not adjusted. The toxicity of 2000 mg L–1 Amaranth was found to be much higher than the toxicity of JM (when considering the confidence interval), and this concentration was chosen for decoloration experiments.


Figure 1
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  		Fig. 1. Variation of toxicity with Amaranth concentration. Toxicity calculated for the 50% effect and 15-min exposure time (TU50, 15 min) as 100/EC50. Three measurements/mean and 95% confidence level.

 
The absorbance of Amaranth was linearly related to its concentration up to 75 mg L–1 (R2 = 0.95). The calibration curve for Amaranth (data not included) showed that all concentrations above 100 mg L–1 saturate the absorbance signal. However, from Fig. 1 it is apparent that the toxicity increases with the increase in Amaranth concentration. This suggests that the assay can make the distinction between the loss of light due to toxicity and the loss of light due to the light absorption by the colored sample. Consequently, this method of toxicity measurement is suitable for measuring the toxicity of dye-containing aqueous samples.

The variations of pH and dye concentration for all treatments are presented in Fig. 2 . The dye concentration in the treated viable cultures decreased rapidly in the first 12 d after dye addition and showed a slower decrease between Days 12 and 24. After Day 24, the absorbance of the culture filtrate remained constant, suggesting that the decoloration process was completed. The absorbance of the treated culture filtrate remained higher than that of the control. The dissolved oxygen values remained constant during all treatments and were between 6 and 7.5 mg L–1. These numbers are close to the solubility limit of oxygen in water at atmospheric pressure and room temperature (8.23 mg L–1) (American Public Health Association, American Water Works Association, and Water Environment Federation, 1999), confirming that the system was aerobic.


Figure 2
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  		Fig. 2. Variation of Amaranth concentration, pH, and dissolved oxygen in treatment, control and boiled treatment during the decoloration of 2000 mg L–1 Amaranth by Trametes versicolor. BDA, before dye addition; ADA, after dye addition. Three measurements/mean and 95% confidence level.

 
All samples collected during the treatment were scanned to monitor any changes in {lambda}max. The results are presented in Table 1 . Immediately after dye addition, the {lambda}max in the treatment increased from 289 to 522 nm. On Day 12, there were two peaks: One had {lambda}max at 290 nm, and the other was at 521 nm. The presence of the peak at 521 nm is consistent with the observation that there was some color due to the nondecolorized dye in the culture filtrate. On Day 24, the scan of the samples collected from the viable cultures treated with Amaranth showed only one peak, having {lambda}max at 290 nm. This suggests that the dye's chromophore was degraded and that the dye was transformed to other chemical compounds. On Day 30, the {lambda}max was 290 nm, which was close to the value for the untreated viable culture (296 nm). This suggests that the chemical compounds resulting from Amaranth's decoloration were similar to the type of compounds resulting from fungi's own metabolism. In the boiled treatment, {lambda}max remained constant (521 nm) throughout the treatment because the dye was not decolorized. A detailed study of the chemical nature of metabolites and the chemical mechanism of decolorations has been published elsewhere (Gavril and Hodson, 2007a).


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  		Table 1. Chemical composition of growth medium (modified Jönsson medium).

 
During the treatment, the pH of the viable cultures treated with the dye and the pH of the control varied in the same pattern, whereas the pH of the boiled treatment remained constant. The nature of the pH for the treatment and control changed from acidic on Day 0 (3 < pH < 4) to more neutral values on Day 12 (5 < pH < 6.5) and remained constant for the remainder of the treatment. The acidic pH before the dye addition was due to the natural fungal metabolites before the start of the decoloration process. The more neutral values registered on Day 12 are due to a combination of dye metabolites and fungal metabolites in the treatment and fungal metabolites only in the control. In the boiled treatment, the enzymes responsible for decolorations were inactivated through boiling and were therefore unable to perform decoloration. Consequently, all the compounds present at the start of the process were preserved in the same state until the end of the treatment, consistent with the lack of change in pH observed.

The pH value for the treated viable cultures on Day 24 (5.3) was close to the accepted water quality standards for pH (6.5–8.5) (Ontario Ministry of the Environment and Energy, 1994). The pH of the treatment had slightly lower values than those of the control (6), suggesting that the chemical compounds resulting from the dye degradation are of acidic nature.

The important moments for the decoloration process were Day 0 (before and after dye addition), Days 12 and 24 (when the concentration curve changed slope), and Day 30 (end of the treatment). Therefore, the changes in the toxicity for all treatments were assessed by performing toxicity assays on the samples collected on these days. To account for the toxicity due to the pH, the assays were performed on samples having their original pH (Fig. 3a ) and on samples for which the pH was adjusted to be in the optimum range for the MAT test (between pH 6 and 8) (Fig. 3b). The total toxicity of the sample is the sum of the toxicity due to the pH and the toxicity due to the chemical components (CC) of the samples:

Formula


Figure 3
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  		Fig. 3. Variation of toxicity in time for the decoloration of 2000 mg L–1 Amaranth by Trametes versicolor. Toxicity assays performed on samples with their original pH (a) and on pH adjusted to be between 6 and 8 (b). Toxicity calculated for the 50% effect and 15-min exposure time (TU50, 15 min) as 100/EC50. CC = chemical components. Three measurements/mean and 95% confidence level.

 
In both situations, the toxicity variation followed the same pattern: the toxicity of the boiled treatment remained constant in time, and the toxicity of the cultures treated with the dye increased significantly after dye addition and decreased to close to or to the same level as the control at the end of decoloration.

For the samples having their original pH (Fig. 3a), the toxicity of the treatment and the control decreased with time. The toxicity of the treatment was slightly higher than that of the control. The toxicity in the treatment is due to pH and dye metabolites. The only difference between treatment and control is the dye addition, which produced dye metabolites after decolorations. The change in pH (from acidic to more neutral values) was due to natural metabolic processes and is associated with the change in the ionic form, which makes the ionic compounds less available for the bacteria and therefore less toxic. The pH adds toxicity to the overall value of sample toxicity. Because the pH of the treatment is more acidic than that of the control (Fig. 4 ), it is apparent that the nature of the dye metabolites is acidic, which is consistent with the results obtained in the pH-treated experiment discussed below.


Figure 4
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  		Fig. 4. Variation of toxicity (ph adjusted samples), ph and absorbance in time during the decoloration of 2000 mg L–1 amaranth by trametes versicolor. Bda = before dye addition. Ada = after dye addition. Toxicity calculated for the 50% effect and 15 minutes exposure time (tu50, 15 min) as 100/ec50. Three measurements/mean and 95% confidence level.

 
When the toxicity due to the pH of the samples was eliminated by adjusting the pH to be in the optimal range for the assay (6 < pH < 8), the toxicities of the samples were

Formula

The toxicities of the control and the treatment overlapped on Days 24 and 30 (Fig. 3b) and were smaller than the toxicities of nonadjusted samples. This suggests that the pH contributed to sample toxicity and that the dye degradation products were of acidic nature. On Day 12, the toxicity of the metabolites formed after decoloration was higher than the toxicity of the control, suggesting that these metabolites are different from the natural fungal metabolites. The fact that the toxicity of the treatment continued to decrease from Day 12 to Day 24 to control's value (when considering the confidence interval) suggests that these metabolites suffer further transformation into fragments that are as nontoxic as natural fungal metabolites released by the mycelium. These observations are consistent with the mechanism of Amaranth decoloration by T. versicolor proposed by Gavril and Hodson (2007b) and with the reports regarding the mechanism of degradation (Spadaro and Renganathan, 1994) and mineralization (Paszczynski et al., 1992) of various azo dyes by another member of the white-rot fungi family, Phanarochaete chrysosporium. These researchers suggest that the dyes are reduced to smaller molecular mass compounds similar in structure to the compounds of fungal metabolism (Gavril and Hodson, 2007b) or to CO2 and water (Paszczynski et al., 1992).

Because the toxicity of the treatment where the enzymes were irreversibly inactivated by the temperature (boiled treatment) remained constant in time, although the toxicity of the viable culture decreased in time to the level of the control during the decoloration, the viable culture (i.e., the enzymes released by the mycelium) was responsible for the decoloration. Furthermore, because the toxicity decreased at the same time with the decoloration (Fig. 4), it seems that there is a link between decoloration and detoxification.

These observations are not in agreement with the research results published by Ramsay and Nguyen (2002) for the decoloration of Amaranth by T. versicolor grown on Kirk's medium (Kirk et al., 1978). They observed that after the decoloration of 100 ppm Amaranth, the culture filtrate did not change its toxicity after 48 h of treatment. This was not surprising because these researchers investigated an Amaranth concentration that was too low. Kirk's medium composition is similar to that of JM. As shown by our study, the dye concentration used by these researchers was not toxic by itself, and therefore there was no significant increase of toxicity when the dye was added to the culture. In essence, the toxicity of their growth medium masked the toxicity of the dye; therefore, the changes in toxicity brought by the decolorations could not be observed. Consequently, no meaningful conclusion in regards to the decoloration–detoxification relationship could be drawn at the end of their experiment.

The result of the present study agrees with the result found by Heinfling et al. (1997) for the detoxification of the nickel-containing phthalocyanine dye Reactive Blue 38 by T. versicolor (although 21% of the dye was not decolorized) and by Abadulla et al. (2000) for the decolorization and detoxification of anthraquinonic dyes by laccases extracted from the fungal cultures of T. hirsuta. However, although Heinfling et al. (1997) could not obtain complete decoloration and Abadulla et al. (2000) could not establish a relationship between the detoxification and decoloration, we have shown that complete decoloration occurred for the treatment of substituted monoazo dye Amaranth with T. versicolor and that the relationship decoloration–detoxification exists.

The fact that the toxicity decreased during the decoloration process but took 12 d after the dye addition to observe a substantial decrease in color suggests that this treatment may not be suitable for short-term industrial application (0–24 h). However, these results show promise for a treatment that spans 3 wk. If an industry were to treat an effluent containing dye with T. versicolor, they could take advantage of the conversion to decolorized metabolites and help decrease the toxicity by adjusting the pH of the effluent to more basic values.

The pre-screening results obtained with the MAT test need to be confirmed by the standard toxicity assessment methods, such as acute lethality to fathead minnow (Pimephales promelas), zebra fish (Bracydanyo rerio), or rainbow trout (Onchorynchus mykiss). Nevertheless, these results show the potential of T. versicolor to be used in the detoxification of dye-containing wastewaters.


   Conclusion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results and Discussion
 Conclusion
REFERENCES
 
We determined with the pre-screening MAT test that a synthetic effluent containing Amaranth does not constitute a hazard to the receiving aquatic environment after it was treated with the white-rot fungus T. versicolor, suggesting the fungus' potential for use in the detoxification of dye-containing wastewaters. Because the loss of toxicity occurred at the same time as the loss of color, it is clear that there is a relationship between the decoloration and detoxification. The fact that the loss of toxicity occurs 24 d after the dye addition may make this treatment more suitable for a long-term rather than a short-term industrial application. We have also determined that the MAT test can differentiate between the loss of color due to chemical toxicity and the loss of color due to the light absorption by a colored sample, making this technique suitable for measuring the toxicity of dye-containing environmental aqueous samples.


   ACKNOWLEDGMENTS
 
We thank Dr. Peter Adriaens (Department of Environmental and Water Research Engineering, University of Michigan) for allowing the use of the resources in his laboratory facilities and for his support and Dr. Frederick Archibald (Pulp and Paper Research Institute of Canada, Montreal), Dr. Andrew Daugulis (Queen's University), and Dr. Jim McLellan (Queen's University) for their suggestions and useful comments during our discussions. We thank NSERC and Queen's University for financial support.


   NOTES
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 INTRODUCTION
 Materials and Methods
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 Conclusion
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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.


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