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Changes in toxicity and genotoxicity of industrial sewage sludge samples containing nitro- and amino-aromatic compounds following treatment in bioreactors with different oxygen regimes
Örebro University, Department of Natural Sciences.
Örebro University, Department of Natural Sciences.ORCID iD: 0000-0001-7338-2079
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2004 (English)In: Environmental science and pollution research international, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 11, no 5, p. 313-320Article in journal (Refereed) Published
Abstract [en]

GOALS, SCOPE AND BACKGROUND: From 2005, deposition of organic waste will be banned in Sweden. Likewise, in Germany and Austria, similar bans are being planned, and further countries will probably follow. Thus, there is a need to develop new methods and to refine established techniques for sludge management in the whole of the European Union. For this end, there is also an urgent need for appropriate ecotoxicological approaches to elucidate and assess the hazard potential of sewage sludge. Therefore, the present study was designed to assess the capacity of various established sludge treatment methods using different oxygen regimes to degrade recalcitrant nitro-substituted organic compounds and reduce their toxicity. Sewage sludge samples from a wastewater treatment plant in Sweden (Cambrex Karlskoga AB, industrial area Björkborn) receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives were processed with different sludge treatment methods. Among other treatment methods, bioreactors (for anaerobic and aerobic sludge treatment) were used. In the present investigation, a battery of in vitro bioassays was employed to compare the cytotoxic and genotoxic potentials of different fractions of sludge samples in order to elucidate whether the treatments were suitable to reduce the toxicity of the sludge.

METHODS:

In order to investigate the cytotoxicity of the extracts of treated and untreated sludge samples, the acute cytotoxicity test with the permanent cell line RTL-W1 was used. Genotoxicity was tested by means of the comet assay (single cell gel electrophoresis) with RTL-W1 cells, and mutagenicity was assessed with the Ames test using the Salmonella typhimurium strains TA98, TA98NR and TA100. Sludge toxicity was tested in different fractions of organic extracts produced by acetone and hexane extractions. The subsequent clean-up procedure (silica gel chromatography and elution with hexane and dichloromethane) resulted in two fractions, a lipophilic hexane-fraction and a semi-lipophilic dichloromethane-fraction. For the genotoxicity and mutagenicity tests, these fractions were reunited at equal ratios.

RESULTS AND DISCUSSION:

The acute cytotoxicity test with RTL-W1 cells revealed a high cytotoxic potential for the semi-lipophilic DM-fractions of all sludge samples with NR50 values (= effective concentration for 50% cell death in the neutral red test) from 8.9 up to 20 mg sludge d.w./ml medium. A low cytotoxic potential for the hexane fractions of the untreated sludge samples (NR50 400 to > 400 mg sludge d.w./ml medium) was observed, whereas the hexane fractions of the treated sludge samples showed elevated cytotoxicity increasing further with treatment in the bioreactors. The comet assay indicated that three out of eight of the reunited fractions had a significant genotoxic potential. Whereas the genotoxic potential of one sample treated anaerobically was very high with an induction factor of 11.6, a similar sample (taken from the same anaerobic reactor four months later) and one untreated sample showed lower potentials. The samples treated in another anaerobic bioreactor as well as the samples treated aerobically showed no genotoxic potential. Results indicate that aerobic treatment was basically adequate for reducing the genotoxicity of the sludge, whereas anaerobic treatment was only partly useful for reduction of genotoxicity. The Ames test revealed a very high mutagenic potential for the reunited fractions of the untreated sludge samples with strain TA98 (maximum induction factors (IFmax) up to 45) and a relatively high potential for one of the samples treated aerobically (S2, IFmax = 18 (TA98, S9-)), thus documenting the suitability of both anaerobic and aerobic treatments to reduce the mutagenicity of the samples, however, with the aerobic treatment being less effective.

CONCLUSIONS:

Overall, none of the microbiological treatments for wastewater sludge in bioreactors was found to be ideal for general toxicity reduction of the sludge samples. Whereas cytotoxicity of the sludge increased or levelled off in most cases following either treatment, genotoxicity both increased or decreased after anaerobic treatment, depending on the specific sample. However, mutagenicity could generally be reduced by anaerobic treatment and, to a lesser degree, by aerobic treatment.

RECOMMENDATIONS AND PERSPECTIVES:

The complex modification of the diverse damage potentials of sludge sample extracts by use of an in vitro biotest battery following treatment for toxicity reduction in bioreactors showed that considerations of different toxicological endpoints is essential for an adequate hazard assessment. Whereas in the case of cytotoxicity reduction, the reactors proved ineffective, mutagenicity could be reduced significantly at least in some cases in this case study.

Place, publisher, year, edition, pages
2004. Vol. 11, no 5, p. 313-320
National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
URN: urn:nbn:se:oru:diva-2917DOI: 10.1007/BF02979645PubMedID: 15506634OAI: oai:DiVA.org:oru-2917DiVA, id: diva2:135511
Available from: 2005-10-07 Created: 2005-10-07 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Change of toxicity during secondary treatment of industrial sludge containing nitroaromatics
Open this publication in new window or tab >>Change of toxicity during secondary treatment of industrial sludge containing nitroaromatics
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wastewater treatment plants in Sweden are facing a great challenge due to the prohibition of depositing organic waste which gained legal force in January 2005. Biological and commercial available alternatives to disposal are composting and anaerobic digestion. A promising technique for wastewater and sludge treatment is the use of constructed wetland.

In this thesis we have looked at the sludge from a wastewater treatment plant receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives. The wastewater and sludge contains high concentrations of nitro-aromatic compounds and amino-aromatic compounds, both original compounds and degradation products. The degradation of nitroaromatics under different oxygen conditions is well examined and several studies have reported the alteration of nitroaromatics to more potent cytotoxic and genotoxic compounds after degradation. The use of bioassays is a practicable approach to estimate the toxic potency of complex samples such as sludge, since it is difficult to analyse all toxic compounds in a sample by using chemical analysis.

The aim of this study was to follow change in toxicity in three different sludge treatment methods; aerobic composting and anaerobic digestion and constructed wetland to follow change in general and mechanism-specific toxicity.

In order to detect both lipo- and hydrophilic compounds, different extraction and bioassays are necessary. We used organic solvents and multi-layer cleaned-up samples in the DR-Calux assay to detect the persistent lipophilic compounds causing dioxin-like activity. We also used both water and acetone extracts in the umu-C assay to detect genotoxicity and in the fishegg assay to detect embryotoxicty of water and semi-water soluble compounds in low concentrations.

The results showed that anaerobic treatment is less suitable for this particular sludge, since the anaerobic residues showed high induction in all toxicity tests compared to the residues of the aerobic treatment. The anaerobic treatment also transformed the toxicants in the sludge to more lipophilic and persistent forms as well as to more water soluble, genotoxic compounds. This makes the treated material difficult to handle due to the toxic potential of the material as well as of the leachate. The aerobic treated material also showed an increased toxic potential of the material but the leachate showed no toxicity. However, high concentrations of nitrite were formed during both aerobic and anaerobic treatment, which is of environmental concern.

The constructed wetlands eluated a non-toxic effluent and had a bed material with lower toxicity than expected considering the sludge concentrations and loaded sludge amount. The bed material contained concentration of TEQ considered as acceptable levels for sensitive ground use such as parks, lawns and other grounds without groundwater protection.

However, all three treatment methods need to be optimised and the residual needs further evaluation in order to establish a suitable biodegradation method.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek, 2005. p. 45
Series
Örebro Studies in Environmental Science, ISSN 1650-6278 ; 7
Keyword
Anaerobic, aerobic, AhR agonists, CALUX, constructed wetlands, Danio rerio, embryotoxicity, genotoxicity, nitroaromatics, sludge
National Category
Other Environmental Engineering
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-181 (URN)91-7668-453-9 (ISBN)
Public defence
2005-10-28, Hörsal P1, Prismahuset, Fakultetsgatan 1, 70182 Örebro, 10:00
Opponent
Supervisors
Available from: 2005-10-07 Created: 2005-10-06 Last updated: 2017-10-18Bibliographically approved

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Gustavsson, LillemorEngwall, Magnus

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