Evaluation of phytotoxicity of municipal landfill leachate before and after biological treatment

Avaliação da fitotoxicidade de chorume de aterro sanitário antes e após tratamento biológico

CR Klauck MAS Rodrigues LB Silva About the authors

Abstracts

In the present study, leachate toxicity of a municipal solid waste landfill located in the Sinos River Valley region (southern Brazil) was evaluated using plant bioassays. Leachate toxicity was assessed by analysis of seed germination and root elongation of lettuce (Lactuca sativa L.) and rocket plant (Eruca sativa Mill.) and root elongation of onions (Allium cepa L.). Bioassays were performed by exposing the seeds of L. sativa and E. sativa and the roots of A. cepa to raw leachate, treated leachate (biological treatment) and negative control (tap water). The levels of metals detected in both samples of leachate were low, and raw leachate showed high values for ammoniacal nitrogen and total Kjeldahl nitrogen. There is a reduction in the values of several physicochemical parameters, which demonstrates the efficiency of the treatment. Both L. sativa and A. cepashowed a phytotoxic response to landfill leachate, showing reduced root elongation. However, the responses of these two plant species were different. Root elongation was significantly lower in A. cepa exposed to treated leachate, when compared to negative control, but did not show any difference when compared to raw leachate. In L. sativa, seeds exposed to the raw leachate showed significant reduction in root elongation, when compared to treated leachate and negative control. Seed germination showed no difference across the treatments. The results of the study show that plant species respond differently and that municipal solid waste landfill leachate show phytotoxicity, even after biological treatment.

plant bioassays; water pollution; wastewater treatment; toxic effects


No presente trabalho, a toxicidade do lixiviado (chorume) de um aterro sanitário municipal, localizado na região do Vale do Rio dos Sinos, foi avaliada utilizando bioensaios em plantas. A toxicidade do chorume foi analisada pelo teste de germinação e crescimento radicular de alface (Lactuca sativa L.) e rúcula (Eruca sativa Mill.) e pelo teste de crescimento radicular em cebola (Allium cepa L.). Os bioensaios foram realizados com a exposição de sementes de L. sativa e E. sativa e raízes de A. cepa a amostras de chorume bruto, tratado por processo biológico e controle negativo (água de abastecimento público). Os níveis de metais detectados nas amostras de chorume foram baixos, e o chorume bruto apresentou valores elevados de nitrogênio amoniacal e nitrogênio Kjeldahl total. Ocorreu redução nos valores de vários parâmetros físico-químicos, demonstrando a eficiência do tratamento biológico. Os resultados indicam fitotoxicidade do chorume em L. sativa e A. cepa, evidenciada pela redução do crescimento radicular. Entretanto, as respostas destas duas espécies diferiram. O crescimento radicular foi significativamente inferior em A. cepa exposta ao chorume tratado quando comparado ao controle negativo, mas não apresentou diferença quando comparado ao chorume bruto. Em L. sativa, a exposição das sementes ao chorume bruto causou redução no crescimento radicular quando comparado com o chorume tratado e controle negativo. Não foram observadas diferenças entre os tratamentos para o parâmetro germinação de sementes. Os resultados deste trabalho indicam que as espécies de plantas estudadas são diferentes em suas respostas e que o chorume apresenta toxicidade, mesmo após o tratamento biológico.

bioensaios com plantas; poluição da água; tratamento de efluentes; efeitos tóxicos


1 Introduction

One of the main environmental problems caused by the urbanisation in cities concerns the disposal of municipal solid waste (Renou et al., 2008Renou, S., Givaudan, JG., Poulain, S., Dirassouyan, F. and Moulin, P., 2008. Landfill leachate treatment: review and opportunity. Journal of Hazardous Materials, vol. 150, no. 3, p. 468-493. http://dx.doi.org/10.1016/j.jhazmat.2007.09.077. PMid:17997033.
http://dx.doi.org/10.1016/j.jhazmat.2007...
). Waste disposal in landfills is an increasingly common practice in large cities (Abrelpe, 2011Associação Brasileira de Empresas de Limpeza Pública e Resíduos Especiais – ABRELPE, 2011. Panorama dos resíduos sólidos no Brasil. vol. 1. São Paulo: ABRELPE. 186 p.), and generates large volumes of leachate as the product of waste decomposition and percolation of rainwater. Leachate is a dark liquid, with unpleasant odour; it is highly toxic and should be handled properly before its release in receiving bodies (Baun et al 2003Baun, A., Reitzel, LA., Ledin, A., Christensen, TH. and Bjerg, PL., 2003. Natural attenuation of xenobiotic organic compounds in a landfill leachate plume (Vejen, Denmark). Journal of Contaminant Hydrology, vol. 65, no. 3-4, p. 269-291. http://dx.doi.org/10.1016/S0169-7722(03)00004-4. PMid:12935953.
http://dx.doi.org/10.1016/S0169-7722(03)...
; Foul et al., 2009Foul, A., Aziz, HA., Isa, MH. and Hung, Y-T., 2009. Primary treatment of anaerobic landfill leachate using activated carbon and limestone: batch and column studies. Waste Management (New York, N.Y.), vol. 44, no. 4, p. 282-298.).

The most common conventional treatments for this type of effluent are biological aerobic and anaerobic treatments (Renou et al 2008Renou, S., Givaudan, JG., Poulain, S., Dirassouyan, F. and Moulin, P., 2008. Landfill leachate treatment: review and opportunity. Journal of Hazardous Materials, vol. 150, no. 3, p. 468-493. http://dx.doi.org/10.1016/j.jhazmat.2007.09.077. PMid:17997033.
http://dx.doi.org/10.1016/j.jhazmat.2007...
). However, this kind of treatment often presents low efficiency in the case of leachate coming from old landfills, due to reduced biodegradable fraction, presence of high molecular weight substances (Mahmud et al., 2012Mahmud, K., Hossain, MD. and Shams, S., 2012. Different treatment strategies for highly polluted landfill leachate in developing countries. Waste Management (New York, N.Y.), vol. 32, no. 11, p. 2096-2105. http://dx.doi.org/10.1016/j.wasman.2011.10.026. PMid:22088960.
http://dx.doi.org/10.1016/j.wasman.2011....
), in addition to high concentrations of ammoniacal nitrogen and other highly toxic compounds, which inhibit the biological treatment process and reduce the leachate treatability by conventional processes (Oller et al 2011Oller, I., Malato, S. and Sánchez-Pérez, JA., 2011. Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination--a review. The Science of the Total Environment, vol. 409, no. 20, p. 4141-4166. http://dx.doi.org/10.1016/j.scitotenv.2010.08.061. PMid:20956012.
http://dx.doi.org/10.1016/j.scitotenv.20...
; Rocha et al 2011Rocha, EMR., Vilar, VJP., Fonseca, A., Saraiva, I. and Boaventura, RAR., 2011. Landfill leachate treatment by solar-driven AOPs. Solar Energy, vol. 85, no. 1, p. 46-56. http://dx.doi.org/10.1016/j.solener.2010.11.001.
http://dx.doi.org/10.1016/j.solener.2010...
).

Hazard assessment of landfill leachate is traditionally based on the evaluations of individual chemicals identified through chemical analysis. However, chemical data alone do not allow for the evaluation of toxic effects. Toxicity bioassays, in contrast to physicochemical analysis, integrate the biological effects of all compounds present and other factors, such as bioavailability and toxicants interactions (Žaltauskaitė and Čypaitė, 2008Žaltauskaitė, J. and Čypaitė, A., 2008. Assessment of landfill leachate toxicity using higher plants. Environmental Research. Engineering and Management, vol. 4, p. 42-47.). Some studies show that leachate can cause deleterious effects on organisms at various trophic levels (Bakare and Osibanjo, 2000Bakare, AA. and Osibanjo, O., 2000. Effect of simulated leachate on chromossomes and mitosis on roots of (L.). Allium cepaJournal of Environmental Biology, vol. 21, no. 3, p. 263-271.; Christensen et al., 2001Christensen, TH., Kjeldsen, P., Bjerg, PL., Jensen, DL., Christensen, JB., Baun, A., Albrechtsen, HJ. and Heron, G., 2001. Biogeochemistry of landfill leachate plumes. Applied Geochemistry, vol. 16, no. 7-8, p. 659-718. http://dx.doi.org/10.1016/S0883-2927(00)00082-2.
http://dx.doi.org/10.1016/S0883-2927(00)...
; Bortolotto et al., 2009Bortolotto, T., Bertoldo, JB., Silveira, FZ., Defaveri, TM., Silvano, J. and Pich, CT., 2009. Evaluation of the toxic and genotoxic potential of landfill leachates using bioassays. Environmental Toxicology and Pharmacology, vol. 28, no. 2, p. 288-293. http://dx.doi.org/10.1016/j.etap.2009.05.007. PMid:21784018.
http://dx.doi.org/10.1016/j.etap.2009.05...
; Li et al., 2010Li, H., Han, M., Hou, L., Li, G. and Sang, N., 2010. Landfill leachate ingestion induces protein oxidation and DNA-protein crosslinks in mouse viscera. Journal of Hazardous Materials, vol. 174, no. 1-3, p. 54-58. http://dx.doi.org/10.1016/j.jhazmat.2009.09.015. PMid:19783094.
http://dx.doi.org/10.1016/j.jhazmat.2009...
). Among the various toxicity tests available, the seed germination and root elongation is a widely used, quick and accurate phytotoxicity test, showing sensitivity, simplicity, low cost and suitability for unstable chemicals or samples (Wang et al., 2001Wang, X., Sun, C., Gao, S., Wang, L. and Shuokui, H., 2001. Validation of germination rate and root elongation as indicator to assess phytotoxicity with . Cucumis sativusChemosphere, vol. 44, no. 8, p. 1711-1721. http://dx.doi.org/10.1016/S0045-6535(00)00520-8. PMid:11534903.
http://dx.doi.org/10.1016/S0045-6535(00)...
). Different model species are used in bioassays, including lettuce (Lactuca sativa L.), rocket plant (Eruca sativa Mill.) and onions (Allium cepa L.) (Barbero et al., 2001Barbero, P., Beltrami, M., Baudo, R. and Rossi, D., 2001. Assessment of Lake Orta sediments phytotoxicity after the liming treatment. Journal of Limnology, vol. 60, no. 2, p. 269-276. http://dx.doi.org/10.4081/jlimnol.2001.1.269.
http://dx.doi.org/10.4081/jlimnol.2001.1...
).

In the Sinos River Basin, located in the state of Rio Grande do Sul, Brazil, a large portion of municipal landfills has been disabled. However, in these locations, there is still generation and treatment of leachate, which is ultimately released in the water resources. The water quality in the basin is influenced by the direct discharge of domestic and industrial sewage, which have the potential to cause toxic effects on genetic and cellular levels (Blume et al., 2010Blume, KK., Macedo, JC., Meneguzzi, A., Silva, LB., Quevedo, DM. and Rodrigues, MAS., 2010. Water quality assessment of the Sinos River, Southern Brazil. Brazilian Journal of Biology = Revista Brasileira de Biologia, vol. 70, no. 4, supplement, p. 1185-1193. http://dx.doi.org/10.1590/S1519-69842010000600008. PMid:21225160.
http://dx.doi.org/10.1590/S1519-69842010...
; Scalon et al., 2010Scalon, MCS., Rechenmacher, C., Siebel, AM., Kayser, ML., Rodrigues, MT., Maluf, SW., Rodrigues, MAS. and Silva, LB., 2010. Evaluation of Sinos River water genotoxicity using the comet assay in fish. Brazilian Journal of Biology = Revista Brasileira de Biologia, vol. 70, no. 4, supplement, p. 1217-1222. http://dx.doi.org/10.1590/S1519-69842010000600011. PMid:21225163.
http://dx.doi.org/10.1590/S1519-69842010...
; Rechenmacher et al, 2010Rechenmacher, C., Siebel, AM., Goldoni, A., Klauck, CR., Sartori, T., Rodrigues, MT., Rodrigues, MAS., Gehlen, G., Ardenghi, PG. and Silva, LB., 2010. A multibiomarker approach in rats to assess the impact of pollution on Sinos River, Southern Brazil. Brazilian Journal of Biology = Revista Brasileira de Biologia, vol. 70, no. 4, supplement, p. 1223-1230. http://dx.doi.org/10.1590/S1519-69842010000600012. PMid:21225164.
http://dx.doi.org/10.1590/S1519-69842010...
; Costa and Droste, 2012Costa, GM. and Droste, A., 2012. Genotoxicity on var. plants exposed to urban and rural environments in the metropolitan area of Porto Alegre, southern Brazil. Tradescantia pallidapurpureaBrazilian Journal of Biology = Revista Brasileira de Biologia, vol. 72, no. 4, p. 801-806. http://dx.doi.org/10.1590/S1519-69842012000500004. PMid:23295507.
http://dx.doi.org/10.1590/S1519-69842012...
). Although the release of leachate poses an environmental risk, the effectiveness of its treatment and its toxicity in the Sinos River Basin were not assessed. This study aims to evaluate the phytotoxicity of leachate from a municipal landfill in three plant species, before and after biological treatment.

2 Material and Methods

2.1 Sample collection

The leachate collection took place during September 2012 (spring season), in a municipal solid waste landfill located in a large municipality in the Sinos River Valley region. The landfill is approximately 50 years old and has been disabled, but its pits still generate leachate, which passes through a biological treatment system (biodegradation is carried out by microorganisms in a treatment pond).

An aliquot of raw leachate was collected at the input and another aliquot of treated leachate was collected at the output of the biological treatment pond.

2.2 Physicochemical analyses of the samples

Immediately after collection, the samples were sent for physicochemical characterisation and the following parameters were determined: chlorides, conductivity, chemical oxygen demand (COD), biochemical oxygen demand (BOD5) total phosphorus, ammoniacal nitrogen, nitrate, nitrite, total Kjeldahl nitrogen, pH, turbidity, metals (cadmium, lead, chromium, zinc, nickel, manganese and iron). All analyses were carried out at the laboratories of Feevale University, according to the methods described in Standard Methods for Examination of Water and Wastewater (APHA, 2005American Public Health Association – APHA, 2005. Standard methods for the examination of water and wastewater. 21st ed. Washington: APHA. 1220 p.).

2.3 Allium cepa bioassay

Onion bulbs (Allium cepa) were purchased commercially and kept in a moisture-free location, protected from light. Prior to the test, roots that were old and dried were removed. In order to stimulate root growth, onions were kept in tap water for a period of 24 hours before exposure. Leachate samples were tested at a concentration of 100%. A negative control group was treated with tap water. Five onion bulbs were exposed to each treatment at room temperature and insulated from direct sunlight for a period of 48 hours. At the end of the exposure period, the length of the three longest roots in each bulb was measured. The average length of the roots in each treatment was calculated and compared to the growth in the control group. Toxicity was assessed by inhibition of root growth in the leachate samples, when compared to the control group.

2.4 Bioassay with Lactuca sativa and Eruca sativa seeds

The germination and root growth tests were performed using Lactuca sativa and Eruca sativa seeds obtained from local retailers. Protocol consisted of exposure of the Lactuca sativaand Eruca sativa seeds in Petri dishes prepared with a filter paper and 5 mL of the raw and treated leachate samples, and tap water for the control group. For each treatment, fifty seeds were exposed in one Petri dish. Time of exposure was 120 hours, at room temperature and insulated from direct light. At the end of the treatment, germination rate and root growth were estimated.

2.5 Statistical analysis

The statistical analysis was performed using ANOVA, followed by the Tukey multiple comparison test, when appropriate. Seed germination was analysed by the Chi-square test. All analyses were carried out using the Statistical Package for the Social Sciences (SPSS) 15.0 for Windows, considering a significance level of p ≤ 0.05.

3 Results

The results of the physicochemical analyses are presented in Table 1. Among the parameters evaluated in the sample of raw leachate, the nitrogen compounds in the series, ammoniacal nitrogen and total Kjeldahl nitrogen, showed very high values. The other parameters, with the exception of manganese, were found to be within the emission limits established in the Consema Resolution No. 128/2006 (which sets emission standards for the discharge of liquid effluent to superficial waters in the State of the Rio Grande do Sul). A change was observed in the characteristics of the leachate after the biological treatment. There is a reduction in the values of conductivity, BOD5, COD, chlorides, total phosphorus, turbidity and metals, which demonstrates the efficiency of the treatment. In contrast, an increase in the concentration of nitrite and nitrate was observed. Total Kjeldahl Nitrogen parameter was still found to be outside the limit set by state law (20.0 mg/L). The biodegradability of the leachate obtained by the ratio BOD5/COD ratio shows low values, both for the raw sample (0.17) and for the treated sample (0.23).

Table 1
Results of physicochemical analyses of the samples of raw and treated leachate and effluent emission standards of state law in effect (Consema Resolution No. 128/06, Rio Grande do Sul, 2006Rio Grande do Sul. Conselho Estadual do Meio Ambiente – CONSEMA, 2006. Resolução nº 128/06. Dispõe sobre a fixação de Padrões de Emissão de Efluentes Líquidos para fontes de emissão que lancem seus efluentes em águas superficiais no Estado do Rio Grande do Sul. Diário Oficial do Estado, Porto Alegre. 7 dec. Available from: Disponível em: <http://www.sema.rs.gov.br/conteudo.asp?cod_menu=216&cod_conteudo=7206>. Access in: 11 Fev. 2013.
http://www.sema.rs.gov.br/conteudo.asp?c...
), considering a flow rate of up to 100m³ per day.

The results of the toxicity assessment in A. cepa are presented in Table 2. Both leachate samples showed a reduction in root growth, but only post-biological treatment leachate showed a significantly lower growth rate (64%) than the control (p = 0.036).

Table 2
Root growth of A.cepa exposed to samples of raw and treated leachates, and comparison with negative control.

The results of seed germination and root growth in Lactuca sativaand Eruca sativa are shown in Table 3. The exposure of L. sativa and E. sativa seeds to the raw and treated leachate samples did not cause a significant reduction in the germination rate, when compared to the control group. For the other toxicity parameter assessed, namely root growth, the raw leachate caused a significant reduction (p = 0.0001) in L. sativa, when compared to both the negative control and the treated leachate. The same effect was observed in E. sativa, but in this case the differences were closer to the statistical significance threshold (p=0.055).

Table 3
Seed germination and root growth in L. sativa and E. sativa exposed to samples of raw and treated leachate and comparison with negative control.

4 Discussion

The monitoring of landfill leachate after treatment, in order to ensure safe levels for its disposal in the environment, can be accomplished through a series of physicochemical parameters (Barker and Stuckey, 1999Barker, DJ. and Stuckey, DC., 1999. A review of soluble microbial products (SMP) in wastewater treatment systems. Journal of Water Research, vol. 33, no. 14, p. 3063-3082. http://dx.doi.org/10.1016/S0043-1354(99)00022-6.
http://dx.doi.org/10.1016/S0043-1354(99)...
; Baun and Christensen, 2004Baun, DL. and Christensen, TH., 2004. Speciation of heavy metals in landfill leachate: a review. Waste Management & Research : the Journal of the International Solid Wastes and Public Cleansing Association, ISWA, vol. 22, no. 1, p. 3-23. http://dx.doi.org/10.1177/0734242X04042146. PMid:15113110.
http://dx.doi.org/10.1177/0734242X040421...
). However, none of these parameters alone is able to determine whether the sample may have toxic effects on aquatic biota (Rizzo, 2011Rizzo, L., 2011. Bioassays as a tool for evaluating advanced oxidation processes in water and wastewater treatment. Water Research, vol. 45, no. 15, p. 4311-4340. http://dx.doi.org/10.1016/j.watres.2011.05.035. PMid:21722938.
http://dx.doi.org/10.1016/j.watres.2011....
). In this sense, the bioassays are useful tools for assessing the risks to the biota posed by pollutants (Knie and Lopes, 2004KNIE, JLW. and LOPES, EWB. 2004. Testes ecotoxicológicos: métodos, técnicas e aplicações. Florianópolis: FATMA. 289 p.). In southern Brazil, studies assessing the toxicity of landfill leachates are still scarce (Bortolotto et al., 2009Bortolotto, T., Bertoldo, JB., Silveira, FZ., Defaveri, TM., Silvano, J. and Pich, CT., 2009. Evaluation of the toxic and genotoxic potential of landfill leachates using bioassays. Environmental Toxicology and Pharmacology, vol. 28, no. 2, p. 288-293. http://dx.doi.org/10.1016/j.etap.2009.05.007. PMid:21784018.
http://dx.doi.org/10.1016/j.etap.2009.05...
).

Germination and root growth tests allow for an assessment of acute toxicity, both of a pure pollutant and of a complex mixture (Torres et al., 2003Torres, AC., Nascimento, WM., PAIVA, SAV. and ARAGAO, FAS., 2003. Bioassay for detection of transgenic soybean seeds tolerant to glyphosate. Pesquisa Agropecuaria Brasileira, vol. 38, no. 9, p. 1053-1057. http://dx.doi.org/10.1590/S0100-204X2003000900005.
http://dx.doi.org/10.1590/S0100-204X2003...
). Toxicity tests based on seed germination and root growth have been proposed by government agencies as part of the evaluation of the potential for contamination of waste and effluents disposed into the environment (USEPA, 1996U.S. Environmental Protection Agency – USEPA, 1996. Proposed guidelines for ecological risk assessment. Washington: Risk Assessment Forum. (EPA 630-R95-002B).). Among the possible environmental contaminants, ammonium, volatile organic acid, heavy metal and salt contents can cause harmful effects on plant development, by inhibiting seed germination or root growth (Varnero et al2007Varnero, MT., Rojas, C. and Orellana, R., 2007. Índices de fitotoxicidad en residuos orgánicos durante el compostaje. Revista de la Ciencia del Suelo y Nutrición Vegetal, vol. 7, no. 1, p. 28-37.).

In this study, the seed germination parameter was considered to be less sensitive to the toxicity of the leachate. Similar results have also been obtained by other authors (Kapustka et al., 1995Kapustka, LA., Lipton, J., Galbraith, H., Cacela, D. and Lejeune, K., 1995. Metal and arsenic impacts to soils, vegetation communities and wildlife habitat in Southwest Montana uplands contaminated by smelter emissions: II. Laboratory phytotoxicity studies. Environmental Toxicology and Chemistry, vol. 14, no. 11, p. 1905-1912. http://dx.doi.org/10.1002/etc.5620141112.
http://dx.doi.org/10.1002/etc.5620141112...
; Gunderson et al., 1997Gunderson, CA., Kostuk, JM., Gibbs, MH., Napolitano, GE., Wicker, LF., Richmond, JE. and Stewart, AJ., 1997. Multispecies toxicity assessment of compost produced in bioremediation of an explosives-contaminated sediment. Environmental Toxicology and Chemistry, vol. 16, no. 12, p. 2529-2537. http://dx.doi.org/10.1002/etc.5620161214.
http://dx.doi.org/10.1002/etc.5620161214...
; Meier et al., 1997Meier, JR., Chang, LW., Jacobs, S., Torsella, J., Meckes, MC. and Smith, MK., 1997. Use of plant and earthworm bioassays to evaluate remediation of soil from a site contaminated with polychlorinated biphenyls. Environmental Toxicology and Chemistry, vol. 16, no. 5, p. 928-938. http://dx.doi.org/10.1002/etc.5620160512.
http://dx.doi.org/10.1002/etc.5620160512...
; MarČiulionienė and Montvydienė, 2002MarČiulionienė, D. and Montvydienė, D., 2002. Application of plants test-organisms in ecotoxicological investigations. Botanica Lithuanica, vol. 4, p. 75-90.). In this aspect, substances considered to be toxic seem to not directly affect the process of ontogeny of the seed, in the transition from heterotrophic to autotrophic metabolism. The direct contact of the meristematic tissue of the root with the toxic effluent probably causes an increased sensitivity, influencing permeability, production of growth hormones and cell differentiation (Kummerová and Kmentová, 2004Kummerová, M. and Kmentová, E., 2004. Photoinduced toxicity of fluoranthene on germination and early development of plant seedling. Chemosphere, vol. 56, no. 4, p. 387-393. http://dx.doi.org/10.1016/j.chemosphere.2004.01.007. PMid:15184002.
http://dx.doi.org/10.1016/j.chemosphere....
).

The evaluation of root growth indicates that Lactuca sativa and Allium cepa are sensitive to the toxic effects of substances present both in raw and treated leachates. According to Žaltauskaitė and Čypaitė (2008)Žaltauskaitė, J. and Čypaitė, A., 2008. Assessment of landfill leachate toxicity using higher plants. Environmental Research. Engineering and Management, vol. 4, p. 42-47., root growth is the parameter with the highest sensitivity in the evaluation of toxicity using plant species. Raw leachate was found to be toxic only for L.sativa. Studies have found that the lettuce seed is very sensitive to the presence of metals and organic compounds, which makes it suitable for testing the toxicity of effluents (Wang, 1987Wang, W., 1987. Root elongation method for toxicity testing of organic and inorganic pollutants. Environmental Toxicology and Chemistry, vol. 6, no. 5, p. 409-414. http://dx.doi.org/10.1002/etc.5620060509.
http://dx.doi.org/10.1002/etc.5620060509...
; Toussaint et al., 1995Toussaint, MW., Shedd, T., Van Der Schalie, WH. and Leather, GR., 1995. A comparison of standard acute toxicity tests with rapid-screening toxicity tests. Environmental Toxicology and Chemistry, vol. 14, no. 5, p. 907-915. http://dx.doi.org/10.1002/etc.5620140524.
http://dx.doi.org/10.1002/etc.5620140524...
). The inhibition of L. sativa root growth in raw leachate samples has also been reported by Žaltauskaitė and Čypaitė (2008)Žaltauskaitė, J. and Čypaitė, A., 2008. Assessment of landfill leachate toxicity using higher plants. Environmental Research. Engineering and Management, vol. 4, p. 42-47., with root growth inhibition reaching up to 80%, when compared to the control. In contrast, after biological treatment, the leachate was found to be toxic only for A. cepa. The reason for this variable response on the tested species could be attributed to inherent differences between the species, such as tissue permeability, differential uptake and metabolism (Cutillo et al. 2003Cutillo, F., D’Abrosca, B., DellaGreca, M., Di Marino, C., Golino, A., Previtera, L. and Zarrelli, A., 2003. Cinnamic acid amides from . Chenopodium album: effects on seeds germination and plant growthPhytochemistry, vol. 64, no. 8, p. 1381-1387. http://dx.doi.org/10.1016/S0031-9422(03)00511-9. PMid:14630003.
http://dx.doi.org/10.1016/S0031-9422(03)...
).

The physicochemical analyses indicate that the leachate presents most parameters within the boundaries of what is acceptable by law, except for nitrogen compounds. However, it is worth noting that some parameters detected in high concentrations in this study, such as chloride, nitrate, nitrite and conductivity, have no legal limits for disposal. The levels of metals detected in both samples of leachate were low, thus indicating a typical domestic waste landfill (Christensen et al, 2001Christensen, TH., Kjeldsen, P., Bjerg, PL., Jensen, DL., Christensen, JB., Baun, A., Albrechtsen, HJ. and Heron, G., 2001. Biogeochemistry of landfill leachate plumes. Applied Geochemistry, vol. 16, no. 7-8, p. 659-718. http://dx.doi.org/10.1016/S0883-2927(00)00082-2.
http://dx.doi.org/10.1016/S0883-2927(00)...
).

Some results of this study cast doubt on the apparent effectiveness of biological treatment, which is evidenced only when considering the parameters contained in the legislation. The biodegradability of the treated leachate, obtained by the BOD5/COD ratio, was 0.23, while the minimum value for an effective biological treatment is 0.3 (Scott and Ollis, 1995Scott, JP. and Ollis, DF., 1995. Integration of chemical and biological oxidation processes for water treatment: review and recommendations. Environment and Progress, vol. 14, no. 2, p. 88-103. http://dx.doi.org/10.1002/ep.670140212.
http://dx.doi.org/10.1002/ep.670140212...
; Marco et al., 1997Marco, A., Esplugas, S. and Saum, G., 1997. How and why to combine chemical and biological processes for wastewater treatment. Water Science and Technology, vol. 35, no. 4, p. 321-327. http://dx.doi.org/10.1016/S0273-1223(97)00041-3.
http://dx.doi.org/10.1016/S0273-1223(97)...
; Parra et al., 2002Parra, S., Malato, S. and Pulgarin, C., 2002. New integrated photocatalytic-biological flow system using supported TiO and fixed bacteria for the mineralization isoproturon. 2Applied Catalysis B: Environmental, vol. 36, no. 2, p. 131-144. http://dx.doi.org/10.1016/S0926-3373(01)00293-4.
http://dx.doi.org/10.1016/S0926-3373(01)...
). Furthermore, the phytotoxicity tests showed that toxicity also occurs after conventional biological treatment, thus corroborating the results found by other studies on the toxicity of treated effluents (Oral et al., 2007Oral, R., Meriç, S., De Nicola, E., Petruzzelli, D., Della Rocca, C. and Pagano, G., 2007. Multi-species toxicity evaluation of a chromium-based leather tannery wastewater. Desalination, vol. 211, p. 48-57. http://dx.doi.org/10.1016/j.desal.2006.02.084.
http://dx.doi.org/10.1016/j.desal.2006.0...
; De Nicola et al., 2007De Nicola, E., Meriç, S., Della Rocca, C., Gallo, M., Iaccarino, M., Manini, P., Petruzzelli, D., Belgiorno, V., Cheggour, M., Di Gennaro, A., Moukrim, A., Tünay, O. and Pagano, G., 2007. Wastewater toxicity of tannin- versus chromium-based leather tanneries in Marrakesh, Morocco. Archives of Environmental Contamination and Toxicology, vol. 53, no. 3, p. 321-328. http://dx.doi.org/10.1007/s00244-006-0181-5. PMid:17728989.
http://dx.doi.org/10.1007/s00244-006-018...
; Bortolotto et al., 2009Bortolotto, T., Bertoldo, JB., Silveira, FZ., Defaveri, TM., Silvano, J. and Pich, CT., 2009. Evaluation of the toxic and genotoxic potential of landfill leachates using bioassays. Environmental Toxicology and Pharmacology, vol. 28, no. 2, p. 288-293. http://dx.doi.org/10.1016/j.etap.2009.05.007. PMid:21784018.
http://dx.doi.org/10.1016/j.etap.2009.05...
). This occurs because some toxic chemicals will not undergo degradation during wastewater treatment, owing to a high degree of persistence. Moreover, waste treatment does not always reduce the toxicity of an effluent and, in some instances, may increase toxicity (Claxton et al., 1998Claxton, LD., Houk, VS. and Hughes, TJ., 1998. Genotoxicity of industrial wastes and effluents. Mutation Research, vol. 410, no. 3, p. 237-243. http://dx.doi.org/10.1016/S1383-5742(98)00008-8. PMid:9630652.
http://dx.doi.org/10.1016/S1383-5742(98)...
).

This study has shown that the higher plants species L. sativa and A. cepa can be effectively used to assess toxicity of landfill leachate and that an integrated analysis of wastewaters should be considered, in which chemical analysis can determine the presence and concentrations of compounds, while bioassays can evaluate the toxic and synergistic effects of these compounds. Regarding the toxicity of leachate, additional knowledge is required in order to address the potential toxicity of untreated leachate and the efficiency of treatment technology considering the influence of environmental conditions on the dynamics of the decomposition processes that take place in the landfill.

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Publication Dates

  • Publication in this collection
    May 2015

History

  • Received
    24 May 2013
  • Accepted
    28 Aug 2013
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