Chromosome aberration and micronucleus frequencies in Allium cepa cells exposed to petroleum polluted water—A case study

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Abstract

In the present study, we applied Chromosome Aberration (CA) and Micronucleus (MN) tests to Allium cepa root cells, in order to evaluate the water quality of Guaecá river. This river, located in the city of São Sebastião, SP, Brazil, had been affected by an oil pipeline leak. Chemical analyses of Total Petroleum Hydrocarbons (TPHs) and Polycyclic Aromatic Hydrocarbons (PAHs) were also carried out in water samples, collected in July 2005 (dry season) and February 2006 (rainy season) in 4 different river sites. The largest CA and MN incidence in the meristematic cells of A. cepa was observed after exposure to water sample collected during the dry season, at the spring of the river, where the oil leak has arisen. The F1 cells from roots exposed to such sample (non-merismatic region) were also analyzed for the incidence of MN, showing a larger frequency of irregularities, indicating a possible development of CA into MN. Lastly, our study reveals a direct correlation between water chemical analyses (contamination by TPHs and PAHs) and both genotoxic and mutagenic effects observed in exposed A. cepa cells.

Introduction

Petroleum is a raw material that has become one of the most important sources of energy on the planet. However, the petroleum industry activities have been leading to several environmental impacts, mainly into water systems [1]. Most of the worldwide hydrocarbon environmental contaminations are related to different production stages of such industry, from oil extraction to refinement process, by the release of pollutants likely to affect the environment [2]. Moreover, among the hydrocarbons described so far, the Polyclyclic Aromatic Hydrocarbons (PAHs), present in crude oil, are some of the most dangerous environmental contaminants due to their toxic, carcinogenic, and mutagenic effects [3].

Plant test systems have been often employed as genetic models for the screening and monitoring of environmental pollutants [4], [5]. These tests have proved to be of great value, since they combine a high sensibility to detect mutagens in different environments and a great capacity to evaluate distinct genetic endpoints, from point mutations to chromosomal aberrations, either in individual cells or in organs such as leaves, pollens and endosperm [5].

Among the several higher plants used as test organisms, the species Allium cepa has been used as an efficient genetic standard for environmental monitoring. Since Levan's introduction of this species as test system [6], the Allium test protocol has been improved in order to accomplish a better assessment of complex environmental contaminations [4], [7], [8]. After such adjustments, this test became more popular and its sensitivity in detecting genetic damages induced by environmental pollutants was increased [9], [10], [11], [12], [13], [14]. Moreover, the species A. cepa also presents other advantages, including low raising costs, easy handling, and suitable chromosomal features; this plant bears large and few chromosomes (2n = 16) what facilitates the evaluation of chromosome damages and/or disturbances in cell division cycle, including eventual aneuploidy risks [4], [15].

Since petroleum hydrocarbon contamination (mainly PAHs) may cause several environmental problems, the present study aimed to analyze the genotoxic and mutagenic effects induced by petroleum polluted waters, using A. cepa root cells as a test system.

Section snippets

Characterization of the studied geographic area and water sampling

The area chosen in the present study was the Guaecá river, located in the Serra do Mar State Park, next to the city of São Sebastião-SP, Brazil (Fig. 1). This river runs through a permanent preservation area, being characterized by a high surrounding biodiversity and by the proximity to the city water reservoir. By February 2004, the river waters were impacted by an oil pipeline leak. As the pipeline is located underground, the leaked oil first affected the underground waters. Later, the oil

Results

Amongst water samples, only that from S1, collected in the dry season, presented TPHs and PAHs concentrations above the quantification limit of the chemical analyses methods performed (Table 1).

The results from CA assay and MN test in A. cepa root cells are shown in Table 2, Table 3.

In relation to the positive control treatments, the data showed a lack of a consistent response, since significant MN and CA values were absent, respectively, in July 2005 and February 2006.

No significant

Discussion

Firstly, the lack of consistent response in the positive control treatment (MMS) needs to be ascertained. Such fact can be explained because the MMS used in the tests were stored for more than 6 months. According to Rank [18], the MMS is quickly degraded, even when kept at cold temperature, and therefore, it is recommended not to be used for over half a year. Because we were unaware of such issue, the assays were carried out with an “old-stored MMS”, leading to the weak effects of the positive

Acknowledgements

We would like to thank Dr. João Carlos C. Milanelli and Instituto Florestal, São Sebastião-SP, Brazil, for his collaboration during field works, the Centro de Biologia Marinha (CEBIMar), Universidade de São Paulo (USP) for providing the weather data about the sampling periods and the Programa de Recursos Humanos ANP/FINEP/MCT-CTPETRO, PRH-05 of Universidade Estadual Paulista (UNESP), Rio Claro-SP, Brazil, for the financial support.

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