This work investigated the cytotoxic and genotoxic potential of water from the River Paraíba do Sul (Brazil) using Allium cepa roots. An anatomo-morphological parameter (root length), mitotic indices, and frequency of micronuclei were analysed. Eight bulbs were chosen at random for treatment for 24 to 120 hours with the River water collected in the years of 2005 and 2006 from sites in the cities of Tremembé and Aparecida (São Paulo state, Brazil). Daily measurements of the length of the roots grown from each bulb were carried out throughout the experiment. Mitotic index (MI) and frequency of micronuclei (MN) were determined for 2000 cells per root, using 3-5 root tips from other bulbs (7-10). Only in the roots treated with samples of the River water collected in 2005 in Tremembé city was there a decrease in the root length growth compared to the respective control. However, a reduction in MI values was verified for both sites analysed for that year. Considering the data involving root length growth and especially MI values, a cytotoxic potential is suggested for the water of the River Paraíba do Sul at Tremembé and Aparecida, in the year of 2005. On the other hand, since in this year the MN frequency was not affected with the river water treatments, genotoxicity is not assumed for the river water sampled at the aforementioned places.

A mutagenicidade pode estar relacionada com quebras cromossômicas induzidas por poluentes ambientais. O objetivo deste estudo foi caracterizar o potencial mutagênico dos poluentes presentes na água do rio Paraíba do Sul, cidade de Tremembé-SP, analisando alterações cromossômicas em células meristemáticas de Allium cepa, no verão (abril) e inverno (agosto) de 2008. Os bulbos foram expostos aos tratamentos por 72 h: água do rio, solução de Hoagland (controle negativo) e 15 µg/L de MMS-metilmetanosulfonato (controle positivo). Em cada tratamento, 3 bulbos foram expostos, para cada bulbo, 5 lâminas foram confeccionadas. Para análise do índice mitótico (IM) e frequência de micronúcleos (MN) foram analisadas 2.000 células por raiz/lâmina e 100 células para aberrações cromossômicas (AC). Em abril, os poluentes exerceram alto potencial mutagênico nas células meristemáticas de A. cepa, a frequência de MN, stickiness (cromossomos pegajosos) e AC do tipo não identificadas, foram maiores em relação ao controle negativo. Em agosto, a única alteração encontrada em nível significante foram as pontes cromossômicas. Não houve alteração significante para o IM. Esses resultados indicam que os efluentes de origem variada estão exercendo efeitos nocivos no bioindicador utilizado, sendo importante manter o biomonitoramento e adotar medidas de controle de efluentes. Essas medidas são importantes porque essas águas são utilizadas para abastecimento público, irrigação, entre outras utilidades. Palavras-chave: poluição de rios; mutagenicidade; teste Allium cepa; aberrações cromossômicas.

Although the Allium cepa test has been widely used to identify potentially cytotoxic and genotoxic pollutants in aquatic environments, variable non-standardized choices have been made regarding the number of plant bulbs and roots analyzed. We propose numbers for bulbs and roots per bulb when comparing the frequencies of micronuclei, mitotic anomalies and mitotic index with this test. Roots that had been treated with aqueous solutions, such as water samples collected in August 2007 from the Paraíba do Sul River at the Brazilian cities of Tremembé and Aparecida; negative and positive controls were used for bioassays. The presence of pollutants in the river water had been presumed based on our previous cytological data and an official report by the São Paulo State Environmental Agency (Brazil) on presence of fecal contaminants (Tremembé and Aparecida) and elevated dissolved aluminium (Aparecida) in the water under study. The sampling of ten bulbs and five roots per bulb was found adequate for comparative studies to evaluate with the A. cepa test the potential damage inflicted by pollutants in aquatic environments. Furthermore, even one bulb and one root per bulb was sufficient in discerning this damage, thereby shortening the time required to attain a statistically confident comparative evaluation. However, to allow for the use of statistical programs based on the evaluation of average values, and to avoid criticism based on genetic variability, we propose that three bulbs and three roots per bulb be considered as standard sample sizes for the A. cepa test.