Avaliação ecotoxicológica do efluente da ETE-MARATOAN utilizando sementes de Lactuca sativa L. e Cucumis sativus L.

Abstract

Domestic sewage effluents are complex mixtures of various toxic organic and inorganic compounds. Traditionally, the monitoring of effluents is carried out by physical-chemical and

microbiological parameters to prove the efficiency of the treatment. However, physical- chemical and microbiological analyzes alone are not able to predict the real effect of the effluent

on living beings. In this work, the toxic potential evaluation of domestic effluent samples from the Crateús Sewage Treatment Station (ETE - Maratoan) was carried out using phytotoxicity tests with Lactuca sativa L.(lettuce) and Cucumis sativus L. (cucumber) seeds. For this purpose, sampling was carried out in each of the treatment stages of the ETE-Maratoan: raw effluent, effluents from the facultative pond, the maturation pond and the final effluent. Successive dilutions were made only for the final effluent in order to obtain the following series: 6.25, 12.5, 25, 50 and 100%. Then, the seeds of Lactuca sativa L. and Cucumis sativus L. were placed in Petri dishes with filter paper substrate and moistened with 4 ml of each sample, under a controlled temperature of 20 ± 1 oC for a period of 120 h. At the end of the incubation period, the parameters of germination, radicle length and seedling hypocotyl were evaluated. The following measurements were calculated: Mean, Standard Error, Analysis of Variance (ANOVA), Germination Index (IG), Normalized residual germination percentage Index (IGN) and the Normalized residual radical elongation percentage index (IER). The physico-chemical analysis results showed that the effluent is in accordance with Federal and State legislation. The results of the toxicity tests indicated that there was a reduction in toxicity during the treatment stages, identified by the induction of radicle and hypocotyl growth in the effluents of the facultative and maturation ponds, for both tested species. These parameters proved to be more sensitive when compared to the germination rate. In general, the toxicity tests showed that the effluents have low acute toxicity for both species tested. Therefore, further ecotoxicological studies are recommended in order to discard any toxicity that domestic effluents may present.