Padronização de bioensaios com Lactuca sativa L. e sua aplicação na avaliação toxicológica de efluentes contendo azocorantes tratados por foto-fenton

Abstract

Different types of toxicity assessments have been used, but for some of them there is a need for high capital investment, which is not the case with plant bioassays, which have been used with success in checking the toxicity of different substances, such as for example, the synthetic dyes used by the textile industry that have in their structures triple bonds between two nitrogen atoms (azodyes). Thus, it is necessary to standardize and understand this test, which can help predict the effects of industrial substances on living organisms. Aiming to reduce the impacts generated by these substances in environments such as vegetable cultivation, several methodologies are being used, among them the advanced oxidative processes (POAs) are highlighted due to the high efficiency of the oxidizing potential of hydroxyl radicals (·OH), which have the ability to completely oxidize most organic contaminants, converting them into water, CO2 and inorganic ions. Thus, the objective of this work is to standardize the assays with the bioindicator Lactuca sativa L. (lettuce) based on the evaluation of parameters covered in the literature (plate size, seed quantity, presence or absence of light, seed quality, quantity of the effluent used in this test and analysis of the concentrations of Na+ and SO4 2- ions) and the evaluation of the toxic effect of three reactive azodyes (orange 122, yellow 2R and red 5B) treated by advanced oxidative processes (Photo-Fenton) and application in its raw forms. The results obtained in experiments with the variables selected in the literature for the lettuce bioassays were generated from a 24-1 factorial analysis. Trends that were reflected in their response variables were highlighted, such as increased germination in environments with the presence of constant luminosity, increased radicle and aerial part in environments with lower luminosity and greater amount of effluent. The raw effluents of the dyes showed significant inhibition in the elongation of the lettuce seedlings rootlets, and this statistical analysis was performed using the Dunnett test with a significance level of 5%. The Foto-Fenton process showed high decolorization efficiency, being able to remove up to 100% of the yellow 2R coloration, but this treatment for Red 5B showed an inhibition in all parameters when applied with its untreated effluent. From this test, significant inhibitions were noticed, making it necessary a detailed analysis of the accumulation factor of chemical species in lettuce seedlings, which will be implemented in further studies.