Fitotestes para avaliação eco-geno-toxicológica de arsênio em solos tropicais: implicações para valores de prevenção

Abstract

High levels of arsenic (As), a toxic metalloid, in the soil can pose threats to all organisms in the ecosystem. Thus, besides the soil screening guidance for this element, it is also important to focus on efforts to monitor its values in soils. Current methodologies using superior plants do not include parameters for genotoxicity studies. Therefore, this study aimed to assess the As toxicity in tropical soils using a new methodology for risk assessment that includes macroscopic aspects and mutagenic effects. In addition, we aim to provide data for Asecotoxicological screening. Seeds of Lactuca sativa, Allium cepa, Zea mays, PennisetumglaucumandPhaseolus vulgaris were exposed in Petri dishes to typical tropical soils (Oxisol and Inceptisol) and to a tropical artificial soil (TAS) containing different doses of As (0; 8; 14.5; 26; 46.5; 84; 150 and 270 mg kg-1) and stored in a B.O.D-type chamber at 24 ºC, without photoperiod, for 120 hours. After that, macroscopic (germination and growth) and microscopic (chromosomal aberrations and nuclear alterations) analyzes were performed. For the macroscopic parameters, germination was not as sensitive to evaluate the phytotoxicity of As in the tested soils and the initial development of the species was more affected in ATS, followed by Oxisol and Inceptisol. Regarding the microscopic variables, the exposure to As increased the frequency of chromosomal abnormalities and micronuclei, with a decreased frequency of the mitotic index in the cells of the root tips of A. cepa. There was a predominance of the clastogenic effects of As in the cells. The accepted values of EC50 (concentration that results in 50% inhibition of the parameters) allowed to plot the sensitivity distribution curve of the species and to obtain the threatening concentration for 5% of the tested plant species (HC5), which corresponded to a value of 11.87 mg As kg-1. This value is similar to the Prevention Value (PV) set for As in the state of Minas Gerais, Brazil. The results indicate that the new microplate methodology is valid and that the variables related to the cell cycle and DNA fragmentation are important and ought to be used in ecotoxicological tests. Therefore, it is believed that such a methodology could be an alternative to tests carried out under greenhouse conditions. This study provided important data for ecotoxicological screening of As in tropical soils.