Estudos ecotoxicológicos sobre arsênio em solos tropicais: avaliação do valor de prevenção de arsênio

Abstract

Arsenic (As) is a trace element toxic to most living organisms and soil contamination with As is a major threat to soils and human health. Thus, developing ecotoxicological studies for As not only at global but also at local scale contributes to develop a more robust database to be used in decision-making actions related to environmental issues. Therefore, the objective of this work was to select and to use the most adequate endpoints - which were obtained in plant growth ecotoxicological assays -, in the study of the toxicity of As in tropical soils. In addition, the aim was to evaluate the effect of As contamination on soil organisms and to test the adequacy of the current soil screening value (i.e., prevention value) in Brazil for As. For this purpose, two natural soils (Latosol and Cambisol) and one artificial tropical soil (ATS) were spiked to obtain a gradient of increasing As concentrations (0; 8; 14.5; 26; 46.5; 84; 150; 270 mg of As kg -1 ) and used in trials with plants and soil organisms. For the plant trials, six plant species (Zea mays, Oryza sativa, Sorghum bicolor, Phaseolus vulgaris, Helianthus annuus and Raphanus sativus) were grown and the effect of As on the early germination count, plant height, relative leaf area, stem diameter, total germination, germination speed index, dry mass, number of completely expanded leaves, plant survival, soil plant analysis development chlorophyll level, and the final germination count were assessed. These endpoints were ranked for sensitivity (EC50 value) and reliability (range of confidence interval) in order to select the most appropriate ones. These parameters, together with As contents in the shoot and the bioconcentration factors, were used to show the toxicity of As on the studied plants. In general, higher toxicity was observed for the ATS, followed by the Latosol and the Cambisol. From the evaluated endpoints, the early germination count and the dry mass were considered the most adequate since they present the lowest EC50 values with the lowest confidence intervals. The species P. vulgaris and Z. mays were the most and least sensitive to As toxicity, respectively. Both species accumulated the lowest levels of As in the tissues. For the evaluated soil organisms, i.e., Eisenia andrei, Enchytraeus crypticus, Folsomia candida and Hypoaspis aculeifer, no effect was observed on the reproduction and survival of any of the organisms tested in the Cambisol. Just as in the plant trial, higher arsenic toxicity was observed for the ATS. The species least affected was H. aculeifer and the most affected were E. crypticus in ATS and F. candida in the Latosol. Our findings demonstrated that the current prevention value in Brazil for arsenic is protective for soils with high adsorption capacity and probably not for soil with lower arsenic adsorption capacity.