Mercúrio em solos: determinação de valores de prevenção para o Estado de Minas Gerais e avaliação de extratores para fitodisponibilidade

Abstract

The Hg is a trace element and it is potentially toxic. It is found in nature in different valence states as Hg2+, Hg+ e Hg0 and it can form organic and inorganic compounds. Hg toxicity to human beings is very concerning due to the biomagnification and so, it is of high interest to know the contents and effects of Hg in environment. For that, environmental agencies use threshold values like the prevention value (VPs) for some chemical elements. This study aimed to investigate the toxicity of Hg in soils, from the determination of the prevention value for Minas Gerais State, and a selection of an extractor that better relates with Hg contents in the aerial part of the plants was performed. The experiment was performed in a greenhouse, following the guidelines from ISO 11.269-2 e OECD-208. The species studied were Avena sativa (oat) and Phaseolus vulgaris (bean), grown in dystrophic Red Yellow Latosol (LVAd) and dystroferric Red Latosol (LVdf), contaminated with HgCl2 at the following concentrations: 0; 2,5; 5,0; 10,0; 20,0; 40,0 and 80,0 mgkg-1 of dry soils. Mehlich-1, Mehlich-3, DTPA and water were the chemical extractors used to measure the metal phytoavailability. The data referring to the biological variables that decreased with increasing Hg dose were analyzed non-linear regression models to determine the EC10 (effective concentration that reduced by 10% variable). From the calculated EC10 values, the HC5 values were derived (concentration deleterious to 5% of the evaluated variables). HC5 value was added to the Hg quality reference value, already determined, and the VP was obtained. The chemical extractors were related to the contents in the tissues of aerial parts of the plants, using Pearson correlation. The VP for Hg estimated for the species of oats, beans, Eisenia andrei and Pontoscolex corethrurus was 0.98 mg kg-1. The VP for Hg in the soil LVAd was more restrictive (3,17 mg kg-1) due to the soil characteristic that allows low Hg retention. For LVdf, the VP was 6,07 mg kg-1 , due to its clay content, character dystroferric, high contents of organic matter and high cation exchange capacity. The results are very different from the current Brazilian legislation. The value of 0.98 mg kg-1 is suggested as the preventive for Hg in soils of the State of Minas Gerais. Even being not considered an extractor for phytoavailable contents, the extractor which best correlates with Hg in soil and the absorbed from plants species was USEPA 3051A (r = 0,75). It is important to develop further studies on Hg in the soil-plant-atmosphere system in order to ensure a better understanding of its toxicity and mobility.