Determinação do valor de prevenção para o chumbo em solos: testes fitotoxicológicos

Abstract

Evaluation and diagnosis of soil quality is usually assessed by environmental agencies through the use of soil screening values, e.g., the soil prevention value (PV), a guideline that limits additions of elements or chemicals to the soil, so that its main functions are preserved. These screening values are set in Brazil by CONAMA directive 420/2009 and are the same adopted by the Environmental Company of São Paulo State (CETESB). Due to differences among the country's soils, it is necessary to validate these values seeking greater representativeness for each state. Until now, PVs have not been validated for the state of Minas Gerais and, according to the aforementioned directive, these values should be established based on phytotoxicity tests or ecological risk assessment. Thus, the aim of this work was to propose a prevention value for lead (Pb), from biological parameters obtained in phytotoxicological tests. The experiment was conducted in a greenhouse, following ISO 11269-2 recommendations. The species tested were corn, radish, rice, and beans, grown in a Latosol (LVAd) and a Cambisol (CXbd) with the following Pb concentrations (mg kg-1 of dry soil): 0, 50, 100, 200, 400, 800, 1600, and 3200 during 21 days. We evaluated the following biological parameters: emergence, growth, chlorophyll content, gas exchange, and chlorophyll a fluorescence. For each of these parameters we calculated the ecotoxicity indices: NOEC (effective concentration that there were no observable effects), LOEC (minimum effective concentration that there were observable effects) and EC50 (effective concentration which reduced 50% of the evaluated parameter). From the lower EC50 values calculated, along with EC50 values taken from the literature, we derived HC5 values (hazardous concentration to 5% of the evaluated parameters). To each HC5 value we added the Quality Reference Value (QRV) for Pb, thus obtaining the following PVs (mg kg-1 ): 104 for the LVAd, 179 for the CXbd and 132 for both soils. All these values are above the current PV established for Pb in Brazilian legislations (72 mg kg-1 ). We believe that the PV calculated for the LVAd (104 mg kg-1 ) is the most suitable to be used because of it is representativeness for both soil types, and although it is less restrictive than the current PV, he has the distinction of being consistent with the reality of soil conditions of the State of Minas Gerais. The results of this study contribute for setting a database on ecological risk assessment for the state environmental agency, yet it is still of great importance the implementation of additional work in order to improve this database. We recommend using a greater number of species and biological parameters to be evaluated in order to obtain a VP of greater representativeness.