Avaliação de plantas cultivadas em solos de Minas Gerais contaminados por chumbo e derivação de seu valor de prevenção

Abstract

Lead (Pb) is a persistent element in the soil and can be transferred to plants and reach humans. It is listed by the Agency for Toxic Substances and Disease Registry as the second most dangerous chemical element. For several consecutive years, Pb was the most present element in Minas Gerais contaminated soils. The CONAMA resolution 420/2009 stipulates that the Brazilian states may define their prevention values (VP) for metals in soils. VP is defined as the maximum concentration of a substance that does not affect the major functions of the soil. The present study was carried out with the objective of evaluating the Pb ecotoxicity, in order to subsidize the determination of VP. The experiment was carried out in a greenhouse following ISO 11.269-2 and OEDC standards. The species tested were sorghum and soybean, cultivated in distrophic Red-Yellow Latosol (dRYL) and typical dystrophic Red Latosol (LVdf), both contaminated with lead acetate, in the concentration of 0, 200, 400, 800, 1.200, 1.600, 2.200 e 2.800 mg kg-1 of dry soil. In the experiment with soybean in LVdf, the concentrations were slightly modified to 0, 50, 100, 200, 400, 800, 1,600, 3,200 mg kg -1 of dry soil. The experiment lasted 21 days, counting from the germination of 50% of the control treatment. Biological variables were evaluated, such as germination, vegetative growth, antioxidant system, carbohydrates, photosynthetic apparatus and macro content and micronutrients content, as well as Pb concentration in aerial part. For each variable a value of EC50 was calculated (effective concentration causing damage in 50% of the population). Using EC50 from the variable aerial part of dry mass, together with other literature data, which include organisms other than soybean and sorghum, species sensitivity curves were generated and their respective HC5 calculated (hazardous concentration to 5% of variables evaluated). The analyzed variables were affected as a consequence of the Pb doses increase in the soils, but the sorghum showed greater tolerance to the metal when compared to the soybean. The VP obtained for LVAd was 134 mg kg-1, while for LVAd, Lvdf and CXbd, this value was 152 mg kg-1. It was not possible to obtain a VP for LVdf, in isolation. It is recommended to use the VP of 152 mg kg-1. This value is less restrictive than the VP of Resolution 420/2009 (72 mg kg-1), but represents, more appropriately, the soil conditions of Minas Gerais State.