Avaliação dos efeitos da contaminação de cobre no solo sobre Mentha crispa L.

Abstract

The objective of this study was to evaluate the effects of copper on Mentha crispa L., cultivated in soils contaminated with increasing doses of this metal. The experiment was carried out with eight different concentrations of Cu in five replicates, totalling 40 samples. The study was carried out under natural light and temperature conditions, in the vegetation house, from July to September 2016, respecting the 120-day growth period of Mentha crispa L.. Soil analyses were carried out to verify the physical and chemical factors characterizing the soil (Dystroferric Red Latosol), to determine the maximum Cu adsorption capacity (529.02877 mg kg-1) through the Freundlich's isotherm. From the maximum adsorption, was defined the increasing doses of contamination used in the experiment, C0 to C7, were C0 without addition of copper (control), C1 with 1/8 of the maximum capacity, C2 with 1/6, C3 with 1/4, C4 with 1/2, C5 maximum capacity, C6 double and C7 quadruple. During the period determined for the experiment, biweekly counts of the number of leaves and shoots were taken, as well as the measurement of plant length and visual symptomatology. After this period, the plant was removed from the pot, duly cleaned and dried, for then, prepare and digest the samples. The copper determination was carried out using a graphite furnace atomic absorption spectrometer, and background correction based on the Zeeman effect, with the aid of a permanent modifier (Palladium). Bioaccumulation and Translocation Factor was calculated for copper on Mentha crispa L. and statistical analysis, ANOVA and MANOVA, were carried out to analysis and validation of the results found. Effects such as chlorosis and decrease in plant growth were observed during the growing period at the highest concentrations of copper. The reduction in growth in relation to the control ranged from 20 to 25%. The decrease in the number of shoots and leaves reached 40% for C7 for both parameters. Considering the concentration of the metal in the peppermint, it accumulates mainly in the roots, being approximately six times greater in C6 and C7 than in the control (C0). For FB and FT the values found were lower than 1, which characterizes the plant as being tolerant to the contaminant and showing that it is retained in the root. At the highest concentrations C6 and C7, the average metal accumulation was 235 mg.kg-1, which is much higher than the Europeans safe limits for copper in soil (140 mg.kg-1). The results presented strongly indicate the potential of Mentha crispa L. as a phytostabilizing plant, and can be used as an option for the removal of excess Cu from the soil, a fact that can be of great importance to the crops and the development of the plants in general.