Avaliação de Pennisetum purpureum Schum na fitorremediação de zinco e cádmio em solo enriquecido com resíduo

Abstract

To meet growing demand for goods and services of modern society there is an increase in industrial activity, is highlighting the versatility of steel for use of its products. Meanwhile, as well as all human activity there is the generation of waste that may contain contaminants, among these heavy metals, which are arranged in an inappropriate manner pose a risk to humans and other living organisms. In soil heavy metals can exist in different chemical forms, presented each of them a degree of availability, and the total content of an indication of soil contamination. The phytoremediation is a technique of bioremediation, which uses the cultivation of plants to remediate contaminated soil and water, either by the extraction (phytoextraction) or stabilization (phytostabilization) of the contaminant in the environment. The objective was to evaluate the effect of the culture of Pennisetum purpurem Schum., the distribution of chemical fractions of zinc and cadmium in the soil, in three of pH values, after contamination with industrial waste containing high levels of these elements, and their possible influence germination and development of the plant. It was conducted in a completely randomized experiment 2x2x3 factorial system, in a sample of Bt horizon of a Argisol Yellow, contaminated and not contaminated with residue from Cia Mercantile and Industrial Ingá, with and without cultivation of Pennisetum purpurem Schum., and receiving the application of three doses of CaCO3. The soil used was collected in the municipality of Pinheiral - RJ, being part of the sample contaminated with waste (66.67 g kg-1) to raise the level pseudo-Zn total of the values above 1500 mg kg-1. The sample was contaminated and not contaminated divided into three groups each received a different dose of CaCO3 (0.00, 0,75; 1,5 mg kg-1). After being incubated for 40 days to 80% of the field capacity, there were planted three Seedpieces of Pennisetum purpurem Schum., genotype Cameroon, in each unit cultivated. At 18 days after planting and germination were evaluated at the average height of the seedlings. At 135 days after planting were collected to shoot and root plants. The substrates were sampled after hatching and at the end of the experiment. In substrates was determined the pH in water and, for the treatments that received waste, the levels of Zn and Cd in the following fractions: soluble (F1), exchangeable (F2), precipitated (F3), absorbed more strongly (F4) and residual (F5). The extractors used to determine the fractions were: deionized water, MgCl2, acetic acid, DTPA and aqua regia. The results showed that the germination and development of Pennisetum purpurem Schum. were limited by the content of Cd and mainly in fractions of Zn more bioavailable (F1, F2). The levels of Zn in the soluble fraction (F1) exceeding 125 mg kg-1, caused a reduction in the germination and the initial development of culture. The cultivation of Pennisetum purpureum Schum. promoted reduction of soil pH of all treatments, and favored the solubility of Zn of contaminated substrates. Leaf contents of Zn greater than 1380 mg kg-1 caused sharp reduction in growth and phytotoxicity symptoms. The Pennisetum purpureum Schum did not show a behavior as plants hyperaccumulative of Zn and Cd, but they showed Zn accumulation and they were efficient in the remediation of Zn and Cd.