RESUMO -(Efeitos do cádmio na anatomia e na fotossíntese de duas macrófitas aquáticas). As macrófitas aquáticas vêm sendo usadas no monitoramento de águas poluídas por metais pesados, dessa forma, avaliou-se a capacidade fitorremediadora de Alternanthera philoxeroides (Mart.)
Palavras-chave: Alternanthera philoxeroides, fluorescência da clorofila, metal pesado, Polygonum ferrugineumABSTRACT -(Effects of cadmium on the anatomy and photosynthesis of two aquatic macrophytes). Aquatic macrophytes have been used to monitor waters polluted by heavy metals. The phytoremediation capacity of Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae) and Polygonum ferrugineum Wedd. (Polygonaceae) was therefore evaluated. These two species were submitted to treatments of 0, 25 and 50 mg L -1 Cd in nutritive solution. Seven days after treatment application, leaf gas exchange and chlorophyll fluorescence were measured in mature and fully expanded leaves. Fragments of roots, shoots and leaves were fixed in FAA 70, embedded in historesin and cut with a rotating microtome, and the sections stained with 1% toluidine blue. The Cd content in plant biomass was determined using ICP-MS. In P. ferrugineum exposed to 25 and 50 mg L -1 Cd, an increase in the central leaf-vein-and root-aerenchyma lacunae was observed. Furthermore, in plants exposed to 50 mg L -1 Cd, an increase in leaf glandular trichomes and mesophyll compacting was observed. In the stem of A. philoxeroides exposed to 50 mg L -1 Cd, the nuclei of the cortex cells became elliptic, and at 25 and 50 mg L -1 Cd, the number of druses in the cells of the central leaf vein was reduced. Cd accumulation was higher in the roots, followed by the stem and leaves in A. philoxeroides. The net photosynthesis rate of P. ferrugineum was more affected by Cd than that of A. philoxeroides. There was no variation in photosystem II (Fv/Fm) activity between the two species and the Cd treatments. A. philoxeroides was more cadmium-tolerant than P. ferrugineum, which indicates its capacity for use in phytoremediation programs.
In the last years metal pollution has become one of the most important environmental problems. Concerning the high toxicity of these elements, both sensitive analytical measurements and methods for the control of the ecosystem are required to reveal and localize metals on organism. Due to high transportations rates and exchange phenomena of sediment bound metals and changes of imission concentrations, the estimation of pollution in aquatic systems like the river Cachoeira is problematic. Recent studies have demonstrated that the river´s water basin is polluted by several metals (M.I.G. Severo, A.H. Oliveira, P. A. O. Mangabeira, M.R.V. Veado, P. Galle and R.B. Souza[1]). Water and sediments samples can only refect momentary concentrations. In this context the use of biomonitoring methods offers the possibility to assess the heavy metals pollution. Secondary Ion mass Spectrometry (SIMS) and Inductively coupled plasma mass spectrometry (ICP-MS) were used to localize chromium in Eichhornia crassipes. The pollution in chromium is bound to the clandestin tannery activity on the basin of the Cachoeira region south of Bahia (Brazil). Measurements were performed with the scanning ion microprobe instrument developed at the University of Chicago (UC-HRL) (Levi-Setti, Chabala, Gavrilov, Espinosa and Le Beau [5]. A focused gallium scanning ion probe is used, in conjunction with an efficient secondary ion mass spectrometry system, to obtain high lateral resolution mass-resolved images of specimen surfaces. Secondary ions were collected and analyzed with a magnetic sector mass spectrometer. Each detected secondary ion is recorded discretely (pulse counting) for further analysis. The SIMS signals are detected by na active film electron multiplier (ETP AF820), operating in the pulse counting mode and capable of accepting count rates up to 50 MHz. The images containing 512 x 512 picture elements from single square raster scans, are stored in digital memory with a KONTRON IMCO image processing system for subsequent analysis.Scanning of the samples to locate chromium is carried out using the 52 Cr + SIMS signal displayed on a CRT, at fields of view 80 and 160 µm wide, when detecting positive ions.
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