engleski

Observation of Brown Hydra Susceptibility to Aluminum Ions

Aluminum is one of the most abundant chemical elements in the Earth's crust. Due to its chemical nature, its abundance is mainly bound in various types of ore. The effect of aluminum on living beings was little known until recently (1). Aluminum is almost insoluble in water so the overall effect of its ions is very low (2). However, with the recent industrial development and high toxic gas emissions, acid rains proved to be an interesting environmental problem. Since it is possible for the aluminum to be drained to surface and subterranean waters and having thus the potential effect upon the food chains in ecosystems, the environmental danger of aluminum for the aquatic organisms and ecosystems was traced. Aluminum solubility greatly increases with decreasing pH value making the aluminum a possible toxic element in aquatic habitats. The aim of this research was to explore the potential dangers of concentrated aluminum ions in aquatic environment and to observe the extent of damage it can cause upon brown hydra. Hydra is a simple aquatic organism, a member of the phylum Cnidaria. It is usually found in unpolluted freshwater, having a cylindrical body with an adhesive foot on one end and a mouth surrounded by six to eight tentacles on the other (3). They comprise of two cellular layers separated by mesoglea (Fig. 1). Comparative toxicity test was performed using the individuals of brown hydra (Hydra oligactic Pallas, 1766, sort S1M-K1). They were treated with four concentrations of aqueous solution of aluminum sulphate (25, 50, 80, 100 mg/L ; Kemika, Croatia) in laboratory conditions (22.80 C) in subacute exposure for five days. They were compared to the control group of organisms. After the exposure animals were put in clean aquarium water, recovering for ten days. Binocular light microscope Carl Zeiss, Jena was used for morphological analysis. For cytological and histological analysis hydras were fixed in Bouine fixative after the period of recovery. Preparations were cut on the microtome Shandon Finesse 325 at 4-5 μ m. Cuts were differentially stained with 0.2% acid eriochrome cyanine, and 0.1% toluidine blue pH 4.4 and hämalaun-eosine. Using a sample of 200 cells, we determined the percentage containing aluminum depositions and measured the surface area of those depositions in comparison to the area of cells containing them. Morphometrical analysis was performed using Lucia G DXM 1200 version 4.81 software. Micrographs were made by using Reichert and Nikon Eclipse E600 microscopes, Pentax and Nikon DXM1200 cameras. Aluminum triggered numerous morphological, cytological and behavioral changes. The most prominent morphological changes were tentacle reduction and mucous secretion of the foot. Higher concentrations caused greater locomotive disorders, incoherent and sluggish reactions and migration towards water surface. Cytotoxic effects were best observed as apical region degradation of ectodremal myoepithelial cells. Zymogene cells were in the process of dedifferentiation to other cell types. They migrated towards mesoglea due to regenerative processes. Membrane degradation remained as permanent damage to both cellular layers. Aluminum depositions were found in ectodermal cells only, more abundant in the foot than in the body of hydra. Higher concentrations yielded a greater number of aluminum containing cells (Fig. 2) especially in the foot region of the animal (Fig. 3). There were no changes in the control group (Fig. 1). This was the first time hydras and aluminum were brought close in a laboratory experiment and staining was performed by eriochrome cyanine on hydras for the first time. This hydra bioassay was shown to be a useful tool for quick corroboration of expected results. Aluminum appeared to be a potentially hazardous water pollutant and showed the deleterious effects upon brown hydra. After these preliminary results, further research on symbiotic issues of green and brown hydra, including SEM and TEM, are in perspective.

brown hydra; aluminum; depositions

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