Comparative Observation of Brown and Green hydra Susceptibility to Aluminum Ions

Aluminum is one of the most abundant chemical elements in the Earth's crust. The effect of aluminum on living beings was little known until recently. Since it is possible for the aluminum to be drained to surface and subterranean waters and to present the potential environmental danger for freshwater organisms and ecosystems, the aim of this research was to explore the effect of concentrated aluminum ions in aquatic environment and to observe the extent of damage it can do to brown and green hydra. Hydra is a member of the phylum Cnidaria, usually found in unpolluted freshwater. It has a simple, cylindrical body with an adhesive foot on one end and a mouth surrounded by six to eight tentacles on the other. It comprises two cellular layers separated by mesoglea. Green hydra forms a symbiotic relationship with algae of Chlorella genus. Hydras regenerate at a tremendous rate. Comparative static toxicity test was performed using the individuals of brown (Hydra oligactis Pallas, 1766 ; sort S1M-K1) and green (Hydra viridissima Pallas, 1766 ; sort S1J-J1) hydra. They were treated with seven concentrations of aqueous solution of aluminum sulphate (25, 50, 80, 100, 150, 200 and 250 mg/L ; Kemika, Croatia) in laboratory conditions (22.80 C) in subacute exposure for five days and compared to the control groups of organisms. After the exposure, animals were put in clean aquarium water, recovering for ten days. For cytological and histological analysis hydras were fixed in Bouine fixative after the period of recovery. Preparations 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. Histomorphological and morphometrical analysis was performed by using Lucia G DXM1200 version 4.81 software. Micrographs were made by using Reichert and Nikon Eclipse E600 microscopes, Pentax and Nikon DXM1200 cameras. Higher concentrations of aluminum triggered greater morphological and cytological damages. Both mucous secretion of the foot region and tentacle reduction were noted. Cytotoxic effects of higher concentrations yielded a greater number of aluminum containing cells and larger deposition surface in the cells. Aluminum depositions were found in ectodermal cells only, in the form of single and multiple (2-4 separate) depositions and clusters. No significant differences concerning aluminum depositions were observed between brown and green hydra. Control animals did not show any changes. Aluminum was proved to be a potentially hazardous freshwater pollutant and showed a strong deleterious effect on hydras. In spite of its potent deleterious impact, hydras regenerated nearly completely as only aluminum deposits remained. Since depositions were found in ectodermal layer only, we suggest that mesoglea could present an aluminum buffer in itself. This was the first time green and brown hydras were treated with aluminum ions as well as the first time they were stained with eriochrome cyanine, using an appropriately modified technique. The results of this experiment provided many new interesting aspects for further research on evolutionary and ecotoxicological issues of hydra symbiosis, including TEM and SEM.