Hydrogels are very attractive materials due to their multifunctional properties. Many natural polymers, such as polysaccharides, are used for the preparation of hydrogels. The most important and commonly used polysaccharide is alginate because of its biodegradability, biocompatibility, and non-toxicity. Since the properties of alginate hydrogel and its application depend on numerous factors, this study aimed to optimize the gel composition to enable the growth of inoculated cyanobacterial crusts for suppressing the desertification process. The influence of alginate concentration (0.1–2.9%, m/v) and CaCl₂ concentration (0.4–4.6%, m/v) on the water-retaining capacity was analyzed using the response surface methodology. According to the design matrix, 13 formulations of different compositions were prepared. The water-retaining capacity was defined as the system response maximized in optimization studies. The optimal composition of hydrogel with a water-retaining capacity of about 76% was obtained using 2.7% (m/v) alginate solution and 0.9% (m/v) CaCl₂ solution. Fourier transform infrared spectroscopy was used for the structural characterization of the prepared hydrogels, while the water content and swelling ratio of hydrogels were determined using gravimetric methods. It was concluded that alginate and CaCl₂ concentrations play the most important role regarding the gelation time, homogeneity, water content, and swelling ratio of the hydrogel.

A large part of Central Serbia experiences continual shortage of sufficient ground water resources. For that reason, more than 20 reservoirs serve as drinking water suppliers. Significant and persistent cyanobacterial “blooms” have been recognized in nine of them. Samples for cyanotoxin analyses were taken during and after “blooms” in Ćelije Reservoir and from Kruševac town-supplied tap water from that reservoir two days later. Concentration of microcystin-LR was 650 μ gL^–1 in the reservoir, while the tap water contained 2.5 μ gL^–1. In the two investigated periods, the high primary liver cancer (PLC) mortality of 11.6 from 1980–1990 and extremely high PLC incidence of 34.7 from 2000–2002 were observed in the regions affected by heavy cyanobacterial “blooms.” In contrast, PLC mortality and incidence rates were substantially lower in the regions not affected by cyanobacterial blooms: in 1980–1990 the rate of PLC mortality amounted to 2.7 in Kosovo, 7.6 in Vojvodina, and 8.3 in the non-affected regions of Central Serbia; while in 2000–2002 PLC incidence amounted to 4.1 in Kosovo, 5.2 in Vojvodina, and 13.6 in the non- or less-affected regions of Central Serbia. Keeping in mind that the most affected PLC regions in Central Serbia (Toplički, Niški, and Šumadijski regions) have the water supply systems based on six reservoirs found regularly in bloom during summer months and that some of the regions are also connected with two boundary “blooming” reservoirs, representing a total of eight of nine blooming reservoirs, it is easy to presume that the PLC incidence could be related to drinking water quality. The uneven geographic distribution of liver cancer in Serbia is conspicuous and hot spots could be related to drinking water supply. It is very clear that the high-risk regions for PLC occurrence correspond with drinking water reservoirs continually found with cyanobacterial blooms, and the low risk regions correspond with water supplies not affected by cyanobacteria.