Porphyridum cruentum (Ege-MACC 09) was obtained from the microalgae culture collection of Ege University (Ege-MACC). The culture medium was F/2 prepared in sea water. The pH was adjusted to 7.5 after the medium was sterilized by autoclaving. Exponentially growing cells were used for the inoculum. The microalgae were grown in a 5 L bio-reactor continuously illuminated at a light intensity of 80 μmol photon m^–2 s^–1 with fluorescent cool-white lamps. The culture temperature was controlled at  23° C. The vessel was aerated at 1.5 L/min. The aeration gas was filter sterilized by passing through a 0.22 μm mili­pore membrane filter. At the late exponential phase of growth (after ~16-21 days), the cells were separated by centrifugation (10⁴ rpm, 20 min.). The supernatant contain­ing the extracellular polysaccharides was collected and lyophilized. The lyophilized exopolysaccharide was dis­persed in bidistilled water or in an appropriate salt solution by prolonged gentle stirring using a magnetic stirrer under ambient conditions [14].

      After the appropriate institutional ethics committee and informed consent procedures had been completed, we obtained blood samples from five subjects (one female and four males who were between 20 and 35 years of age) who had worked as radiology technicians for at least 5 years and been exposed to low dose radiation (0.05 Sievert/ year). Blood lymphocytes (PBL) were isolated by phycol-hypaque separation and cultured at 37° C in 5 mL of cul­ture medium containing 100 U/mL penicillin, 100 mcg/mL streptomycin (KO3-031-1B; Biological Industries, Jerusa­lem, Israel), 1200 mM L-glutamine (K 0283; Biochrome AG, Berlin, Germany), 1.5% Phytohemagglutinin (M5030; Biochrome AG) and 20% fetal calf serum in basic medium RPMI 1640 (01-106 1B; Biological Industries). Mitomy­cinC (10^–7 M) (827 BIC; Kyowa, Tokyo, Japan), βC (10^–5 M; Sigma Chemicals, Chicago, IL, USA), PC (0.015 μg/ mL and 0.0037 μg/mL), βC + PC were added to the cul­tures at the end of 48 hours. Mitosis was terminated by adding 0.1 μg/mL of Colchicine (L6211; Biochrom AG) 20 hours later. The cells were then kept at 37°C for 30 min. when 0.075 M hypotonic KCl solution was added and the cells were fixed in freshly prepared cold methanol:glacial acetic acid (3:1) solution. The metaphase preparations were stained by GTG-banding/Giemsa stain and evaluated for numeric and structural aberrations according to ISCN-1989 [15-17].

      Statistical analysis was performed using SPSS for Windows (Version 8.0). Comparisons among each culture were performed using non parametric tests (Student’s t Test). The level of critical significance was p <0.05.