Chronic effects of secondary effluent water on <i>Raphidocelis subcapitata</i>

<p>In the case of safety assessments for sewage effluents, it is necessary to consider chronic (long-term) effects on aquatic organism in addition to short-term effects. Here, we examined the chronic effects of secondary effluents on Raphidocelis subcapitata by repeated subcultivation. Secondary effluents diluted to 5% and 80% with MillQ water and added C medium were used as tested samples. Precultured algal cells were added in each sample (start concentration: 2x10⁵ cells/ml) and cultured at 25 °C, 1,500 Lux, and 100rpm. After 7 days of incubation, algal cells grown in each sample were replaced into new medium at each treated water-concentration. Specific growth rates of algae cells did not differ among the treated water-concentrations after repeated incubations. On the other hands, repeated cultivations in 5% treated water increased in cell numbers, though no significant change in 80% was observed. Cell sizes in 5% treated water were not significant change after repeated subcultivation, while those in 80% enlarged 2.1-fold at the 8th cultivation compared to 0% control. In the AFLP analysis, the 0% treated water was classified into the same cluster regardless of the number of passages, while the 80% treated water was classified into independent cluster. The concentration of Zn in the treated water used in this study was detected at 47.7 mg/L, which was higher than the other metals. These results may suggest that Zn may one of the factor of cell hypertrophy based on previous reports. *This research was supported by Kurita Water and Environment Foundation.</p>