Toxicological effects of cadmium and lead on two freshwater diatoms

In recent years, there have been significant advances in the knowledge and understanding of the pollution attributed to effects of aquatic toxic metals on fresh water benthic diatoms. In this study, the cell growth, chlorophyll a content and superoxide dismutase activity in Halamphora veneta (Kützing) Levkov and Surirella crumena Brébisson exposed to cadmium and lead, were investigated. Furthermore, in order to explore the potential function of H. veneta on environmental monitoring and environmental remediation, expression of two genes (psbA, psaB) and morphological analysis of H. veneta were carried out. The cells growth of H. veneta and S. crumena were generally inhibited with cadmium and lead exposure during 96 h, while cells density of H. veneta was significantly increased under the low concentration at 24 h cadmium exposure. Our results indicated that H. veneta had a certain tolerance to toxic metals at initial treated time. In addition, the significantly changes of chlorophyll a content and SOD activities in H. veneta and S. crumena indicated that both photosynthetic system and the antioxidant system in benthic diatom might play important roles on the toxic metals tolerant mechanism. Meanwhile, it can be confirmed that the diatom photosynthetic systems play roles on toxic metals resistance inferred from the gene expression of psbA and psaB in H. veneta. Finally, the results of scanning electron microscopy showed that there was a slightly deformation on cells following the cadmium exposure in H. veneta, while obvious deformation with cell greatly widened after lead exposure. The present work will be helpful to understand the effect mechanisms of toxic metal by comparing two kinds of diatom on cell inhibition, biological response and morphological changes, which will provide more information for possible use of benthic diatoms in bioremediation.