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Abstract
In this article, the effects of As alone and in combination with other pollutants on the flagellate Dunaliella tertiolecta were studied. Cultures of this microalga were subjected to growth-inhibition tests, according to the ISO protocol, using the same As concentration range for all tests; the results showed an obvious toxic effect for cultures exposed to As and As combined with Zn, whereas for cultures exposed to As combined with the nonionic surfactant Triton X-100 and ethylene glycol, hormetic effects were also observed. The same acetone extracts of cultures used in the growth-inhibition test were further examined using 3D visible (Vis) and attenuated total reflectance infrared (FTIR-ATR) spectroscopy. 3D Vis spectroscopy showed that As and As mixed with other pollutants did not have common dose–response effects. For example, most chlorophyll and carotenoid pigments were shown to be increased and/or decreased within the same growth-inhibition test. FTIR-ATR examination of the same solutions showed other differentiated effects of As alone and As combined with other pollutants, revealing quantitative modifications of phospholipid and fatty acid contents and structural modification of DNA and RNA. In addition, a multivariate elaboration of FITR spectra, performed by means of a multivariate statistical technique, principal component analysis (PCA), showed that the observed molecular modifications in D. tertiolecta can be clustered according to the different types of exposure to pollutants. These findings suggest that the molecular modifications caused by As exposure are also related to the type of toxic mechanism (i.e. synergic or additive) which results from the presence of other pollutants.
Acknowledgements
The authors are grateful to Dr Elena Sturchio and Dr Priscilla Boccia, Department of Production Plants and Anthropic Settlements, ISPESL in Rome, for their valuable comments to the paper. The authors are also grateful to two anonymous reviewers for their helpful comments and suggestions.