Prevention of biofilm growth on man-made surfaces: evaluation of antialgal activity of two biocides and photocatalytic nanoparticles

As algal growth on man-made surfaces impacts their appearance, biocides and surfaces with self-cleaning properties are widely used in the building and paint industries. The objective of this study was to evaluate the antialgal activity of two biocides ( triazine and isothiazoline) and photocatalytic nanoparticles of zinc oxide (20-60 nm). An aeroterrestrial green, microalgal strain of the genus Stichococcus was chosen as the test organism. By comparing a set of different structural and physiological performance parameters, lethal and also sublethal ( chronic) effects were determined. Even though the herbicide triazine effectively inhibited growth (EC50 = 1.6 mu mol l(-1)) and photosynthetic performance, structural properties (eg membrane integrity) were unaffected at the EC100 (250 mu mol l(-1)), hence this herbicide did not kill the algal cells. In contrast, and due to their multiple modes of action, isothiazoline and the photocatalytic nanoparticles ( the latter activated with low UV radiation) severely impacted all performance and structural parameters.