Separating toxicity and shading in algal growth inhibition tests of nanomaterials and colored substances.

Nanoparticles and colored substances can inhibit algal growth by light shading and chemical toxicity. This study presents two complementary approaches to account for shading in algal growth inhibition tests of engineered nanomaterials (ENMs) and colored substances. The first approach distinguishes between shading effects and toxicity by varying the light path in parallel algal growth inhibition tests. This Multiple Path-Length (MPL) test was applied to TiO2 ENMs and the colored substances sodium picramate and Rhodamine B. A left shifting of concentration-response curves, with increasing light path lengths, indicated shading for Rhodamine B, sodium picramate and TiO2 ENMs. EC50-values obtained at the shortest light path length were generally found best suited to quantify the toxicity of ENMs and colored substances. The second approach addresses shading at the cellular level, where particles can attach to the cell surface and affect photo-pigment content and composition. Pigments associated with photosystem I and II were determined at varying light intensities and concentrations of TiO2 ENMs. The photo-pigments that increased in response to physical shading, decreased after TiO2 ENMs exposure. This indicates that toxicity rather than cellular shading dominated the response of algae exposed to TiO2 ENMs. Additional tests were conducted with the nanomaterials CeO2 and goethite to evaluate the applicability of this approach to other ENMs. On this basis, we recommend MPL testing for determining EC50-values that are not confounded by shading in the test solution, and the pigment-based approach for investigating shading on the cellular level.

Temporal and spatial variability of phytoplankton monitored by a combination of monitoring buoys, pigment analysis and fast screening microscopy in the Fehmarn Belt Estuary.

For 2 years, a baseline investigation was carried out to collect reference information of the present environmental status in the Fehmarn Belt and adjacent area. The temporal and spatial variability of phytoplankton was monitored by a combination of monitoring buoys, pigment analysis and fast screening microscopy. The overall phytoplankton succession in the Fehmarn Belt area was found to be influenced primarily by the seasonal changes, where various diatoms dominated the spring and autumn blooms and flagellates like Chrysochromulina sp., Dictyocha speculum and various dinoflagellates were occasionally abundant in late spring and summer. The phytoplankton groups were remarkably uniform horizontally in the investigation area while large differences in both biomasses and composition of individual phytoplankton groups were seen vertically in the water column, especially in the summer periods, in which the two-layer exchange flow between the North Sea and the Baltic Sea is showing a particularly strong stratification in the Fehmarn Belt. The chlorophyll a concentrations ranged continuously from 1 to 3 µg/L at the three permanent buoy stations during the 2 years of monitoring, except for the spring and autumn blooms where chlorophyll a increased up to 18 µg/L in the spring of 2010 and up to 8 µg/L in the autumn of 2009. Recurrent blooms of filamentous cyanobacteria are common during the summer period in the Baltic Sea and adjacent areas, but excessive blooms of cyanobacteria did not occur in 2009 and 2010 in the Fehmarn Belt area. The combination of the HPLC pigment analysis method and monitoring buoys continuously measuring fluorescence at selected stations with fast screening of samples in the microscope proved advantageous for obtaining information on both the phytoplankton succession and dynamic and, at the same time, getting information on duration and intensity of the blooms as well as specific information on the dominant species present both temporally and spatially in the large Fehmarn Belt area.