title: Are carbon nanotube effects on green algae caused by shading and agglomeration?
abstract: Due to growing production, carbon nanotubes (CNT) may soon be found in a broad range of products and thus in the environment. In this work, an algal growth test was developed to determine effects of pristine and oxidized CNT on the green algae Chlorella vulgaris and Pseudokirchneriella subcapitata. CNT suspensions were prepared in algal test medium and characterized taking into account the suspension age, the reduced light transmittance of nanoparticle suspensions defined as shading of CNT and quantified by UV/vis spectroscopy, and the agglomeration of the CNT and of the algal cells. Growth inhibition and photosynthetic activity were investigated as end points. Growth of C. vulgaris was inhibited with effect concentrations of 50% (EC(50)) values of 1.8 mg CNT/L and of 24 mg CNT/L in well dispersed and in agglomerated suspensions, respectively, and 20 mg CNT/L and 36 mg CNT/L for P. subcapitata, respectively. However, the photosynthetic activity was not affected. Growth inhibition was highly correlated with the shading of CNT and the agglomeration of algal cells. This suggests that the reduced algal growth might be caused mainly by indirect effects, i.e. by reduced availability of light and different growth conditions caused by the locally elevated algal concentration inside of CNT agglomerates.
authors.affiliation: Empa-Swiss Federal Laboratories for Materials Science and Technology , CH-9014 St. Gallen, Switzerland.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Schwab
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Bucheli
authors.forename: Lungile P
authors.initials: LP
authors.lastname: Lukhele
authors.forename: Arnaud
authors.initials: A
authors.lastname: Magrez
authors.forename: Bernd
authors.initials: B
authors.lastname: Nowack
authors.forename: Laura
authors.initials: L
authors.lastname: Sigg
authors.forename: Katja
authors.initials: K
authors.lastname: Knauer
mesh_terms: D000460:Chlorophyta / Q000187:drug effects / Q000254:growth & development*; D004785:Environmental Pollutants / Q000737:chemistry / Q000633:toxicity*; D008027:Light; D008856:Microscopy, Fluorescence; D037742:Nanotubes, Carbon / Q000737:chemistry / Q000633:toxicity*; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology; D012044:Regression Analysis; D013056:Spectrophotometry, Ultraviolet
chemical_list: D004785:Environmental Pollutants; D037742:Nanotubes, Carbon