Abstract
Different effects of multi-walled carbon nanotubes (MWCNTs) on the freshwater diatom Nitzschia palea were examined. MWCNTs used in this study (MWCNT) were dispersed either by sonication without (MWCNTsonicated) or with a realistic concentration (10 mg L−1) of Natural Organic Matter (MWCNT+NOM). A pocket-size device was designed to distinguish shading effect (using MWCNT suspensions as external filters) from total exposure effect of MWCNTsonicated and MWCNT+NOM on benthic algae. This study demonstrates that cell division was strongly inhibited after a 48 h exposure to MWCNT+NOM compared to MWCNTsonicated. This device did not yield a quantifiable contribution of shading to growth inhibition of MWCNTsonicated and below 10 mg L−1 of MWCNT+NOM. In all cases, neither lethal effects nor drops in photosynthetic quantum yield were observed. After a 6-d exposure, a complete growth recovery was observed for all conditions except at the highest concentration of MWCNT+NOM. Different microscopic approaches using carbohydrates markers revealed the strong affinity between MWCNT and extracellular polymeric substances (EPS) produced by N. palea. These seem to constitute a defensive mechanism against MWCNT.
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