Sorption kinetics and equilibrium of the herbicide diuron to carbon nanotubes or soot in absence and presence of algae (original) (raw)
Carbon nanotubes (CNT) are strong sorbents for organic micropollutants, but changing environmental conditions may alter the distribution and bioavailability of the sorbed substances. Therefore, we investigated the effect of green algae (Chlorella vulgaris) on sorption of a model pollutant (diuron, synonyms: 3-(3,4-Dichlorophenyl)-1,1-dimethylurea, DCMU) to CNT (multi-walled purified, industrial grade, pristine, and oxidized; reference material: Diesel soot). In absence of algae, diuron sorption to CNT was fast, strong, and nonlinear (Freundlich coefficients: 105.79–106.24 μg/kgCNT·(μg/L)−n and 0.62–0.70 for KF and n, respectively). Adding algae to equilibrated diuron-CNT mixtures led to 15–20% (median) diuron re-dissolution. The relatively high amorphous carbon content slowed down ad-/desorption to/from the high energy sorption sites for both industrial grade CNT and soot. The results suggest that diuron binds readily, but – particularly in presence of algae – partially reversibly to CNT, which is of relevance for environmental exposure and risk assessment.
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Diuron Sorbed to Carbon Nanotubes Exhibits Enhanced Toxicity to Chlorella vulgaris
Carbon nanotubes (CNT) are more and more likely to be present in the environment, where they, will associate with organic micropollutants due to strong sorption. The toxic effects of these CNT-micropollutant mixtures on aquatic organisms are poorly characterized. Here, we systematically quantified the effects of the herbicide diuron on the photosynthetic activity of the green alga Chlorella vulgaris in presence of different multiwalled CNT (industrial, purified, pristine, and oxidized) or soot. The presence of carbonaceous nanoparticles reduced the adverse effect of diuron maximally by <78% (industrial CNT) and <34% (soot) at 10.0 mg CNT/L, 5.0 rug soot/L, and diuron concentrations in the range 0.73-2990 mu g/L. However, taking into account the measured dissolved instead of the nominal diuron concentration, the toxic effect of diuron was equal to or stronger in the presence of CNT by a factor of up to S. Sorbed diuron consequently remained partially bioavailable. The most pronounced increase in toxicity occurred after a 24 h exposure of algae and CNT. All results point to locally elevated exposure concentration (LEEC) in the proximity of algal cells associated with CNT as the cause for the increase in diuron toxicity.
DISS. ETH NO. 20319
In this thesis, a complex system has been built up to study in the laboratory under controlled conditions the interactions among carbon nanotubes (CNT), a model herbicide and algae. The three experimental chapters represent the various possible interactions, namely effects of carbon nanotubes to these algae, sorption of the model herbicide diuron on the CNT and the combined effects of carbon nanotubes and diuron to the algae. A brief introduction presents the topic and the questions to be addressed. This experimental work has provided insights into possible environmental interactions of carbon nanotubes, their effects on algae and their combined effects with other pollutants. It has shown that complex interactions between these nanoparticles and other pollutants may occur, such as shading and agglomeration, or synergistic toxicity, and that the consequences of exposure of organisms to such pollutant mixtures cannot be readily predicted by the fraction of desorbed pollutant. This work has also proposed mechanisms of interactions of carbon nanotubes with algae and pollutants, which should be further confirmed by subsequent research in this area. The three main chapters of the thesis are published in the peer-reviewed literature.
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