Abstract
In the present study, adsorption of dissolved phenanthrene to aqueous dispersions of a suite of different CNTs containing dissolved natural organic matter (NOM) was investigated. The study also investigated the influence of the adsorption process on the bioavailability and subsequent ecotoxicity of dissolved phenanthrene to standard freshwater test species representing two different trophic levels; the microalga Pseudokirchneriella subcapitata and the cladoceran water flea Daphnia magna. The dispersion concentration and stability of the different CNTs in different ecotoxicity media was determined with and without NOM present. In addition, the direct ecotoxicity of the CNT suite was investigated with both species at environmentally realistic dispersion concentrations.
The influence of CNT surface area and surface chemistry on phenanthrene adsorption and its subsequent ecotoxicity were investigated. Five different CNTs, including one single walled carbon nanotube (SWCNT), two multi walled carbon nanotubes (MWCNT-2 and MWCNT-3) and two functionalised MWCNTs (MWCNT-OH and MWCNT-COOH) were used in the study.
Specific surface area and surface chemistry of the CNTs appeared to be important factors in controlling both the fate of CNTs (dispersion concentration and dispersion stability) and their interaction with phenanthrene in aqueous environments. Polar surface functional groups increased the dispersion and stability of CNTs, but reduced their adsorption capacity for phenanthrene. The higher specific surface area of SWCNT compared to the MWCNTs was related to higher phenanthrene adsorption. The CNT having the highest surface area also exhibited the lowest dispersion concentration and the lowest stability in aqueous media over time.
A significant change in phenanthrene toxicity to P. subcapitata was only seen in the presence of one type of CNT (SWCNT) when considering total phenanthrene concentration in the system. Based on the measured concentrations of phenanthrene in the water phase, however, an increase in toxicity in the presence of CNTs was observed relative to phenanthrene only. This indicates that not only the phenanthrene remaining in the water, but also the phenanthrene adsorbed to CNTs, is available to the algae. An increased exposure concentration to algae attached to CNT aggregates might explain the increased toxicity observed based on the dissolved phenanthrene concentration. Data for D. magna are currently being generated.
The influence of CNT surface area and surface chemistry on phenanthrene adsorption and its subsequent ecotoxicity were investigated. Five different CNTs, including one single walled carbon nanotube (SWCNT), two multi walled carbon nanotubes (MWCNT-2 and MWCNT-3) and two functionalised MWCNTs (MWCNT-OH and MWCNT-COOH) were used in the study.
Specific surface area and surface chemistry of the CNTs appeared to be important factors in controlling both the fate of CNTs (dispersion concentration and dispersion stability) and their interaction with phenanthrene in aqueous environments. Polar surface functional groups increased the dispersion and stability of CNTs, but reduced their adsorption capacity for phenanthrene. The higher specific surface area of SWCNT compared to the MWCNTs was related to higher phenanthrene adsorption. The CNT having the highest surface area also exhibited the lowest dispersion concentration and the lowest stability in aqueous media over time.
A significant change in phenanthrene toxicity to P. subcapitata was only seen in the presence of one type of CNT (SWCNT) when considering total phenanthrene concentration in the system. Based on the measured concentrations of phenanthrene in the water phase, however, an increase in toxicity in the presence of CNTs was observed relative to phenanthrene only. This indicates that not only the phenanthrene remaining in the water, but also the phenanthrene adsorbed to CNTs, is available to the algae. An increased exposure concentration to algae attached to CNT aggregates might explain the increased toxicity observed based on the dissolved phenanthrene concentration. Data for D. magna are currently being generated.