Effects of carbon nanotubes on plant growth and gas exchange in Arabidopsis thaliana: first results in cradle to grave life cycle analysis

Background/Question/Methods

The benefits of using nanomaterials in modern technologies are said to be no longer questioned. Nano materials have been used to develop advanced materials and novel devices. As such, anthropogenic sources of these materials, from combustion of byproducts to intentionally manufactured, are abundant in nature. Carbon nanotubes (CNTs) are the “eminent” members of the nanomaterial family. CNTs in materials and products, e.g., cell phones, will ultimately end up in the environment. CNTs are manufactured “pure” and then distributed to a user, where the CNT is altered (functionalized) for a given use (e.g., structural material in sports equipment). To date, research on their interactions with biological organisms is at a very early stage. Moreover, they are barely on the radar of ecologists. I addressed the question: are pure CNTs produced for distribution to manufactures “toxic” to plants through their effects on physiological processes? I germinated and grew Arabidopsis thaliana seedlings on basal salt medium in Petri plates with or without CNTs and polyhydroxy fullerenes [C₆₀(OH)₂₄] at a concentration of 25 µg/mL. CNTs are hollow cylindrical carbon nano molecules. Fullerenes act as a positive control and are spherical carbon nano molecules. I measured ambient and maximum photosynthetic rates, and photosynthetic responses to light and carbon dioxide, after 7, 15, and 26 days of growth. Plant fresh and dry weight was then determined. I also measured the effects of an aged CNT (exposure to high UV)  on chlorophyll fluorescence.

Results/Conclusions

I found that gas exchange in Arabidopsis thaliana was marginally negatively affected by CNTs; while there were no differences in gas exchange between control and positive control plants. Maximum and ambient photosynthetic rates were reduced by 7% in plants grown in CNTs versus control plants, and this was consistent throughout the 26 days of growth. Responses to light and carbon dioxide were likewise mostly unaffected by growth in pure CNT. However the carbon dioxide compensation point, as determined by ACi curve analysis, was significantly higher in CNT grown plants than control plants. Plant fresh weight was 32% lower in plants grown in CNTs compared to control plants, while dry weight was not significantly affected. I did find a significant reduction in Fv/Fm (11%) between plants grown in aged CNTs versus control. I will examine other pure, waste stream and functionalized CNTs in future research, but the pure CNTs I examined appear to not be “toxic” to plants at the whole plant level.