Studies with regard to potential ecotoxicological effects of graphene have been carried out mainly in bacteria, and comparing various surface modifications of graphene. Graphene mainly occurs in flake or film form with dimensions in the micrometer range. Findings on the effects of graphene appear to be very inconsistent, as it shows both, inhibitory and growth-promoting effects in bacteria.

 

Graphene as a nanomaterial is so in only one dimension (out of three), i.e. as nano-sheets or nano-films. In the biological tests graphene flakes are used.

 

PantoffeltierchenThe various graphene surface modifications have been shown to exhibit varying degrees of antibacterial activity, with smaller graphene platelets being significantly more toxic than larger ones and with different sensitivities for effects across bacterial species [1,2,3,4]. The mechanism of effect for graphene is most likely to be damage to cell membranes by direct contact with the sharp-edges of graphene in its sheet form. Oxidative stress resulting from exposure to graphene has also been observed. In bacteria graphene has been shown to be toxic, but only at very high levels of exposure [5]. Sludge bacteria show reduced viability after exposure to graphene, inhibiting their capacity to purify sewage [6]. In contrast with these findings, there are also reports for improved growth of bacteria in the presence of graphene [7]. In this case, material was thoroughly cleaned before experimental testing, possibly indicating that the toxic effects seen for other studies probably arise from impurities. Some types of bacteria are able to metabolize oxygen from functional groups of modified graphene surfaces, hence change their surface [8].

Algen

Similar to effects observed in bacteria, the sharp-edged graphene can also cause irreversible cell wall damage in green algae [5].

 

WasserflohWater fleas actively incorporate graphene nanomaterial by filtration of the surrounding water. The water flea however appears to be capable of excreting the graphene and no toxicity was observed [9]. For Artemia (brine shrimps), graphene is also non-toxic but there are signs of oxidative stress. However, similar to water fleas it is taken up into the intestine [5].

 

WurmGraphene flakes have been detected in the intestine and in freshly deposited eggs of C. elegans, a nematode [4]. However, no toxicity based on mortality, reproduction or genetic changes was observed. When the worms were chronically exposed to graphene, however, both movements and oviposition were impaired. These observations have been attributed to oxidative stress [10].

 

MuschelBarnacles are sedentary organisms and hence they do no change their location in the adult state. Their larvae, however, are free swimming and graphene was shown to prevent the attachment process as the barnacle larvae settle on rocks to begin their adult life stage. In addition, the swimming behavior of the larvae is slowed down and there is a higher mortality rate [11].

 

FischOne study examining the influence of differently modified graphene nanomaterial on the development of zebrafish [12] and some malformations were observed in graphene-exposed embryos, but in small numbers only. The survival rate was not affected. Another study showed similar effects of graphene on zebrafish embryos. There was no increase in mortality, but impairments of heartbeat, in the hatching rate and there was a reduced body size [13].

 Blume

Graphene nanomaterial has been shown to have inhibitory effects on the growth of plants, including tomato, cabbage and spinach seedlings but not for young lettuce plants [14]. The exposure of plants with graphene triggered oxidative stress.

 

 

In summary, according to most recently available studies graphene nanomaterials may be toxic to bacteria, but this is not an unanimous finding. In general, graphene was found to be non-toxic for most higher animals. An exception here is for barnacles, whose larvae were adversely affected by graphene exposure. Any non-physical effect of graphene on an organism was generally related to oxidative stress.

 

Literature arrow down

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  2. Akhavan, O et al. (2010), ACS Nano, 4(10): 5731-5736.
  3. Hu, W et al. (2010), ACS Nano, 4(7): 4317-4323.
  4. Zanni, E et al. (2012), Nano Lett, 12(6): 2740-2744.
  5. Pretti C et al. (2014), Ecotox Environ Saf 101: 138-145.
  6. Ahmed F & Rodrigues DF (2013), J Hazard Mater 256-257: 33-39.
  7. Ruiz, ON et al. (2011), ACS Nano, 5(10): 8100-8107.
  8. Akhavan, O et al. (2012), Carbon, 50(5): 1853-1860.
  9. Guo X et al. (2013), Environ Sci Technol 47(21):12524-12531.
  10. Wu Q et al. (2013), Nanoscale 47(5): 6288-6296.
  11. Mesarič T et al. (2013),Chem Ecol 29(7): 643-652.
  12. Gollavelli, G et al. (2012), Biomat 33(8): 2532-2545.
  13. Liu XT et al. (2014), Biomed Environ Sci 27(9): 676-683.
  14. Begum, P et al. (2011), Carbon, 49(12): 3907-3919.

 

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