Graphene

Endpoint summary

Description of key information

The short-term toxicity of the test item graphene towards fish was assessed in a semi-static test according to OECD TG 203 under GLP: Gobiocypris rarus LL₅₀(96h) > 100 mg/L

The short-term toxicity of the test item graphene towards aquatic invertebrates was assessed in a semi-static test according to OECD TG 203: Daphnia magna EC₅₀(48h) > 16 mg/L

The toxicity of the test item graphene towards aquatic freshwater algae was assessed in a study according to OECD TG 201: Chlorella pyrenoidosa EC₅₀(96h) = 62.2 mg/L

Additional information

Short-term toxicity to fish

In the present study the acute toxicity of the test substance toGobiocypris raruswas determined by a semi-static test according to OECD TG 203 under GLP.

0.500 g of the test substance were mixed with a small amount of test water, ultrasonicated and then diluted in 5000 mL test water to prepare a stock suspension with a nominal loading rate of 100 mg/L.

The suspension was stirred for about 48 hours, after stirring, the suspension wasfiltered through 0.45 µm PESfilter membrane to discard insoluble parts.

The test duration was 96h.

No mortality occurred in the control during the test and the dissolved oxygen concentration was greater than 60.0 % of the air saturation value (ASV) throughout the test duration.Hence, the test was considered to be valid.

During the test, the measured concentrations of the test substance were determined by TOC analysis, but the results of treatment and blank control were similar. The 96h LL₅₀value for the test substance to Gobiocypris rarus was based on nominal loading rate and stated to be >100 mg/L. The maximum loading rate causing no mortality and the minimum loading rate causing 100 percent mortality within the period of the test were stated with ≥ 100 mg/L and >100 mg/L, respectively.

 

Short-term toxicity to aquatic invertebrates

The acute toxicity of graphene (GN) to Daphnia magna was determined in a 48-hour static test similar to the EU Commission Directive 92/69/EEC, Part C.2 (1992) and the OECD TG 202, Part I (1984).This study is classified as reliable with restrictions (reliability 2) and satisfies the guideline requirements for an acute toxicity study with freshwater invertebrates.

The study was conducted with test concentrations of nominal 0.2 - 16 mg/L. The GN stock suspension was obtained by adding 10 mg of GN to 100 mL of a 1 g/L PVP solution (PVP dissolved in SM7 medium) followed by sonication using a sonication bath (ultrasonic bath KQ-500DB, Kun Shan, China) for 2 h at room temperature to obtain optimal particle dispersion. Most of the GN were suspended and no precipitate was observed after sonication. The nominal concentration (100 mg/L) was considered as the concentration of the GN stock suspension, although it was difficult to reach the full extent of exfoliation by sonication. The test media with different concentrations were prepared by diluting the GN stock suspension followed by sonication for 20 min before exposure. To characterize the stability of graphene in suspension, the hydrodynamic diameter, electrophoretic mobility and zeta potential of graphene were recorded on a Zetasizer Nano ZS system (Malvern Instruments, UK) during a period of 48 h. Application of up to nominal 16 mg/L graphene induced < 50% daphnid mortality. The 48h EC₅₀was determined to be > 16 mg/L (derived from graph).

  

The results reported in the key study are supported by a study conducted by Guo et al., 2013. In the supporting study by Guo et al. no Daphnia were immobilized after being exposed to graphene concentrations up to 250 µg/L for 48h. Thus, this study underlines the absence of acute toxicity of graphene to Daphnia magna at low concentrations.

 

Toxicity to aquatic algae and cyanobacteria

The effect of graphene on the freshwater green algal speciesChlorella pyrenoidosa was investigated by Zhao et al (2017). In a 96 h study conducted similar to OECD TG 201 and EPA OPPTS 850.5400, cultures of Chlorella pyrenoidosa were exposed to nominal concentrations up to 200 mg/L graphene under static conditions. The 96h EC₅₀value of graphene to freshwater algae (Chlorella pyrenoidosa) was examined to be 62.2 mg/L. Graphene showed no shading effect on algal growth due to the poor dispersibility while it more readily heteroagglomerated with algae and thus, likely leading to direct contacts with algae. Furthermore the test substance could adsorb macronutrients (N, P, Mg, and Ca) from the algal medium, thus leading to nutrient depletion-induced indirect toxicity (27% of the total toxicity). Flow cytometry results showed significant decrease of membrane integrity after graphene exposure.

In conclusion Multi-layer Graphene inhibited algae growth with an EC₅₀ (96h) of nominal 62.2 mg/L.

Considering all available data no acute toxicity is recorded for all three trophic levels in the respective aquatic test media. However, taking into account that the test substance is not rapidly degradable it has to be classified as Aquatic Chronic 3 according to Regulation (EC) No 1272/2008 with toxicity data above 10 mg/L and below or equal to 100 mg/L.