Registration Dossier
Registration Dossier
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EC number: 936-414-1 | CAS number: -
Endpoint summary
Administrative data
Description of key information
- Testing is technically not feasible,
- Scientifically not justified,
- The aquatic compartment is not the target compartment for MWCNT.
Aquatic toxicity testing is waived because
Additional information
Based on reliable testing data on dispersion stability (OECD TG 318) the set of MWCNT is very difficult to disperse in the first place, re-agglomerating and adsorbing instantly to glass walls and the sonotrode. A very low dispersion stability under all conditions with natural organic matter (NOM), electrolyte concentrations and pH was found from the OECD TG 318 data, with almost identical results for all triplicates and over all environmental conditions. This demonstrates that the performance of aquatic toxicity tests is technically not feasible.
Further, in reliable tests according to OECD 105 and OECD GD 29 it was impossible to detect any dissolution of the test item. MWCNT are an allotropic form of carbon very similar to graphite, which is known to be insoluble in water due to its chemical structure. The covalently bonded MWCNT lack polarity and thus will not dissolve in water (covalent bonds of high binding enthalpy of 348 kJ/mol for each C-C bond; no hydrolysable functional groups, no enthalpy gain by hydration - no compensation of the binding enthalpy of covalent C-C bonds). Accordingly, any dissolved fraction potentially causing any aquatic toxicity can be excluded with absolute certainty.
MWCNT are large molecules with typically several million carbon atoms and consequently high molecular weight. According to the criteria for low absorption probability given in ECHA guidance chapter R11 (2017), any relevant potential for membrane permeation can be excluded for single MWCNT already. Considering that MWCNT are "entangled", forming assemblies of a bundle diameter in the low µm-range and a bundle length around 30 - 80 µm, even oral absorption can be concluded to be irrelevant with high probability.
Finally, due to their hydrophobic nature MWCNT will associate with sludge solids in the STP and will be efficiently be eliminated via surplus sludge, i.e. removed from the water phase. To account for this, a reliable OECD TG 209 study (activated sludge respiration inhibition test) was performed, resulting in an EC50 (3h) >1000 mg/L. This confirms the conclusions drawn above based on physico-chemical characteristics (non-bioavailable).
Via the sludge to soil pathway, soil is the main target compartment. Accordingly, long-term soil toxicity testing is proposed to exclude any toxicity towards terrestrial organisms.
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