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Environmental fate & pathways

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Recent ECHA guidance on aquatic bioaccumulation assessment for REACH registration observes that it is not possible to make log Kow or solubility based estimates of nanomaterial bioaccumulation as nanomaterials within test systems are “dispersed” and not in solution. As such, measured BCF values are required to fulfil data requirements under REACH.

The guidance also states that it is also of vital importance to consider the influence of aggregation/agglomeration as well as dissolution on bioaccumulation. If possible, information on bioaccumulation of nanomaterials should be supported with information on the form of the substance present in the animal tissue (i.e. are nanoparticles of silver bioaccumulated or just ionic silver released from nanomaterials).

Handy et al. (2012) outline several problems with the performance of conventional bioaccumulation tests using nanomaterials. Critically, they question the founding assumption of the “steady-state” required for BCF measurements from aqueous exposures as colloidal dispersions (of nanomaterials) are dynamic systems which do not achieve steady equilibrium state (Handy et al. 2008). Equally, uptake by endocytosis (a potential mechanism of accumulation of nanoparticles) may also confound the use of standard kinetic relationships employed in bioaccumulation tests that are based on diffusion (i.e. the Fick equations). Handy et al. (2012) warn against the application of bioaccumulation tests without an appreciation of the underlying mechanism of uptake and kinetics. Handy et al. (2012) also discuss the use of diet borne studies. However, limited potential for the verification of particle size distribution of nanomaterials when incorporated into food (as per studies conducted in soils) are considered to restrict the usefulness of diet-based bioaccumulation tests with nanomaterials.

Read-across from the dissolved silver ion is also applied to fulfil information requirements for silver and silver-based (coated) nanomaterials. Supporting information for this read-across is summarised in endpoint summaries and in further detail in the appended nanosilver read-across summary/justification document.

Literature cited

Handy RD, Henry TB, Scown TM, Johnstone BD, Tyler CR. 2008. Manufactured nanomaterials: their uptake and effects on fish – a mechanistic analysis. Ecotoxicology. 17: 396-409.

Handy R, van den brink N, Chappell M, Mühling M, Behra R, Dušinská M, Simpson P, Ahtiainen J, Jha AN, Seiter J, Bednar A, Kennedy A, Fernandes TF, Riediker M. 2012. Practical considerations for conducting ecotoxicity test methods with manufactured nanomaterials: what have we learnt so far? Ecotoxicology. 21: 933-972.