Electrolytes, copper-manufg., spent

Endpoint summary

Additional information

Silver

There are many studies in the literature relevant to the bioaccumulation of silver. However, many of these studies do not report sufficient information for BCF values to be calculated. In addition, many of the data were obtained from studies of short duration which did not achieve steady-state conditions. The available reliable studies suggest low BCF values for fish, although studies of the accumulation of silver by molluscs, such as Hedouin et al. (2006), indicate the potential for higher BAF values for these organisms.

As data on bioaccumulation for fish are preferentially selected for this information requirement under REACH, the key study selected for this endpoint is Baudin et al. (1993) in which carp were exposed to silver in water for a six-week period, followed by a depuration phase. A steady state concentration in fish was achieved after 30 days exposure and a BCF value of 70 was calculated for the whole fish on a wet weight basis.

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.