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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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short-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Substance considered to fall within the scope of the read-across 'Silver metal: Justification of a read-across approach for environmental information requirements' (document attached in IUCLID section 13).
Reason / purpose for cross-reference:
read-across source
48 h
Dose descriptor:
Effect conc.:
0.22 µg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
Basis for effect:
Remarks on result:
other: 95% CL 0.19–0.25 µg Ag/L. Filtered (0.45 mm), silver concentration.
Details on results:
Results also for 24 hour LC50 and with added sulphide. Reactive sulfide protects D. magna against acute silver toxicity.
Results with reference substance (positive control):
Not applicable
Reported statistics and error estimates:
The 48 hour LC50 values and the respective 95% confidence intervals were estimated on the basis of the cumulative mortality data using probit analysis. These values were estimated on the basis of both nominal and mean measured total and filtered silver concentrations over the respective periods of the test and the results were compared.
Validity criteria fulfilled:
not applicable
The freshwater 48 hour LC50 values for Daphnia magna when exposed to silver nitrate are 0.18 to 0.26 µg Ag/L based on measured total silver concentration and 0.22 µg Ag/L based on measured filtered silver concentration.
Executive summary:

The study is a non-guideline study, published in peer reviewed literature and considered suitable for use as a key study for this endpoint. The freshwater 48 hour LC50 values for Daphnia magna when exposed to silver nitrate are 0.18 to 0.26 µg Ag/L based on measured total silver concentration and 0.22 µg Ag/L based on measured filtered silver concentration.

Description of key information

Read across from ionic silver

Plus supporting published data from several studies included in the REACH dossier as Endpoint Study Records with various sizes of nanoparticles and coating types, showing that nanosilver is less toxic than ionic silver

Key value for chemical safety assessment

Additional information

Summary of available data for uncoated and coated nanosilver

Reliable and relevant data on the short-term toxicity of uncoated and coated nanosilver to invertebrates are available from 12 studies (Griffitt et al. 2008, Gao et al. 2009, Kennedy et al. 2010, Li et al. 2010, Gaiser et al 2011, Gaiser et al. 2012, Hoheisel et al. 2012, McLaughlin and Bonzongo 2012, Poynton 2012, Wang et al. 2012, Zhao and Wang 2012, Blinova et al. 2013).

A total of 55 LC50 values are available from studies investigating effects on five species (Daphnia magna, Daphnia pulex, Ceriodaphnia dubia, Thamnocephalus platyurus, Chydorus sphaericus). However, data predominantly relate to the crustacean species conventionally used in laboratory ecotoxicity testing i.e. Daphnia magna (seven studies – 35 LC50 values) and Ceriodaphina dubia (three studies – seven LC50 values).

The available reliable data includes various sizes of nanoparticles and, in addition to uncoated nanosilver materials, a range of coating/capping materials, including: PVP, citrate, EDTA, lactate and sodium dodecylbenzene sulfonate.

Studies predominantly report effects of spherical nanoparticles but there are also data for mixtures of spherical particles and nano rods (Kennedy et al. 2012), mixtures of spherical, prismatic and rod-shaped colloids (Li et al. 2012) and face-centred cubic crystal structures (McLaughlin and Bonzongo 2012). All studies were conducted in freshwater media.

The particle size of raw nanomaterials across the studies ranged from 8.4 to 123.9 nm (Particles >100 nm would not usually fall under the proposed definition of a nanomaterial, but as this threshold is not based on any scientific criteria toxicity data from studies with particle sizes >100 nm are included in this assessment for completeness). However, the majority of studies report effects associated with primary particle sizes between 8.4 and 51.86 nm (10th to 90th percentile). Aggregation/agglomeration behaviour of primary particles within experimental media or stock solutions varied between studies but in almost all instances authors report that some degree of aggregation/agglomeration in the test systems occurs, increasing the size of particles in environmental media. The characterisation results for nanosilver in test systems report particle sizes after aggregation/agglomeration of between 50.7 and 1,584 nm, with the majority of studies reporting particle sizes between 50.7 and 360.0 nm (10th to 90th percentile).

LC50 values range from 0.43 µg/L to 221 µg/L, after 48 hour exposure. Interestingly, both of these LC50 values are from the study by McLaughlin and Bonzongo (2012) which investigated the toxicity of uncoated nanosilver particles (25.4 nm) to Ceriodaphnia dubia in both synthetic and natural waters. The greatest toxicity (LC50 value of 0.4 µg/L) was recorded in river water, whilst the lowest toxicity was recorded in water from a wetland. A similar observation was recorded in Pseudokirchnerialla subcapitata exposed to nanosilver in the same water. Differences in observed toxicity may be the result of variable bioavailability of silver in these waters. The 10th to 90th percentile range of LC50 values for all forms of nanosilver assessed for acute invertebrate toxicity range from 1.31 to 187.8 µg/L.

All of the nanosilver LC50 values are less sensitive than the 48 hour LC50 of 0.22 µg/L for Daphnia magna (Bianchini et al. 2002) used in the REACH CSR for silver.

In addition, where studies undertook a comparative assessment of the relative toxicity of nanosilver and ionic silver within their own study designs (Griffitt et al. 2008, Kennedy et al. 2010, Zhao and Wang 2012, Poynton 2012, Hoheisel et al. 2012, Wang et al. 2012, Blinova et al. 2013) nanosilver was only observed to be more toxic than ionic silver on a single occasion (Griffitt et al. 2008 – 48 hour exposure of C. dubia neonates). The relative toxicity of bulk silver (0.6 - 1.6 µm particles) in comparison to nanosilver was tested on a single occasion (Gaiser et al. 2011). In this test, bulk silver was approximately an order of magnitude less toxic than nanosilver.

Overall, there is no statistically significant correlation between smaller particle sizes and increased toxicity (Kendall test, p>0.05). However, Hoheisel et al. 2012 report a clear reduction in toxicity (greater LC50) with increasing particle size. This relationship was effectively normalised when results were expressed on the basis of surface area rather than mass concentration, which suggests that the toxicity observed was related to the dissolution rate of silver ions from the surface of the particles. Smaller particles have much greater surface area than larger particles.

When the LC50 values from materials with different coatings were compared using a non-parametric ANOVA procedure (Kruskal-Wallis, p<0.05) a statistically significant difference between coating material and LC50 value was identified. Protein coated nanosilver materials appear to have lower toxicity than other coating materials and uncoated materials. However, this cannot be confirmed using a statistical post-hoc test as the variance and normality of the different treatment groups was homogenous.