Silver

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation: terrestrial

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting 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

Type:

BCF

Value:

0.62 dimensionless

Basis:

whole body w.w.

Time of plateau:

30 d

Calculation basis:

kinetic

Remarks on result:

other: 30 day BAF bioavailable value for ionic silver

Kinetic parameters:

The time course of accumulation during the exposure period had high initial accumulation which leveled off and approached a plateau after 28 days.

Metabolites:

Not applicable

Details on results:

- Control: During the five months duration of the experiment, no worms died in either the treated or the control terraria. Their average mass increased from 394 ± 76 mg ww to 566±144 mg ww and cocoons and juveniles were found in all treatments during the whole duration of the experiment.
- Results: At the end of the exposure period (day 28), but prior to emptying their gut content, worms had body concentrations (mean±SEM, n=30) corresponding to 5.1±0.5% and 11.0±0.3% of the concentration in the food for Ag NPs and Ag ions. After emptying their gut content for 48 hours, the corresponding value was 2.3±0.1%, for Ag ions. 80% of Ag ions were excreted within 48 hours and 97% during the two-month depuration period. At this time the remaining 110m Ag concentration in individual worms was close to the detection limit and the depuration study was terminated. Further localization of Ag in worms’ organs was not possible due to extremely low amounts of Ag in worms.
- Conclusion: 30 day BAF bioavailable value of 0.62 ± 0.11 was reported for ionic silver.

Reported statistics:

The counting uncertainties were calculated from the counting uncertainty of individual activity measurements using the square root of sum of squares. Evaluation of statistical differences between ionic and particulate silver was performed by a Student’st-test.

Validity criteria fulfilled:

not applicable

Conclusions:

30 day BAF bioavailable value of 0.62 ± 0.11 was reported for ionic silver.

Executive summary:

Coutris et al. 2012 used neutron activated soluble silver (silver nitrate) to asses the uptake, excretion and bio-distribution of silver in the earthworm Eisenia fetida exposed in standard OECD artificial soil (pH 5.95) amended with spiked, air dried, horse manure (0.55 ± 0.15 µg/g dissolved silver). A 30 day BAF_bioavailablevalue of 0.62 ± 0.11 was reported.

Description of key information

Read across from ionic silver

Plus supporting published data from 2 studies included in the REACH dossier as Endpoint Study Records with nanoparticles, showing that ionic silver is more bioavailable than nanosilver

Additional information

Summary of available data for uncoated and coated nanosilver

Bioaccumulation in terrestrial invertebrates

Coutris et al. (2012) used neutron activated nanosilver particles (20.2 ± 2.5 nm by TEM) and soluble silver (silver nitrate) to assess the uptake, excretion and bio-distribution of silver in the earthworm Eisenia fetida exposed in standard OECD artificial soil (pH 5.95) amended with spiked, air dried, horse manure (0.55 ± 0.15 µg/g dissolved silver; 0.77 ± 0.15 µg/g nanosilver). 30 day BAF_bioavailable values of 0.31 ± 0.12 and 0.62 ± 0.11 were reported for nanosilver particles and ionic silver, respectively. Ionic silver was approximately twice as bioavailable as nanosilver. Silver accumulated from soluble salts and nanoparticles was excreted rapidly.

Hunde-Rinke and Klawonn (2013) also measured bioaccumulation of nanosilver (NM-300K, 15 nm particle size) with Eisena fetida. Worms were exposed to silver via either soil or feed in a long-term (28 day) chronic toxicity study. No depuration phase was included and measurements were made at 28 days only. Despite these limitations, a bioaccumulation factor (BAF) of 0.52 can be calculated from silver accumulation observed in the lowest test concentration (13.43 mg/kg dry weight) of the soil exposure after 28 days (no adverse effects were observed on survival or reproduction at this nanosilver concentration). It is not clear if steady-state concentration was achieved after this exposure. Exposures to higher concentrations of silver in soil (by factors of up to 13), whilst resulting in toxicity, did not result in broadly greater accumulation of silver. It is unclear if the silver was located in the tissues or the gut of the worm. These results compare favourably to those reported by Coutris et al. (2012). No comparative exposure to ionic silver was conducted.