Tin dioxide

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2016

Reliability:

2 (reliable with restrictions)

Qualifier:

no guideline available

Principles of method if other than guideline:

- Principle of test: tin dioxide nanoparticles (SnO2 NPs) were radiolabelled using neutron activation, and employed to assess the uptake and excretion kinetics in the earthworm Eisenia fetida. Through sequential extraction, NPs bioavailability in two contrasting soils and in earthworm feed was also investigated

GLP compliance:

not specified

Specific details on test material used for the study:

INFORMATION ON NANOMATERIALS
- Chemical Composition: Tin Dioxide (SnO2)
- Average particle size: 61 nm
- Specific surface area: 14.2 m2 g-1]

Radiolabelling:

yes

Details on preparation and application of test substrate:

-SnO2 NPs mixed into soil or earthworm feed (horse manure) was subjected to a sequential extraction protocol (Salbu et al., 1997). Horse manure (air dried and sieved to <0.5 mm) was
spiked, moistened, mixed thoroughly, and left for 24 h at 20 C (as used in the subsequent uptake experiment) prior to sequential extraction. The two soils were spiked and left for aging at 20 °C for 1, 3, 14, 28 (CeO2) and 1, 14, 28 days (SnO2), before sequential extraction,

Test organisms (species):

Eisenia fetida

Details on test organisms:

TEST ORGANISM
- Common name: earthworm
- Strain: Eisenia fetida
- Source: permanent culture at NIBIO
- Age at test initiation (mean and range, SD): adult
- Weight at test initiation (mean and range, SD): The average wet weight of the worms was 1.31 ± 0.24 g


ACCLIMATION
Eisenia fetida were acclimated at 20 °C and a photoperiod of16:8 h (light:dark) for one week in the respective experimental soils and given the same feed as during the subsequent uptake experiment.
- Health during acclimation (any mortality observed): no mortality observed

Total exposure / uptake duration:

14 d

Total depuration duration:

d

Test temperature:

20°C

pH:

Organic soil: 4.8
Mineral soil: 5.8

TOC:

Organic soil: 14.2 [g/100 g dw]
Mineral soil: 1.49 [g/100 g dw]

Details on test conditions:

TEST SYSTEM
- Amount of soil or substrate: 500 g / 10 earthworm
- No. of replicates per treatment group: 10 earthworm

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): soils formed on the same parent bedrock were sampled at the experimental fields of the Norwegian University of Life Sciences in southern Norway (Aas, Akershus County) and were characterized by an accredited laboratory (Eurofins, Moss, Norway).
- Depth of sampling:
- Soil texture : Loamy
- Soil taxonomic classification:
- Soil classification system:
- Composition (if artificial substrate):
- pH water:
- pH soil: 4.8 (organic soil), 5.8 (Mineral soil)
- Organic carbon (%): 14.2 (Organic soil), 1.49 (mineral carbon)
- Moisture (%):
- Maximum water holding capacity (in % dry weight): 65%


OTHER TEST CONDITIONS
- Adjustment of pH: 6.2

Horse manure (air dried and sieved to <0.5 mm) was spiked, moistened, mixed thoroughly, and left for 24 h at 20 °C (as used in the subsequent uptake experiment) prior to sequential
extraction. The two soils were spiked and left for aging at 20 °C for 1, 14, 28 days (SnO2).

Type:

BSAF

Value:

ca. 1 other: mg g-1 ww worm/mg g-1 ww food

Elimination:

yes

Parameter:

other: 96% of the ingested tin dioxide was excreted within 2 days of depuration

Depuration time (DT):

2 d

Remarks on result:

other:

Details on results:

During the two weeks of exposure, the average body mass of worms increased from from 1.33 ± 0.07 g ww to 1.46 ± 0.02 g ww for SnO2 NPs. At the end of the exposure period, but prior to emptying their gut content, worms had the following body concentrations (mean ± SD): 1.5 ± 0.36% and 1.7 ± 0.45% of the concentration in the food for CeO2 NPs and Ce ions, respectively, whilst corresponding values for SnO2 NPs were 1.0 ± 0.10%. After depuration for 48 h, the corresponding values were 0.012 ± 0.05%, 0.024 ± 0.11% and 0.04 ± 0.03% of the concentration in the feed for CeO2 NPs, Ce ions and SnO2 NPs, respectively.

Conclusions:

SnO2 NPs does not bioaccumulated in earthworms, and was rapidly excreted when worms were transferred to clean soil. Low bioavailability was also indicated by low amounts of NPs recovered during extraction with non-stringent extractants.

Executive summary:

The use of radioactively labelled tin oxide NPs allowed to quantify the uptake and excretion kinetics in earthworms at low exposure concentrations. We were similarly able to estimate the bioavailability of NPs via chemical extraction of various matrixes, evenwhen the bioaccumulation factors were very low (<0.002%) and metals strongly bound to soil components.

It can be concluded that the experiment points toward the tin Oxide NPs relatively low exposure and therfore low risks associated with these types of nanomaterials.

Reference 2

Endpoint:

bioaccumulation: terrestrial

Type of information:

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

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The main assumption for this read across approach is that the source substance ionic Tin (IV) and the target substance Tin (IV) dioxide NP have a common moiety (Tin ion).
Although the target substance, Tin (IV) dioxide NP, is insoluble in water, it is an amphoteric oxide (F. Sherwood Taylor, 1942). The dissolving part of Tin (IV) dioxide NP in aqueous media will react with acids and become ionic Tin (IV).

2. SOURCE AND TARGET CHEMICAL(S)
Material Purity [%] APS [nm] SSA [m2 g -1] Morphology
SnO2 use in the earthworm study 99.5% 61 14.2 Faceted
SnO2 Legal entity 99% NA 7.2 Spherical
APS e Average particle size, SSA e Specific surface area.


3. ANALOGUE APPROACH JUSTIFICATION
A reliable bioevaluation (dietary exposure) study on earthworm is available for the source substance ionic Tin (IV), showing that SnO2 NPs does not bioaccumulated in earthworms, and it is rapidly excreted when worms are transferred to clean soil. Low bioavailability is also indicated by low amounts of NPs recovered during extraction with non-stringent extractants.

Since the target and the source substance dissociate to the same ion, both target and read-across substance, do share the same toxicological mechanisms and the effects of the target substance is predicted to be equal to the effects of the source substance.
The common compound ionic Tin (IV) is solely responsible for the absence or presence of effects.

Reason / purpose for cross-reference:

read-across source