Indium

Long-term toxicity to aquatic invertebrates

Description of key information

As predicted by chemical equilibrium models and confirmed by TD testing, the higher valence (trivalent) metal In has very low solubility in natural waters and/or ecotoxicity testing media, due to the readily formation of hydroxy complexes In(OH)3. As shown for Aluminium, (which has comparable characteristics in water) such hydroxy complexes may contribute to toxicity (Gensemer et al, 2018), e.g. by polymerisation and/or physical precipitation on the gill surface and as such clogging the gill surface and inhibit its function. As a result, toxicity values for In are expressed as "total recoverable Indium", to include both the In3+ ionic fraction and the In(OH)3 fraction. Consequently, ecotoxicity reference values and PNECs for Indium substances are expressed on a "total recoverable In" basis. The general PNECs are used for the assessment of all In substances, including those with very low solubility, like In metal, too. Considering the very low release of In-ions from In metal as following from the solubility tests and chronic ecotoxicity tests on In metal powder, it is emphasised that this general approach is very conservative.

The review of the aquatic toxicity literature where indium salts are used for assessing the toxicity of the metal ion or hydroxide have limited direct application to the substance represented in this CSR. The use of a PNEC, once derived, has to take into consideration the transformation/dissolution of the indium powder.

Thus, the chronic exotoxicity of In-metal is documented more specifically by a) transformation/dissolution data, and b) chronic ecotoxicity testing on Ceriodaphnia dubia, (which was the most sensitive species identified in the chronic ecotoxicity dataset on soluble In-compounds) and on the unicellular alga P. subcapitata, which was the most sensitive species in the acute ecotoxicity dataset on InCl3 (see section 6.1.5.).

Based on the evidence, it can be concluded that the solubility of In metal (powder) is extremely low, and that very low concentration of In ion and In(OH)3 complexes are formed in solution. Consequently, the chronic aquatic toxicity of In metal powder is very low too: NOECs of 100mg In/L were observed for both organisms (highest nominal dose tested; very low In concentrations measured in test solutions). Based on these results on the powder, it is concluded that Indium metal is not chronically toxic for aquatic invertebrates.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

100 mg/L

Marine water invertebrates

Marine water invertebrates

Effect concentration:

825 µg/L

Additional information

specific assessment of chronic toxicity of In metal powder for invertebrates

Chronic ecotoxicity are available on the effect of In metal powder on Ceriodaphnia dubia, (which was the most sensitive species identified in the chronic ecotoxicity dataset on soluble In-compounds). The NOEC was 100mg In/L.

Chronic aquatic toxicity of In ion combined with In(OH)3 complexes to invertebrates

Ecotoxicity tests with InCl3 on two freshwater species (C. dubia and Daphnia magna) and two marine species were available, too. These data are used for the general PNEC setting for (general) risk assessment on In substances, including In metal.

Freshwater

For freshwater, 5 tests in total were conducted with C. dubia as the test species and two tests with D. magna. In precipitates under neutral (6 -8) pH conditions as In(OH)3. Therefore, no dose-response could be correlated with the observed dissolved In concentrations. The effect concentrations are expressed as total (recoverable) In concentrations. Indium binds strongly to DOC, as the dissolved In concentration in the Aecom (2012d) study was comparable to the total In concentration.

NOEC nominal (µg In/L)	NOEC dissolved (µg In/L)	NOEC total recoverable (µg In/L)	Hardness	DOC	reference
62	3.6	52.9	96	ND	Aecom (2011a)
62	1.9	58.1	400	ND	Aecom (2012c)
1847	1184	1710	90	10	Aecom (2012d)
1000	5.4	809	170	ND	Aecom (2012e)
<3300	3.6	2780	500	ND	Aecom (2012e)

The study of Aecom (2011b) was a range finder test, where the scale of the tested concentrations is not according to standard OECD protocols. The Aecom (2012d) study was conducted in test water with high DOC concentration. The NOEC of that study was actually determined by the differences in the control; therefore, the NOEC of that study was not used to derive the geomean NOEC of C. dubia.

When the lowest NOECs found for C. dubia are compared as a function of hardness, it appears that hardness and DOC had an effect on the toxicity, when expressed as EC10, of InCl3 for C. dubia. The geomean of the 3 test results in a geomean NOEC for C. dubia of 39.46 µg total In/L. The geomean of 4 studies results in a geomean EC10 of 32.47 µg total In/L.

Hardness (mg CaCO3/L)	DOC (mg/L)	NOEC  (µg total In/L)	EC10 (µg total In/L)	Reference
96	ND	20	8.4*	Aecom (2011c)
90	ND	52.9	11.68	Aecom (2011a)
402	ND	58.1	87.2	Aecom (2012c)
90	10	Not used as lower reproduction in control determines NOEC	130	Aecom (2012d)

*there is significant uncertainty on this value, since In total recoverable concentration was not measured, but the IC10 is expressed as nominal concentration (this is done because other data show that in these media, the total recoverable In concentration can be considered as similar to nominal), and the value is estimated from an "<20µg/L" result, so actually unbound. The value is still considered for the calculation of the geomean IC10, which is thus to be considered as a worst case.

The effect of water hardness was also seen in the studies with Daphnia magna. The NOEC and EC10 was lower in the hard water (170 mg CaCO3/L) compared to the NOEC and EC10 in the very hard water (510 mg CaCO3/L):

Hardness (mg CaCO3/L)	NOEC (µg total In/L)	EC10 (µg total In/L)	Reference
170	809	1398	Aecom (2012e)
510	<2780	<2780	Aecom (2012e)

Marine water

Strongylocentrotus purpuratus (purple sea urchin) was the most sensitive marine species and had a 72 times lower NOEC than the Blue Mussel exposed to InCl3.

species	NOEC (µg In/L)	EC10 (µg In/L)	reference
Strongylocentrotus purpuratus	130	825	Nautilus (2012a)
Mytillus galloprovincialis	9450	18100	Nautilus (2012a)