Indium

Endpoint summary

Description of key information

General introduction

Directly after introduction of Indium metal powder in aqueous test media, only very low In-concentrations (≤1 μg/L) are detected. This is explained on one hand, by the very limited solubility of In metal and, on the other hand, by the general and immediate precipitation of Indium ions to In(OH)3.

Indeed, 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.

PNECs

As a general worst case approach to the assessment of In toxicity, information obtained on soluble In-compounds (usually InCl3) is used for determining PNECs for Indium risk assessment. The In solubilising from these compounds will, upon release in the water, transform into In(OH)3, and the observed toxicity will be a result of the presence of In-ion and In(OH)3 complexes in the "total recoverable" fraction. The general PNECs are used for the assessment of all In substances, including those with very low solubility. Considering the very low release of In-ions from such insoluble substances, it is emphasised that this general approach is very conservative.

Hazard assessment

The acute hazard of In metal is based on the general data, obtained on soluble In substances, that show no acute hazard of In substances in general.

The chronic hazard assessment of In metal is based on a) transformation/dissolution testing and b) chronic ecotoxicity testing on Ceriodaphnia dubia, (which was the most sensitive species identified in the chronic ecotoxicity dataset on soluble In-compounds -see section 6.1.4.) 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.).

Transformation/dissolution test results show that the solubility of In metal (powder) is extremely low. Consequently, the chronic aquatic toxicity of In metal powder is also extremely low: NOECs of 100mg In/L were observed for both organisms (highest dose tested). Based on these results on the powder, it is concluded that Indium metal is not chronically toxic for aquatic effects.

For reasons of completeness, the general ecotoxicity data on soluble In-substances are presented below. These data are used for a) the PNECs, and b) for the acute hazard assessment of the In substances, including In metal.

Short-term aquatic toxicity

There were several studies available on short-term aquatic effects of indium substances, mostly on indium trichloride.

Since, like for the other metals, the ecotoxicity of Indium and its compounds is basically related to the effect of the Indium-ion, In3 +, studies

obtained on InCl3 and other soluble In-substances can be read across to the other In-substances. All PNECs derived are expressed as total indium (ion) concentration. They are consequently relevant for all In-substances.

A total of 12 LC/EC50s, from 9 different species, representing 3 trophic levels (1 algae, 6 invertebrate and 2 fish species) is available. Below is a table showing the species in the indium trichloride acute dataset, the respective LC/EC50 values, species group and the references.

Species	LC/EC50 mg/L	Endpoints	Species group	Reference
Oreochromis mossambicus	19.5	48-h, mortality	Fish	Lin & Wang, 1998
Sillago japonica*	>20.0	24-h, mortality	Fish	Onikura et al. 2008
Brachionus plicatilis*	24.4	24-h, mortality	Invert.	Onikura et al. 2008
Artemia salina*	51.0	48-h, mortality	Invert.	Onikura et al. 2008
Artemia salina	7.1	48-h, mortality	Invert.	Onikura et al. 2008
Americamysis bahia*	30.5	96-h, mortality	Invert.	Onikura et al. 2008
Daphnia magna	>455.5	48-h, mortality	Invert.	Aecom, 2012
Daphnia magna	31.9	24-h, mobility	Invert.	Zurita et al. 2007
Hyalella azteca	>3.1	7-d, mortality	Invert.	Borgmann et al. 2005
Hyalella azteca**	>1	7-d, mortality	Invert.	Borgmann et al. 2005
Macrobrachium nipponense	6.9	96-h, mortality	Invert.	Yang et al. 2014
Pseudokirchneriella subcapitata	1.6	72-h, biomass	Algae	Aecom, 2012

*Test conducted in marine water; ** soft water.

The ecotoxicity reference value (erv) (= lowest acute toxicity value) is 1.6 mg In/L.

Chronic aquatic toxicity

For assessing the chronic aquatic toxicity of In metal, results from two specific tests performed on In metal powder were available:

-For Ceriodaphnia dubia, which was the most sensitive species identified in the chronic ecotoxicity dataset on soluble In-compounds, the NOEC was 100mg In/L.

-For the unicellular alga Pseudokircherniella subcapitata, which was the most sensitive species in the acute ecotoxicity dataset on InCl3, the NOEC was 100mg In/L .

The very low toxicity of the In metal could be explained by the very low solubility of the In metal.

Chronic data for the derivation of the chronic erv and PNEC for In substances

The PNEC was derived based on chronic data obtained on soluble In substances. A total of 11 NOEC/EC10s, from 7 different species, representing 3 trophic levels (1 algae, 4 invertebrates and 2 fish species) were used to derive the PNEC. The species used in the PNEC assessment, the respective NOEC/EC10 values, endpoints, species group and the references, all obtained on testing with InCl3, are presented in table below.

Species	NOEC/EC10 µg/L	Endpoint	Species group	Reference
Oreochromis mossambicus	1950	16-d, length	Fish	Lin & Wang, 1998
Pimephales promelas	25000	14-d, weight	Fish	Aecom, 2012
Ceriodaphnia dubia*	92.92*	7-d reproduction	Invert.	Aecom, 2011a,b,c; Aecom, 2012c,d
Daphnia magna	410	21-d, reproduction	Invert.	Aecom, 2012e
Strongylocentrotus purpuratus	825	48-h, development	Invert.	Nautilus, 2012
Mytilus galloprovincialis	18100	48-h, development	Invert.	Nautilus, 2012
Pseudokirchneriella subcapitata	366	72 -h, biomass	Algae	Aecom, 2012g

*Geometric mean calculated from 5 separate studies. 

 

from the data above, it follows that ythe lowest species NOEC observed for Ceriodaphnia dubia of 93µg In/L is used as ecotoxicity reference value (ERV) for In-substances.

It is noted that for the hazard assessment of In metal, the results of the ecotoxicity tests performed on the most sensitive species from the InCl3 database (C.dubia) and the generally sensitive taxonomic group of the unicellular algae, are used, only (see above) These specific results are used for the hazard assessment and classification of In metal, only.

reference:

Gensemer, R. W., Gondek, J. C., Rodriquez, P. H., Arbildua, J. J., Stubblefield, W. A., Cardwell, A. S.,

Santore, R. C., Ryan, A. C., Adams, W. J. & Nordheim, E. (2018). Evaluating the effects of pH,

hardness, and dissolved organic carbon on the toxicity of aluminum to freshwater aquatic

organisms under circumneutral conditions. Environmental Toxicology and Chemistry, 37, 49-60.

Additional information

There is evidence that higher loading of InCl3 during experiments leads to a shift in pH: addition of In at higher loading (i.e. > 10mg InCl3/L) causes a pH effect, which could influence metal speciation and subsequently the ecotoxicity results.

Acute aquatic toxicity

There were two studies conducted with Daphnia magna as a test species where in a first test pH was adjusted to test conditions and in a second test pH was not adjusted

(Aecom 2012). The study with the unadjusted pH (lower pH shift in the higher In concentrations) had an 8.5 time lower LC50 compared to the adjusted pH test. As the higher In concentrations in the unadjusted pH tests had pH lower than 4.5, the LC50 of the adjusted pH test was used as an appropriate toxicity endpoint for acute freshwater toxicity tests.

Several acute studies did not record the pH. For example, Lin and Hwang (1998) tested the toxicity of InCl3 on 3-day-old larvae of Oreaochromis mossambicus. The LC50 observed on Oreochromis mossambicus is 19519 µg total In/L. Lin and Hwang (1998) did not measure pH. High loading with In in the tests (>15 mg In/L) could result in a pH-drop and subsequently contribute to an observed ecotoxicity. However, even if pH were not recorded the data were still used, as this would represent a ‘worst-case’ scenario (i.e. very conservative dataset). Given that all acute data reviewed in the dataset showed LC/EC50 values greater than 1 mg/L, this results in there being no classification for acute aquatic effects.

Chronic aquatic toxicity

The long-term aquatic toxicity database covers 7 different species, representing 3 trophic levels (1 algae, 4 invertebrates and 2 fish species).

Indium precipitates under neutral (6-8) pH conditions. Therefore, no dose-response could be correlated with the observed dissolved In concentrations. The effect concentrations

are expressed as total recoverable In concentrations, including In ion and In(OH)3, formed upon release of In in solution. Total and dissolved indium concentrations were measured in 3 tests with Ceriodaphnia and 2 tests with D. magna. In the study of Aecom (2012d) DOC was used in the test medium (nominal concentration of 10 mg C/L). This study clearly indicates that Indium binds strongly to DOC, as the dissolved In concentration was comparable to the total In concentration; whereas in the other studies where no DOC was used, the dissolved concentrations were much less than the total In concentrations. Results are shown in Table below:

Species	NOEC nominal (µg total In/L)	NOEC dissolved (µg In/L)	NOEC total (µg In/L)	DOC	Reference
Ceriodaphnia dubia	62	3.6	52.9	ND	Aecom (2011a)
Ceriodaphnia dubia	62	1.9	58.1	ND	Aecom (2012c)
Ceriodaphnia dubia	1847	1184	1710	10	Aecom (2012d)
Daphnia magna	1000	5.4	809	ND	Aecom (2012e)
Daphnia magna	<3300	3.6	2780	ND	Aecom (2012e)

The studies of Aecom (2011b,c; 2012 a,c,d,e) also clearly indicate that the ecotoxicity of Indium towards invertebrates is influenced by hardness, see table below:

Fish:

Species	pH	Hardness (mg CaCO3/L)	DOC  (mg C/L)	NOEC (µg total In/L)	EC10 (µg total In/L)	EC50 (µg total In/L)	Reference	Remarks
Pimephales promelas	7.8 -8.2	ND	ND	>25000	>25000	ND	Aecom (2012a)
Oreochromis mossambicus	ND	ND	ND	1951.9	ND	ND	Lin and Hwang (1998)	pH was not measured

Invert.:

Species	pH	Hardness (mg CaCO3/L)	DOC  (mg C/L)	NOEC (µg total In/L)	EC10 (µg total In/L)	EC50 (µg total In/L)	Reference	Remarks
Ceriodaphnia dubia	8.0	90	ND	10	ND	ND	Aecom (2011b)
Ceriodaphnia dubia	8.1	96	ND	52.9	>20.4	ND	Aecom (2011a)	Test was range finder study; test result not used for classification and PNEC derivation
Ceriodaphnia dubia	8.2	90	ND	20	<20	ND	Aecom (2011c)
Ceriodaphnia dubia	7.9	402	ND	58.1	87.2	ND	Aecom (2012c)
Ceriodaphnia dubia	7.9	90	10	<1710	130	ND	Aecom (2012d)	NOEC test result not used for PNEC derivation as lower reproduction in control determines NOEC
Daphnia magna	7.3 -8.5	170	1.55 -2.21	809	1398	412	Aecom (2012e)	Tests conducted in hard water
Daphnia magna	6.8 -7.6	510	1.43 -2.03	<2780	<2780	<2780	Aecom (2012e)	Tests conducted in very hard water

Algae:

Species	pH	Hardness (mg CaCO3/L)	DOC  (mg C/L)	NOEC (µg total In/L)	EC10 (µg total In/L)	EC50 (µg total In/L)	Reference	Remarks
Pseudokirchneriella subcapitata	7.4 -9.6	14	1.39	321	1164	>5025	Aecom (2012f)

Given the number of species data and the taxonomic coverage, the PNEC was derived using a species sensitivity distribution approach.

3. Aquatic chronic toxicity: marine water

Two marine species are included in the aquatic chronic dataset, Mediterranean mussel (Mytilus galloprovincialis) and the purple sea urchin (Strongylocentrotus purpuratus) (see Section 6.1). They are neither the most sensitive or tolerant species in the SSD and are included with the freshwater species-sensitivity distribution. Given the lack of difference observed in toxicity in freshwater and marine water, the same PNEC is derived for the marine water.

4. STP

There were two test results available. In a first test, the respiration sludge study was carried out without pH adjustment. This resulted in a NOEC of 460 mg InCl3/L and an EC50 of 680 mg InCl3/L. The pH in the controls and substance series, before addition of sludge was 7.3 at 10 mg/L and decreased to 2.9 at 1000 mg/L. After 3 hours exposure period the pH in the Indium trichloride series was 7.8 at 10 mg/L and decreased to 3.4-3.7 at 1000 mg/L.

In a second test, the pH was adjusted to 7.2. This resulted in a NOEC of 1000 mg/L and an EC50 of >1000 mg InCl3/L. As pH was very low in the pH non adjustment treatment, the results of the pH adjusted treatments were taken to set the PNEC for STP. The NOEC was 1000 mg InCl3/L or 516 mg In/L. Using an AF of 10, this results in a PNEC of 51.6 mg In/L for STP.