Gallium

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

As gallium is quite insoluble (ca 46 µg/L) toxicity testing has been performed with gallium(III) nitrate hydrate, which has a higher water solubilty. A read-across approach is followed assuming that the toxicity of gallium (III) nitrate hydrate is completely attributed to the dissolved gallium ion. Even if the nitrate ion would contribute partly to the toxicity of the substance, it is considered worst case to completely attribute the toxicity to the gallium ion.

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 0.3 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

gallium

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

<= 0.3 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

Gallium

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

0.46 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

Gallium

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

14.65 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

Gallium

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

< 0.3 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

Gallium

Basis for effect:

other: yield

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

<= 0.3 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

Gallium

Basis for effect:

other: yield

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

0.63 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Remarks:

Gallium

Basis for effect:

other: yield

Validity criteria fulfilled:

yes

Conclusions:

The following results for the test item Gallium(III) nitrate hydrate were determined:

Results of the test item (based on dissolved Gallium concentration)
Endpoint                   NOEC              LOEC              EC10            EC50
Growth Rate        < 0.3 mg/L       ≤ 0.3 mg/L      0.46 mg/L      14.65 mg/L
Yield               < 0.3 mg/L       ≤ 0.3 mg/L        n.d.        0.63 mg/L

Executive summary:

The study was performed using 5 concentrations ranging from 5.8 to 581 mg/L (test item) and respectively 1 to 100 mg/L Gallium (III) nominal concentration. Incubation time (test system Desmodesmus subspicatus) was 72 hours. The cell concentration of each replicate was determined by measuring the cell numbers every 24 hours with an electronic particle counter. Growth rate μ and the yield1 were determined from the cell number at the respective observation times.

Significant inhibition of algal growth was observed in all tested concentrations.

At the beginning and at the end of the test, the content of Gallium (Ga) as part of the test item (17.2 % Gallium content) in the test solutions was determined using ICP-OES - determination. The measured values are not in the range ± 20% of the nominal value. A precipitation of

the test item was observed when adjusting the pH during the preparation of the stock solution for the test solutions and during the preparation of the stock solution for the stability test for the validation of the analytical method. The deviation from the 20% of the nominal value can therefore be explained. This is again confirmed by the very small margin of the % of nominal values observed for the test solutions (25 - 27%) and for the stability samples (25 - 30%). Therefore, the results are related to the geometric mean value of the measurements at the start and the end of the exposure (t = 0 and 72 h, respectively) (cf. OECD Guideline No. 201).

The results are given in relation to the dissolved test item content and additionally in relation to the dissolved Ga content. Due to the high inhibitory values, no EC10 value (yield) can be calculated.

The 72h-EC50 values of potassium dichromate (K2Cr2O7, CAS No. 7778-50-9) were determined in a separate reference test. The values lay within the range of the laboratory (growth rate 0.65 - 1.10 mg/L, yield 0.21 – 0.66 mg/L).

The following results for the test item Gallium(III) nitrate hydrate were determined:

Results of the test item (based on dissolved test item concentration)

Endpoint                    NOEC              LOEC                      EC10              EC50

Growth Rate          < 1.5 mg/L        ≤ 1.5 mg/L       2.54 mg/L       85.58 mg/L

Yield                       < 1.5 mg/L        ≤ 1.5 mg/L            n.d.               3.35 mg/L

Results of the test item (based on dissolved Gallium concentration)

Endpoint                   NOEC              LOEC                   EC10            EC50

Growth Rate        < 0.3 mg/L       ≤ 0.3 mg/L      0.46 mg/L      14.65 mg/L

Yield                     < 0.3 mg/L       ≤ 0.3 mg/L         n.d.                0.63 mg/L

Description of key information

A GLP conform study was performed on toxicity of gallium(III) nitrate hydrate towards the alga Desmodesmus subspicatus according to the OECD 201 guideline. The results were expressed based on the measured dissolved Ga concentration.

Key value for chemical safety assessment

EC50 for freshwater algae:

14.65 mg/L

EC10 or NOEC for freshwater algae:

0.46 mg/L