Arsenic acid

Endpoint summary

Additional information

Solubility and stability of Arsenic acid in water

 

The available data on arsenic acid indicate a high solubility of the substance with a value of 302 g/L in water. This means that the ranges of testing concentrations are far below the solubility limit of Arsenic in water. 

 

Moreover, Henry’s law constant (H) quantifies the partitioning of chemicals between the aqueous phase and the gas phase.

For chemicals with H values less than 0.01 Pa m³/mole, the chemical is less volatile than water and as water evaporates the concentration of the chemical in the aqueous phase will increase; for chemicals with H values around 100 Pa m³/mole, volatilisation will be rapid.

For arsenic acid, the H value was calculated to be 0.868 Pa m³/mole at 25 °C (EUSES calculations based on the Vapour pressure = 1845 pa, water solubility = 302 g/L and mol. weight = 142 g/mol).

 

Therefore, based on his physico-chemical properties, Arsenic acid is not expected to volatilise.

 

Moreover, several in several studies the tested concentrations were measured analytically. The recoveries were quite high (more than 90%) indicating a good solubilisation of the test substance.

 

Based on these observations it can be concluded that the test substance arsenic acid stays in solution in water. Therefore the absence of concentrations monitoring is not invalidating for the aquatic studies.

 

Arsenic acid toxicity to aquatic organisms

 

A large set of data on aquatic toxicity of arsenic acid is available.

 

Large differences of toxicity were observed between the tested species. Individual studies as well as data reviews are available.

The validated references are listed in the table below.

 

Freshwater organisms

 

Species	Test duration/ conditions	Endpoint	Result (mg/L)	Reference
Fish
Rainbow trout, juvenile Rainbow trout,alevin	96 h 96 h	LC50 LC50	= 67.5 > 360	Buhl KJ & Hamilton SJ (1990)
Fathead minnow (Pimephales promelas)	96h	LC50	25.6	Eisler R (1988)
Fathead minnow (Pimephales promelas)	35 d	LOEC NOEC	1.9 0.97	Machado M.W
Rainbow trout, juvenile	24 weeks	NOEC	13 µg As/g diet	Cockell K.A (1991)
Daphnia
Daphnia pulex	96h	LC50	3.4	Theegala, C. S. (2007)
Daphnia magna	96h	NOEC	44.66 mg/l (35.22-50.93)	Fargasova A., (1994)
Daphnia pulex	21d	NOEC	> 1	Theegala, C. S. (2007)
Daphnia pulex	26d	LOEC   NOEC	0.020 arsenate = 10.5 arsenic 5 µg/L As	Chen, CY (1999) cited in Lepper P., 2007
Algae and other aquatic plants
Scenedesmus obliguus	96h	EC50	0.159	Chen, F (1994) cited in Lepper P., 2007
Asterionella	24 d	NOEC	0.160	ConwayHL (1978)
Ankistrodesmus falcatus	14 d	EC50 NOEC	0.256 0.01	Vocke, R.W. (1980)
Scenedesmus obliquus	14 d	LC50	0.048	Vocke, R.W. (1980)
Selenastrum capricornutum	14 d	LC50 NOEC	30.7 12	Vocke, R.W. (1980)
Microorganisms
Pseudomonas putida	16h	EC10	6.75	Bringmann, G (1976)

 

Marine organisms

 

Species	Test duration/ conditions	Endpoint	Result (mg/L)	Reference
Sheepshead minnow (cyprinodon vertegatus)	96 h	LC50 NOEC	28 13	Lelievre, M.K. (1990)
Mysid shrimp (Mysidopsis bahia)	96h	LC50	2	Lelievre, M.K. (1990)
Strongylocentrotus purpuratus	48 h	LOEC EC10	0.011 0.006	Garman(1997) cited in Lepper P., 2007
Skeletonema costatum	6 d	LOEC	0.013	Sanders J.G. (1979) cited in Lepper P., 2007

Conclusion:

 

The available toxicity data on freshwater and marine organisms belong to the same growth order. The lowest long term data belong to the range 5-10 µg/L and were observed on invertebrate and algae species.