Diarsenic trioxide

Endpoint summary

Additional information

The available reliable ecotoxicity data about the effect of arsenic on aquatic organisms are based on dissolved elemental arsenic concentrations. Reliable chronic NOEC and EC₁₀ values were identified for 27 freshwater species and 11 marine species. The reliable data were based on tests with inorganic As(III) and As(V) substances.

The available data do not allow a conclusion regarding the As source or the effect of specific water parameters, including hardness, pH, phosphate level, on the toxicity of arsenic to aquatic organisms. All reliable bounded NOEC and EC₁₀ values were taken forward to the derivation of the PNEC according to the statistical extrapolation approach. In case several data were available for one species, the lowest NOEC or EC₁₀ value for the relevant endpoints (e.g. growth rate for algae) is selected.

The most sensitive chronic NOEC/EC₁₀ -values for arsenic toxicity to the 27 freshwater species covered that were selected for the PNEC derivation are shown below:

Test organism	Taxonomic group	Endpoint	NOEC/EC10 (µg As/L)
Achnanthidium minutissimum	Alga	Growth rate	122.1
Asellus aquaticus	Isopod	Mortality	97.3
Botryococcus braunii	Alga	Growth rate	749.2
Brachionus patulus	Rotifer	Mortality	1500.0
Ceriodaphnia dubia	Crustacea	Reproduction	793.0
Chironomus riparius	Insect	Reproduction	629.3
Chlorella sp.	Alga	Growth rate	6403.0
Closterium aciculare	Alga	Growth rate	4.6
Cyclopoids taxa 1	Copepod	Mortality	2670.0
Cyclopoids taxa 2	Copepod	Mortality	40.0
Daphnia magna	Crustacea	Reproduction	633.0
Gammarus pseudolimnaeus	Amphipod	Mortality	88.0
Gammarus pulex	Crustacea	Mortality	380.0
Harpactoid taxa	Copepod	Mortality	130.0
Hyalella azteca	Amphipod	Growth (weight)	200.8
Hydropsiche pellucidula	Mayfly	Mortality	98.0
Jordanella floridae	Fish	Growth (weight)	2130.0
Lemna minor	Plant	Growth rate (number of fronds)	938.0
Lermna disperma	Plant	Growth (surface area)	292.0
Monoraphidium arcuatum	Alga	Growth rate	71.2
Navicula sp.	Alga	Growth rate	149.8
Oncorhynchus mykiss	Fish	Development (abnormalities)	234.0
Pediastrum duplex	Alga	Growth rate	4.6
Pimephales promelas	Fish	Growth (weight)	2130
Scenedesmus actus	Alga	Growth rate	50.1
Staurastrum paradoxum	Alga	Growth rate	670.4
Wolffia arrhiza	Plant	Growth rate (number of fronds)	192.0

No-effect levels for arsenic toxicity to freshwater were situated between 4.6 µg As/L and 6403 µg As/L, i.e., a difference of a factor of 1391 between the most and least sensitive species. The most sensitive species appeared to be the algae Closterium acculare and Pediastrum duplex, the least sensitive species of the data set was for another alga, i.e. Chlorella sp.

The most sensitive chronic NOEC/EC₁₀ -values for arsenic toxicity to the 11 marine species covered that were selected for the PNEC derivation are shown below:

Test organism	Taxonomic group	Endpoint	NOEC/EC10(µg As/L)
Americamysis bahia	Crustacea	Mortality	631
Fucus serratus	Macroalga	Growth (length)	18.7
Lytechinus variegatus	Echinoderm	Mortality	120
Macrocystis pyrifera	Macroalga	Growth & development	40
Paracentrotus lividus	Echinoderm	Development	56
Penaeus indicus	Crustacea	Growth	13.2
Platichthys stellatus	Fish	Growth (length & weight)	312
Skeletonema costatum	Alga	Growth rate	32.6
Crassostrea angulata	Mollusc	Development	23.6
Crassostrea gigas	Mollusc	Development	73.1
Champia parvula	Macroalga	Reproduction	60

No-effect levels for dissolved arsenic were situated between 13.2 µg As/L and 631 µg As/L, i.e., a difference of a factor of 48 between the most and least sensitive species. The crustacean Penaeus indicus was the most sensitive trophic level. The least sensitive species was observed for another crustacean, i.e. the mysid Americamysis bahia.

Relevant information on acute toxicity of arsenic to standard fish species, invertebrates and algae were retained for classification purposes when tests were in line with accepted standard testing guidelines. An overview of the critical data is given hereunder:

• For fish, the lowest reliable data point for arsenic, added to the test medium as sodium arsenate, was put forward for hazard assessment purposes: 96h-LC₅₀of 12600 µg As/L for the fish P. promelas.
• For invertebrates, the following lowest reliable data point for sodium arsenate (test organism: D. magna) was put forward for hazard assessment purposes: 48h-LC₅₀of 1500 µg As/L for the cladoceran D. magna.
• For algae, two reliable acute data points, representing the most sensitive strain of Chlorella sp. were available for hazard assessment purposes. The lowest value of those two data points was 25200 µg As/L and is considered as a reliable acute toxicity value for hazard assessment purposes. No reliable EC₅₀-values were reported for other relevant algal species.

The identified long-term data for standard species (and trophic levels) that are considered for classification purposes, revealed a chronic ERV of 234 µg As/L. An overview of the most sensitive freshwater species-specific NOEC/EC₁₀-values for arsenic used for chronic ERV derivation is shown below:

Test organism	Taxonomic group	Endpoint	NOEC/EC10 (µg As/L)
Ceriodaphnia dubia	Crustacea	Reproduction	793.0
Chlorella sp.	Alga	Growth rate	6403.0
Daphnia magna	Crustacea	Reproduction	633.0
Lemna minor	Plant	Growth rate (number of fronds)	938.0
Oncorhynchus mykiss	Fish	Development (abnormalities)	234.0
Pimephales promelas	Fish	Growth (weight)	2130