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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
- Read-across hypothesis: "Different compounds have the same type of effect(s)"

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
- Target chemical: 2-Propenoic acid, homopolymer (purity ≥ 99.0%) = UVCB substance composed of acrylic acid monomers (Mw = 72 g/mol) and 2-carboxyethyl acrylate oligomers (average Mw = 208.8 g/mol)
- Source chemical: Acrylic acid = monoconstituent substance composed of acrylic acid monomers (Mw = 72 g/mol)

3. ANALOGUE APPROACH JUSTIFICATION
- Common structure: the constituents of the target and source chemicals share identical functional groups (i.e. one terminal carboxylic acid group and one terminal vinyl group) and only differ in the presence/absence of one or several -CH2-CH2-COO- pattern(s) in their structural backbones. This pattern being introduced as a result of (poly)addition reactions, it is only present in the polymerized units of acrylic acid (average number of -CH2-CH2-COO- patterns per vinyl group: < 3) and is absent from the monomer units.
- Common physico-chemical/fate properties: the target and source chemicals are both hydrophylic substances (log Pow < 1) with a high solubility in water and a low volatility (VP < 5 hPa). Both substances have a low potential for bioaccumulation in living organisms (log Pow < 4) and a low potential for persistence in environmental compartments (rapidly degradable).
- Common mode of action: the toxic effects of the target and source chemicals are expected to result from their acidic character (carboxylic acid group) and from the reactivity of their double bond (vinyl group). As the polyaddition reactions lead only to an increase in the chain length/molecular weight without an increase in the number of reactive functional groups, the low molecular-weight polymerized units of acrylic acid (from the test item) are not expected to exert higher toxicity than the monomer units. As a result, the target chemical, although only partially composed of acrylic acid monomers, is considered at the very worst to be as toxic as the source substance.

Further information (including data matrix) is available in the attached read-across justification document.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
47 - 95 mg/L
Basis for effect:
mobility
Remarks on result:
other: Daphnia magna (freshwater sp.)
Remarks:
read-across from acrylic acid
Key result
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
97 mg/L
Basis for effect:
mobility
Remarks on result:
other: Americamysis bahia (marine sp.)
Remarks:
read-across from acrylic acid
Conclusions:
Using a read-across approach, the REACH substance is expected to exhibit a 48-hour 50% effective concentration EC50 in the range >10-100 mg/L when exposed to freshwater invertebrate species; toxic effects are expected to be similar in marine invertebrate species.

Description of key information

As no data were available to characterize the acute toxicity of the REACH substance to freshwater invertebrate species, a read-across approach was followed to fill in the endpoint. The REACH substance is composed of polymerized units of acrylic acid (identified as "2-carboxyethyl acrylate oligomers") and residual monomers of acrylic acid. As the toxicity of acrylic acid derivates is not expected to increase with their increasing molecular weight, a worst-case analogy was made between the REACH substance and acrylic acid, the latter being considered as its most toxic constituent.

 

According to the data available on acrylic acid, the REACH substance is expected, by analogy, to exhibit a 48-hour 50% effective concentration EC50 in the range >10-100 mg/L when exposed to freshwater invertebrate species; toxic effects are expected to be similar in marine invertebrate species. The lowest EC50 value obtained with acrylic acid (i.e. 47 mg/L) was used, by analogy, for the environmental hazard assessment of the REACH substance.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
47 mg/L

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