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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
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 (avergae 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 behaviour: 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 behave much differently from the monomer units in the environment. As a result, the target chemical, although only partially composed of acrylic acid monomers, is considered to exhibit a partition behaviour similar to the one of 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
Key result
Type:
Koc
Value:
6 - 137 L/kg
Matrix:
soil
Remarks on result:
other: arithmetic mean = 45.3 L/kg
Remarks:
read-across from acrylic acid
Type:
Kd
Value:
0.2 - 0.63 L/kg
Matrix:
soil
Remarks on result:
other: arithmetic mean = 0.41 L/kg
Remarks:
read-across from acrylic acid
Key result
Type:
Koc
Value:
33
Matrix:
sediment
Remarks on result:
other: read-across from acrylic acid
Type:
Kd
Value:
0.41
Matrix:
sediment
Remarks on result:
other: read-across from acrylic acid
Conclusions:
Using a read-across approach, the REACH substance is expected to exhibit an adsorption coefficient Koc in the range 6-137 L/kg (Kd = 0.20-0.63) in the soil compartment, depending on the pH and organic carbon content. Using the same read-across approach, the REACH substance item is expected to exhibit an adsorption coefficient Koc of 33 L/kg (Kd = 0.41) in the sediment compartment.

Description of key information

As no data were available to characterize the adsorption/desorption behaviour of the REACH substance in soil and sediment compartments, 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, and is expected to exhibit a partition behaviour similar to the one of acrylic acid: both are indeed hydrophylic substances (log Pow < 1) with a high solubility in water, a low volatility (VP < 5 hPa) and a low potential for bioaccumulation in living organisms (log Pow < 4).

According to the data available on acrylic acid, the REACH substance is expected, by analogy, to exhibit an adsorption coefficient Koc in the range 6-137 L/kg (Kd = 0.20-0.63) in the soil compartment, depending on the pH and organic carbon content; an average Koc of 45.3 L/kg (arithmetic mean) was used for the exposure assessment of the REACH substance in the soil compartment.

As well, according to the data available on acrylic acid, the REACH substance is expected, by analogy, to exhibit an adsorption coefficient Koc of 33 L/kg (Kd = 0.41) in the sediment compartment; this value was used for the exposure assessment of the REACH substance in the sediment compartment.

Key value for chemical safety assessment

Koc at 20 °C:
45.3

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
-0.38

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
-0.38

Additional information