2-methylbutyl acrylate

Long-term toxicity to aquatic invertebrates

Description of key information

21-day NOEC (growth): 0.249 mg/L (OECD 211)

Additional information

Chronic toxicity of 2-methylbutyl acrylate (2-MBA) to Daphnia magna was determined in a 21-day study conducted according to OECD TG211 under GLP criteria.  Growth in adults was the most sensitive endpoint.  The key study is considered reliable without restrictions.  The key result is similar to a supporting study for the analogous compound n-butyl acrylate (n-BA), which had a 21-day NOEC (reproduction) of 0.136 mg/L (study conducted under GLP according to OECD211).  For comparison, the 21-day NOEC (growth) for n-BA was 0.457 mg/L, demonstrating that growth is a less sensitive endpoint for n-BA than for 2-MBA.  The supporting study is considered reliable without restriction for n-BA, but as read-across to 2-MBA is reliable with restriction (Klimisch 2).  Both acrylates are readily biodegradable, which would mitigate long-term toxicity under environmental conditions.  2-MBA and n-BA are acrylate esters which exert toxicity by virtue of electrophilic (Michael-type) addition to cellular nucleophiles such as glutathione⁽¹⁾or cellular proteins⁽²⁾.  The result of this addition is glutathione depletion followed by oxidative damage to cells, or alternatively protein inactivation.  Detoxification is by ester hydrolysis followed by downstream conversion and entry of acrylic acid to the citric acid cycle⁽³⁾.  n-Butyl acrylate (n-BA) differs from 2-MBA by the latter's additional methyl branch adjacent to the ester moiety on the alcoholic side of the molecule.  Molecular weight, hydrophobicity and vapor pressure are similar between 2-MBA and n-BA. The entirely linear structure of n-BA is expected to be somewhat more amenable to esterase activity and beta-oxidation than the 2-methyl branched structure of 2-MBA.  In addition, n-BA has a slightly lower log Kow.  Taken together, n-BA may be slightly less toxic than 2-MBA with slightly faster detoxification (by ester hydrolysis), but is expected to have generally similar toxicity values.

 

References:

1. A. P. Freidig, H. J. M. Verhaar, J. L. M. Hermens.  1999.  Comparing the Potency of Chemicals with Multiple Modes of Action in Aquatic Toxicology:  Acute Toxicity Due to Narcosis versus Reactive Toxicity of Acrylic Compounds.  Env. Sci. Technol. 33 (17): 3038–3043.

2. K. Chan & P. J. O’Brien.  2008. Structure–activity relationships for hepatocyte toxicity and electrophilic reactivity of a,b-unsaturated esters, acrylates and methacrylates.  J. Appl. Toxicol. 28 (8): 1004–1015.

3.  H. Greim, J. Ahlers, R. Bias, B. Broecker, H. Hollander, H.-P. Gelbke, S. Jacobi, H.-J. Klimisch, I. Mangelsdorf, W. Mayr, N. Schön, G. Stropp, P. Stahnecker, R. Vogel, C. Weber, K. Ziegler-Skylakakis, E. Bayer.  1995.  Assessment of structurally related chemicals: Toxicity and ecotoxicity of acrylic acid and acrylic acid alkyl esters (acrylates), methacrylic acid and methacrylic acid alkyl esters (methacrylates).  Chemosphere 31 (2): 2637–2659.

 

Data matrix – Analog approach
	Target substance	Source substance
CHEMICAL NAME	2-methylbutyl acrylate	n-butyl acrylate
CAS#	44914-03-6	141-32-2
Molecular formula	C8H14O2	C7H12O2
Molecular Weight	142.2	128.2
PHYSICO-CHEMICAL DATA
Melting Point	≤ -75 °C	Not available
Boiling Point	161.7 °C at 1013hPa	147 °C at 1013hPa
Density	0.8886 g/cm3 at 25 °C	0.9 g/cm3 at 20.0 °C
Vapour Pressure	1.7 hPa at 20°C	5 hPa at 22.2°C
Partition Coefficient (log Kow)	2.9	2.38 (at 25°C)
Water Solubility	316 mg/L at 23 °C	Not available
ENVIRONMENTAL FATE and PATHWAYS
Photodegradation	DT50 1.04 d (AOPWIN v1.92)	Not determined
Stability in Water	Adaptation, readily biodegradable	DT50, 1100 day at pH 7, 25 °C (40CFR796.3500)
Aerobic Biodegradation	60% after 11 days (OECD 301D)	80 - 90% after 28 days (OECD 310)
Bioconcentration	Not bioaccumulative (Low log Kow, extensive metabolism)	Not bioaccumulative (Low log Kow, extensive metabolism)
Transport and Distribution	Koc 263 – 302 (Calculated by TGD method)	Koc 40-148 (EPA OTS 796.2750)
Henry's Law constant	96 Pa*m3/mol at 23.1 °C	Not determined
ENVIRONMENTAL TOXICITY
Long-Term Toxicity to Aquatic Invertebrates (D. magna)	21-day NOEC (growth) 0.249 mg/L (OECD 211)	21-day NOEC (reprod) 0.136 mg/L (OECD 211)