reaction products of acetic anhydride and adipic acid

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

The substance is a UVCB substance. At start of the reaction adipic acid (solid) and excess of acetic anhydride (liquid) are mixed under nitrogen atmosphere. The reaction will take place for few hours at > 60 deg. C. At the equilibrium, the reaction mixture contains adipic acid, dianhydride with bis(acetic acid) (EC 253-964-1)(50-62 % w/w), acetic acid (EC200-580-7)(30-35 % w/w), acetic anhydride (EC203-564-8) (5-10 % w/w), adipic anhydride (EC 218-001-1) (0-2 % w/w), and oligomeric adipic anhydrides (0-2 % w/w). The exact composition is dependent on the reaction temperature and the concentration of the starting materials.

P

The intrinsic properties of the UVCB substance are related to the most hazardous component, acetic anhydride. Bio-degradation is an important fate process for the substance. Acetic anhydride will rapidly hydrolyse (t_1/24.4 min) to acetic acid. Adipic acid anhydrides decompose rapidly to acetic acid and adipic acid. One of the screening criteria for persistence (P) is that if a substance is considered to be readily biodegradable. Various studies indicate that acetic acid is readily biodegradable in water (e.g. Malaney, GW and Gerhold, RM, 1969, and Price et al, 1974). Biodegradation screening tests indicate that adipic acid is readily biodegradable in soil and water (OECD SIDS, 2004). Based on the chemical composition and the rapid hydrolysis of the target substance it is not considered as persistent (P) or very persistent (vP).

B

The bioconcentration factors and log Kow values were estimated for acetic anhydride and for the hydrolysis products of the target substance ie. acetic acid and adipic acid. Substance fulfils the bioaccumulation criterion (B) when the Bioconcentration factor is higher than 2000. Furthermore, for organic substances with a Log Kow value below 4.5 it is assumed that the affinity for the lipids of an organism is insufficient to exceed the B criterion, i.e. a BCF value of 2000.

The calculated log Kow of acetic anhydride is -0.58 which is lower than the screening criteria and Log Kow of acetic acid is -0.17 suggesting the low potential for bioconcentration in aquatic organisms.

The bioconcentration factor BCF=3 for adipic acid calculated from the octanol-water partition coefficient indicates that there is only a low potential for bioaccumulation (OECD; SIDS, 2004).

On the basis of this screening assessment the target substance is not considered to be bioaccumulative (B) or very bioaccumulative (vB).

T

Acetic anhydride will rapidly hydrolyse to acetic acid upon exposure to the aquatic environment. It was therefore appropriate to base the toxicity assessment on acetic acid. None of the studies evaluated for acetic acid meet the toxicity (T) screening criteria ie. NOEC or EC50 values are lower than 0.01 mg/L OECD; SIDS (1997). Therefore, acetic anhydride or acetic acid is not considered to be toxic (T) on the basis of the screening criterion. Also, available data do not indicate adipic acid to be considered as toxic (T) OECD; SIDS (2004).

This target substance does not meet the criteria for classification for carcinogenic, mutagenic or toxic to reproduction. Furthermore, there is no other evidence of chronic toxicity as the substance does not meet the criteria for classification for target organ toxicity after repeated exposure (STOT-RE).

Therefore, the target substance, reaction products of acetic anhydride and adipic acid, does not meet the toxicity criterion (T)