Isophthalic acid

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.907 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

9.07 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.091 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

16 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1.246 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.125 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

1.69 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Conclusion on classification

Classification of isophthalic acid for effects in the environment

No studies of the aquatic toxicity of isophthalic acid (IPA) in the free acid form are available, however read-across from studies (Klimisch 1) of effects on fish, daphnia and algae exposed to its structural analogue terephthalic acid suggest negligible acute toxicity up to the limit of IPA's moderate solubility in water (ca 120 mg IPA/L). This view is supported by three guideline- and GLP-compliant acute toxicity studies (Klimisch 1) in which isophthalic acid was converted to its highly water-soluble sodium salt(s) prior to acute exposure of fish, Daphnia and algae. Similar conversion to isophthalates would be expected to precede the exposure of aquatic organisms in surface waters receiving IPA residues. The acute toxicity endpoints provided by these studies all exceeded the maximum exposures applied, which ranged from >907 to >996 mg IPA-equiv/L (mean measured). These data provide a clear indication of the very low intrinsic toxicity of the benzene-1,3-dicarboxylate structure. A further Klimisch 1 study is available of the long-term toxicity of the free acid form of terephthalic acid, in which the 21-d NOEC was 19.5 mg TPA/L (mean, measured) equivalent to the limit of solubility of TPA under the conditions of the test. Based on read-across, the long-term toxicity of IPA to aquatic invertebrates is expected to be qualitatively similar to that of TPA, however the location of the endpoint with respect to the aqueous solubility limit of IPA (ca. 120 mg/L at 25 degrees C) is uncertain.

 

In determining the classification appropriate to isophthalic acid, it is necessary to consider all available evidence concerning its persistence, potential to accumulate and predicted or observed environmental fate and behaviour that may present a long-term and/or delayed danger to the structure and/or functioning of aquatic ecosystems. These points are considered below.

 

Persistence.

Reliable studies are available to demonstrate that isophthalic acid is readily biodegradable. Isophthalic acid may therefore be expected to degrade rapidly, and to be completely mineralised, i.e. converted to CO2 and H2O without forming any recalcitrant metabolites. Isophthalic acid and its degradation intermediates are non-persistent. Isophthalic acid is expected to degrade under anaerobic as well as aerobic conditions.

Potential to accumulate.

QSAR-predicted and measured log10 Kow values for isophthalic acid (free acid, unbuffered, and after conversion to isophthalate salts, buffered at pH 7) are less than 3.0. The potential for isophthalic acid to bioaccumulate in the tissues of organisms that inhabit aquatic or terrestrial matrices contaminated with IPA is therefore negligible. The risk that isophthalic acid may biomagnify through successive trophic levels of aquatic or terrestrial food chains is consequently also negligible. 

Environmental fate and behaviour.

IPA is a dicarboxylic acid. The first step that may be predicted in its environmental fate, prior to biodegradation, is its conversion to isophthalate salts. Three reliable, GLP-compliant short-term studies are available in which IPA was treated with NaOH solution to convert the free acid to its highly soluble sodium isophthalate salt(s) prior to exposure to fish, daphnia and algae. No adverse effects occurred in these studies, up to and including the highest nominal IPA-equivalent concentrations of 1000 mg/L. The lowest endpoint from these three studies (the 96 -h LC50 for L. idus melanotus) was >907 mg IPA-equiv/L (mean measured). These studies demonstrate the low intrinsic toxicity of isophthalate to aquatic biota, and - taking into account its susceptibility to rapid biodegradation - provide assurance that isophthalic acid does not present a long-term and/or delayed danger to the structure and/or functioning of aquatic ecosystems. 

 

No classification is triggered based on available data, according to EEC Council Directive 79/831/EEC Annex VI, Part II (D) as described in Commission Directive 93/21/EEC or Regulation (EC) No 1272/2008.

 

Isophthalic acid is readily biodegradable and therefore does not satisfy the criteria for classification as persistent (P). 

The calculated BCF of isophthalic acid is 3.16 L/kg wet weight and below the threshold of 2000. 

Isophthalic acid does not satisfy the criterion for classification as bioaccumulative (B).

 

Based on read-across from the structural analogue terephthalic acid, and taking account of the low short-term aquatic toxicity of the sodium salt(s) of isophthalic acid, long-term NOECs for freshwater algae and invertebrates are expected to be at least ca. 19 mg/L, for the free acid form of IPA. Both values exceed the trigger value of 0.01 mg/L.

IPA does not satisfy the environmental effects criterion for classification as toxic (T).

 

Isophthalic acid is therefore not a PBT (or vPvB) substance.