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Toxicity to aquatic algae and cyanobacteria

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No studies are available on the toxicity of the free acid form of isophthalic acid to aquatic algae, however a reliable (Klimisch 1, guideline- and GLP- compliant) study addresses the toxicity of its structural analogue terephthalic acid.    
In this study (Government of Japan, Ministry of the Environment, 2003d), Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum) was exposed to high purity TPA (free acid), dosed from a stock solution prepared with DMSO, at a concentration intended to approximate to TPA's aqueous solubility limit. No toxicity was observed under these test conditions:
P. subcapitata 72 -h ErC50 (static): >19.0 mg TPA/L, 72 -h NOErC: 19.0 mg TPA/L.
This endpoint is a mean measured value and represents the maximum concentration achievable under the test conditions. It demonstrates an absence of toxicity at concentrations up to the solubility limit of TPA in water. Based on read-across, the same is considered to apply to IPA at the corresponding, higher solubility limit of ca. 120 mg/L at 25 degrees C .
Support for this proposition is provided by the low toxicity of IPA observed in another study (Knacker et al., 1993c, Klimisch 1) following conversion to its sodium salt(s), indicating the low intrinsic toxicity of the isophthalate moiety. Desmodesmus subspicatus (formerly known as Scenedesmus subspicatus) was exposed to IPA following its treatment with NaOH solution. No toxicity was observed under these conditions:
D. subspicatus 72 -h ErC50 (static): >996 mg IPA-equiv/L, 72 -h NOEC: 996 mg IPA-equiv/L.
These endpoints are mean measured values and represent the highest concentration applied.
Isophthalic acid and its more environmentally relevant isophthalate sodium salt(s) exhibit very low toxicity to unicellular aquatic algae.

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