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Short-term toxicity to fish

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No studies are available on the short-term toxicity of the free acid form of isophthalic acid to freshwater fish, however a reliable (Klimisch 1, guideline- and GLP- compliant) study addresses the short-term toxicity of its structural analogue terephthalic acid.  
In this study (Government of Japan, Ministry of the Environment, 2003a), himedaka (Oryzias latipes) were 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 (ca. 17 mg/L at 25 degrees C):
Himedaka (O. latipes) 96 -h LC50 (semi-static): >18.6 mg TPA/L, 96 -h NOEC: 18.6 mg TPA/L.
This endpoint is a mean measured value and represents the maximum limit 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 IPA/L at 25 degrees C.
Support for this proposition is provided by another study (Knacker et al., 1993a, Klimisch 1) in which golden orfe (Leuciscus idus melanotus) were exposed to IPA following conversion to its sodium salt(s). IPA was first treated with NaOH solution, and exposure in this study was consequently to sodium isophthalate. No toxicity was observed under these conditions:
Golden orfe (L. idus melanotus) 96 -h LC50 (static): >907 mg IPA-equiv/L, 96 -h NOEC: 907 mg IPA-equiv/L.
These endpoints are mean measured values that represent the highest concentration applied and demonstrate the low intrinsic toxicity of the isophthalate moiety.
Isophthalic acid and its more environmentally relevant isophthalate sodium salt(s) exhibit very low short-term toxicity to fish.

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