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Tetrachlorophthalic anhydride reacts rapidly with water, forming tetrachlorophthalic acid (CAS 632-58-6). Tests with tetrachlorophthalic anhydride in aquatic solutions measure effects of tetrachlorophthalic acid rather than effects of tetrachlorophthalic anhydride. Consequently, tetrachlorophthalic acid can also be used to evaluate the aquatic effects of tetrachlorophthalic anhydride.

Tetrachlorophthalic acid is a weak to medium strong acid and partly dissociating in water causing a pH shift (pKa1: 3.01; pKa2: 0.55). The tolerance of water organisms towards pH is diverse. Recommended pH values for test species listed in OECD guidelines are between 6 and 9.

Toxicity to fish:

Acute toxicity to fish (Oryzias latipes) was determined according to the OECD TG 203 at the National Institute of Technology and Evaluation, Japan . Tetrachlorophthalic acid was used as test substance and the test was carried out in buffered medium. No toxic effect and abnormal behavior were observed. Analytical monitoring was carried out in this test showing stability of the test substance during 96 hours of exposure. A LC 50 of > 106 mg/l, based on measured concentration was obtained.

Toxicity to daphnia:

Concerning the toxicity towards aquatic invertebrates, an acute toxicity test to Daphnia magna with the hydrolysis product tetrachlorophthalic acid is taken into account to draw a conclusion on toxicity towards aquatic invertebrates for tetrachlorophthalic anhydride. The study was performed according to the OECD TG 202 at the National Institute of Technology and Evaluation, Japan. No toxic effect and abnormal behavior were observed during 48 hours of exposure in buffered medium. As analytical monitoring was performed showing stability of the test substance, the result of EC 50 > 104 mg/l relates to measured concentrations.

Toxicity to algae:

In a test, the fresh water alga Pseudokirchenerilla subcapitata was exposed to the hydrolysis product tetrachlorophthalic acid for 72 hours. The experiment was conducted according to the OECD TG 201 at the National Institute of Technology and Evaluation, Japan. An EC50 of 84 mg/l and a NOEC of 25 mg/l, based on measured concentrations was obtained in this test. Analytical monitoring was carried out and stability of the test substance was confimed during the duration of exposure. Although, at the highest test concentration the pH decreases below the tolerance limit of algae, and the effect observed may be mainly caused due to the pH shift of the substance, the result of this study is regarded as reliable and is used for assessment.

Toxicity to microorganisms:

The effect of tetrachlorophthalic anhydride on aerobic biological sewage treatment processes was assessed according to Official Journal of the EG L 133 Part C: Biodegradability, by determining inhibition of respiration of the mixed community of microorganisms present in a sample of activated sludge. Activated sludge obtained from a laboratory unit fed with predominantly domestic sewage was exposed for a period of three hours. No respiration inhibition, relative to the mean control rate, occurred in any of the tetrachlorophthalic anhydride treatments and the 3-h EC50 was therefore >10000 mg tetrachlorophthalic anhydride/L, the highest concentration tested.

All studies are classified as acceptable and satisfy the guideline requirements for the toxicity studies to aquatic organisms.