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In agreement with the OECD guidance document on aquatic toxicity testing of difficult substances and mixture (Guidance n°23, Sept. 2000), as the stability study indicates that phosphorous acid, tri-C12-C14-alkyl esters is completely stable over a 24h period (100% recovery at 24h), it has been decided to test the parent substance. This consideration has also been taken since the toxicity of the major degradation products (phosphorous acid, dodecan-1-ol and tetradecanol) have already been investigated in their own registration dossiers.

In order to ensure the exposure to the parent substance, semi-static tests with a 24h medium renewal have been considered for assessing acute aquatic toxicity to daphnids and fish, while no other possibility than a static test has to be considered for algae. Furthermore, due to the surfactant property of the substance, precautions were taken to avoid the presence of non-dissolved materials or micelles/micro-dispersions that may lead to the mortality of tested organisms by physical action.

Thus, several preliminary studies have been performed to define the best adapted protocol to prepare the saturated solution and ensure that exposure to the substance was maximised, especially as no suitable analytical method could be determined for the test media. DOC measurements were therefore performed to ensure exposure. The acute toxicity tests carried out on freshwater invertebrates and fish show no mortality at the limit of solubility of the substance. The loading rate in these studies was > 780 mg/L. In the algae study, a slight toxicity was observed at the limit of solubility. An EC10 of 2.6 mg/L could be derived, which is nearly the water solubility determined in the test medium (2.7 mg/L).

As renewal of the medium was not possible in the algal test, it is assumed that the observed toxicity might be related to the degradation products (probably dodecan-1-ol currently classified as H400 and H411) rather than the parent substance.

Therefore, the three available acute toxicity tests performed on phosphorous acid, tri-C12 -C14 -alkyl esters lead to the following conclusion : L(E)L50 > limit of solubility (loading rate > 780 mg/L).

No chronic toxicity test is available but as no acute toxicity of the parent substance has been observed at the limit of solubility and due to its rapid degradation in water, it seems not relevant to investigate long-term aquatic toxicity of phosphorous acid, tri-C12-C14-alkyl esters.

Regarding toxicity to microorganisms, the conducted biodegradation test included a toxicity control that indicated no toxicity of the substance up to the nominal concentration of 27 mg/L, considered as a NOEC (29d).

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