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Long-term toxicity to aquatic invertebrates

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Description of key information

(96 h) NOEC 85 mg/L (r-a) C. virginica

Key value for chemical safety assessment

Additional information

The endpoint is waived based on the favourable outcome of the risk characterisation.

No data on short term toxicity of DTPM-xNa salts, CAS 22042-96-2, to freshwater invertebrates are available. However, a reliable 96 h NOEC value of 67 mg active acid/L and an EC50 187 mg active acid/L have been determined for the effects of DTPMP acid on the growth (shell deposition) of the eastern oyster Crassostrea virginica. Although not a true long-term study it is a sub-lethal endpoint with a sensitive endpoint and has been included in this section

The results of tests conducted on DTPMP and its salts are directly comparable, because the substance will fully dissociate in solution and the ionisation state will depend only on the pH of the test medium. The counterion is not considered to contribute to effects in fish. At environmentally-relevant pH values, DTPMP will be ionised typically 6-7 times, and will form stable complexes with metal ions.

Here, the value of 67 mg equivalent active acid/L may be directly read-across. It is convenient to convert the result into units of mg DTPMP-xNa salt/L at relevant conditions of pH by considering the ionisation state of DTPMP (CAS 15827-60-8) at the 67 mg/L concentration.

The pH of the test medium at this concentration has been reported as 8. At this pH DTPMP is ionised 8 times (pKa6= pH 8.3), hence the calculation is to determine the concentration of HEDP-xNa (where x = 8) which would be equivalent to 67 mg active acid/L. In the calculation we also remove the number of hydrogen atoms substituted by the sodium salt from the MW of HEDP, in this case 8.

The 96 h LC50 for DTPMP acid is 67 mg/L, which is equivalent to a 96 h LC50 value of 67 * 1.26 = 85 mg/L DTPMP-xNa

[using MW(DTPMP-7Na)/MW(DTPMP) = 573.2+((21.982-1.008)*8) / 573.2= 1.29