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Long-term toxicity to fish

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Description of key information

(60 d) NOEC 31 mg active acid/L (r-a) Salmo gairdneri (new name: Oncorhynchus mykiss).

Key value for chemical safety assessment

Additional information

No data on short term toxicity of DTPM-xNa salts, CAS 22042-96-2, to freshwater invertebrates are available. However, a reliable 60 day ELS toxicity test has determined a NOEL value of 25.6 mg active acid/L for the effect of DTPMP acid based on fry weight of the freshwater fish Salmo gairdneri (new name: Oncorhynchus mykiss).

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 times, and will form stable complexes with metal ions.

Here, the value of 25.6 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 25.6 mg/L concentration.

The pH range of the test medium is thought to be around 6. At this pH DTPMP is ionised 6 times (pKa6= pH 6.23), hence the calculation is to determine the concentration of HEDP-xNa (where x = 6) which would be equivalent to 25.6 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 7.

The 96 h LC50 for DTPMP acid is 25.6 mg/L, which is equivalent to a 96 h LC50 value of 25.6 * 1.22 = 31 mg/L DTPMP-xNa

[using MW(DTPMP-7Na)/MW(DTPMP) = 573.2+((21.982-1.008)*6) / 573.2= 1.22