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Short-term toxicity to aquatic invertebrates

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Description of key information

(48 h) EC50 9500 mg active acid/L C. tentans
(96 h) LC50 >252 mg active acid/L A. tonsa

Key value for chemical safety assessment

Additional information

Freshwater

A reliable 48 h EC50 value of 7589 mg active acid/l has been determined for the effects of DTPMP acid on the mortality of the freshwater insect Chironomus tentans. The organisms is normally used for sediment tests, however since this is an aqueous exposure, the study has been considered in the freshwater aquatic assessment. No water quality data has been presented. Since there were no mortality in the controls and the pattern of mortality appeared regular it can be safely assumed that water quality parameters were within the norm.

No data on short term toxicity of DTPM-xNa salts, CAS 22042-96-2, to freshwater invertebrates are available. However, a reliable 48 h EC50 value of 7589 mg active acid/l has been determined for the effects of DTPMP acid on the mortality of the freshwater insect Chironomus tentans.

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 7589 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 7589 mg/L concentration.

The pH range of the test medium has not been reported but is assumed to be around 7. At this pH DTPMP is ionised 7 times (pKa6= pH 7.23), hence the calculation is to determine the concentration of HEDP-xNa (where x = 7) which would be equivalent to 7589 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 7589 mg/L, which is equivalent to a 96 h LC50 value of 9500 * 1.26 = mg/L DTPMP-xNa

[using MW(DTPMP-7Na)/MW(DTPMP) = 573.2+((21.982-1.008)*7) / 573.2= 1.26

 

 

Marine

 

A reliable 48 h EC50 value of >252 mg active acid/l has been determined for the effects of DTPMP-xNa on the immobility of the marine copepod Acartia tonsa.