A mixture of: tetrasodium-phosphonoethane-1,2-dicarboxylate; hexasodium-phosphonobutane-1,2,3,4-tetracarboxylate

Short-term toxicity to aquatic invertebrates

Description of key information

There is conflicting information between the four studies available. See discussion below.

Additional information

Four studies are available on the acute toxicity of ITC 288/S to Daphnia magna.

The results obtained are summarised as follows:

1) Safepharm (1992): 48-h EC50 = 5mg/l (substance tested as dried “total” active substance = 100% notified substance)

2)Institute of Freshwater Ecology (1993): 48-h EC50 > 1000 mg/L (substance tested as it is supplied, a 50% aqueous solution = 57.4% notified substance => Result quoted relative to total notified substance: 48-h EC50 > 574 mg/L)

3) Safepharm (2000): 48-h EC50 > 1000 mg a.i./L (substance tested as a 40% aqueous solution = 44.3% notified substance => Result quoted relative to total notified substance: 48-h EC50 > 1148 mg/L)

4) Safepharm (1995): 48h EC50 > 1000 mg/l (Substance tested as dried “total” active substance = 114.6 % notified substance => Result quoted relative to total notified substance: 48-h EC50 > 1148 mg/L);

 

The three first studies listed above were performed according to the OECD testing Guideline and followed the GLP. The last one was considered as reliable with restrictions as no analytical monitoring was performed and problems of solubility and calcium precipitation were observed in the range-finding study.

 

In order to determine the reasons for the disparity in the results, a thorough evaluation of the OECD 202 guideline methodology employed at the two laboratories was undertaken. The disparity in the results of the 48-h immobilisation study for the tested new substance and the 50% aqueous sample was attributable to the use of water of different hardness. The first study had been conducted in "soft water" (hardness 50ppm expressed as CaCO3) whereas the second assay using the 50% aqueous dilution was conducted in "harder" water (270 ppm as CaCO3).

It was established that ITC 288/S exerted an effect on the exposed Daphnia as a result of sequestration of calcium ions from the dilution water (osmotic shock). This sequestering (chelation) effect is a recognised effect associated with phosphonates. Subsequently two acute (in 1995 and 2000) and one chronic toxicity (in1998) studies were conducted on Daphnia magna with dry powder or aqueous solution of ITC 288/S. In these studies, no acute toxicity was observed up to 1000 mg/l of test material, and no chronic toxicity was observed up to 100 mg/l of test material.

Since these investigations the OECD 202 and the EC test guideline were updated in 2004 and the revised guideline recommended dilution waters of higher hardness values be employed (“Hardness between 140 and 250 mg/l (as CaCO3) is recommended for D. magna”). Currently, contract laboratories use dilution water with a hardness of ~270 mg/l as CaCO3.

Considering that the immobilisation observed in the first study was due to a physical effect (osmotic shock), this study is not considered as reliable and not used for the risk assessment of the substance. Instead, as a valid chronic toxicity to Daphnia test is available showing no effects up to 100mg/L, this is used in the risk assessment.