[[(phosphonomethyl)imino]bis[ethylenenitrilobis(methylene)]]tetrakisphosphonic acid, potassium salt

Endpoint summary

Description of key information

There are no data for the potassium salts of DTPMP. Therefore data have been read across from sodium salts of DTPMP. 
In a good quality 90-day feeding study (CTL, 1998) conducted to OECD 408 and GLP, groups of 12 male and 12 female Wistar-derived rats were fed diets containing 0 (control), 100, 1000 or 10000 ppm (equivalent to 8.2, 82.5 and 841.9 mg/kg bw/day in males and 9.2, 92.3 and 902.6 mg/kg for females) Dequest 2066A (sodium salt of DTPMP) for 90 consecutive days. There were no deaths and the majority of parameters were unaffected by the treatment. Minor changes in certain haematological parameters (red blood cell count was significantly increased, mean cell volume and mean cell haemoglobin concentration were significantly decreased) were noted at the highest dose. There was also a decreased incidence in Perls' staining of the spleen. Bone density was significantly increased in both sexes in the highest dose group, and the incidence of microlithiasis in the kidney was reduced at all dose levels. These changes are indicative of the influence of Dequest 2066A on calcium homeostasis, however, without causing any changes in calcium plasma levels. Therefore, the changes were not considered to be of toxicological significance, and the NOAEL was 10000 ppm (equivalent to to 841.9 and 902.6 mg/kg bw/day of the salt in males and female, respectively).
However, it is the opinion of the author of this study summary that anaemia in humans is of concern, and therefore the NOAEL is reduced to 1000 ppm (equivalent to 82.5 and 92.3 mg/kg bw/day for males and females, respectively). 

Additional information

The key study was the most reliable study available for the sodium salt of DTPMP. The category hypothesis is that at a defined pH, a salt will behave no differently to the parent acid, at identical concentration of the particular speciated form present, and will be fully dissociated.Hence some properties for the aqueous salt can be directly read across (with suitable mass correction) to the parent acid andvice versa(see CSR for mass correction values). In the present context the effect of the alkaline metal counter-ion (sodium/potassium/calcium) will not be significant and has been extensively discussed in the public literature. In biological systems polyvalent metal ions will be present, and the phosphonate ions show very strong affinity to them.

Justification for classification or non-classification

The data suggest that there is no need to classify for adverse effects following repeated exposures. Although the NOAEL for effects on haematological parameters was within the classifiable range, the effects are not sufficiently severe to trigger classification.