Potassium salts of [hexane-1,6-diylbis[nitrilobis(methylene)]]tetrakisphosphonic acid (4-7 K:1)

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

1 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.1 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

3 703 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

370 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

10.86 mg/kg soil dw

Assessment factor:

50

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

HMDTMP and its salts are phosphonic acid substances of very high water solubility, and low octanol-water partition coefficient. The phosphonic acid groups are multiply ionised at pH values relevant to biological and environmental systems. Ionisation gives them the ability to form stable complexes with metal ions, particularly polyvalent ones. Phosphonates are found to adsorb strongly to inorganic matrices, and hence they adsorb strongly to sewage sludge and to soil. They will be removed to a high extent in biological waste water treatment by adsorption.

The toxicity of HMDTMP and its salts to environmental species is presented and interpreted in terms of the concentration of active HMDTMP acid in the test media. As such the results of tests conducted on HMDTMP and its salts are directly comparable, because the ionisation state will depend only on the pH of the test medium. Section 1 describes the pKa values for the ionisation of HMDTMP. Eight pKa values, of 1.3, 2, 3.4, 4.1, 5.9, 6.6, 8.0, >10.0 are reported. At environmentally-relevant pH values HMDTMP will be ionised typically around six times, and will form stable complexes with metal ions.

The substances have the potential to cause effects on aquatic plants as a consequence of nutrient limitation caused by complexation of trace metals. As complexing agents, these substances could remobilise metals in the environment; however, their high degree of adsorption to sediments suggests that this is unlikely to occur. The substances are acids and when present at high concentration they have the potential to cause local effects on aquatic organisms as a consequence of lowered pH.

Effects on aquatic organisms arising from exposure to the acid form of the substance are thought to result from a reduction in the pH of the ambient environment (arising from an increase in the H⁺concentration) to a level below their tolerable range. It is not considered appropriate or useful to derive a PNEC with studies in which pH deviations may have been attributable to the cause of effects seen because any effects will not be a consequence of true chemical toxicity and will be a function of, and dependent on, the buffering capacity of the environment.

 

Open sea PNEC

HMDTMP and its salts are used in some scenarios (offshore oilfield) in open sea. The methodology of CHARM (2005 and van der Wal, 2003) has been used to derive the PNEC for risk characterisation in this setting. These can be found in the CSR.

Conclusion on classification

Hazards to the aquatic environment (acute/short-term): not classified on the basis of the lowest E(L)C₅₀ in short-term test results in fish, invertebrates and algae being 28 mg active acid/L (Pseudokirchneriella

subcapitata).

Hazards to the aquatic environment (long-term): not classified on the basis of the lowest NOEC or E(L)C₁₀ in long-term test results in fish, invertebrates and algae being ≥10 mg active acid/L

(Pseudokirchneriella subcapitata).