Pentapotassium triphosphate

Endpoint summary

Additional information

Summary of degradation

 

Pentapotassium triphosphate is an inorganic phosphate and therefore a ready biodegradation test is not applicable.

The key study to assess the hydrolysis as a function of pH shows that the estimated half-life’s at 25°C of the test material were determined to be; 14.5 days at pH 4 and > 1 year at pH 7 and 9. Under the physiologically relevant conditions of pH 1.2, 37.0 ± 0.5°C, the half-life of the test material was determined to be 6.25 hours. As the substance is ionic it will naturally dissociate into a cation and anion. The triphosphate anion was shown to undergo further hydrolysis to orthophosphate and pyrophosphate subunits.

The additional supporting literature provides data to show that the rate of hydrolysis in natural waters is far greater than in distilled water.

Potassium tripolyphosphate will not persist in natural waters it will first dissociate to its cationic and anionic forms, subsequently the triphosphate anion will be undergo hydrolysis (as discussed in the key study) and at a great rate breakdown by biotic degradation and assimilation by algae and/or microorganisms. The breakdown products of such reactions are pyrophosphate anions and the ubiquitous orthophosphate anion. Furthermore, via similar processes the pyrophosphate anion will ultimately hydrolyse to orthophosphate.

 

Soil and sediment degradation studies are not considered to be scientifically feasible as there is no available analytical method that could differentiate between the contributions to the analysable solution originating from the test material and that originating from the required soil / sediment matrix / solution matrix due to the ubiquitous nature of the K⁺ and PO₄^3-ions.

 

Data on volatilisation is not available. Pentapotassium triphosphate is an inorganic solid and therefore can be considered to be non volatile.

 

No experimental data on bioaccumulation exist. However due to the hydrophilic nature of the substance, bioaccumulation is not expected as accumulation in fats is not possible. The substance when dissolved in water (and so animal tissues/fluids) will effectively separate into/become simply the two ions "phosphate" and "potassium" which are natural ionic components of blood, cell fluids, etc and therefore no further testing is considered to be necessary. In addition, no risk of secondary poisoning is anticipated for the same reasons.

Eutrophication

 

Pentapotassium triphosphate is hydrolysed or biotically degraded (by the action of phosphatases) to soluble inorganic orthophosphate (PO₄^3-) in wastewater, sewerage systems and natural waters. Sources of inorganic phosphate are human urine and faeces, animal waste, food and organic waste, mineral fertilisers, bacterial recycling of organic materials in ecosystems, etc. Phosphates are bio-assimilated by the bacterial populations and the aquatic plants and algae found in these different compartments and are an essential nutrient (food element) for plants, and stimulate the growth of water plants (macrophytes) and/or algae (phytoplankton) if they represent the growth-limiting factor.

Nutrient enrichment (eutrophication), can be a problem in some circumstances, and in particular increased phosphate loads to surface waters may be a problem when the conditions are such that P is a growth-limiting factor . The effects of eutrophication can range from ecosystem modifications changes in balance between different species or communities), through to algal blooms and in extreme cases (through decomposition of plant biomass leading to oxygen depletion) collapse of the ecological community.

To avoid such undesirable effects, phosphate emissions to surface water via industrial wastewater are regulated in the Council Directive 96/61/EC concerning integrated pollution prevention and control. This states that phosphates have to be taken into account for fixing emission limit values for industrial wastewater. In order to meet the requirements it may be necessary to add a treatment step for phosphate removal from industrial wastewaters before these waters are released to the aqueous environment.

The limitation of phosphorus discharges to surface waters is similarly required by the Urban Waste Water Treatment Directive 1991/271 (EU) which requires the removal of phosphate (P) from municipal waste water in all but very small conurbations (> 10 000 person equivalents = around 6 000 population taking into account small industry and commerce inputs), wherever discharge occurs into waters potentially susceptible to eutrophication (defined as “Sensitive Areas”).. The EU Water Framework Directive 2000/60 confirms this obligation, and reinforces it by requiring further treatment, e. g. of smaller conurbations, if this is necessary to achieve water quality status objectives.

De Madariaga BM (INIA,2007) developed a conceptual model and protocol for performing European quantitative eutrophication risk assessments of (poly) phosphates in detergents. In this model, the risk probability for eutrophication occurring in the most sensitive areas of a river basin (lakes, reservoirs, meadow zones, estuaries), is based on the TP (total phosphorous) concentration of the inflow water. The variability observed for similar TP concentrations is the consequence of variations in concentrations of N and/or other nutrients, other ecosystem factors (flow regimes, climate, algal grazer communities ...) and other natural variability. The study also covered the implementation of the model and a set of examples based on generic European scenarios as well as a pan European probabilistic estimation covering the diversity observed for the European conditions and enabled a probabilistic risk assessment of eutrophication relating to the use of STPP (sodium tripolyphosphate / pentasodium triphosphate) in detergents. The scientific validity of this methodology was confirmed by the EU scientific committee SCHER (Opinion of 29th November 2007). This model is considered relevant for all phosphates as the ultimate degradation products of polyphosphates (including STPP) in municipal sewage are orthophosphates.

Assessment of PBT/vPvB properties; comparison with the criteria of Annex XIII (Regulation EC (No.) 1907/2006.

 

According to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT Assessment, the PBT and vPvB criteria of Annex XIII to the regulation do not apply to inorganic substances. Therefore pentapotassium triphosphate is not considered to require any further assessment of PBT properties.