Orthophosphoric acid

Endpoint summary

Additional information

In accordance with Annex VII to XI of Regulation (EC) No. 1907/2006 (REACH) the environmental fate endpoints for phosphoric acid are waived on the following grounds.

Phosphoric acid is an inorganic substance and as such the following studies are not applicable and cannot be performed:

- OECD 106;Adsorption - Desorption Using a Batch Equilibrium Method

- OECD 309:Aerobic Mineralisation in Surface Water – Simulation Biodegradation Test

- OECD 310: Ready Biodegradability - CO2 in sealed vessels (Headspace Test)

Furthermore, environmental fate (Q)SAR applications are not validated for inorganics and therefore cannot be used in place of test data.

Despite the lack of test data the following is known about the environmental behaviour of phosphoric acid. Phosphoric acid is highly soluble in water and as a consequence will be dissociated into its ions (H⁺and mainly H₂PO₄^-and HPO₄^2-) at pH 3, 7 and 10. In water the H⁺ions will form H₃O⁺ions. The hydrolysis endpoint can thus be waived.

The Guidance on information requirements and chemical safety assessment Chapter R.7c Appendix R.7.10-1, states that a substance is unlikely to pose a risk to predatory organisms or humans if “it is an essential element and internal concentrations will be well-regulated at the exposure concentrations anticipated”. In biological systems phosphoric acid exists as phosphate and hydrogen ions. Phosphate levels in the body are regulated via homeostasis and therefore phosphoric acid is not considered to be bioaccumulative. Therefore, bioaccumulation is not a relevant endpoint for phosphoric acid.

According to Annex IX-X, Section 9.2, Column 2 of Regulation (EC) No. 1907/2006 (REACH) “Further biotic degradation testing shall be proposed by the registrant if the chemical safety assessment according to Annex I indicated the need to investigate further the degradation of the substance and its degradation products”.

Adequate information on the degradation of phosphoric acid is available and the degradation products are clearly identified. The chemical safety assessment does not indicate the need for further testing and therefore no further testing for environmental fate is proposed.

Eutrophication

Phosphoric acid rapidly dissociates to soluble inorganic orthophosphate 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. Soluble phosphates are then bio-assimilated by the bacterial populations and the aquatic plants and algae found in these different compartments. Phosphates 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 caused by excess of phosphate (when the conditions are such that P is a growth-limiting factor) can be a problem in some circumstances. The effects of eutrophication can range from ecosystem modifications, through to algal blooms and in extreme cases (through decomposition of plant biomass) oxygen depletion and collapse of the ecological community in a surface water causing considerable detrimental impacts on fish and other organisms as the increase in primary production leads to increased oxygen consumption, which may reduce the oxygen concentration to critical low levels.

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. It 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. This method for limiting the concentration of phosphates in industrial wastewater emissions is supported by theUrban 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. The EU Water Framework Directive 2000/60 confirms this obligation, and reinforces it by requiring further treatment, e.g. of small conurbations, if this is necessary to achieve water quality status objectives.

De Madariaga BM (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 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 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).