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Environmental fate & pathways

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Summary of degradation

 

Disodium hydrogenorthophosphate is an inorganic phosphate and therefore a ready biodegradation test is not applicable. In addition, no experimental determination of the abiotic degradation, hydrolysis as a function of pH was performed for the individual phosphate materials detailed, using Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004, since the phosphate anion has no potential mechanism for further hydrolysis, itself being the final common hydrolysis product of higher polyphosphates.

 

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 Na+ and PO43-ions.

 

Data on volatilisation is not available. Disodium hydrogenorthophosphate 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 “sodium” which are natural ionic components of blood, cell fluids and physiological fluids. Therefore, no further testing is considered to be necessary. In addition, no risk of secondary poisoning is anticipated for the same reasons.

Eutrophication

Inorganic orthophosphates will dissociate to soluble orthophosphate (PO43-) in sewerage systems, sewage treatment plants and in the environment. These same orthophosphates are also formed by natural hydrolysis of human urine and faeces, animal wastes, food and organic wastes, 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.