Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

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Additional information

The substance diphosphoric acid, compound with 1,3,5-triamine (1:2) is a solid salt that dissociates in aqueous environments forming melamine and pyrophosphate ions. The experimentally determined water solubility of the substance is 385.6 ± 1.1 mg test item/L based on P and 233.1 ± 2.4 mg/L based on non purgeable carbon (OECD 105). Experimental data on the ready biodegradability of diphosphoric acid, compound with 1,3,5-triamine (1:2) are not available. Based on the expected dissociation in water the degradation of the substance compounds melamine and pyrophosphate is assessed separately. In the available read across study, testing the ready biodegradability of melamine, no biodegradation of the substance was observed under test conditions (OECD 301C; NITE, 2010). However, a rapid degradation of melamine by adapted activated sludge microorganisms in industrial sewage treatment plants (STPs) has been demonstrated by Fimberger (1997). The second dissociation product pyrophosphate is an inorganic substance and thus the concept of biodegradation is not applicable and no data are included in the dossier. Abiotic degradation by hydrolysis in water is no relevant degradation pathway for melamine since the molecule comprises no hydrolysable functional groups. The pyrophosphate ion undergoes further hydrolysis and is ultimately converted into orthophosphate ions. Bioaccumulation or adsorption of diphosphoric acid, compound with 1,3,5-triamine (1:2) is not expected due the experimentally determined low log Pow (log Pow -1.24 at 20 °C, OECD 107). Furthermore the substance is not volatile and thus accumulation in the air and subsequent transport to other environmental compartments is not likely. Thus, if released to the environment, the substance will presumably distribute mainly to natural water bodies. Persistence in this compartment cannot be excluded based on the available data on ready biodegradability. However, a degradation of melamine via nitrification in soil is possible even though the DT50 was derived to be > 2 to < 3 years (Hauck, 1964). Phosphate is ubiquitous in the environment and an essential micronutrient for many organisms. Inorganic phosphates 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. The phosphate anion in soil will precipitate with Fe, Al or Ca cations. Thus, the mobility of phosphate in soil is limited. In natural water bodies phosphates are bio-assimilated by bacteria, aquatic plants and algae. 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.