Registration Dossier
Registration Dossier
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EC number: 231-987-8 | CAS number: 7783-28-0
Endpoint summary
Administrative data
Description of key information
Additional information
In aqueous solution, ammonium salts are completely dissociated into NH4+ and a corresponding anion. This equilibrium depends on temperature, pH and ionic strength of the water in the environment. Non-ionized NH3 species exist also in aquatic environments and the fraction (NH3/( NH3 + NH4 +)) steeply increases with elevated pH value or temperature. It is well known that toxicity to aquatic organisms has been attributed to non-ionized ammonia (NH3) species, and that the NH4+species is considered to be non- or significantly less-toxic (Emerson et al., 1975). However, recent developments in assessing ammonia toxicity clearly show that in contrast to earlier assumptions where non-ionized ammonia was considered to be the toxic component, both the uncharged and charged molecule are toxic. Therefore, a joint toxicity model has been proposed, with ammonia causing most toxicity at high pH values and ammonium ion also contributing to toxicity at lower pH values (U.S. EPA 1999, OECD 2007).
It is generally accepted that the principal toxic component of ammonium salts such as ammonium nitrate, -sulphate or -chloride is ammonia, rather than the corresponding anion (see also: OECD2004, SIDS ammonium chloride or OECD 2007 ammonium sulphate). Therefore toxicity values for ammonium salts (such as: ammonium -sulphates, phosphates, carbonates, chlorides or nitrates), where the major toxic component is ammonia, can be considered as equivalent. Consequently, this hazard assessment comprises the total topic of ammonia toxicity.
U.S. EPA (1999) published an excellent review on Ammonia toxicity, with special consideration on the pH- and temperature dependence. A huge amount of studies is available on ammonia toxicity, however it is difficult to compare these toxicity data, since various temperature- and pH conditions were present during testing. U.S. EPA (1999) re-evaluated existing data on ammonia toxicity by adjusting toxicity values to definite temperature and pH- conditions and by thereby allowing comparability.
Considering the group of phosphates, ammonium dihydrogenorthophosphate (MAP), diammonium hydrogenorthophosphate (DAP), single superphosphate (SSP) and triple superphosphate (TSP), it is clear that all phosphates show a low or negligible toxicity to aquatic species:
- for fish: LC50 >100 mg/L (nominal concentration, confirmed by chemical analysis with >80% recovery) (MAP) and >100 mg/L for DAP (based on nominal concentrations);
- for invertebrates: EC50 >100 mg/L (DAP, based on nominal concentrations);
- for algae: NOEC ≥100 mg/L (for TSP and DAP) (based on nominal concentrations).
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