Reaction mass of Ammonium dihydrogenorthophosphate and diammonium hydrogenorthophosphate.

Endpoint summary

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. Un-ionized NH₃species exists in the 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 un-ionized ammonia (NH₃) species, and 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 un-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 a comparability of these toxicity data is difficult, 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 >85.9 mg/L (100 mg/L based on nominal conc.) (MAP), and 1700 mg/L for DAP; for invertebrates EC50 =1790 mg/L (SSP); for algae NOEC =87.6 mg/L and = 97.1 mg/L (for TSP and DAP respectively) (100 mg/L based on nominal conc.). As a higher than value is not relevant for a predicted no effect level, the lowest fixed value is used in the derivation of PNECs. This is the LC50 for fish of 1700 mg/L with DAP. For respiration inhibition rate a NOEC of 100 mg/L (SSP and DAP) was observed.