Ammonium magnesium orthophosphate

Short-term toxicity to fish

Description of key information

One key study for acute toxicity of diammonium phosphate to fish is available. The study was conducted according to the guideline "Standard Methods for the Examination of Water and Wastewater" (American Public Health Association) and is judged reliable.
Read across from diammonium phosphate to magnesium ammonium phosphate is considered justified based on following background:
Since both the magnesium ammonium phosphate and diammonium phosphate dissociate to their respective ammonium, (magnesium) and phosphate ions, it is considered acceptable to approach the assessment of magnesium ammonium phosphate based on the individual components.
Since Diammonium phosphate is very soluble in water and therefore much more bioavailable (588 g/l; The Merck Index“, 14th Edition, M. J. O’Neil (Editor), Merck Research Laboratories, Division of Merck & Co., Inc., Whitehouse Station, NY, USA (2006)) read across to the only slightly soluble magnesium ammonium phosphate (0.1 g/l) is considered as worst-case assumption. The only difference between the two inorganic salts is the replacement of one ammonia ion  and one hydrogen ion by magnesium.
Magnesium from magnesium ammonium phosphate is not assumed to pose an additional risk for acute ecotoxicity since it is an essential mineral and ubiquitous present in food. Magnesium is the eighth most abundant element, constitutes about 2% af the Earth's crust by weight and is an essential element in biological systems, present in every cell type and organism. 
The most common source of magnesium in groundwater is through the erosion of rocks, such as dolomite and minerals, such as  magnesite. It is also
naturally present in sea water and salt deposits. It is found naturally in many foods such as vegetables, nuts, grains, fish and dairy products. 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

1 700 mg/L

Additional information

The reported study has Klimisch score 2 and was conducted after "Standard Methods for the Examination of Water and Wastewater" (American Public Health Association). The 96h LC50 of diammoniumphosphate is 1700 mg/l. The LC50 for fry was selected since life stage phases are more sensitive than fish.