Ammonium fluoride

Endpoint summary

Additional information

Based on NH₄Cl and KF data, NH₄F is unstable and will rapidly hydrolyse in the environment and react to form other fluorine-containing compounds and ammonia.

As ammonia is rapidly mineralized by numerous bacteria into nitrite compounds bioavailable for organisms. So it is assumed that soil is not a compartment of interest for hazard and exposure assessmment. On the other hand, fluoride is essentially immobile in soil due to its incorporation into insoluble complexes. Adsorption to the soil solid phase is stronger at slightly acidic pH values (5.5 – 6.5). Fluoride is not readily leached from soils and so may lead to exposure of soil organisms when acidic conditions are changing. Therefore, fluoride is considered as the key factor for terrestrial toxicity and ammonium is considered as of low impact.

Toxicity to soil macro-organisms

The toxicity of various fluoride compounds to Eisenia fetida was investigated over a period of 22 weeks. At higher concentrations sodium fluoride, potassium fluoride and the sodium salt of fluoroacetic acid reduced significantly. Calcium fluoride had no effect. The rate of maturity of the earthworms was also significantly reduced when sodium fluoride and potassium fluoride was used. The number of hatchlings was reduced in the presence of sodium fluoride, while the number of cocoons was reduced in the presence of a low concentration of sodium fluoride and potassium fluoride (Vogel & Ottow, 1992).

Impact of NH4Cl on Eisenia fetida was studied according to the guideline EPA/600/3-88/029 (1988) by testing 5 nominal concentration 100, 200, 300, 400, 500 mg/kg of soil. Based on mortality, the 14d LC50 for Eisenia fetida was calculated as 163 mg/kg soil d.w. (Yeardley et al., 1995)

Toxicity to terrestrial arthropods

The effects of fluoride concentration were investigated on the numbers of Porcellio scaber in leaf litter. Leaf litter was collected from eight sites at various distances away from an aluminium reduction plant. Results showed that litter collected far from the plant had a lower fibre content, was more sapric and was less acid. Total acid extractable F^- in the litter and upper 15 cm of soil was about 41 times as much at the closest site (700 mg/kg) as at the most distant sites (12 and 16 mg/kg). In a bioassay of litter from the study sites, woodlice (Porcellio scaber) had an abnormally high mortality in litter that contained 440 mg/kg or more of acid extractable F^-. When F^- was added in the form of NaF to the litter, a significant increase in mortality was observed only in treatments exceeding 800 mg/kg (Beyer et al, 1987).

Toxicity to terrestrial plants

On the basis of a large number of fumigation experiments with plants (ornamental crops, fruit crops and conifers) exposed to HF, a relationship was derived between the NOEC and exposure time (all plant species). NOEC values were calculated for highly sensitive, sensitive and slightly sensitive plant species. NOEC values of between 0.2 - 7.5 mg/m³ HF are reported for plant species (EU RAR, 2001).

The 6 year effect of ammonium sulphate spread as a solid fertilizer was investigated in a stand of trees (Picea abies, 12 years old at the beginning of the test) in southern Sweden (Rosengren-Brinck and Nihlgard, 1995). Spreading at 471 kg ammonium sulphate (calculated from 100 kg N) per ha per year affected resistance to drought, which was evident in a reduction in the flushing of new shoots. This effect can be explained by salt effects. (Rosengren-Brinck & Nihlgard, 1995)

Toxicity to soil micro-organisms

The EU RAR (2001) reports NOEC values from 106 to 3000 mg/kg. The 63 day experiments were carried out in a micro-ecosystem containing poplar litter (30% o.m) and the isopod Porcellio scaber.Nitrification was found to be the most sensitive endpoint investigated in the micro-ecosystem test.

A 3 years study on rice fields tested with ammonium sulphate showed at 17.5, 35, 70, and 140 kg N /ha a reduced the numbers of cyanobacteria and the nitrogen fixation observed. However, the ammonium sulphate inputs of up to 70 kg N /ha gave rise to a moderate increase in grain yield, without severely affecting the N₂ fixing ability (less than 50% reduction) or cyanobacteria numbers.

The trend shown in this study might be linked to bioavailability of N to crop, having an impact on N₂ fixing cyanobacteria population, and any direct toxicity of ammonium on cyanobacterial population cannot be proven (Fernández Valiente et al., 2000).