Ammonium fluoride

Endpoint summary

Additional information

As ammonium fluoride decomposes in an aqueous environment into ammonium and fluoride ions, toxicity of these two ions has been studied and the most conservative one has been kept for assessment.

Fluoride toxicity was studied on a read across approach based on available studies performed with other fluoride compounds (NaF, KF, HF); read-across is appropriate as all the surrogates are highly water soluble and therefore will dissociate into their constituent ions in the aquatic environment. The toxicity of both substances is essentially due to the fluoride ion. The EU RAR notes a clear relationship between the aquatic toxicity of fluoride and water hardness. Tests performed in soft water (<50 mg CaCO₃/L) showed greater toxicity than those performed in hard water (>50 mg CaCO₃/L) due to the precipitation of fluoride as CaF₂. All endpoints are expressed in terms of concentrations of the fluoride ion (F^-).

Ammonium toxicity was studied on read across approach with Ammonium chloride as a surrogate. Ammonia ions obtained from the dissociation of the substance (NH₃ or NH₄⁺) are easily mineralized into nitrite ions (NO₂^-) by numerous bacteria. Under this bioavailable form, ammonium is not considered as key factor for aquatic toxicity.

Short-term toxicity to fish

LC50 value of 107.5, 92.4, 118.5, 105.1 and 64.1 ppm at 96, 120, 144, 168 and 192 h respectively are reported for rainbow tout (Camargo & Tarazona, 1991). The same authors report LC50 value for brown trout of 164.5, 135.6, 118.5, 105.1 and 97.5 ppm after 96, 120, 144, 168 and 192 h respectively. The EU RAR for hydrogen fluoride reports additional LC50 values of 299 mg/L (48h in Leuciscus idus); 51 mg/L in (96h in Onchorynkus mykiss) and 340 mg/L (96h in Gasterosteus aculeatus). The RIVM Integrated Criteria Document reports additional data, with LC50 values ranging from 128 -460 mg/L (Sloof et al, 1988).

Ammonium toxicity was studied on read across approach with Ammonium chloride. The key study was a study conducted in similar conditions as an OECD 203 testing on Cyprinus carpio (according to E03-05:APHA, AWWA & WPCF (1960)). The LC50 -96h observed was 209 mg/L.

Long-term toxicity to fish

In a 21 day test with Oncorhynchus mykiss, reviewed in the ICD and EU RAR, an LC5 value of 4 mg/L is reported (actual concentration). This value is considered to be equivalent to the NOEC for mortality. The test was conducted in very soft (12 mg CaCO₃/L) natural water with daily renewal of the test water.

Ammonium toxicity was studied in a chronic toxicity test, in which Pimephales promelas embryos were exposed to various concentrations of ammonium chloride under flow through conditions. The methodology followed was ASTM E729-8 (similar to OECD 212 guideline).

The result obtained is a 28-d NOEC was 0.17 mg/L as NH₃-N and calculated 11.8 mg/L of NH₄Cl.

Short-term toxicity to aquatic invertebrates

Camargo & Tarazona (1991) report that benthic larvae are sensitive to the concentration of fluoride, with EC50 values ranging from 26-48 mg/L (actual concentration); however the study was performed in soft water. The EU RAR reviews and summarises the available data on short-term toxicity to aquatic invertebrates. The reported EC50 values for Daphnia sp. range from 97 - 352 mg/L and are based on nominal concentrations; EC50 values of 10.5 - 39 mg/L are reported for marine invertebrates. The ICD summarises the available data on the short-term toxicity of sodium fluoride to aquatic invertebrates and reports EC50 values of 109 - 340 mg/L; EC50 values of 30 - 500 mg/L are reported for marine invertebrates.

Ammonium toxicity was studied in an acute toxicity test, in which Daphnia magna were exposed to the tested substance under static conditions. The methodology followed was ASTM E729-8 (similar to OECD 202 guideline).

The result obtained is a 48h EC50 (survival) = 2.94 mg/L (95% CL; 2.70-3.22 mg/L) as NH₃-N and calculated as 101 mg/L (95% CI; 92.4-110 mg/l) as NH₄Cl.

Long-term toxicity to aquatic invertebrates

The EU RAR summarises the effects of two reproductive studies of sodium fluoride on Daphnia magna. The two studies report NOEC values of 3.7 and 14.1 mg/L, with an arithmetic mean of 8.9 mg/L. The ICD reports EC50 values in the range of 10 - 48 mg/L

Ammonium toxicity was studied in a 21 days chronic toxicity test, in which adult Daphnia magna were exposed to various concentrations of ammonium chloride under semi-static conditions.

Analytical monitoring for concentration in NH₃ -N was conducted at the beginning and end of each renewal period of test solution.

Results were as follows: 21 d NOEC was 0.60 mg/L as NH₃-N and was calculated as 14.6 mg/L of NH₄Cl ( average of measured concentrations).

Toxicity to algae

The EU RAR reviews and summarises the available data on the toxicity of sodium fluoride to freshwater and marine algae species. The EC50 values for freshwater algae are reported to range from 43 to 122 mg/L. For marine algae the EC50 was 81 mg/L in a single study with Skeletonema costatum. NOEC values of 50 - 249 mg/L and 50 - 200 mg/L are reported for freshwater and marine algae, respectively.

Regarding ammonium toxicity, one key study Bentic diatoms from field (Eems Dollard estuary) is available for ammonium chloride. Tests were conducted in saltwater during 10 days, with 10 different species.

For most of them NOEC-10d was 26 mg/L as NH₄Cl.

Toxicity to microorganisms

An OECD 209 guideline-compliant Bayer study reports a 3-hour NOEC of 510 mg/L for activated sludge. The EU RAR summarises and reviews the other available data on the toxicity of fluoride to aquatic microorganisms; NOEC values of between 7.1 - 226 mg/L are reported.

Ammonium toxicity was evaluated in an activated sludge short term respiratory inhibition was tested on ammonium chloride according to ISO 8192 guideline.

The activated sludge inoculum used in this study originated from laboratory wastewater treatment plants fed with municipal sewage.

In the test conditions, after 30 min exposure, the EC50 obtained was graphically estimated at 1300 mg/L. At the highest concentration tested, 2000 mg/L, inhibition rate is 67%.