Magnesium fluoride

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Study period:

2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Read-across justification is provided in Appendix 3 of the CSR.

The available ecotoxicological data for the target and source substances are outlined in the data matrix (Table 7).

Given high solubility of magnesium chloride and sodium fluoride in water, they will dissociate and release Mg2+, and Cl- and Na+ and F- ions, respectively. As the target substance releases magnesium cations (Mg2+) and fluoride anions (F-) in water the ecotoxicological information on other magnesium salts and inorganic fluorides is justified in the environmental assessment.

Data obtained on sodium fluoride and sodium chloride indicate that the toxic effects in aquatic environment are due to fluoride ions. Thus, it is justified to use data on sodium fluoride to assess toxicity of fluoride.
Magnesium chloride does not present a hazard to the environment due to its low hazard profile. Magnesium is widespread in living cells and does not bioconcentrate in aquatic organisms. Magnesium (Mg+2) is actually essential nutrient for normal plant growth.
Read-across data is used to fulfil information requirements for following endpoints: adsorption/desorption, short-term toxicity to fish, short-term toxicity to aquatic invertebrates, toxicity to algae and cyanobacteria and toxicity to microorganisms. Also presented in table 7 are additional ecotoxicological and environmental fate data on the source substance for stability, long-term toxicity and terrestrial toxicity endpoints. This data is not used for read-across.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

not specified

Remarks:

Not reported

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Sodium fluoride used was obtained from Sigma Chemical Co. (St. Louis, MO, USA)

Analytical monitoring:

yes

Details on sampling:

no specified

Vehicle:

not specified

Details on test solutions:

No specified

Test organisms (species):

activated sludge

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: The different mesophilic inocula were taken from Industriewater, Eerbeek, The Netherlands and Aviko, Steenderen, The Netherlands.
- Pretreatment: Both inocula were washed and sieved to remore fine particles and stored under nitrogen gas at 4 celsius degrees.

Test type:

not specified

Water media type:

freshwater

Limit test:

no

Total exposure duration:

180 min

Test temperature:

30+-2 celsius

Nominal and measured concentrations:

no available

Details on test conditions:

TEST SYSTEM
- Test vessel: glass serum flasks (165 mL) were used as test vessels.
- Material, size, headspace, fill volume: Narrow-neck glass bottles with flat bottoms (50 mL) were used as measuring flasks.

Duration:

180 min

Dose descriptor:

IC50

Effect conc.:

149 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Duration:

180 min

Dose descriptor:

other: IC20

Effect conc.:

105 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Duration:

180 min

Dose descriptor:

other: IC80

Effect conc.:

180 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Validity criteria fulfilled:

yes

Conclusions:

IC50=149 mg/l, IC20=104 mg/l , IC80=180 mg/l

Executive summary:

Inhibitory effect of fluoride towards the main microbial populations responsible for the removal of organic constituents and nutrients in wastewaters treatment processes were evaluated. The results of short-term batch bioassays indicated that the toxicity of sodium fluoride varied depending on the microbial population. Fluoride was inhibitory to nitrification, albeit at relatively high levels (IC50: 149 mg/l). Nitrifying bacteria appeared to adapt rapidly to fluoride, and a near complete recovery of their metabolic activity was observed after only 4d of exposure to high fluoride levels (up to 500 mg/l). Other microbial populations were evaluated i.e., glucose fermenters, aerobic glucose-degrading heterotrophs, denitrifying bacteria, and H2 -utilizing methanogens, tolerated fluoride at very high concentrations (>500 mg/l).

Description of key information

There are no studies available on toxicity to microorganims with magnesium fluoride. However, an existing publication with sodium fluoride (Ochoa-Valeria, V. et al.) showed that very high concentrations of soluble fluoride (>500 mg/l) can be tolerated by microbial communities involved in the activated sludge and in denitrification processes without significant inhibitory impact. Fluoride was also inhibitory to nitrification, albeit at high levels (IC50=149 mg/l) Therefore, there is enough evidence to conclude that the substance does not cause adverse effects on microbial activity at low concentrations.

Key value for chemical safety assessment

EC50 for microorganisms:

149 mg/L

EC10 or NOEC for microorganisms:

149 mg/L