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Fluoride

6. To what extent can fluoride exposure be harmful to organisms in the environment?

  • 6.1 What levels of fluoride exposure are harmful to aquatic organisms?
  • 6.2 What levels of fluoride exposure are harmful to microbes and plants?
  • 6.3 What levels of fluoride exposure are harmful to birds and mammals?

6.1 What levels of fluoride exposure are harmful to aquatic organisms?

The source document for this Digest states:

Fluoride did not affect growth or chemical oxygen demand degrading capacity of activated sludge at concentrations of 100 mg/litre. The EC50 for inhibition of bacterial nitrification was 1218 mg fluoride/litre. Ninety-six-hour EC50s, based on growth, for freshwater and marine algae were 123 and 81 mg fluoride/litre, respectively.

Forty-eight-hour LC50s for aquatic invertebrates range from 53 to 304 mg/litre. The most sensitive freshwater invertebrates were the fingernail clam (Musculium transversum), with statistically significant mortality (50%) observed at a concentration of 2.8 mg fluoride/litre in an 8-week flow-through experiment, and several net-spinning caddisfly species (freshwater; family: Hydropsychidae), with "safe concentrations" (8760-h EC0.01s) ranging from 0.2 to 1.2 mg fluoride/litre. The brine shrimp (Artemia salina) was the most sensitive marine species tested. In a 12-day static renewal test, statistically significant growth impairment occurred at 5.0 mg fluoride/litre.

Ninety-six-hour LC50s for freshwater fish range from 51 mg/litre (rainbow trout, Oncorhynchus mykiss) to 460 mg/litre (threespine stickleback, Gasterosteus aculeatus). All of the acute toxicity tests (96 h) on marine fish gave results greater than 100 mg/litre. Inorganic fluoride toxicity to freshwater fish appears to be negatively correlated with water hardness (calcium carbonate) and positively correlated with temperature. The symptoms of acute fluoride intoxication include lethargy, violent and erratic movement and death. Twenty-day LC50s for rainbow trout ranged from 2.7 to 4.7 mg fluoride/litre in static renewal tests. "Safe concentrations" (infinite hours LC0.01s) have been estimated for rainbow trout and brown trout (Salmo trutta) at 5.1 and 7.5 mg fluoride/litre, respectively. At concentrations of >3.2 (effluent) or >3.6 (sodium fluoride) mg fluoride/litre, the hatching of catla (Catla catla) fish eggs was delayed by 1–2 h.

Behavioural experiments on adult Pacific salmon (Oncorhynchus sp.) in soft-water rivers indicate that changes in water chemistry resulting from an increase in the fluoride concentration to 0.5 mg/litre can adversely affect migration; migrating salmon are extremely sensitive to changes in the water chemistry of their river of origin.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Summary of the Report, Chapter 1.8: Effects on other organisms in the laboratory and field 

For more information, see the full IPCS document,

Chapter 9: Effects on other organisms in the laboratory and field 

6.2 What levels of fluoride exposure are harmful to microbes and plants?

The source document for this Digest states:

In laboratory studies, fluoride seems to be toxic for microbial processes at concentrations found in moderately fluoride polluted soils; similarly, in the field, accumulation of organic matter in the vicinity of smelters has been attributed to severe inhibition of microbial activity by fluoride.

Signs of inorganic fluoride phytotoxicity (fluorosis), such as chlorosis, necrosis and decreased growth rates, are most likely to occur in the young, expanding tissues of broadleaf plants and elongating needles of conifers. The induction of fluorosis has been clearly demonstrated in laboratory, greenhouse and controlled field plot experiments. A large number of the papers published on fluoride toxicity to plants concern glasshouse fumigation with hydrogen fluoride. Foliar necrosis was first observed on grapevines (Vitis vinifera) exposed to 0.17 and 0.27 µg/m3 after 99 and 83 days, respectively. The lowest-observed-effect level for leaf necrosis (65% of leaves) in the snow princess gladiolus (Gladiolus grandiflorus) was 0.35 µg fluoride/m3. Airborne fluoride can also affect plant disease development, although the type and magnitude of the effects are dependent on the specific plant–pathogen combination.

Several short-term solution culture studies have identified a toxic threshold for fluoride ion activity ranging from approximately 50 to 2000 µmol fluoride/litre. Toxicity is specific not only to plant species, but also to ionic species of fluoride; some aluminium fluoride complexes present in solution culture may be toxic at activities of 22–357 µmol fluoride/litre, whereas hydrogen fluoride is toxic at activities of 71–137 µmol fluoride/litre. A few studies have been carried out in which the fluoride exposures have been via the soil. The type of soil can greatly affect the uptake and potential toxicity of fluorides.

Aluminium smelters, brickworks, phosphorus plants and fertilizer and fibreglass plants have all been shown to be sources of fluoride that are correlated with damage to local plant communities. Vegetation in the vicinity of a phosphorus plant revealed that the degree of damage and fluoride levels in soil humus were inversely related to the distance from the plant. Average levels of fluoride in vegetation ranged from 281 mg/kg in severely damaged areas to 44 mg/kg in lightly damaged areas; at a control site, the fluoride concentration was 7 mg/kg. Plant communities near an aluminium smelter showed differences in community composition and structure due partly to variations in fluoride tolerance. However, it must be noted that, in the field, one of the main problems with the identification of fluoride effects is the presence of confounding variables such as other atmospheric pollutants. Therefore, care must be taken when interpreting the many field studies on fluoride pollution.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Summary of the Report, Chapter 1.8: Effects on other organisms in the laboratory and field 

For more information, see the full IPCS document,

Chapter 9: Effects on other organisms in the laboratory and field 

6.3 What levels of fluoride exposure are harmful to birds and mammals?

The source document for this Digest states:

In birds, the 24-h LD 50 was 50 mg/kg body weight for 1-day-old European starling (Sturnus vulgaris) chicks and 17 mg/kg body weight for 16-day-old nestlings. Growth rates were significantly reduced at 13 and 17 mg fluoride/kg body weight (the highest doses at which growth was monitored).

Most of the early work on mammals was carried out on domesticated ungulates. Fluorosis has been observed in cattle and sheep. The lowest dietary level observed to cause an effect on wild ungulates was in a controlled captive study with white-tailed deer (Odocoileus virginianus) in which a general mottling of the incisors characteristic of dental fluorosis was noted in the animals at the 35 mg/kg diet dose.

The original findings of fluoride effects on mammals were from studies in the field on domestic animals such as sheep and cattle. Fluoride can be taken up from vegetation, soil and drinking-water. Tolerance levels have been identified for domesticated animals, with the lowest values for dairy cattle at 30 mg/kg feed or 2.5 mg/litre drinking-water. Incidents involving domesticated animals have originated both from natural fluoride sources, such as volcanic eruptions and the underlying geology, and from anthropogenic sources, such as mineral supplements, fluoride-emitting industries and power stations. Symptoms of fluoride toxicity include emaciation, stiffness of joints and abnormal teeth and bones. Other effects include lowered milk production and detrimental effects on the reproductive capacity of animals. The lowest dietary concentration of fluoride to cause fluorosis in wild deer was 35 mg/kg. Investigations of the effects of fluoride on wildlife have focused on impacts on the structural integrity of teeth and bone. In the vicinity of smelters, fluoride-induced effects, such as lameness, dental disfigurement and tooth damage, have been found.

Source & ©: IPCS "Environmental Health Criteria for Fluorides", (EHC 227), 
Summary of the Report, Chapter 1.8: Effects on other organisms in the laboratory and field 

For more information, see the full IPCS document,

Chapter 9: Effects on other organisms in the laboratory and field 


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