Ambient Water Quality Criteria for Fluoride

Water Quality

8.0 Irrigation

Effects

Although the effects of airborne gaseous and particulate fluoride on vegetation are well known and documented (Weinstein, 1977), there are few data on the effects of soil or waterborne fluoride on plants (Rose and Marier, 1977). Neutral and alkaline soils can deactivate fluoride or restrict its uptake by plant roots (Anon, 1973; and Bollard and Butler, 1966), but uptake is not so restricted in acidic soils. The use of fluoride-containing insecticides does not appear to cause deleterious levels of fluoride in soils (MacIntire et al., 1951). Fluoride levels found in natural or polluted waters will usually have no detrimental effect on plants. Addition of fluoride to soil or water generally has little or no effect on the fluoride content of crops (MacIntire et al., 1951; Cobleigh, 1934; and Smith et al., 1945).

The amount of fluoride taken up by a plant is small, and is not generally related to the level in soil or irrigation water, but rather to soil type, soil pH, calcium and phosphorus levels and the plant species being grown (Anon, 1968; Murray and Wolley, 1968; Chapman, 1966; MacIntire et al., 1949; Jacobson et al., 1966; Adams, 1956; and Hansen et al., 1958). The application of lime to reduce the acidity of soil will greatly reduce fluoride uptake (Prince et al., 1949). Most fluoride in or on plants results from aerial fluoride, but small amounts will be taken up from irrigation water (Rand and Schmidt, 1952), and soluble fluoride salts can be taken up by the leaves from spray irrigation (Weinstein and McCune, 1970; Brewer et al., 1967; Brewer et al., 1969; Brewer et al., 1960; Facteau and Wang, 1972; and McCune et al., 1965). Barley roots (Bale and Hart, 1973), and Cordyline terminalis leaves (Conover and Poole, 1971) are damaged when grown in 0.02 and 0.5 mg/L fluoride nutrient solutions, respectively. Fluoride may be released during brush or forest fires.

Several native plants used as browse species in Australia, Africa and South America synthesize monofluoroacetic acid which is very toxic. However, this compound has not yet been found to occur in forage crops (Weinstein et al., 1972; Hall, 1974; Bell et al., 1955; Renner, 1904; Alpin, 1967; McEwan, 1964a; McEwan, 1964b; Oliveira, 1963; and Marais, 1944).

Table 8.1 lists some effects of fluorides in irrigation water on plants.

Literature Criteria

Criteria from the literature are summarized in Table 8.2. Manitoba's surface water quality objectives for fluoride in Class 4B waters, used for agriculture and wildlife, state that fluoride should not exceed 1.0 mg/L (Anon, 1980). The U.S. EPA (Anon, 1973), Ontario (Anon, 1984) and CCME (Anon, 1987), propose 1.0 mg/L for fluoride in irrigation water on acidic soils and 15 mg/L for a 20-year period for use on fine-textured soils of pH 6.0 to 8.5.

Recommended Criteria

Total fluoride in irrigation water should not exceed 1.0 mg/L as a 30-day average or a maximum of 2.0 mg/L. The CCME guideline is a maximum of 1 mg/L.

Rationale

Most plants do not take up very much fluoride from the soil or from irrigation water; the major source is airborne deposition. Neutral and alkaline soils deactivate fluoride or restrict its uptake even more. Lower fluoride levels may be required for plants grown hydroponically, but there are insufficient data to set a criterion for this use at present (Leone et al., 1948; Adams and Zulzbach, 1961; Daines et al., 1952; and Pack, 1966). Much of the total fluoride on a forage crop likely comes from the soil in which it is growing, not by uptake through the roots, but by deposition of soil particles on the surface of the plant. This deposition may be due to splashing during irrigation or rainfall or due to dust and particle suspension caused by cultivation and harvesting. In areas of high pollution fallout, the fluoride deposition will not be related to the local soil levels. These sources of fluoride are likely more important than uptake from irrigation water. As discussed in Sections 2.1 and 2.2, it would be unusual to find water supplies in British Columbia which had fluoride levels in excess of 3.0 mg/L, except immediately downstream from grossly contaminated industrial discharges.

The use of higher levels of fluoride for a fixed short-term period on fine-textured alkaline soils is not recommended. While such soils deactivate fluoride for a while, eventually their capacity to do so will be used up and such use would have to stop. Knowingly depleting a finite buffering capacity in a relatively short time, for a short-term gain, is not acceptable or sustainable management.


	Water Quality Ambient Water Quality Criteria for Fluoride 8.0 Irrigation Effects Although the effects of airborne gaseous and particulate fluoride on vegetation are well known and documented (Weinstein, 1977), there are few data on the effects of soil or waterborne fluoride on plants (Rose and Marier, 1977). Neutral and alkaline soils can deactivate fluoride or restrict its uptake by plant roots (Anon, 1973; and Bollard and Butler, 1966), but uptake is not so restricted in acidic soils. The use of fluoride-containing insecticides does not appear to cause deleterious levels of fluoride in soils (MacIntire et al., 1951). Fluoride levels found in natural or polluted waters will usually have no detrimental effect on plants. Addition of fluoride to soil or water generally has little or no effect on the fluoride content of crops (MacIntire et al., 1951; Cobleigh, 1934; and Smith et al., 1945). The amount of fluoride taken up by a plant is small, and is not generally related to the level in soil or irrigation water, but rather to soil type, soil pH, calcium and phosphorus levels and the plant species being grown (Anon, 1968; Murray and Wolley, 1968; Chapman, 1966; MacIntire et al., 1949; Jacobson et al., 1966; Adams, 1956; and Hansen et al., 1958). The application of lime to reduce the acidity of soil will greatly reduce fluoride uptake (Prince et al., 1949). Most fluoride in or on plants results from aerial fluoride, but small amounts will be taken up from irrigation water (Rand and Schmidt, 1952), and soluble fluoride salts can be taken up by the leaves from spray irrigation (Weinstein and McCune, 1970; Brewer et al., 1967; Brewer et al., 1969; Brewer et al., 1960; Facteau and Wang, 1972; and McCune et al., 1965). Barley roots (Bale and Hart, 1973), and Cordyline terminalis leaves (Conover and Poole, 1971) are damaged when grown in 0.02 and 0.5 mg/L fluoride nutrient solutions, respectively. Fluoride may be released during brush or forest fires. Several native plants used as browse species in Australia, Africa and South America synthesize monofluoroacetic acid which is very toxic. However, this compound has not yet been found to occur in forage crops (Weinstein et al., 1972; Hall, 1974; Bell et al., 1955; Renner, 1904; Alpin, 1967; McEwan, 1964a; McEwan, 1964b; Oliveira, 1963; and Marais, 1944). Table 8.1 lists some effects of fluorides in irrigation water on plants. Literature Criteria Criteria from the literature are summarized in Table 8.2. Manitoba's surface water quality objectives for fluoride in Class 4B waters, used for agriculture and wildlife, state that fluoride should not exceed 1.0 mg/L (Anon, 1980). The U.S. EPA (Anon, 1973), Ontario (Anon, 1984) and CCME (Anon, 1987), propose 1.0 mg/L for fluoride in irrigation water on acidic soils and 15 mg/L for a 20-year period for use on fine-textured soils of pH 6.0 to 8.5. Recommended Criteria Total fluoride in irrigation water should not exceed 1.0 mg/L as a 30-day average or a maximum of 2.0 mg/L. The CCME guideline is a maximum of 1 mg/L. Rationale Most plants do not take up very much fluoride from the soil or from irrigation water; the major source is airborne deposition. Neutral and alkaline soils deactivate fluoride or restrict its uptake even more. Lower fluoride levels may be required for plants grown hydroponically, but there are insufficient data to set a criterion for this use at present (Leone et al., 1948; Adams and Zulzbach, 1961; Daines et al., 1952; and Pack, 1966). Much of the total fluoride on a forage crop likely comes from the soil in which it is growing, not by uptake through the roots, but by deposition of soil particles on the surface of the plant. This deposition may be due to splashing during irrigation or rainfall or due to dust and particle suspension caused by cultivation and harvesting. In areas of high pollution fallout, the fluoride deposition will not be related to the local soil levels. These sources of fluoride are likely more important than uptake from irrigation water. As discussed in Sections 2.1 and 2.2, it would be unusual to find water supplies in British Columbia which had fluoride levels in excess of 3.0 mg/L, except immediately downstream from grossly contaminated industrial discharges. The use of higher levels of fluoride for a fixed short-term period on fine-textured alkaline soils is not recommended. While such soils deactivate fluoride for a while, eventually their capacity to do so will be used up and such use would have to stop. Knowingly depleting a finite buffering capacity in a relatively short time, for a short-term gain, is not acceptable or sustainable management.