San Diego Growers please need your input

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The possibility that fluoride may play a contributing role to the toxic effects attributed to "aluminum" is supported by laboratory research on both fish and vegetation. Hamilton (1995), for instance, found that the toxic effects of aluminum on fish were enhanced if 0.25 ppm fluoride was added to acidic water (5.5 pH). In addition, Hamilton also reported that gill damage among fish increased when he raised the fluoride concentration from 0.1 to 0.2 ppm, an effect which he suggests may result from fluoride's reported ability to increase the aluminum concentration at the gill surface.
In addition to research on aluminum fluoride's effect on fish, scientists have also investigated the impact of aluminum fluoride on vegetation. Most notably, Facanha in 2002 found that aluminum fluoride in acidic soils reduces the growth and yield of corn plants in a manner analagous to "phosphate starvation." Facanha makes a convincing case that aluminum fluoride complexes are able to cause this growth-suppressing effect through its "well-known phosphate-mimicking property." According to Facanha, the aluminum fluoride complex is treated as identical to phosphate by the corn's roots, thereby competing with phosphate uptake at the binding sites of the root. The end result is that less phosphate is absorbed into the plant, resulting in less energy and lower yields
1. Laboratory soil experiments have found that plants do not absorb fluoride from soils with a neutral pH. However, when the acidity increases, fluoride complexes with aluminum, and the rate of fluoride and aluminum uptake by plants greatly increases.
2. Laboratory soil experiments have found that aluminum fluoride complexes in acidic soils cause the very type of growth inhibitiion associated with acid rain damage
This study has provided the first documented evidence that acid rain and fluoride may act synergistically in inhibiting plant growth via soil deposition." - Horner JM, Bell JNB. (1995). Effects of fluoride and acidity on early plant growth. Agriculture, Ecosystems and Environment. 52: 205-211.
3b) Fluoride Uptake By Plants Increases When Soil's Acidity Increases:
"Our experiment showed clearly that, when enough calcium was available to give a pH of about 6.5, the fluorine absorption through the roots was very low, but the important thing is pH, it seems. We had high absorption of fluorine at low pH. We must know the pH of the soil."
SOURCE: Daines RH, Leone I, Brennan E. (1949). The Effect of Fluorine on Plants as Determined by Soil Nutrition and Fumigation Studies. In: Air Pollution. Proceedings of the United States Technical Conference on Air Pollution. McGraw-Hill Book Co, New York. pp. 97-105.
"Soil pH is a determinant factor for fluorine solubility, but there exist different explanation models."
SOURCE: Wenzel W, Blum W. (1992). Fluorine Speciation and Mobility in F-Contaminated Soils. Soil Science. 153(5): 357-364.
"Soil reaction, or pH, is a factor in the movement of fluorides from soil into plant tops, and hence acid-loving vegetation may contain fluorine well beyond the 4 to 7 ppm content that is usual in forage vegetation devoid of fluoric contamination."
SOURCE: MacIntire WH. (1949). Air Versus Soil as Channels for Fluoric Contamination of Vegetation in Two Tennessee Locales. In: Air Pollution. Proceedings of the United States Technical Conference on Air Pollution. McGraw-Hill Book Co, New York. pp. 53-58.
"The effect of fluoride pollution of soils on plants has generally been discounted, primarily because it is well known that F adsorbs strongly to most soils at neutral pH and is, therefore, assumed to be unavailable to plants."
SOURCE: Stevens DP, McLaughlin MJ, Randall PJ, Keerthisinghe G. (2000). Effect of fluoride supply on fluoride concentrations in five pasture species: Levels required to reach phytotoxic or potentially zootoxic concentrations in plant tissue. Plant and Soil. 227: 223-233.
3d) In Acidic Soils, Aluminum Fluoride Complexes Facilitate the Uptake of Both Aluminum & Fluoride:
"The linkage of fluoride and aluminum accumulation can be explained by the formation of stable soluble aluminum-fluoride complexes in the soil, particularly under acid conditions, and the resulting increase of uptake of both elements."
SOURCE: Klumpp A, Klumpp G, Domingos M, Dias Da Silva M. (1996). Fluoride impact on native tree species of the Atlantic forest near Cubatao, Brazil. Water Air and Soil Pollution. 87: 57-71.
"The high solubility of fluorine under acid conditions can be explained by the occurrence of cationic [AlF]2+ and [AlF2]+ complexes... Aluminum solubility is increased by fluoride."
SOURCE: Wenzel W, Blum W. (1992). Fluorine Speciation and Mobility in F-Contaminated Soils. Soil Science. 153(5): 357-364.
"The increased solubility of fluoride at lower pH is attributable to formation of soluble AlFx3-x complexes..."
SOURCE: Gago C, Fernandez Marcos ML, Alvarez E. (2002). Aqueous Aluminum Species in Forest Soils Affected by Fluoride Emissions from an Aluminum Smelter in NW Spain. Fluoride. 35(2): 110-121.
"The degree of [fluoride] accumulation depends on several factors, including soil type and, most prominently, pH. At acidic pH (below pH 5.5), fluoride becomes more phytoavailable through complexation with soluble aluminium fluoride species, which are themselves taken up by plants or increase the potential for the fluoride ion to be taken up by the plant."
SOURCE: World Health Organization. (2002). FLUORIDES. Environmental Health Criteria 227. World Health Organization, Geneva
"The uptake of positively charged AlFx complexes may explain the positive correlations between F and Al concentrations in the shoot."
SOURCE: Arnesen AKM. (1997). Availability of fluoride to plants grown in contaminated soils. Plant and Soil. 191: 13-25.
"Aluminum increased fluoride concentrations in roots and shoots but the pattern of distribution between root and successive leaves was not substantially altered... Aluminum might affect the uptake and transport of fluoride in several ways."
SOURCE: Takmaz-Nisancioglu S, Davison AW. (1988). Effects of aluminum on fluoride uptake by plants. New Phytol. 109: 149-155.
"Increasing the AlCl3 concentration caused a very marked increase in soluble fluoride in Soils 1 and 2, probably due to formation of soluble aluminum fluoride complexes."
SOURCE: Larsen S, Widdowson AE. (1971). Soil Fluorine. Journal of Soil Science. 22: 210-221.
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3e) In Acidified Soils, Aluminum-Fluoride Complexes Reduce Plant Growth and Yield:
"Results obtained in this study showed that high levels of F in acid soils reduce crop yield due to increasing aluminum and depressing phosphate uptake."
SOURCE: Elrashidi M, Persaud N, Baligar VC. (1997). Effect of fluoride and phosphate on yield and mineral composition of barley grown on three soils. Agricultural Research Service. United States Department of Agriculture. Approved date: March 4, 1997.
"The results of this study support our hypothesis that the toxicity of Al is enhanced in acidic environment contaminated with fluoride."
SOURCE: Rai LC, Husaini Y, Mallick N. (1996). Physiological and biochemical responses of Nostoc Linckia to combined effects of aluminum, fluoride and acidification. Environmental and Experimental Botany. 36: 1-12.
"the strong inhibition of H+ -ATPase observed in medium containing fluoride and aluminum may suggest that fluoroaluminate could play a role in the mechanism of aluminum toxicity and inhibition of plant growth observed in acid soils. However, at present we do not know whether fluoroaluminate is able to penetrate the cells of the corn roots."
SOURCE: Facanha AR, Meis L. (1995). Inhibition of Maize Root H+ -ATPase by Fluoride and Fluoroaluminate Complexes. Plant Physiology. 108: 241-246.
"fluoroaluminum complexes have been shown in the present study to be toxic to root elongation, but sulfatoaluminum species appear to have little or no toxicity."
SOURCE: Kinrade, TB. (1996). Reconsidering the rhizotoxicity of hydroxyl, sulfate, and fluoride complexes of aluminum. Agricultural Research Service. United States Department of Agriculture. Approved date: August 14, 1996.
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3f) Mechanism of Aluminum Fluoride's Toxicity to Plants:
AlF mimics phosphate, reduces root uptake of phosphate, and causes a reduction in the plant's energy and yield similar to the effects seen in cases of "phosphate starvation")
"Contrary to prior expectations, Al-F complexes have been shown to be toxic to plants. Although several hypotheses for the mechanism of Al-F toxicity have been considered, so far all of them have been rejected. The present study focuses on the description of an alternative mechanism for the toxicity of AlFx through a well-known phosphate-mimicking property attributed to these complexes. Phosphorus is acquired by plant roots primarily via high-affinity Pi transporters. Several pieces of evidence support a model where AlFx complexes can mimic the tetrahedral phosphate group competing with it for the same binding sites on the Pi carriers and possibly stabilizing an inactive conformation. First, AlFx-induced inhibition of Pi uptake was antagonized by raising the Pi concentration in the reaction medium. Second, the stimulation of Pi uptake in corn roots after AlFx pretreatment is similar to that observed after Pi starvation... This supports the model where the fluoroaluminates act as physiological Pi analogs by competing directly for the same binding sites of Pi transport rather than any indirect effect on the proton motive force of the process... These evidences support the proposal that the property of AlFx to mimic Pi may describe the most important mechanism of AlFx toxicity whenever AlF3 and AlF4 are the dominant species."
SOURCE: Facanha AR, Okorokova-Facanha AL. (2002). Inhibition of Phosphate Uptake in Corn Roots by Aluminum-Fluoride Complexes. Plant Physiology. 179: 1763-1772.
"Results obtained in this study showed that high levels of F in acid soils reduce crop yield due to increasing aluminum and depressing phosphate uptake."
SOURCE: Elrashidi M, Persaud N, Baligar VC. (1997). Effect of fluoride and phosphate on yield and mineral composition of barley grown on three soils. Agricultural Research Service. United States Department of Agriculture. Approved date: March 4, 1997.
"The possibility remains that Al-F is an effective vehicle for the intracelluar uptake of Al and F where these elements, once dissociated from each other, may exert a toxic effect."
SOURCE: Kinraide TB. (1997). Reconsidering the rhizotoxicity of hydoxyl, sulphate, and fluoride complexes of aluminum. Journal of Experimental Botany. 48(310): 1115-1124
"Higher intracellular Al uptake from the media containing AlF3 and NaF+AlCl3 as opposed to that with only AlCl3 in the presence of phosphate indicates the existence of different modes of entry for Al in the presence and absence of fluoride."
SOURCE: Rai LC, Husaini Y, Mallick N. (1996). Physiological and biochemical responses of Nostoc Linckia to combined effects of aluminum, fluoride and acidification. Environmental and Experimental Botany

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http://www.icmag.com/ic/showthread.p...=1#post3132807

Here is a link to another good thread about flouride issues