Cg. Rodriguez et al., Comparison of methods for fluoride extraction from forest and cropped soils in vicinity of an aluminum smelter in Galicia (NW Spain), COMM SOIL S, 32(15-16), 2001, pp. 2503-2517
Four extracting solutions (1 M NH4Cl, 0.02 M NH4Cl, 0.01 M CaCl2, and water
) have been tested to determine mobile fluoride in forest and cropped soils
having high fluoride contents resulting from emissions by an aluminum smel
ter in Galicia. NW Spain. Seventy-two acid forest soil samples and 47 cropp
ed soil samples were analyzed. Linear regression analysis was performed by
SPSS 9.0 statistical package. Significant correlations (P < 0.01) were foun
d between fluoride concentrations in different extracts provided that soils
had similar pH and exchange aluminum (Al) and calcium (Ca) values. The 1 M
NH4Cl, 0.02 M NH4Cl. and 0.01 M CaCl2 extractants were more efficient than
water in extracting fluoride from acid forest soils, due to displacement o
f exchange aluminum and. therefore. Al-bound fluoride. Highest extractions
were achieved by I M NH4Cl, due to its higher ionic strength. Water extract
ed more fluoride than salt solutions from cropped soils. usually fertilized
and limed, and consequently having high (> 10 cmole(c) kg(-1)) exchange Ca
values. When extracting cropped soils by NH4Cl and CaCl2, the CaF2 solubil
ity product is presumably reached due to displacement of exchangeable calci
um, and fluoride is removed from solution. Water extractions seem adequate
to estimate mobile F from soils high in exchange Ca (> 10 cmole(c) kg(-1)),
while salt solutions seem suitable for soils high in exchange Al (> 1 cmol
e(c) kg(-1)).