Soil fluoride spiking effects on olive trees (Olea europaea L. cv. Chemlali)

• A 30 percent loss of total plant biomass was observed with 100 mM NaF treatment.
• Olive tree roots accumulated the most F; while, olive fruits contained the lowest.
• Olive fruits were not affected by added NaF levels.
• The retention of fluoride in olive trees was roots>shoot>leaves>fruits.
• Olive consumption is not a direct threat to consumer health.

A pot experiment under open air conditions was carried out to investigate the uptake, accumulation and toxicity effects of fluoride in olive trees (Olea europaea L.) grown in a soil spiked with inorganic sodium fluoride (NaF). Six different levels (0, 20, 40, 60, 80 and 100 mM NaF) of soil spiking were applied through NaF to irrigation water. At the end of the experiment, total fluoride content in soil was 20 and 1770 mg F kg−1 soil in control and 100 mM NaF treatments, respectively. The comparative distribution of fluoride partitioning among the different olive tree parts showed that the roots accumulated the most fluoride and olive fruits were minimally affected by soil NaF spiking as they had the lowest fluoride content. In fact, total fluoride concentration varied between 12 and 1070 µg F g−1 in roots, between 9 and 570 µg F g−1 in shoots, between 12 and 290 µg F g−1 in leaves, and between 10 and 29 µg F g−1 in fruits, respectively for control and 100 mM NaF treatments. Indeed, the fluoride accumulation pattern showed the following distribution: roots>shoots>leaves>fruits. On the other hand, fluoride toxicity symptoms such as leaf necrosis and leaf drop appeared only in highly spiked soils (60, 80 and 100 mM NaF).