High-fluoride Hekla eruptions pose a threat to foraging livestock, especially sheep. Fluoride poisoning can start in sheep at a diet with fluorine content of 25 ppm. At 250 ppm, death can occur within a few days. In 1783, 79% of the Icelandic sheep stock were killed, probably as a result of fluorosis caused by the eruption of Laki. The effect also spread beyond Iceland. Ash from the current Eyjafjallajökull eruption contains one-third the concentration typical in Hekla eruptions, with a mean value of 104 mg of fluoride per kg of ash. Large-scale release of sulphur dioxide into the troposphere also poses a potential health risk, especially to people with pre-existing breathing disorders.