Exact health risks from the eruption of Mount Eyjafjallajokul are not yet clear, but citizens with asthma and other respiratory problems should be especially vigilant. Although the ash is not toxic, particles from the dust cloud should be avoided.
The concentration of ash will vary from country to country as the cloud moves around the world, but particles of ash are settling through the atmosphere and have already been identified on the ground in Sheffield, England.
According to the Daily Mail, analysis found the particles are composed of silicon, oxygen, calcium, aluminum, and sodium, the composition of volcanic rock which has been melted and re-frozen in the atmosphere. Hope is that the bulk of the cloud remains in the upper atmosphere where exposure and possible risk will be minimal.
The content of the silica within the volcanic ash, especially the minerals quartz, cristobalite, and tridymite are of concern. These free crystalline silica, or silicon dioxide, are known to cause silicosis that damages the lungs, heart, and increases the potential for lung cancer. Silicosis is irreversible and is often seen in miners and quarry workers with prolonged exposure to high concentrations of silica. Exposure to breathable sized silica for short durations (days or weeks) does not seem to trigger silicosis.
Near the site of the volcano, hundreds of residents have been evacuated to escape the danger of huge chunks of ice thrown from the volcano. Hot gasses melt the ice into torrents of water filled with pumice and ash are also a danger. There is also the fear that roofs of houses will collapse from the weight of the ash or that burns or asphyxiation will result from intense heat.
Eye, nose, and respiratory irritations are likely, but short-term exposure does not seem to pose a significant hazard. The result of long-term exposure is not clear.
Most commonly reported symptoms are:
* General discomfort
* Runny noses and sore throats, sometimes accompanied by a dry cough
* People with pre-existing lung and chest conditions have developed severe bronchitis that lasted days beyond the period of initial exposure
* People with asthma or bronchitis have experienced in increase in the severity of symptoms.
* Eyes are likely to feel as if there are foreign particles in them. They become painful, itchy and reddened, often with excessive discharge or tearing.
* Corneal abrasions or scratches might occur
* Minor skin irritations might occur, but there are no known reports of chronic skin irritations.
* Driving an automobile during or after heavy ash fall is unsafe. Roads can become slippery and hazardous.
Best advice is follow local advisories and forecasts. Widely varying factors, including concentration and proportion of breathable particles within the ash, frequency and duration of exposure, meteorological conditions, plus existing health conditions of exposed individuals, all determine the severity of symptoms.
http://volcanoes.usgs.gov/ash/health/index.html
