Volcanic ash cloud – latest situation

date16 April 2010

The Scottish Environment Protection Agency (SEPA) is monitoring the situation regarding the volcanic ash cloud currently affecting the UK and its possible impact on Scotland's environment.

A sample of the ash which fell in Lerwick, Shetland has been collected and delivered to SEPA's laboratory in Aberdeen where it is currently being anaylsed.

The Scottish Air Quality Database contains the most up to date continuous ambient monitoring information across Scotland. Members of the public can access this information at www.scottishairquality.co.uk/.

Typical chemical composition of volcanic ash

Volcanoes emit a variety of gases including H2O, CO2, SO2, HCl, NH3, H2S, HF. These gases interact rapidly with the ash particles of a volcanic plume and especially atmospheric water to form acidic aerosols.

Volcanic ash may therefore contain potentially harmful substances in the form of water-soluble materials, mostly acids and salts, which cling to the particles of glass and crystals. The most common are sulphate, chloride, sodium, calcium, potassium, magnesium and fluoride. Other elements reported but in lower concentrations include metals such as zinc, cadmium and lead.

Finer ash is able to carry more soluble ions than coarser ash because of its larger surface area; fine ash and smaller-sized ash travel greater distances from an erupting volcano, typically extend over very wide areas than larger ash particles and may stay airborne for lengthy periods.

Human Health Effects

Particulate matter has potential health effects such as causing eye and skin irritation and increased respiratory effects for conditions such as asthma or other lung conditions. Information on possible health effects has been issued by Health Protection Scotland www.hps.scot.nhs.uk/. They have said that the levels of particles reaching ground level are likely to be low and should not cause serious harm.

Wider Environmental Risks

Newly fallen volcanic ash may result in short-term physical and chemical changes in water quality although the information that we have found indicates that historical eruptions have caused few water quality problems. The most common effects are from the suspension of ash on uncovered water supplies such as reservoirs. This may result in a change in turbidity and acidity although this is generally short-lived (a few hours to days). Such impacts seem to be associated with significant ash falls e.g. greater than three millimetres.

Whilst the weather remains dry, there will be no impact on the water environment.  Should it rain, there may be a slight increase in the acidity of the rain but there would be a minimal effect on the water environment as much of the rain would land on open land and percolate through the soil.

The main concern of fluorine poisoning is for livestock, which graze on ash-contaminated grass and feed, but significant deposits are usually required.

Summary

Continuous monitoring of the situation is ongoing but the current available evidence suggests that there is a minimal risk to human health and the wider environment.