Volcanic ash cloud – the latest news from SEPA – update 6

date22 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.

SEPA's Director of Science and Strategy, Professor James Curran, said:

The greatest environmental concern from volcanic ash, and the most significant risk to grazing livestock, would be fluoride content in ash deposits. Information from SEPA's analysis of Scottish dust samples, and from similar analysis in Norway, indicates low levels of fluoride in the current Icelandic ash plume.

"The latest rainwater samples analysed also indicate no cause for concern - pH and fluoride levels are entirely consistent with normal rainwater in Scotland. We are detecting small increases in some volcanic contaminants, particularly iron, manganese and copper. We will continue our programme of monitoring but, based on the ash, rainfall and snowfall samples analysed so far, there is minimal risk to the environment."

Ongoing monitoring

SEPA has been carrying out monitoring and analysis on four areas of the Scottish environment – ambient air quality; rainwater and snowfall; deposited ash particles; and vegetation. Samples collected, covering all these areas, have been conveyed to SEPA laboratories by SEPA staff, other volunteers and partner organisations such as the Scottish Agricultural College (SAC). Ongoing analysis is being supported by the Macaulay Institute and Edinburgh University. 

Air quality

The Scottish Air Quality Database (SAQD) 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.

All concentrations remain generally low across Scotland and therefore there is no cause for concern. Some monitoring sites have been experiencing some small changes in the concentration of sulphur dioxide (SO2) and particulate matter. These fluctuations are entirely normal and reflect daily ongoing activities eg road traffic.

Radiation measurements are taken across the UK and Europe via the RIMNET monitoring network. Readings show no evidence that the volcanic ash contains radioactive materials of any significance.

Rainwater analysis

Analysis of 28 samples of rainwater and snow has been undertaken to assess the environmental impact of the volcanic ash deposition across Scotland.

All sample results to date for fluoride, sulphate, nitrate and chloride show levels which are below accepted standards and guideline values.

The pH level of the samples was also analysed. pH measures the concentration of hydrogen ions in solution and is the commonly accepted measure of acidity and alkalinity, using pH units that range from 0 to 14, with 0 to 7 reflecting acidic conditions, 7 neutral and 7 to 14 alkaline conditions.

Rainwater in Scotland is normally between 4 and 7 pH units. Occasional acidic events are observed in Scotland and pH readings can be as low as 2.5.

The results from the samples analysed by SEPA are all between 4 and 7 pH units and as such are typical of normal Scottish rainfall.

The samples analyzed to date indicate no cause for concern with minimal risk to the environment.

Deposited ash analysis

SEPA is monitoring deposits of ash taken right across the country and ash deposition rates remain low.  Analysis of the particles collected is being undertaken by SEPA.

The analysis of sticky pads continues to show that very few dust particles are being deposited.

The majority of the samples analyzed have displayed properties consistent with those of volcanic ash.


On behalf of SEPA, the Scottish Agricultural College (SAC) has collected 10 samples of grass from across Scotland. These are now being analyzed by SEPA scientists, who will wash the samples and analyse the run off to ascertain if there are any potential hazards for grazing animals and the wider environment.  Given that no adverse effects have been observed in rainwater and dust deposits, we do not expect to see any issues of concern.

Future work

Although it is spring, there have been recent snowfalls in upland areas across Scotland. Snow is a particularly good medium for absorbing dust particles from the atmosphere. Snow melt can pass straight into rivers and, given that spring time is a particularly important time of the year for spawning and junior aquatic species, it is important that we monitor and assess its likely environmental impact. The Scottish Avalanche Information System (SAIS) is now collecting samples of snow on behalf of SEPA and transporting them to our laboratories. We have now analysed a number of snow samples and are not finding any indications of areas of concern, but our ongoing monitoring allows us to provide further reassurance about the environmental impacts.


Questions and answers

Q: What is Fluoride?

A: Fluoride is a commonly occurring chemical. It is present in small amounts in the body and its primary function is to strengthen the bones. It is well known for its use in toothpastes to prevent tooth decay.

Fluorides are naturally occurring in the environment through the weathering of rocks and in releases of gases from volcanoes. The most important natural source of fluoride is from bedrock. Fluoride can enter groundwater from the weathering of bedrock and can subsequently reach surface and sea water.

Environmental releases of fluoride can occur through industrial processes such as aluminium smelting and through natural processes including volcanic eruptions. Volcanoes emit a variety of gases both between and during eruptions, including hydrogen fluoride. The hydrogen fluoride reacts with the ash particles to form various forms of fluoride.

Q: Why are we concerned about fluoride?

A: Like many chemicals, a small amount of fluoride is essential for life, but an excessive amount can cause concern. High levels of fluoride can have adverse effects on the environment, including impacts on sensitive species, such as caddis flies and migratory salmon, impacts on crops and on livestock.

The levels of fluoride that we have detected are consistent with background levels expected and far lower then accepted standards and therefore present no cause for concern.

Q: What is pH and why are we measuring it?

A: pH is a measure of acidity and is related to the concentration of hydrogen ions. pH values range from 0 to 14. Pure water has a pH of 7 and is described as neutral. Water with pH below 7 is described as acidic and above 7 as alkaline.

The presence of acidic substances in water will influence the pH because acids provide hydrogen ions. Alkaline substances in water will raise the pH. Rain water is naturally mildly acidic because of interactions with gases in the atmosphere, and the normal range of pH is from approximately 4 to 7.

Acids can be released naturally from soils and plants and so streams can have a pH in the range of 4.5. Due to alkaline substances which can be released from soils and rocks streams can also naturally have a higher pH up to around 8.5. Acidifying substances can be released into the environment from natural and man-made sources. These can include emissions to air from natural sources such as volcanic eruptions.

pH is one of the most important variables in the environment and it is known as a 'driving variable' because it can influence most chemical and biological processes. For this reason, it is one of the primary parameters monitored in the environment.

Q: What are the environmental consequences of lower pH?

A: Inputs of acidifying substances can lead to acidification of the environment. In freshwater acidification can have impacts on the ecology and water quality. Some species of fish, aquatic invertebrates and plants are sensitive to acidic (or lowered pH) conditions. Fish eggs and fry are particularly at risk, as lowered pH can affect their chance of survival and development. If acidification is severe, it can lead to the disappearance of some sensitive species and potentially to a loss of biodiversity.

Some pollutants including metals (such as lead, aluminium, zinc and cadmium) become more water soluble and so can be more toxic at lower pH. This may be an underlying cause of some of the damaging effects of acidification in freshwaters.

Q: How do we recognise the effects?

A: SEPA monitors pH routinely across Scotland in rivers and lochs, so we are well placed to recognise the occurrence and effects of a pH change. We also monitor aquatic invertebrates at numerous sites and have long-term data from sites that have historically been affected by acid rain.

Q: What is SEPA doing?

A: SEPA have already collected and analysed rainfall samples for fluoride and pH. The pH of rainwater (4.7 – 6) analysed since the volcanic ash event are within the normal range we would expect for rainwater.

The concentrations of fluoride detected are similar to natural background concentrations reported elsewhere and are well below those of environmental concern.

Samples of snowmelt, dust/ash and vegetation have been collected and we are in the process of analysing these samples.