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How soils keep us healthy

"Not very many people are aware of the ways in which they keep us healthy.

Dr Rupert Hough, Information and Computational Sciences, James Hutton Institute; Jon Stubberfield, Ph.D. student

Soils are one of the most complex and dynamic natural systems studied by scientists. Although usually out of sight, everything in our lives is underpinned by them — our roads, our homes, the food we eat, and the water we drink. It makes sense to reflect on their importance, particularly as 2015 is the International Year of Soil. However, not very many people are aware of the ways in which they keep us healthy.

Most land use regulations associated with public health are almost exclusively focussed on the potential negative impacts of contaminants in soil. Such pollutants may be in the form of heavy metals, organic compounds such as pesticides, or physical contaminants such as asbestos. Protection of public health against these contaminants is of obvious importance, and as such various guidance, soil quality standards, and statutory instruments for contaminated land risk assessment have been developed over the years.

If contaminated soil is sealed over with a shopping mall, there will be no pathway for soil contaminants to reach the shopping public; however, where land is used for gardens or allotments, there is a much greater risk of exposure to contamination through contact with the soil and through consumption of any produce grown on the site.

This approach is very logical from the perspective of exposure; however, it precipitates the perception that soils are dangerous and can cause harm, especially in urban areas where people are growing and consuming fresh produce.

However, the potential risks are only part of the picture and we don’t tend to look at other situations in the same way. It seems perverse that soils are viewed only from the risk angle, with little or no thought given to potential health benefits.

There are a range of health benefits provided by soils and by activities involving soil, and it could be argued that only by combining the risks and benefits can we see a real picture of the impact of soil on public health. For some individuals, outdoor activities that make use of soils such as gardening may contribute to a significant extent to a healthy lifestyle, providing a regular supply of fruit and vegetables and exercise. 

Research has shown a correlation between consuming higher proportions of fruit and vegetables and a reduction in the number of individuals developing cancer. Furthermore, regularly taking part in moderate forms of exercise and having a higher fruit and vegetable intake is likely to reduce the likelihood of an individual developing cardiovascular disease.

The importance of vitamin ‘G’, greenspace, to psychological health and well-being is well documented, with public gardens and allotments providing much-needed community groups for the most vulnerable in society. Even the soils themselves are likely to provide some benefit to gardeners contributing many essential nutrients such as iron, zinc and selenium found in multi-vitamin products, transferred to fresh produce that is then consumed by the gardener.

Together, these factors provide a strong argument that there is a number of public health benefits associated with the use of gardens or allotments for growing and consuming food. Indeed, whilst the risk from contaminants in the soil may be considered unacceptable if it contributes to one extra person in a thousand contracting cancer, research has shown that a reduction of just one portion of fruit and vegetables in the diet from the recommended five-a-day could contribute a 1-2% increase in the likelihood that an individual contracts cancer in later life.

It might be over-simplistic to say that the risk from soil contamination is simply cancelled out by the benefits received from an improved diet, but given that both risk and benefit estimates have significant uncertainties associated with them, this approach may not be that far from reality. 

For gardens and allotments where soil contamination exceeds regulatory standards, but exceedance is not that great, the risks posed are possibly outweighed by other benefits. It is imperative that the health benefits of soils are included and weighed up against the risks, especially as remediating soils for contamination is an expensive and often lengthy process.

At the James Hutton Institute, we work on ways to estimate the balance of risks and benefits from growing food on contaminated soils, and how we might go about combining risks and benefits into a single metric. Longer-term, we would hope that such an approach is adopted by regulatory bodies so that the impacts of soils on health can be looked at in-the-round, rather than the current rather artificial focus on risks. 

This article was originally published in the Summer 2015 issue of The Geographer, the magazine of the Royal Scottish Geographical Society, and has been reproduced by kind permission of the RSGS.

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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.