Few people are aware of the ways in which soil keeps us healthy, despite 2015 being the International Year of Soil.
Most land use regulations associated with public health are focused on the potential negative impacts of contaminants in soil, be they heavy metals, organic compounds such as pesticides, or physical contaminants such as asbestos. Protection of public health against these contaminants is of obvious importance.
However, 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 true picture of the impact of soil on public health. For some individuals, outdoor activities which 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 cancer incidence. Furthermore, regularly taking part in moderate forms of exercise and having a higher fruit and veg intake is likely to reduce risk of 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 which 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 veg in the diet from the recommended five-a-day could contribute a 1-2 per cent increase in the likelihood that an individual contracts cancer in later life.
It might be oversimplistic 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 just exceeds regulatory standards, the risks posed are possibly outweighed by other benefits. It is imperative the health benefits of soils are included and weighed up against the risks, especially as remediating soils for contamination is an expensive and time consuming.
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.
•Dr Rupert Hough leads the Information and Computational Sciences Group at the James Hutton Institute and worked on this article with PhD student Jon Stubberfield. www.hutton.ac.uk