Sandy’s Garden

Phytoremediation

To the west of the Kinneil Tip … sorry, that’s politically-incorrect … to the west of the Kinneil Kerse Recycling Centre in Grangemouth Road in Bo’ness, there’s a large quantity of soil. You really have to visit the recycling centre to appreciate that it’s there at all, and even then it’s not easy to see how large it is. It is contaminated soil, which sounds rather frightening until you learn that we’re not talking about radio-active contamination or contamination with some kind of deadly chemical. The soil has come from former industrial sites; and, while you don’t really want to try to sneak in under cover of darkness to fill a couple of wheelbarrows with the stuff with a view to spreading it across your vegetable patch, it is actually lying there harmlessly in Bo’ness in what is colloquially called a ‘soil hospital’. Mark you, it’s not in receipt of much tender, loving care! The general idea is that this soil has been identified as having contaminants that can safely be washed out of it, making the soil suitable for reuse in certain landscaping programmes. And the cheapest way of having the contaminants washed out of it is by letting the rain do the job, perhaps stirring the soil up a bit from time to time to help nature do the job more quickly.

It is in our best interests to try to clean up contaminated or polluted soils by whatever means is best, for pollution in the soil can easily spread to other parts of our natural environment. Rainwater seeps through the soil and makes its way to the nearest watercourse, meaning that pollutants can be leached out of the soil and carried to streams, rivers, wells and sources of drinking water. Dust blows from polluted soils during dry weather and may be inhaled by animals or passers-by, or may settle on arable land and be spread to crops growing there. And either way, we can end up ingesting the pollutants. The risks may be very small: but steps which will minimise even small risks are a good idea.

In general terms, plants do not like growing in polluted soil; and the greater the level of pollution, the less likely it is that plants will thrive: but scientists have known for years that some plants are resistant to high levels of soil toxins and that others actually thrive on them. The really good news is that, while most plants need low levels of certain heavy metals in the soil if they are to thrive but are killed by high levels of heavy metals, the latter category of plants … ‘hyper-accumulators’ … lap up heavy metals. And there is growing interest in a process that has been understood for quite a while now and which rejoices in the name phytoremediation, a word made up of a mixture of Ancient Greek and Latin words, for phyto is Greek for ‘plant’ and remedium is the Latin word for, well, ‘remediation’; so phytoremediation means ‘using plants to restore something to its original state’, in this instance, to clean up polluted soil. And before you assume that this process must require some very unusual plants, barley, sugar beet and sunflower are common enough plants which can be used in phytoremediation.

Since soil contaminated with high levels of heavy metals is found on sites where the paper-making, printing and metal industries once thrived, the phytoremediation process could be very useful locally. The advantages are that the cost is lower than that of traditional processes; the plants can be easily monitored; it may be possible to recover and reuse valuable metals; and using plants preserves the environment in a more natural state. But phytoremediation does have its limitations. It can’t reach beyond the volume of soil occupied by the plants’ roots; it is a slow process; and it requires the safe disposal of the affected plant material. Still, there might well be scope for phytoremediation in central Scotland.

Sanndy Simpson, Polmont Horticultural Society