Urban Soil Contamination

Our urban soils can, unfortunately, hold a multitude of nasty secrets. I actually eluded to this problem in my previous post about compost when I mentioned having a rather depressing reason for keeping one of my compost bins on the hard standing rather than in the garden.

To put it bluntly, our soil is contaminated with pollutants. Our tiny urban garden, 100th of an acre in size, has unsafe levels of lead, asbestos, and several aromatic hydrocarbons (probably from coal). 

You might now be thinking, good God, why do you live in such a frightening place? We asked ourselves the same question when we got the soil test results back, particularly when we saw the high levels of lead. I'm sure I don't need to tell you the health risks associated with this heavy metal.

Ever since receiving these results, we've hunted for an alternate property to buy in the city. What we discovered, however, during our house hunting is that the soil in ALL the properties we tested are contaminated in one way or another, and ALL with lead.

It turns out, our garden's soil isn't some freak isolated phenomenon. We've discovered healthy looking properties with grass lawns and establised shrub borders containing up to 2,500 parts per million (ppm) of lead. Let me put this into context for you, UK Category 4 Screening Level recommendations by DEFRA state that vegetable growing allotments should have soil lead levels no higher than 80ppm. This means some perfectly normal looking gardens in Plymouth have over 31 times the safe limit of lead in their soils. Mind blowing!

Looking into this urban soil contamination issue online and in scholarly articles, this issue is widely understood. However, for reasons beyond my comprehension, if you ask the average gardener or allotmenteer they invariably stare back blankly. It simply isn't an issue in the general public's psyche. Totally, totally baffling...

So, what can we do about this problem? My other half and I dearly wish to remain living in our beloved city, but we also wish to continue growing food. How can we reconcile these two seemingly incompatible ways of life? We now take some significant mitigation measures, based on extensive reading of the literature. 

One of the most important points to appreciate is that different plant species take up lead to differing degrees and, probably even more importantly, different parts of the same plant take up lead differently. This article by Michigan State University summarises it nicely. Plants sequester far more lead in their roots, shoots, and leaves than in their fruit. Due to this, on soils with high levels of lead, growing fruits like tomatoes, courgettes, cucumbers, apples, and raspberries is far safer than growing vegetables like potatoes, carrots, rhubarb, kale, or lettuce. 

Bearing this in mind, I now rigorously segregate our growing space. I use the main garden to grow fruit trees, soft fruit bushes, and a multitude of flowers. In contrast, I grow our vegetables in large pots and half barrels filled with bought in coconut coir and a blend of bought in compost and beautiful worm castings I produce in our compost bin on the hard standing. I only feed that bin with food waste and garden waste recycled from the pots themselves, never with prunings from the main garden. This system felt soul destroying to adopt at first, but now its just business as usual, quite straightforward. 

Boy, it makes me feel more confident consuming what we grow too! Where there is a will, there is a way. Always, always remember that.