Heavy Metal Gardening

By Ian Smith, Systems Analyst for The LEAD Group Inc.

Walking up from the dam, well pond really, and the neighbours are blaring out AC DC VERY LOUD in the otherwise still of a late gold afternoon, breaking the ambience of the bush and I could witness myself railing against the invasion. It gave pause to reflect on neighbours in general and specifically their capacity to pollute adjacent lands with heavy metals, both the musical and the periodic table of the elements kinds. When in the garden, it seems we're all going to need a bit of metallurgist in us. For the record, in the heavy metal music sense, I'd have preferred Led Zeppelin. AC DC is for redneck with mullets (a hairstyle short at front and sides, long at the back.).

The Transition Handbook (Hopkins 2008), a guide to building an oil-independent, resilient community of low-mileage food grown and consumed locally, was insightful into the sociological means to boot-strap that community, but light on for the practical techniques needed to do that in an inner-urban environment. As the cities have grown, the small 'mum & pop' factories on the edge of town have been pushed further out, amalgamated through industrialisation into mega-factories. Small petrol stations have succumbed to consolidation into the current oligopoly. The inner-west of Sydney for instance, where once were factories or petrol stations, now are housing. Before building up our socially-aware network of inner-city gardens, we need to add some metallurgy to our bonhomie.

Driving in the inner-west of Sydney a few weeks back, I saw a newly dug community garden. At first glance it was uplifting to see the dungaree'd inner-city types getting into the swing. But the site is boxed in on three sides by old buildings, the busy road in front & a railway line nearby. It's highly likely over the last few generations of slight ignorance (not even gross negligence), that this garden & the many others like it in a Transitioning world have been contaminated with heavy metals and toxic chemicals. 

 Unfortunately it's not as easy as a Dial Before You Dig Hotline (1100 in Australia) if you think you're going to dig some metal in the form of power, water or phone lines) to see if there's contamination. Where the contamination lies is not in an all-seeing government database. There is a Sydney region map (Vanderheyden 2006 and Birch et al 2010) that Sydney locals can use to at least get an idea of the lead in your locality. This pattern of high contamination in the old hearts of fuel burning cities is likely to be repeated in all old cities, with Australia's relatively new cities likely to be better off than the much older cities in other parts of the world.

Before getting yourself dirty clearing away the weeds and get yourself covered in something you'll regret later, get The LEAD Group DIY Sampling Laboratory test kit (Do_It_Yourself_Lead_Safe_Test_Kits) and get a few soil samples taken, from a couple of different places and have them analysed for the presence of lead or other heavy metals.

While you're at it, have the pH tested - this tells you how acidic or alkaline the soil is, which determines whether you need to add lime for certain vegetables, etc. [ Editor’s update, February 2021: See Andrew Scott’s soil pH measurement / troubleshooting guide at https://wellgardening.com/soil-ph/ ]

Up to 20ppm Lead is background noise. Go your hardest & happy gardening.

Above 100 ppm? "Because of the possibility of bare soil exposure to children through hand to mouth activity, soils with lead levels exceeding 100 ppm should not be used for gardening. If soil exposure to children is not a concern, then plants can be safely eaten from soils with soil lead levels up to 300 ppm." (Rosen, 2002). So, give up growing your own vegies at this point if you've got small children. The primary pathway of lead poisoning in children is ingestion; a child's response to yummy dirt is to eat it, and the worst possible time to be poisoned is as a child, so just don't grow vegetables. A garden can provide more than just food for the stomach.

300 ppm. OK. There's lead there. Lots of. But manageable. We are, after all, hard-rocking metallurgists in the garden this morning.

If the soil pH* is kept up above 6.5, then the plants don't seem to want to take up the lead. So add a bit of lime (and a soil pH meter from the garden supplies shop).

* Soil pH is a measure of the soil acidity or soil alkalinity. An acid solution has a pH value less than 7. (Wikipedia 2010)

  [Ed's note: Vegetables have a pH value at which they produce their best results. Some prefer quite acid soils. See The Garden Helper 2010]

You can also add some good quality humus. Plants don't absorb lead so much when the soil contains real nutrients, and you can seriously thin down the contamination ppm (parts per million) by volume, for a small garden anyway, with a boot* load of soil.

* boot - US, trunk of car

Above 300ppm? Nasty. We're talking serious site remediation. Take off & remove the top soil layer to 10 cm or so [Ed's note: Some councils require a development application to take soil away from a property] or add raised sealed beds and new soil onto the site. [Ed's note: sealed off from the soil by an impermeable barrier, such as a sheet of builders' plastic.] Otherwise it's the farmers' market for your fresh greens. But even then... apparently even with sealed, raised beds, contaminated soil is still finding new pathways especially onto, but also into produce from the raised garden beds. It could be through the gardeners' actions, or rain & wind action lifting or spattering contaminants into the bed from the nearby source (The Geological Society of America 2010). You can get around this by removing the top inch of topsoil each year.

But a good washing of all leafy greens, and peeling & washing the root crops will fix most contamination. There is far more likelihood of surface contamination than through uptake of lead by the plant itself.

Next time I mean to drive past that new community garden, I should take my dungarees, and a sampling kit.

References

1. Birch, G. F., Vanderheyden, and M., Olmos, M. 2010. THE NATURE AND DISTRIBUTION OF METALS IN SOILS OF THE SYDNEY ESTUARY CATCHMENT (AUSTRALIA). WATER, AIR AND SOIL POLLUTION, DOI: 10.1007/s11270-010-0555-1

2. Dial before you dig, http://dialbeforeyoudig.com.au/nsw.html

3. HOPKINS Rob, 2008 THE TRANSITION HANDBOOK. From Oil Dependency to Local Resilience. Published by Green Books, http://transitionculture.org/shop/the-transition-handbook/

4. ROSEN, Carl J., Extension Research Soil Scientist, Department of Soil, Water and Climate, 2002, Lead in the Home Garden and Urban Soil Environment: Sources of Lead in the Environment; Lead in Garden Soils and Plants; Removing Lead on Roots, Leaves, or Fruits; Precautions for Garden Soils; Residential Bare Soil Standards; Soil Tests for Lead; Remediation etc. Published by Copyright Regents of the University of Minnesota,  www.extension.umn.edu/distribution/horticulture/DG2543.html

5. The Garden Helper (2010) Recommended Soil pH for Growing Different Fruits and Vegetables www.thegardenhelper.com/soilPH.htm (Accessed 7 December 2010)

6. The Geological Society of America, 2010 How Lead Gets into Urban Vegetable Gardens, 1st November 2010, www.geosociety.org/news/pr/10-64.htm

7. Vanderheyden, M., 2006. THE NATURE AND DISTRIBUTION OF METALS IN SOILS OF THE SYDNEY ESTUARY CATCHMENT, AUSTRALIA, Unpublished. BSc (Hons) thesis, School of Geosciences, Sydney University, Sydney.

8. WellGardening.com, Andrew Scott, Founder & Writer, Plant Care and Landscaping Tips: How to Test and Manage Soil pH: Tips For Measuring, Increasing and Decreasing Soil pH Levels, 20th January 2021, https://wellgardening.com/soil-ph/

9. Wikipedia (2010) Soil pH, last modified 21 November 2010, http://en.wikipedia.org/wiki/Soil_pH (Accessed 7 December 2010)