Some friends inherited an old fibro garden shed when they bought their house. It was termite damaged, wood rotten, lead-headed nails, rusty iron, asbestos walls painted with several layers of paint and other mysteries. For a few years it sat in the “too hard” basket, best not looked at too closely.
But, with a toddler starting to explore the yard, and keen to start a garden, the moment arrived when the shed had to be dealt with. They paid for it to be professionally demolished. But that wasn’t the end of the shed saga. Was the soil contaminated? Lead paint remnants or flakes of asbestos? Was it safe for a garden?
Lead paint was commonly used up till the late 1970’s. Up until 1965 paint was often 50% lead. Houses, and sheds dating from before that often had a history of being scraped and sanded and repainted, and the lead paint flakes and dust settled as a ring around the building. A building footprint outlined in contaminated soil.
Commercially produced vegetables probably have worse things to worrry about – pesticides and herbicides and anti-microbial post-harvest washes – but kitchen garden vegetables can pick up the lead. Less so in soil with high enough phosphate levels and neutral or slightly basic pH, which luckily is exactly what you want in good kitchen garden soil. Adding chook manure, bone meal, and/or worm castings might be enough. And one of the ways to deal with lead in the soil is to add organic matter, both because lead binds tightly to organic matter making it less available, and also because if you add enough organic matter or imported clean soil, it dilutes it down to naturally occurring kind of levels (lead is naturally present in soil at rates something like 10 to 50 parts per million). By the time you add enough compost to get your soil up to kitchen garden quality, that will probably add up to “enough”. But still …
It’s nice to know what you are dealing with. Most councils will be able to direct you to testing. It’s not crazy expensive – around $85 to test just for lead and up to $150 to include pesticides such as arsenic. Some councils will do it for free. If not, there are lots of commercial and university labs that will do a soil analysis to test for a variety of things including pH, nitrogen, phosphorus, metal analysis including lead, cadmium etc, pesticides residue, POCAS ( acid sulphate soils). Southern Cross University, for example, has an independent laboratory called EAL (environmental analysis laboratory). Here’s a link to their price list.
https://www.scu.edu.au/media/scueduau/eal/pricelists/Contamination-assessment-price-list.pdf
A basic metals/ pesticide test is $144, and they have instructions on how to take the samples and how to enable a secure chain of delivery in case you need to prove your test results.
If you find you have low levels, raised beds filled with imported fresh soil and compost, away from that outline of ancient paint dust might be the safest. Get the pH up to 6.5 – 7 and the phosphate levels high enough by adding chook manure, bone meal, and/or worm castings. If you find it’s really bad, you may have to remove soil. Lead binds to fine soil particles so if the soil hasn’t been stirred up by tilling or excavating, the lead is probably almost all in the top couple of inches. It might be an expensive, but not impossible, disposal problem.
As it turned out our friends had a lucky break. Their shed was probably just painted with poor quality water based paints from washed out brushes from the 1990s. Whew.
(PS – a friend put me on to this wonderful program run by Environmental Science staff at Macquarie University, Sydney – https://www.360dustanalysis.com. They will test garden soil and/or vaccuum dust, from anywhere in Australia, for arsenic, cadmium, chromium), copper, manganese, nickel, zinc, and LEAD. The testing is free but they ask if you could please consider a donation to support the work of the program, starting from $20.)
