Does CCA treated wood have a place in food gardens?

Thanks to Matt for an interesting cross post…

CCA-treated timber is everywhere: parks, decks, jetties even in ours homes, but how safe is it when it comes to food, drink and our children’s safety? CCA-treated timber is timber preserved with Copper Chrome Arsenate (CCA) or Chromated Copper Arsenate, as it is known in some countries, like South Africa. The copper (23-25%) and arsenic (30-37%) in CCA act as fungicides and insecticides, while the chromium (38-45%) fixes the chemicals into the wood (APVMA, 2003; Greaves 2003). The chemical mixture is injected into the wood under pressure so that the wood is saturated with the chemicals.

Of greatest concern is the potential seepage of arsenic, a known human carcinogen, onto the surfaces of CCA-treated timber from where it can be dislodged onto hands and washed off into nearby soil or surrounding water. However, there is a lack of health studies on the combined health impact of copper, chromium and arsenic.

Extensive tests have been done by the Department of Agriculture SA, United States Department of Agriculture and the Environmental Protection Agency, all of which have found it to be ‘food safe’ in the use of raised vegetable gardens. An 8 year study showed a nominal increase in arsenic being leeched into the soil, most of which were stored in root vegetables like carrots and beetroots, but in parts that are normally discarded. The Federal Drugs Administration however disagrees and says it is both unsafe for storing/growing food and or water. In the USA it has been classed as a ‘restricted risk’ product and is banned from being sold to consumers. In countries like Australia, Europe, the USA and Canada have banned its use in recreational settings, such as parks, because of the risk it poses to children.

In 2001 a study done by Sharp and Walker shared this:

‘A 4-6 year old child’s daily exposure to arsenic has been found to be 5 micrograms/l in food, 23 ug/L in water, 25 ug/L from playing on CCA-treated wood and up to 480 ug/L from playing on CCA treated playground equipment’ (p.1). Children could exceed the legally-acceptable lifetime cancer risk in 2 weeks by playing on a treated play set.

Obviously this, along with other factors have forced the hand of these first world countries, but it is still sold here in SA to consumers and contractors alike.

Let me pepper this by saying that organic arsenic is all around us, in our water, our soil etc, so we are exposed daily to these risks, but as shown above the risk CCA timber poses to added exposure is a problem.

Lining the timber or coating it does reduce the risk of leeching further, but only for a year or 2, then a new coat of sealant needs to be applied.

Why do I even raise the issue? Well as some of you know I’m looking to start a business supplying portable food gardens to end users and am at a quandary as to how to go about it and I’m trying to remain impartial and objective.

Currently the 2 largest suppliers of such products here in Cape Town use unlined CCA treated timber in their ‘organic’ food gardens (which is a misnomer as certified organic farms are prohibited from using ANY CCA timber).

Again I see the benefits in that they are long lasting and require no maintenance, but the risk, however slight, remains.

The alternative? Using untreated timber and coating it will an environmentally friendly sealant, or not at all. The downside is that if treated it will need periodic maintenance, if not the wood will eventually rot and need to be replaced, which is a costly exercise, yet environmentally friendly.

So armed with that information, as the general public, what are your feelings? If you were to purchase a said food garden would you be willing to pay 20% more to have sealed or untreated timber planter and deal with the annual maintenance with no risk of contamination or would you be happy to use the CCA timber knowing that the risk is low, but still a risk?

Understand that my focus is solely on food garden usage, not flowers, only edible goods. Pressure-treated wood does last longer as shared than untreated wood, so using it might mean fewer trees would be cut in places where contact with food/water is limited.

Click here or further in-depth reading/study in both the process and undertaken studies visit

Please comment below, your feedback is invaluable.

—–

Matt Allison

I’m no Jamie Oliver

Tel/Fax: +27(0)21 683 4247

Mobile: +27(0)83 324 1477

E-mail

12 Responses to Does CCA treated wood have a place in food gardens?

  1. shaggy May 12, 2011 at 4:06 pm #

    Great to make people aware of this. Here in Holland, you cannot buy CCA timber, However the timber here is treated with copper, giving it a green tinge.

  2. Vicki von Berg May 12, 2011 at 8:40 pm #

    I pondered this very problem when I started the Salad & Herb Gardens (which have been featured in the Gardener Magazine). When I started them I was selling them ready planted and my idea was to offer people an opportunity of growing their own
    herbs and salad greens as organically as possible, as such I opted to use untreated timber, the wooden crates will not last for ever, but my trial crates are still in one piece after 2 years,

  3. Matt Allison May 12, 2011 at 11:06 pm #

    Hi Shaggy and Vicki,

    Thank you both for your comments and input.

    Vicki I’ve not seen your planters, do you have a link to them? Are they pine and complete untreated, i.e no sealant at all or sealed with an eco-friendly solution?

    Use an alien hardwood like red gum has been suggested as it is rot resistant, but I need to look into the costs and availability.

    Thanks

    Matt

  4. shaggy May 13, 2011 at 8:44 am #

    When making a Permaculture food garden, and one wants to surround the garden with wood, it is still far better to use old logs. Not only does it look better, the logs host all sorts of beneficial fungi as well as act a sponge to absorb water.

    These far outweigh sawn, treated timber.

  5. Matt Allison May 13, 2011 at 10:13 am #

    Hi Shaggy,

    As an advocate for both self-sustainability and permaculture methods my own personal food garden is based on that. You can see my garden here: http://ow.ly/i/arg8

    But my garden is 9mx3m, not practical for a guy with small balcony who wants to grow a few salad veggies or herbs.

    Cheers

    Matt

  6. dave May 13, 2011 at 6:27 pm #

    I must admit, all my raised beds have cca timber surrounds. I do line it with plastic though. I have long been aware of the risks involved with using cca treated pine, but at the moment I have no free alternative. I recently made and sold a couple raised beds, for this I choce to use untreated rough sawn Saligna, which was only slightly more than cca pine. When I get a chance I hope to replace my pine beds. It’s great to see this knowledge being spread, and thanks for the link.

  7. Matt Allison May 14, 2011 at 2:31 pm #

    Hi Dave,

    I’m glad you found it useful. I think their isn’t enough awareness around it, but the research is there in black and white, the rest is left to common sense.

    I do find it amazing though that the suppliers and retailers I’ve contacted and shared this link with have elected not to say anything, either on or offline, which further begs the question on how safe it is.

    I like your salinga option, I’ll need to investigate these in time, for now I’m going to forward with untreated pine, yes it will age and rot over the years, but is natural and compostable.

    Cheers

    Matt

  8. dave May 15, 2011 at 7:13 am #

    Arsenic removal from groundwater by MnO(2)-modified natural clinoptilolite zeolite: Effects of pH and initial feed concentration

    http://www.ncbi.nlm.nih.gov/pubmed/21398033

    I have been sourcing zeolite as it is a natural filter and is used in fish tanks to remove ammonia and heavy metals. Turns out that a manganese modified clinoptilolite-CA Zeolite is good for removing arsenic from ground water. Another good thing is that the clinoptilolite is mined locally. Pratley distributes it, as well as perlite. Not sure if they do the mn modified product, but I’ll find out.

    Prevention is better than cure, so rather just avoid cca treated pine.

    Zeolite is a good additive for a worm farm too as it stores ammonium nitrate which is released slowly when applied to your soil.

  9. Elephant's Eye May 15, 2011 at 12:56 pm #

    We built our raised bed with concrete blocks. Dry stone wall effect. Got sidetracked by CCA treated wood as a trellis to support some shade. And now no longer inclined to eat what we might grow.

    One of the North Americans pointed out something I hadn’t realised, which has really put me off. Raised beds are warmer, and a solution for northern gardeners to get their food crops growing earlier! Most south Africans would then be better off with vegetables grown IN the ground, not above.

  10. khalid June 22, 2011 at 4:20 pm #

    howdee folks

    happened upon an article on http://www.bbc.co.uk titled ‘Rice, straw and coconut the new alternatives to wood’ by Fiona Graham.

    the really fun stuff at the end….acetylation of softwoods to render them more durable and resistant to breakdown is mentioned.

    the process is likened to baking pine block in a bath of vinegar

    check out the website http://www.accoya.com

  11. Jane March 5, 2012 at 3:58 pm #

    Hi Matt,
    I’ve researched into the cca treated wood and as I want to grow organic veggies I’m steering clear. I spoke to a lumber yard and they said that the Saligna is a great alternative and could last for up to 10 years untreated as it’s a hardwood.

    I’m curious where you got your logs from though. They look great!

  12. Kobus Wolv. November 21, 2012 at 1:49 pm #

    Dear Matt,

    I have an orchard on the highveldt south of Bronkhorstspruit and this year birds of every description (i am expecting to see multi-colored tropical parrots any day) have converged on the peach trees forcing me to erect a structure to keep them out and, as can be expected CCA treated poles will be used.

    Reading the above posts I have mixed feelings. It is well-known that small amounts of poisons act as stimulants whereas larger doses can be deadly. As for the amount that is absorbed by the roots of the tree the arsenic (and the chromium) will probably negatively affect the microbial life of an area of say 30 cm in radius from the center of a pole of 10 cm radius and if the tree has any “intelligence” at all (and they have) it will not spend a lot of effort mining that infertile part which forms less than 2 1/2% of the area utilized by the tree (5 m by 4 m grid). How much arsenic will one get in a kg of fresh fruit? I suppose it will be detectable if you have a access to a high-class laboratory but it will certainly be less than that found in Napoleon’s hair (not that I would want to eat that)!

    The mixed feelings originate in some reading pointing to the presence of antibiotics in the chicken manure I am using to fertilize the trees and my rather extensive vegetable garden. Obviously one should ascertain that it is sourced from a farm that uses antibiotics sparingly but even then there will be some present in the manure. What’s more the manure is spread on almost 100% of the area of both orchard and garden.

    I will greatly appreciate information on the topic of antibiotics in manure, its quantitative presence, absorption by fruit trees and vegetables, eventual presence in the fruit, and the effect of that on humans.

Leave a Reply

%d bloggers like this: