Treated Timber concern.

[Alicat]

Hi all

I’m not sure how many people are aware of this but I thought you would like to read what I found in the Grow Your Own Magazine. Apologies to those that already Know this, but as a first time Veg grower I found it interesting reading and worrying.

Alicat.

Q.

I made a raised border for my veg about 3 years ago and on the advice of a DIY chain opted for a pressure treated timber. I have just heard that this can contaminate the soil inside the bed with arsenic. Is this true? Would you recommend changing the border and replacing it with something else.

A.

Most treated timber over the last 20 years or so has been impregnated with CCA (Chromated Copper Arsenate) in a process known as pressure treatment or tanalisation . Research carried out in the USA has shown that CCA-treated landscape timber that has been in place for around 10 years leaches chromium, copper and arsenic (all potentially toxic, with arsenic being particularly so) into the soil. The levels of all three elements tend to be highest near the timber, and vegetable plants grown near it will take this arsenic up (although not the chromium or copper).

As you appear to have the timber already in place, you can limit the damage by planting your vegetables at least 30cm (1ft) away from the treated timber and incorporating plenty of compost into your soil. This will bind the toxins to the organic matter. You can always remove the soil and line the edges of your bed with a barrier of plastic sheeting to prevent further release into the bed. If you decide to remove CCA-treated lumber from your house or garden, make sure you dispose of it in a safe manner - it should be treated as toxic material.

Wood alternatives made from recycled plastic are a safe option as they don’t need preservatives-ideal for a hassle free raised bed.

[Chuckles]

Not really sure what to say about it Alicat. My raised beds are made of tanalised wood and all are lined but one. Tanalised wood has long been used for raised beds and I would imagine the strength of the CCA after 10 years is going to be weaker than when it was applied also any that leaches into the ground will mostly draining down into the soil and be diluted by rain and watering, this will also then be weakened even further. The amount that any one plant would take up is also going to be weaker still, IMO. I'm not sure that it is as big a worry as one would imagine. Maybe others have an opinion on this who are more knowledgable in this sort of area.

[Jonah]

Hi Ali
Does sound a bit scary, doesn't it, especially as it is a new venture for you. I never even gave anything like that any thought.
I just found this on google:
www.taunton.com/finegardening/pages/g00028.asp


It doesn't say whether staining or painting the wood helps.

[Deleted]

Perhaps sealing the wood might keep the CCA in the wood and stop it leeching?

Then again the sealer might contain nasty stuff too

[Alicat]

Chuckles - I'm not sure what to make of it either when I first read it I thought OMG, but as you have pointed out surely it will reduce in strength as it rains and we water our plants. This year I/we have lined the veg patches just in-case. - We never did this before.

Jonah - Thank you for the link. I have read some of it but need more time to read and digest it. - I think what is scary is our children. When we were children no one really worried. Now we seem to be bombarded with scientific info. - It is so hard to know what is for the best.

Paul - Thanks for your comments - I have no idea.