tanalised wood

[heather murphy]

Does anyone know how long cca wood leaches for?    I have a client with an existing garden that is fenced with cca all around it (7mx4m) It has been in the ground since 1985. Does anyone know if it stops leaching at any stage??  If it does still leach; does it travel through the soil quite far away from the posts?   My theory is to plant non-food companion plants around the margins but am thinking that the roots web will all interconnect it with the food roots.   I'm stuck - the area needs to be fenced for dog control.  Any advice greatly appreciated

[Hester]

Hi Heather
I am curious about this myself as a friend asked me about it last weekend. There is conflicting information on the internet but one article I have read suggests at least 8 years.
http://files.recycleworks.co.uk/files/Wood%20preservatives.pdf

[heather murphy]

tk-u very much for that.
I have now decided to get the soil tested as am very interested to see what levels are still in the soil. Will test under and next to posts aswell as far away to see if any differences. I will let you know results if interested.

[Hester]

Oh yes please-i would be very interested.

[Hester]

This is a very interesting question and has had me searching for more information. There is a very interesting study of CCA treated vineyard posts in Marlborough. This seems to suggest that the leaching would be ongoing for the life of a post, which the researchers estimate at about 20 years (until it would need replacing in a vineyard). It appears from this study that the toxins didn't travel far from the post horizontally but do accumulate in the soil beneath the post gradually seeping deeper as time goes by.
Here is a link to the study

www.kiwiscience.com/JournalArticles/STOTEN2006.pdf

[Sonya]

Interesting discussion and thanks for that research Hester. :) I did a bit of reading on it after I'd spoken with you about it and it seems as if CCA does leach into the soil it accumulates in the generally non-edible parts of the plant (i.e. roots). Good for eating, but then if the chemicals do accumulate in roots, I wonder how that affects putting those parts in the compost!

What I've settled on is not planting right next to treated timber and trying to keep half to 1 metre away from posts... I wasn't sure whether the chemicals would travel in the soil, but the information I'm finding (and what you've said) seems to indicate that they don't very much, accumulating around and underneath the posts...

Hm!

[heather murphy]

Right - soil results back - just trying to ascertain what the allowable levels are?
rung the council, biogro, to no avail. Dirt doctor trying to find out for me.....
There was approx 40% difference in contamination from the posts to the centre of garden.
I'll let ya know what the levels are when i find out.......
In the meantime I have decided to do a soil cleanse - planting mustard - to remove arsenic, then growing carrots and spinach - to remove chromium and copper. These plants will come out of the ground and go to the tip as general waste, not green waste!
I will get the soil tested again after this and see if it worked! Of course removing the tanalised wood!

[heather murphy]

So the crux of the soil sample = 2 samples - sample one by the post and sample 2 3m away.
sample 1 arsenic 57, chromium 44, copper 122 all mg/kg
sample 2 arsenic 35, chromium 23, copper 74
and as far as i have been able to ascertain allowable levels for
arsenic 10 chromium 10 copper 30-100
Will retest in 6months to see if my cleansing as worked at all....

[heather murphy]

Oh and I just rang bunnings to ask if trellis fencing is treated... The person on the other end of the phone said gleefully - 'oh yes it is -it is H3.1' I cannot believe that there is so much tanalised wood out there for the DIY-er especially when it is banned, restricted in other countries - and we wonder why nzer's have the highest athsmatic and respitory rates! And another thing i found out - the H stands for Hazard! great!......

[Bridge Scully]

Wow this is an awesome discussion and so interesting as there are many out there that dont seem to think theres anything wrong with treated wood..... I just helped my dad build two raised beds in chch and we ended up getting non treated wood from bunnings.....the guy there gleefully said "you know ive had loads of gardeners in here that dont notice any difference" but is it really something you would notice straight away....hmmmmm. We ended up putting linseed oil all over the untreated wood which should prolong the life a bit longer.

[Ketana Saxon]

Yes not only the highest asthmatic and respiratory disease rates but death by cancer at the rate of 1 in 3 !! The other area that NZ is appalling on is the lethal ingredients in herbicides and pesticides not only on commercial growers but in garden centres for domestic use....stuff that is also banned overseas!

Home gardeners innocently asume that if its sold over the counter it must be safe....so not!!

[heather murphy]

yea its not something you notice straight away. And as usual most customers take for granted what is available for them to purchase as being ok to use. Maybe if we replaced the H with Hazard then people would question it.

[Hester]

Thanks so much Heather. Really helpful information that deserves to be more widely known. Perhaps you could post it as a blog so it comes up easily in internet searches.