tanalised wood

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

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  • Sorry, that should have been H4 (the comment editor seems to be broken)
  • Of course the people who designated it H1-H6 were thinking of the hazards posed to the timber by its evironment and not the other way around!
    At our PDC, we were given a figure of 5 metre radius of contamination for a ground-treated (H3) post (I don't have a source for that). Given that our town property is 11 metres wide, that doesn't leave much garden!

    I'd be interested in knowing to what degree setting the post in concrete limits leaching (and whether rain running down the above-ground surface of the post picks up any contaminants.

    I was pleasantly surprised yesterday to find that 150x150 durable eucalyptus was actually cheaper than treated pine.
  • 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.
    • 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.
  • 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!......
    • 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!!

    • 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.
  • 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....
  • 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!
  • 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!
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