I asked this question of a soil expert, Phil Mulvey, Chief Executive Officer of Environmental Earth Sciences and Phil’s advice is:

In regard to CCA treated timber, there has been a lot of research with CCA treated logs and vegetables.  Slow leaching of metals does occur and impacts the soil in contact with the logs (50 mm).  Little uptake does occur to the vegetables but the same issue occurs with roots crops in close proximity to the logs as it does for lead.  The root vegetables should be washed before eating.  People though do worry about it and this worry is where the greatest hazard is on the short term.  Prolonged contact with soil and impact on vegetation has been evaluated in the grapes of Marlborough district in NZ and in the Hawkes Bay horticulture industry.  There is clear evidence that arsenic levels accumulate with time in the soil, but bioavailability remains low.  If people continue to worry lining with plastic or marine ply, or waste plywood from someones thrown out wardrobe would be OK but would have to be replaced every 2 to 3 years as it would probably be decayed by then.

www.environmentalearthsciences.com…

So that’s a yes, but doing so creates some avoidable burdens.

They’re not insurmountable and human health is not at serious risk.

M