1.CCA treated timber has been shown in some studies to leach low levels of chemicals into the soil immediately surrounding the treated timber. Soil tested within 25 mm of the treated timber sometimes slightly exceeded advisable safety levels for arable soil.
Soil tested further than 25 mm from the treated timber showed no significantly raised arsenic levels compared to other NZ soil. (Note, background levels of arsenic in New Zealand soil are between five and nine parts per million approximately or 5-9mg/kg.)
Uptake of these chemicals by fruit and vegetables has been shown to be minimal and is within accepted international food safety thresholds.
If you are particularly concerned, it is suggested you plant no closer than 35cm to the timber edge or place a plastic or polythene barrier between vegetable garden soil and the CCA-treated timber edging.
2.Do not use LOSP treated timber – it is not rated durable for in-ground applications.
3.You could instead use untreated timber from a species with higher natural durability like macrocarpa or some eucalyptus species, however if left in contact with the ground the timber will eventually rot.