#14 - April 2018 - Garden Stuff - © Sandy Lang - slang@xtra.co.nz
TREATED TIMBER April: Mid-autumn, winter’s looming. Time to tidy up the garden. Also the time to build decks, pergolas, fences and raised veggie beds. What’s about not using treated timber in the garden…?
Most NZ timber is ‘radiata pine’. If not treated, pine soon rots when wet (decking, fences) and especially when in soil contact (fence posts).
Treatment: In NZ, outdoor pine is CCA treated - Copper against fungi, Arsenic against insects and Chromium to bind these, so they don’t wash out. Levels of CCA treatment depend on exposure to the elements. The common ones are H3 for rain exposure (decks, pergolas, fences) and H4 for soil exposure (fence posts).
The issues: What about the safety of CCA? At high concentration, the salts of all three metals are poisonous. However, all three occur naturally at low concentrations in the soil, in plants, in your drinking water and in you. Low levels are naturally contained in all the foods we eat and are components of our bodies. More than this, all three are essential micronutrients for humans. So the risk turns not about the mere presence of these metals but about their concentrations.
Health/environmental risks: The use of CCA timber treatment is banned in the USA and EU. The main worry is arsenic. We may see a change in NZ but although the alternative timber treatments avoid arsenic they still pose significant health and environmental risks. No simple choice. So it’s about managing exposure…
Managing exposure: Probably the greatest risks of over-exposure to CCA are:
(1) From handling freshly-treated timber (wear gloves, wash hands before eating, wash clothes afterwards). Avoid inhaling sawdust (use a face mask if sanding).
(2) Next is burning treated timber in a BBQ (ingestion + inhalation), in an open fire (inhalation), or in a closed wood stove (the neighbours). CCA treated timber offcuts should go to landfill.
(3) Research shows there’s negligible risk of significant ingestion of these metals from food plants grown in soil that’s adjacent to CCA-treated timber.
Almost all food produced in New Zealand is from agricultural systems in which CCA treated timber is used in fencing (pasture) or training structures (horticulture).
If making planter boxes, use untreated macrocarpa (naturally rot resistant) or stain/paint an H4 pine board where it is in soil contact to minimise any movement of CCA from wood to soil.___________________________________
Most NZ timber is ‘radiata pine’. If not treated, pine soon rots when wet (decking, fences) and especially when in soil contact (fence posts).
Treatment: In NZ, outdoor pine is CCA treated - Copper against fungi, Arsenic against insects and Chromium to bind these, so they don’t wash out. Levels of CCA treatment depend on exposure to the elements. The common ones are H3 for rain exposure (decks, pergolas, fences) and H4 for soil exposure (fence posts).
The issues: What about the safety of CCA? At high concentration, the salts of all three metals are poisonous. However, all three occur naturally at low concentrations in the soil, in plants, in your drinking water and in you. Low levels are naturally contained in all the foods we eat and are components of our bodies. More than this, all three are essential micronutrients for humans. So the risk turns not about the mere presence of these metals but about their concentrations.
Health/environmental risks: The use of CCA timber treatment is banned in the USA and EU. The main worry is arsenic. We may see a change in NZ but although the alternative timber treatments avoid arsenic they still pose significant health and environmental risks. No simple choice. So it’s about managing exposure…
Managing exposure: Probably the greatest risks of over-exposure to CCA are:
(1) From handling freshly-treated timber (wear gloves, wash hands before eating, wash clothes afterwards). Avoid inhaling sawdust (use a face mask if sanding).
(2) Next is burning treated timber in a BBQ (ingestion + inhalation), in an open fire (inhalation), or in a closed wood stove (the neighbours). CCA treated timber offcuts should go to landfill.
(3) Research shows there’s negligible risk of significant ingestion of these metals from food plants grown in soil that’s adjacent to CCA-treated timber.
Almost all food produced in New Zealand is from agricultural systems in which CCA treated timber is used in fencing (pasture) or training structures (horticulture).
If making planter boxes, use untreated macrocarpa (naturally rot resistant) or stain/paint an H4 pine board where it is in soil contact to minimise any movement of CCA from wood to soil.___________________________________