Important: When setting up and maintaining your garden it is important to take care to avoid products that may cause harm to the health of your garden and students.
CCA treated timber (treated pine)
Timber treated with copper, chromium and arsenic as a preservative has been phased out for all domestic use in the United States, European Union (EU), Canada, Indonesia and Vietnam, and restrictions placed on its uses in Japan.
The Australian Pesticides and Veterinary Medicines Authority (APVMA) conducted a review of CCA treated timbers and, in March 2005, declared this preservative to be a restricted chemical product (RCP) in the public interest.
The review states that the APVMA "were not satisfied that the continuing use of CCA for timber used in structures with which the public (and particularly children) are likely to come into frequent and intimate contact is safe", and APVMA regulations that restrict the uses of CCA treated timbers came into effect at the end of March 2006.
Included in the APVMA regulations is (10.1. iv): "not permitting uses of CCA timber treatment products for timber intended for use as garden furniture, picnic tables, exterior seating, children’s play equipment, patio and domestic decking, and handrails".
Common sense would dictate that the APVMA restrictions would also apply to school garden beds (as they do to sand pits) because these timbers can leach arsenic (a known carcinogen) onto the timber surface and into compost and soil for up to 20 years, and that there are a number of factors that increase the amount of arsenic leached from treated timbers, including high UV light levels.
The APVMA regulations do allow the use of CCA treated timber for 'structural timbers' and the timber industry has included retaining walls in that description. However, the APVMA Review (page 11) clearly states, structural timbers "where frequent contact is unlikely, and the level of exposure and risk, is low". For more information see:
www.apvma.gov.au/products/review/docs/arsenic_summary.pdf
Alternative timber preservation methods are available. However, some contain pesticides that are developmental neurotoxins, and others leach copper or boron – some plants and soil organisms are sensitive to excess amounts of these trace elements. Consequently, we do not recommend the use of preserved timber as edging for garden beds in schools. Suitable edgings are suggested in the 'Garden Beds' section of 'Introduction 2: Getting Down To Earth'.
For other structures in school gardens, timbers preserved with alkaline copper quaternary (ACQ) appear to be the most readily available. Unfortunately, ACQ timbers also have a green tint, which weathers over time to a honey brown. As the labels on CCA treated timbers are affixed with a single staple and easily dislodged, the onus is on the consumer to ensure before purchase that the timbers are preserved with ACQ, not CCA.
For more information on products containing alternative methods of timber preservation, see:
http://www.herinst.org/CCAtimber/alternatives/chemical.html
Carpet and carpet underlays
Natural fibres are treated with persistent pesticides before sale, and many carpets contain toxic chemicals as stain or flame repellents. Some felt underlays were made from asbestos-contaminated hessian. When exposed to the elements, chemicals from these products can leach into beds, compost and worm farms if used as covers or to suppress weeds.
Phospho-gypsum or by-product gypsum
Phospho-gypsum is a by-product of synthetic phosphate fertiliser manufacture. It can contain high levels of cadmium, which is harmful to human health and not suitable for organic gardening. Please check before purchase that the packaging has an organic-allowed label (see below) or the label clearly states that the product is natural or mined gypsum. (See EOG&MP pp 37-8)
Old car tyres
Car tyres can leach cadmium and other heavy metals into soil as they weather, and should never be used for garden or compost containers. Plenty of well-made, mature compost in garden beds can limit cadmium uptake. However, cadmium uptake by plants is increased in acidic soils; soils containing immature compost or uncomposted manures, or where water is high in chlorine. (See EOG&MP p 27)
Uncomposted manures and mulch cut from pastures sprayed with broadleaf weed killers
Aminopyralid, a relatively new herbicide ingredient in Australia, kills broad-leaf plants by disrupting plant cell growth. It does not affect grasses, but can remain active in them, and manures from animals that eat sprayed grasses, until it is completely broken down by soil microbes. Beds contaminated with aminopyralid can remain unusable for up to 20 months. In the United Kingdom, this herbicide ingredient caused widespread damage to allotment gardens in 2008. UK residents were advised not to eat produce from gardens affected by aminopyralid. As a precaution, use only animal manures that have been 'hot' composted (see making compost), and check before purchase that mulch hay does not come from pasture that has been sprayed with 'Archer', 'Hotshot', 'Starane' or 'Grazon'.
Plastics with recycling codes 3 and 7
Recycling code 3 is for polyvinyl chloride (PVC) products (including old plastic shower curtains) that leach toxic chemicals. Recycling code 7 covers polycarbonate and resin products that may leach Bisphenol A (BPA) when exposed to heat.
Herbicides should not be used to clear the garden area of weeds or other vegetation (or at any other time) These products kill, or inhibit, a range of soil organisms, and increase the incidence of soil-borne diseases. They can also cause allergic reactions in humans, especially children. These products will counteract your efforts to produce healthy, organic soil.